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HARVARD UNIVERSITY 




LIBRARY 



OF THE 



Museum of Comparative Zoology 



UNIVERSITY OF KANSAS miscellaneous 

MUSEUM OF NATURAL HISTORY publication 



V#~ 



MUS. COMP. ZOOU 
■*' L/BRARY 

APP 281973 

Systematics of university, 
Three Species of Woodrats 
(Genus Neotoma) in Central 
North America 



By 

Elmer C. Birney 



No. 58 



UNIVERSITY OF KANSAS 

LAWRENCE 1973 April 13, 1973 



UNIVERSITY OF KANSAS PUBLICATIONS 
MUSEUM OF NATURAL HISTORY 

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Kansas 66044. 



University of Kansas 
Museum of Natural History 



Miscellaneous Publication No. 58 
April 13, 1973 



Systematics of Three Species of 

Woodrats (Genus Neotoma) in 

Central North America 



By 

Elmer C. Birney 

James Ford Bell Museum of Natural History 
University of Minnesota 
Minneapolis, Minnesota 



A dissertation submitted in partial fulfillment of the 

requirements for the degree of Doctor of Philosophy, 

The University of Kansas, 1970 



University of Kansas 

Lawrence 

1973 



University of Kansas Publications, Museum of Natural History 



Editor: Linda Trueb 
Managing Editor: William E. Duellman 



Miscellaneous Publication No. 58 

pp. 1-173; 44 figures 

Published April 13, 1973 



Museum of Natural History 

University of Kansas 

Lawrence, Kansas 66044 

U.S.A. 



Printed by 

University of Kansas Printing Service 

Lawrence, Kansas 



CONTENTS 

INTRODUCTION ..... 4 

Materials and Methods 5 

Acknowledgments ___. 7 

TAXONOMIC TREATMENT 8 

Historical Account 8 

Accounts of Species and Surspecies 10 

Western Subspecies of Neotoma floridana 11 

Neotoma micropus 23 

Neotoma angtistipalata 35 

COMPARATIVE MORPHOLOGICAL ANALYSES 36 

Materials and Methods 36 

Non-geographic Variation 42 

Variation with Age 42 

Secondary Sexual Variation 48 

Individual Variation 54 

Variation Resulting from Captivity 56 

Geographic Variation 57 

Pelage, Molt, and Color 57 

Qualitative Cranial Characters 66 

Baculum 76 

Univariate Analyses of Mensural Characters 78 

Multivariate Analyses of Mensural Characters 99 

Multivariate Analyses of Size, Color, and Qualitative 

Cranial Characters 109 

Discriminant Function Analyses 120 

NON-MORPHOLOGICAL CHARACTERS 127 

Comparative Reproduction 127 

Comparative Serology 144 

Starch Gel Electrophoresis of Hemoglobins 144 

Immunoelectrophoresis of Esterases 148 

Comparative Karyology 153 

SUMMARY AND ZOOGEOGRAPHIC CONSIDERATIONS 157 

Suggestions for Additional Research 160 

zoogeographic comments 161 

LITERATURE CITED 166 



INTRODUCTION 



Two species of woodrats, Neotoma 
florid ana and Neotoma micropus, have 
allopatric, but adjacent, distributions on 
the Great Plains; the species inhabit dis- 
tinctly different environments at most 
localities. Because N. floridana is brown 
and N. micropus is gray, the species are 
readily distinguishable. The geographic- 
ranges of the two, as mapped by Hall 
and Kelson (1959:684), were known to 
abut in the central and southern Great 
Plains from southeastern Colorado and 
southwestern Kansas southward to the 
Gulf Coast of eastern Texas; but not a 
single locality of sympatry was known. 
However, it had been discovered 
(Dwight Spencer, pers. com.) that mem- 
bers of the two species would hybridize 
in the laboratory with the production of 
viable offspring. 

The polytypic characteristics of both 
species in the zone of potential sympatry 
and the existence of a geographically 
isolated subspecies of Neotoma floridana 
make the problem even more interest- 
ing from an evolutionary point of view. 
Neotoma floridana baileyi is restricted to 
the region of the Niobrara River in north- 
central Nebraska. Neotoma floridana 
campestris is a large pallid subspecies 
that lives in eastern Colorado, southwest- 
ern Nebraska and northwestern Kansas. 
Rats of this race may have been isolated 
in post-Wisconsin times from presently 
contiguous populations of the species to 
the east (Jones, 1964:26). The eastern 
parts of Kansas, Oklahoma, and northern 
Texas were inhabited by a dark brown 
race known as N. f. osagensis. In south- 
ern Texas the range of N. f. attwateri 
abuts that of N. micropus; specimens of 
floridana from farther east in Texas have 
been referred to the subspecies rubida. 

When this study was begun, Neotoma 
micropus was divided into five nominal 
subspecies. Neotoma micropus micropus 
occupied roughly the eastern half of the 
range of the species from Tamaulipas to 
southern Kansas. Much of the western 



part of the range reportedly was occu- 
pied by N. m. canescens, allegedly a 
smaller and more pallid race. Two other 
subspecies, N. m. leucophea and N. m. 
planiceps, were known only from their 
respective type localities in New Mexico 
and San Luis Potosi. The fifth recognized 
subspecies, N. m. littoralis, was known 
only from a few localities in southern 
Tamaulipas. 

Initially, this study was centered 
in Nebraska, Colorado, Kansas, and 
Oklahoma, an area which includes the 
northern half of a zone in which the 
geographic range of Neotoma floridana 
approaches that of N. micropus. The 
study area was selected principally be- 
cause three subspecies of N. floridana 
(baileyi, campestris, and osagensis) and 
two of N. micropus (canescens and mi- 
cropus) occur within its boundaries. This 
facilitated comparison of a variety of 
parameters in order to determine rela- 
tionships among these five taxa. Al- 
though it had been supposed that the 
ranges of N. f. campestris and N. f. osag- 
ensis met in north-central Kansas, the 
exact zone of contact and the nature of 
the interaction had not been documented. 
Moreover, N. albigula generally is con- 
sidered to be closely related to both N. 
floridana and N. micropus (Burt, 1960; 
Hooper, 1960); this species occurs in 
southeastern Colorado and the western 
part of the Oklahoma panhandle. Finley 
(1958) suggested that N. albigula and 
N. micropus formed natural hybrids in 
this region. Finally, the area was selec- 
ted because of its accessibility to Law- 
rence, Kansas. This facilitated both field 
and laboratory investigations. 

Ultimately, all available specimens of 
both species from the initial region of 
study and from near the zone of potential 
contact in Texas were examined. All 
specimens of N. micropus in the Museum 
of Natural History of the University of 
Kansas were included, and selected spec- 
imens of N. micropus were examined in 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



other museums if it seemed likely that 
they might reveal information on the re- 
lationship of this species to A 7 , floridana. 
Eastern subspecies of A 7 , floridana were 
treated taxonomically by Schwartz and 
Odum ( 1957 ) ; with the exception of A 7 . 
/. rubida, which occurs in extreme south- 
eastern Texas, the eastern subspecies 
were not considered in my investigation. 

One other species, Neotoma angus- 
tipalata, is considered herein. The affi- 
nities of this large woodrat, known only 
from Tamaulipas and San Luis Potosi, 
Mexico, have remained enigmatic since 
it was described by Baker ( 1951 ) as a 
member of the Neotoma mexicana spe- 
cies-group. Neotoma angustipaJata since 
has been considered by different authors 
to be closely related to N. mexicana, N. 
micropus or A 7 , alhigula. 

Parameters studied in the field in- 
cluded habitat preference and utilization, 
exact distributional relationships in those 
areas where members of two taxa might 
come into contact, and seasonal repro- 
ductive patterns of natural populations. 
Parameters studied in the laboratory in- 
cluded data on the following: 1) control 
and experimental matings of members of 
each taxon to those of each other taxon; 
2) mating success and fecundity of hy- 
brids; 3) growth and development of 
hybrids and nonhybrids; 4) karyological 
analyses; 5) serological studies involving 
hemoglobin electrophoretic patterns 
(Birney and Perez, 1970) and immuno- 
electrophoretic reactions of esterases; 6) 
water balance physiology (Birney and 
Twomey, 1970); and 7) univariate and 
multivariate analyses of geographic varia- 
tion of mensural and qualitative morpho- 
logical characters. 

The primary purposes of my research 
have been to elucidate the systematic 
and evolutionary relationships, assess the 
zoogeographic history and re-evaluate 
the nomenclatorial arrangement of the 
woodrats studied. A secondary purpose 
has been to compare so-called classical 
taxonomic procedures with some of the 
newer methods of systematics and 
thereby evaluate the applicability of the 



various methods to systematic studies of 
closely related mammalian taxa. 

MATERIALS AND METHODS 

The general materials and methods 
that pertain to several facets of the study 
are discussed below. Specific materials 
and methods are related in detail pre- 
ceding results and discussion of the vari- 
ous topics covered. 

Initial efforts to collect live woodrats 
for laboratory studies were undertaken 
in September 1966. The last animals of 
the colony were sacrificed in October 
1969. Specimens studied in the labora- 
tory were obtained either by dismantl- 
ing active dens and capturing the rats 
by hand as they fled, or by trapping them 
in live-traps set near active dens. Hava- 
hart traps ( 18 by 5 by 5 inches ) were 
found to be highly successful, easily 
transported, and relatively durable. 
Woodrats are not difficult to trap and 
can be taken in practically any device 
large enough to permit entry and con- 
structed to prevent escape. In rocky 
habitats, usually it was necessary to use 
traps, but in other areas woodrats were 
captured more often by hand. To pre- 
vent undue destruction of available den- 
ning sites at two localities of special in- 
terest ( Major County, Oklahoma, and 
Cherry County, Nebraska), woodrats 
were obtained only by trapping. 

Animals used in laboratory experi- 
ments were obtained during the months 
indicated at the following localities ( here 
specified only to county; see lists of spec- 
imens examined for exact localities of 
record within these counties ) : NE- 
BRASKA: Cherry County (March and 
April 1967, August 1968); Rock County 
(August 1968). COLORADO: Baca 
County (April and May 1968); Prowers 
County (April 1968). KANSAS: Barber 
County ( October 1966, March and July 
1968 ) ; Douglas County ( September, Oc- 
tober, and November 1966, March 1967, 
February and March 1968, March 1969); 
Ellis County (December 1966); Ells- 
worth County ( September 1967, October 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



and December 1968); Finney County 
(September and October 1968); Hamil- 
ton County (September 1968); Haskell 
County ( September and November 1966, 
June 1967, February, May, and August 
1968, April 1969); Hodgeman County 
( September and November 1968 ) ; Logan 
County (August 1967); Meade County 
(November 1966, June 1967); Ness 
County (September 1968); Russell 
County ( December 1968 ) ; Stevens 
County (August 1968). OKLAHOMA: 
Dewey County (June 1968); Major 
County (June 1968, January 1969). 

Woodrats were housed indoors and 
maintained on a daily regime of 14 hours 
of light and 10 hours of darkness from 
1 February to 1 October. Illumination 
from several windows in the animal 
rooms was the only source of light dur- 
ing other months. An attempt was made 
to maintain a stable temperature of 20 C 
in the animal rooms, but temperatures 
ranged from as low as 13°C at times dur- 
ing winter to as high as 30° C on occa- 
sional summer afternoons. During one 
three-day period in June 1968, air con- 
ditioning failed and the temperature 
soared to at least 35°C and may have 
surpassed 38°C. No deaths were attrib- 
uted to extremes in temperature, but con- 
sumption of water increased noticeably 
as temperature increased. Relative hu- 
midity was not measured in the animal 
rooms during the summer or winter, but 
was measured regularly from March to 
June, 1968, when it ranged from 15 to 
45 percent. 

Woodrats were caged individually ex- 
cept when two were placed together for 
breeding or when a female was rearing 
a litter. Litters were weaned at six weeks 
of age. Cages used to house woodrats 
were of three general types. One type 
was constructed of wood and /s-inch 
mesh hardware cloth. Dimensions of 
these cages were 30 by 18 by 18 inches 
with 3.75 square feet of floor space. The 
other two types of cages used were all- 
metal commercially available cages with 
approximately four square feet of floor 
space. Both were satisfactory, but the 



type having a removable pan beneath a 
grated floor could be cleaned easily with- 
out disturbing the occupant. Females 
with unweaned litters were kept in spe- 
cial large metal cages that had eight 
square feet of floor space. Although 
woodrats can be maintained in smaller 
cages, I doubt that these would be satis- 
factory for maintenance of a breeding 
colony (see Wood, 1935:109). All cages 
were supplied with one gallon cardboard 
milk cartons or other disposable nest 
boxes of equivalent size. Cages having 
solid floors were covered with wood 
shavings; shredded newspaper for use as 
nesting material was available in all 
cages. Cages were cleaned at weekly 
intervals. 

Purina Laboratory Chow and water 
were available to woodrats in the labora- 
tory on an ad libitum regime. On occa- 
sion, especially in the early phases of the 
study, this diet was supplemented with 
lettuce leaves and whole-kernel corn; 
when it became evident that supple- 
mentary foods were unnecessary, this 
practice was discontinued. At times in- 
dividual rats would severely reduce food 
intake and begin to lose weight, usually 
indicating that the incisors were broken 
or maloccluding; rats with such teeth 
were removed from the colony. Occa- 
sionally the teeth of rats that were not 
feeding properly appeared to be normal; 
on these occasions feeding of laboratory 
chow was discontinued and the animals 
were given rolled oats ad libitum for a 
few days, then gradually returned to a 
diet of laboratory chow. While conduct- 
ing one experiment wherein it was neces- 
sary to limit protein intake, the experi- 
mental group was fed only corn (see 
Birney and Twomey, 1970 ) . 

Diseases and ectoparasites caused lit- 
tle problem in maintaining a thriving 
woodrat colony. In the spring of 1967 
several rats died after having had diar- 
rhea for two to five days, losing weight, 
and having an inactive, sickly appear- 
ance. Several sick rats and some that 
recently had died were taken to the 
Veterinarv Diagnostic Laboratories affil- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



|ated with Kansas State University at 
Manhattan, Kansas. Although the dis- 
ease was never diagnosed, the necropsy 
report (H. D. Anthony, pers. com.) 
stated that a "hemolytic E. [scherichia] 
coli was isolated from the spleen and in- 
testine of one of the specimens." Anthony 
recommended immediate treatment of 
drinking water with nitrofurazone, fol- 
lowed by prophylactic doses every three 
months. This treatment prevented 
spread of the disease, and generally 
cured all but the sickest rats. On two 
later occasions when more than one rat 
evinced signs of the affliction, the entire 
colony was treated. Cages were cleaned 
after each occupancy and those that had 
housed sick woodrats were washed in a 
dilute lysol solution before being reused. 

To prevent ectoparasites from becom- 
ing a problem, each woodrat was dusted 
with commercial "flea powder" before 
being placed in the animal house. On 
three separate occasions individual wood- 
rats became infested with an unidentified 
species of mite; the entire colony subse- 
quently was dusted and the infested 
animals were dusted on two or three suc- 
cessive days. Although each of the indi- 
viduals survived, two females infested at 
the time of parturition abandoned their 
litters. Rats infested with mites tend to 
be lethargic, lose weight rapidly, and 
have matted, swollen eyes. 

In addition to study of live animals, 
a total of 2163 museum specimens, in- 
cluding seven holotypes or lectotypes, 
was examined by me. Several hundred 
additional specimens were examined. 
These include more than 300 laboratory- 
reared individuals prepared as museum 
specimens and deposited in The Museum 
of Natural History of the University of 
Kansas, specimens of eastern subspecies 
of Neotoma florid ana not treated herein, 
specimens of other species of Neotoma 
(especially N. albigula and N. mexicana) 
examined for comparative purposes, and 
woodrats examined incidentally while 
searching for misidentified specimens of 
the species studied. 



ACKNOWLEDGMENTS 

I thank the following agencies for 
financial support for this investigation: 
1) National Science Foundation Grant 
GB-4446X administered by the Commit- 
tee on Systematics and Evolutionary Bi- 
ology at The University of Kansas, pro- 
vided a Research Traineeship for my 
support from September 1966 until June 
1969 and additional funds for cages and 
equipment to maintain woodrats in the 
laboratory; 2) Travel grants for field 
work and museum visitations were re- 
ceived from the Graduate School and the 
Museum of Natural History (Watkins 
Grant) at The University of Kansas; 
3) Research grants from the Kansas 
Academy of Science supplied monies 
used to purchase Laboratory Chow; 4) 
Funds for computer time were provided 
by the Computation Center of The Uni- 
versity of Kansas; 5) Partial support for 
July and August 1969 was made avail- 
able through The University of Kansas 
General Research Fund ( Biomedical Di- 
vision), under grant no. 3453-5038; 6) 
Equipment and supplies for serological 
experiments and rabbits used for prepa- 
ration of antisera were purchased with 
funds from the Public Health Service and 
research monies of the Department of 
Zoology at The University of Kansas. 

I am indebted to each of the persons 
listed below for permission to examine 
specimens of woodrats in their charge, 
which included both arrangement of 
loans and provision of working space in 
their respective institutions (Museum 
abbreviations used in the accounts be- 
yond are in parentheses ) : Sydney An- 
derson and Richard G. Van Gelder, 
American Museum of Natural History 
(AMNH); William J. Voss, Fort Worth 
Museum of Science and History ( FWCM 
— formerly Fort Worth Children's Mu- 
seum); John P. Farney, Kearney State 
College (KSC); Dwight L. Spencer, 
Kansas State Teachers College (KSTC); 
Robert S. Hoffmann and J. Knox Jones, 
Jr., Museum of Natural History of The 
University of Kansas (KU); George H. 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



Lowery, Jr., Museum of Natural Sciences 
of Louisiana State University (LSU); 
Eugene D. Fleharty, Museum of the 
High Plains of Fort Hays Kansas State 
College (MHP); Walter W. Dalquest, 
Midwestern University (MWU); Bryan 
P. Glass, Oklahoma State University 
(OSU); Edwin D. Michael, formerly at 
Stephen F. Austin State University 
(SFA); J. Keever Greer, Stovall Museum 
of Science and History of the University 
of Oklahoma (SM); Dilford C. Carter, 
formerly with the Texas Cooperative 
Wildlife Collection of Texas Agricultural 
and Mechanical University (TCWC); 
W. W. Newcomb, Texas Natural History 
Collection of the University of Texas 
(TNHC); Robert J. Baker and Robert 
L. Packard of Texas Tech University 
(TT); Bernardo Villa-R., Instituto de 
Biologia, Universidad Nacional Auton- 
oma de Mexico (UNAM); Charles O. 
Handley, Jr., and R. H. Manville, United 
States National Museum, including the 
Biological Surveys Collection (USNM). 
Serological experiments were con- 
ducted in the Charles A. Leone Labora- 
tories at The University of Kansas. Per- 
sons granting permission to use these 
facilities or who were especially helpful 
include Jay D. Gerber, Richard D. 
Koelm, Charles A. Leone, Robert B. 
Merritt, and Julio E. Perez. Karyological 
studies were conducted in the botany 
laboratories at The University of Kansas 
and in the cell biology laboratories at 
Texas Tech University. Raymond C. 
Jackson at Kansas and Robert J. Baker at 
Texas Tech were especially generous 
with their supplies, equipment, and time. 
James Frame and Sievert A. Rohwer as- 
sisted in the use of numerical taxonomy 
programs and other analyses of data, all 



of which were conducted at the Compu- 
tation Center of The University of 
Kansas. 

I am especially indebted to J. Knox 
Jones, Jr., formerly of the Museum of 
Natural History and Department of Sys- 
tematics and Ecology of The University 
of Kansas, for his excellent advice and 
general assistance throughout this study 
and for editorial advice in preparation 
of the manuscript. Frank B. Cross and 
Raymond C. Jackson also critically read 
the manuscript and provided sound edi- 
torial advice. 

Persons deserving of special thanks 
for assistance in the field include David 
M. Armstrong, Russell H. Birney, Jay D. 
Gerber, Thomas H. Kunz, D. Michael 
Mortimer, Robert R. Patterson, Duane 
A. Schlitter, Ronald W. Turner, and 
Larry C. Watkins. Additionally, D. 
Michael Mortimer assisted by cleaning 
woodrat cages in the summer of 196S 
and Hugh H. Genoways fed and watered 
the animals when it was necessary for 
me to be absent. 

Several of my colleagues at The Uni- 
versity of Kansas, especially David M. 
Armstrong, Hugh H. Genoways, Robert 
S. Hoffmann, and Carleton J. Phillips, 
were both stimulating and helpful by 
giving needed technical advice and will- 
ingly discussing topics germane to my 
research. Sydney Anderson, the Ameri- 
can Museum of Natural History, assisted 
this study in a similar maimer. 

My wife, Marcia Birney, has been 
both helpful and patient throughout this 
study and my graduate career. She pre- 
pared most of the figures used herein, 
typed drafts of the manuscript, and pro- 
vided much needed clerical assistance. 



TAXONOMIC TREATMENT 
HISTORICAL ACCOUNT 
Although woodrats were observed in 
North America by early naturalists such 
as John Bartram, no species was treated 
taxonomically until early in the nine- 
teenth century. Ord (1818:181) pub- 



lished a short description and figure of 
Mm fhridanus, a woodrat from eastern 
Florida. Previously, Ord (1815:292) 
described the bushy-tailed woodrat as 
Mus cinereus. Having noted the distinc- 
tive dental characters of the New World 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



rats, Say and Ord (1825:345) diagnosed 
and named the genus Neotoma and des- 
ignated Mus floridanus as the type spe- 
cies. Later Baird (1855:333) named 
Neotoma micropus from the type locality 
of Charco Escondido, Tamaulipas (see 
remarks following synonymy of N. m. 
micropus) . 

Baird (1858:487-490, 492-495) treated 
Neotoma floridana and N. micropus as 
separate species, although he repeatedly 
commented on the similarities between 
the two. Having only the type of micro- 
pus with which to compare specimens 
of floridana, Coues (1877:15) considered 
micropus a synonym of floridana, a con- 
clusion based primarily on his interpreta- 
tion of the gray pelage of micropus as 
being that of an immature animal. With 
additional specimens of micropus from 
Tamaulipas, southern Texas, and from 
"the northwestern corner of the Indian 
Territory" (now western Oklahoma), Al- 
len (1891:282) recognized micropus as 
a species distinct from floridana. Allen 
(1891:285) applied a new subspecific 
name, Neotoma micropus canescens, to 
specimens from the Indian Territory pri- 
marily on the basis of their pallid colora- 
tion. 

Woodrats from a population at Valen- 
tine, Nebraska, were collected in June of 
1888 by Vernon Bailey and later named 
as a new species, Neotoma baileyi, by 
Merriam (1894a: 123). Merriam (1894b) 
published a synopsis of the known mem- 
bers of the genus Neotoma, including 
fossil relatives, and diagnosed the sub- 
family Neotominae. Allen (1894b: 322) 
described Neotoma campestris, the flori- 
dana-like woodrat of northwestern Kan- 
sas and northeastern Colorado, on the 
basis of specimens from Pendennis, Kan- 
sas (type locality), and Fort Lyons, 
Colorado. In the same publication, Allen 
(1894b: 323) noted that he considered 
the woodrats which he previously had 
allocated to Neotoma micropus canescens 
to be "inseparable from N. micropus." 

Neotoma attwateri was named on the 
basis of a sample of woodrats from just 
east of the Edwards Plateau, near Kerr- 



ville, Texas (Mearns, 1897:721). Mearns 
(1897:722) suggested that 'it is not im- 
probable . . . [that N. attwateri, N. 
baileyi, and N. campestris] . . . may 
prove to be but geographic races of N. 
floridana." Prior to the turn of the cen- 
tury, only one other name was applied to 
the woodrats considered here. Elliot 
(1899:279) assigned the name Neotoma 
macropus [sic] surberi to specimens from 
the vicinity of Alva, Oklahoma. Accord- 
ing to Elliot, surberi differed from both 
micropus and canescens in having a 
longer tail and darker pelage. 

Neotoma micropus littoralis, from 
Altamira, Tamaulipas, and Neotoma mi- 
cropus planiceps, based on a single spec- 
imen from Rio Verde, San Luis Potosi, 
were the last names applied (Goldman, 
1905:31 and 32, respectively) to the 
woodrats treated in this study prior to 
the revision of the genus Neotoma by 
Goldman in 1910. In the latter work, 
Goldman recognized three subgenera 
and 28 species. Only two species, Neo- 
toma (Homodontomys) fuscipes and 
Neotoma (Teonoma) cinerea, were not 
considered members of the subgenus 
Neotoma. Woodrats presently included 
within the genus Neotoma, but which 
were considered as separate genera at 
that time are Neotoma (Hodomys) alleni 
and Neotoma (Teanopus) phenax (see 
Burt and Barkalow, 1942:296). Burt and 
Barkalow also placed Homodontomys in 
the synonymy of Neotoma. 

Goldman (1910:14) considered N. 
floridana and N. micropus to be separate 
but closely related species comprising the 
floridana species-group. Neotoma flori- 
dana baileyi was thought to occur in 
South Dakota, most of Nebraska and 
Kansas, and in eastern Colorado. The 
name campestris was treated as a junior 
subjective synonym of baileyi. Wood- 
rats of eastern Texas ( except the extreme 
eastern part, where the name N. f. mbida 
Bangs was applied) and eastern Okla- 
homa, were assigned to N. f. attwateri. 
Goldman (1910:26-31) reinstated N. mi- 
cropus canescens as the best name for 
western populations of that species, 



10 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



placed surberi in the synonymy of N. m. 
micropus, and recognized both N. m. 
littoralls and N. m. planiceps as distinct 
subspecies. 

Since Goldman's revision, the nomen- 
clature of woodrats has remained rela- 
tively stable. Kellogg (1914:5) removed 
campestris from the synonymy of baileyi 
and recognized both as subspecies of 
floridana. Goldman (1933:472) gave a 
slightly paler (as compared to N. m. 
canescens) population of micropus the 
name Neotoma micropus Jeucophea. 
Blair ( 1939a :5) described woodrats from 
eastern Oklahoma, eastern Kansas, and 
adjacent parts of Missouri, Arkansas, and 
Texas as Neotoma floiidana osagensis 
(type locality in Osage County, Okla- 
homa). Recognition of osagensis limited 
the distribution of baileyi to the Noibrara 
Valley of northern Nebraska. Burt and 
Barkalow (1942:290) considered N. mi- 
cropus to be intermediate between N. 
floridana and IV. albigula. On that basis 
they created the micropus species-group 
thus removing micropus from the flori- 
dana group where it had been placed by 
Goldman (1910:14). Neotoma floridana 
and N. micropus were studied by Spen- 
cer ( 1968 ) , who concluded that the two 
species are closely related and incom- 
pletely speciated. 

On the basis of two specimens from 
the Sierra Madre Oriental of southern 
Tamaulipas, Baker (1951:217) named 
the species Neotoma angustipalata. 
Hooper (1953:10) suggested that angus- 
tipalata may represent no more than a 
deeply pigmented population of micro- 
pus, and Hall (1955:329) thought it 
should be placed in the albigula species- 
group. 

ACCOUNTS OF SPECIES AND 
SUBSPECIES 

I regard the biological species con- 
cept (Wilson and Brown, 1953:97-99; 
Mayr, 1963, 1965, and 1969) as the best 
presently available concept of the species 
both for evolutionists and taxonomists, 
and subscribe to Tildens (1961:22) 



statement on the use of subspecies as 
follows: "In defense of the use of the 
subspecies concept, it may be mentioned 
that in our present system of classifica- 
tion the subspecies is the category ex- 
pressly provided for the treatment of 
populations less than species. That this 
tool is imperfect must be admitted. But 
to admit imperfection is not necessarily 
to reject the tool entirely. The point of 
view is held here, that the good results 
outweigh the objections that have been 
brought forward." Because of the arbi- 
trary nature of the subspecies, it is neces- 
sary to state what "kind" of subspecies 
is to be recognized. Lidicker ( 1962:169) 
stated that "a subspecies is a relatively 
homogeneous and genetically distinct 
portion of a species which represents a 
separately evolving, or recently evolved, 
lineage with its own evolutionary ten- 
dencies, inhabits a definite geographical 
area, is usually at least partially isolated, 
and may intergrade gradually, although 
over a fairly narrow zone, with adjacent 
subspecies." Further, it was noted by 
Lidicker (loc. cit.) that although most 
such subspecies will not become species, 
they are populations that have made ini- 
tial steps toward species formation and 
could form species under suitable isolat- 
ing conditions. This interpretation fo- 
cuses on the evolutionary process of spe- 
ciation rather than on individual geo- 
graphically variable characters. It is this 
sort of subspecies that I have attempted 
to recognize. 

Taxonomic decisions were made after 
intensive study and evaluation of the 
morphological, reproductive, serological, 
and karological data discussed beyond. 
Accounts of species and subspecies are 
presented first merely as a matter of con- 
venience so that the nomenclatorial ar- 
rangement proposed herein will obtain 
throughout subsequent discussions. 

Eight nominal taxa of woodrats, rep- 
resenting three species, are treated in the 
accounts that follow. The arrangement 
of species and that of subspecies within 
a species does not imply relationship or 
degree of specialization. Instead, taxa 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



11 



are arranged with respect to geographic- 
distribution, with more northern taxa 
treated before southern ones. Each ac- 
count includes a basic synonymy, which 
is followed by a relatively brief section 
of remarks. Remarks include comments 
on type specimens if such are appropri- 
ate, general comments on the variation 
within and between subspecies, and 
other comments that may be germane to 
the taxonomic status of the taxon under 
consideration. Records of occurrence fol- 
low remarks and include both specimens 
examined and additional records. 

The total number of specimens exam- 
ined is given for each taxon. This is fol- 
lowed by exact localities from which the 
specimens originated, the number of 
specimens examined from each locality, 
and the abbreviated designation for the 
museum(s) in which specimens are 
housed. In the account of N. m. canes- 
pens, specimens from localities in the 
United States are listed before those 
from Mexico. States and counties within 
the United States are arranged alpha- 
betically. Localities within each county 
and Mexican state are arranged from 
north to south. If two localities are at 
the same latitude, the westernmost is 
given first. Locality data of some speci- 
mens examined were specific only to 
county; these are listed as "unspecified" 
after specific localities within the county. 
In a few instances, a group of specimens 
is from the same general locality with the 
exact localities of capture varying only 
slightly; these are totaled and listed col- 
lectively as within a certain radius of a 
single locality. Specimens judged to be 
"hybrids" of two species ( see account of 
N. m. canescens) are listed with speci- 
mens of the taxon that they most resem- 
ble. Subspecific intergrades are included 
under the subspecies to which I consider 
them best assigned. Published citations 
to localities from which specimens have 
been collected but not examined by me 
are listed under "Additional records." 
Also included in this category are reli- 
able, published observations of woodrats 
or their houses in areas known to be in- 



habited by a single species of Neotoma. 

Following records of occurrence, the 
distribution and habitat of each taxon are 
discussed. The latter topics are treated 
in especial detail if they directly con- 
cern the relationships of two species or 
two subspecies. The general ranges of 
all three species (floridana, micropus, 
and angustipalata) are shown in figure 1. 
Most locality records are plotted on re- 
gional maps, but some were not plotted 
to prevent undue crowding of symbols. 
Unplotted localities are set in italic type 
in lists of specimens examined and of 
additional records. Localities specified 
only to county were plotted only in the 
absence of any other county record; sym- 
bols for such records are square and 
placed near the center of the county. 
Localities of specimens bearing ques- 
tionable data are not plotted, but are dis- 
cussed in the account of N. m. canescens. 

Eastern subspecies of Neotoma flori- 
dana were reviewed by Schwartz and 
Odum (1957). With the exception of 
N. f. rubida, which I have treated only 
in eastern Texas, these races of the spe- 
cies are not considered here. Specimens 
of Neotoma micropus were studied 
throughout the range of the species. 
However, because New Mexico is well to 
the west of the range of N. floridana and 
to the north of that of N. angustipalata, 
no attempt was made to examine all 
specimens from that state. Specimens 
from there were studied primarily to 
determine the best taxonomic position of 
the subspecies N. m. leucophea and to 
determine if New Mexican woodrats fit 
the pattern of variation of the species in 
a general way. In the accounts that fol- 
low, therefore, records of IV. micropus 
from New Mexico are not plotted on a 
regional map and records from the pub- 
lished literature are limited to those that 
are distributionally marginal. 

Western Subspecies of 
Neotoma floridana 

Neotoma floridana baileyi Merriam 

Neotoma baileyi Merriam, 1894a: 123 [Holotype 



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104 



Fig. 1. Geographic distributions of Neotoma angustipalata, N. floridana, and N. micropus. Identi- 
fication of species and subspecies is as follows: 1) N. angustipalata; 2) N. f. attwateri; 3) N. f. 
baileyi; 4) N. f. campcstris; 5) N. f. floridana; 6) A 7 . /. haematoreia; 7) N. f. iUinoensis; 8) N. f. 
magister; 9) N. f. rubida; 10) N. f. smalli; 11) N. m. canescens; 12) N. m. micropus; and 13) IV. 
m. planiceps. The symbol in Oklahoma denotes the single known locality of sympatric occurrence 
of N. floridana and N. micropus. Distribution of eastern races of N. floridana follows Hall and Kels- 
son (1959:634). 



— USNM 4311/5034 from Valentine, Cherry 
County, Nebraska]. 
Neotoma floridana baileyi — Bailey, 1905:109. 

Remarks. — Because of its present 
geographic isolation, Neotoma floridana 
baileyi assumes certain characteristics of 
an "insular" subspecies. Although mem- 
bers of this subspecies are distinctive in 
at least minor characteristics of every 
parameter studied, no results obtained in 
this study indicate that baileyi lias 
evolved to a level warranting specific 
status. 



Records of occurrence. — Specimens exam- 
ined (56).— NEBRASKA: Cherry County: Val- 
entine, 6 (USNM); 4 mi E Valentine, 6 (KU); 
6 mi E Valentine, 15 (KU); Clark's Canyon, 
near Valentine, 12 (USNM); 3 mi SSE Valen- 
tine, 1 (KU); 10 mi S Cody, 5 (USNM); 22 
mi SW Valentine, 3 (KU). Keya Paha County: 
6 mi S, 8 mi E Springview, 1 (KU). Rock 
County: 11.5 mi N, 7.5 mi W Bassett, 7 (KU). 

Additional record. — NEBRASKA: Brown 
County: Long Pine (Jones, 1964:218). 

Distribution and habitat. — Selected 
localities of recorded occurrence of Neo- 
toma floridana baileyi are plotted in fig- 
ure 2. Goldman (1910:25) reported as 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



13 



this subspecies a woodrat from 18 mi 
SE Rapid City, South Dakota, but Jones 
(1964:217) stated that the individual re- 
eorded "is without question Neotoma 
cinerea nipicola." I have searched ex- 
tensively for Neotoma floridana in Todd, 
Mellette, and Tripp counties, South 
Dakota, but found neither the woodrats 
nor their distinctive dwellings. Habitat 
that appeared suitable for woodrats was 
extensive along and near the Little White 



and Keya Paha rivers, and in the vicinity 
of Okreek, South Dakota. Although no 
specimens were taken in South Dakota, 
it seems likely that N. f. baileyi will be 
found there eventually. However, it is 
conceivable that dispersal farther north- 
ward is not possible even for a popula- 
tion long in the process of adapting to 
the inclement winters of northern Ne- 
braska. 




ICO 



Fig. 2. Selected locality records for Neotoma floridana baileyi (symbols solid above) and N. f. 
campestris (symbols solid below) in Nebraska. 



In Cherry, Keya Paha, and Rock- 
counties, Nebraska, N. f. baileyi occurs 
in three more or less distinguishable 
habitat types. On the Fort Niobrara 
Wildlife Refuge these rats were abun- 
dant in the heavily wooded floodplain 
of the Niobrara River in March and 
April 1967 and August 1968. Nests were 
constructed in and around fallen trees, 
inside hollow upright trees, at the bases 
of upright trees, and in piles of brush 
and treelimbs. In April, the bark and 
cambium layers of woody twigs appeared 
to serve as a primary source of food. Just 



north of the Snake River Falls in Cherry 
County (22 mi SW Valentine), three 
specimens were taken from nests con- 
structed in the steep, rocky, canyon walls 
bordering the Snake River. In Keya 
Paha County (6 mi S, 8 mi E Spring- 
view) a single specimen was trapped 
under a rocky ledge at the top of a deep 
canyon several miles north of the Nio- 
brara River; no additional nests or signs 
of woodrat activity were located as a 
result of searching similar ledges in the 
immediate area and lower in the same 
and adjacent canyons. Habitat of this 



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MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



type apparently is marginal and not fre- 
quently utilized. 

Woodrats were common in aban- 
doned and little-used buildings at a 
ranch near Long Pine Creek (11.5 mi N, 
7.5 mi W Bassett) in Rock County in 
1968. At this locality I found no evi- 
dence that "natural" nest-site types (e.g. 
rock outcrops, trees, logs, brushpiles) 
harbored woodrats, although these sites 
probably are utilized occasionally. Near 
Long Pine Creek at Long Pine, Brown 
County, where this woodrat has been 
reported to occur (Jones, 1964:218), I 
found the habitat even more extensive 
than at the locality discussed above. A 
superficial search there for woodrats was 
unsuccessful, but I am confident they 
occur in the area and probably are locally 
common along the creek from Long Pine 
to the place where it empties into the 
Niobrara River. I did not revisit the 
locality of record 10 mi S Cody nor have 
I searched for N. f. baileyi along the 
Niobrara or elsewhere to the west of that 
locality. To the east of the easternmost 
locality of record (southwest of Spring- 
view), I have searched for these wood- 
rats as far as eastern Boyd and Holt 
counties. Apparent marginal habitat was 
found on Ponca Creek near Spencer 
(Boyd County) and at several localities 
along the Niobrara River. Another area 
worthy of further search was observed 
south of the Niobrara River just east of 
Midway in Holt County. I suspect that 
N. f. baileyi occurs farther to the east 
than present records indicate. 

Neotoma floridana campestris J. A. Allen 

Neotoma campestris J. A. Allen, 1894:322 
[Holotype— AMNH 7765/6742 from Pen- 
dennis, Lane Co., Kansas]. 

Neotoma floridana campestris — Kellog, 1914:5. 

Remarks. — Although not recognized 
by Goldman (1910:24), Neotoma flori- 
dana campestris is distinctly paler in 
color than adjacent populations of N. f. 
attwateri, occupies relatively distinct 
types of habitat in comparison with other 
populations of the species, and tends 
generally to be larger than rats to the 



east. Although relatively narrow, the 
area of contact between campestris and 
attwateri in eastern Ellsworth and west- 
ern Russell counties, Kansas, forms an 
obvious zone of integradation. The arbi- 
trary line dividing the ranges of the two 
taxa is drawn on a north-south axis gen- 
erally corresponding to the county line 
separating Ellsworth and Russell coun- 
ties. A specimen (KU 119700) assigned 
to campestris from only one mile west of 
that county line might be equally well 
assigned to attwateri, but two specimens 
(KU 14001-02) from one mile east of the 
line clearly are best assigned to attwateri. 
The county line serves as a convenient 
line of demarcation and is as accurate as 
any other would be. 

Records of occurrence. — Specimens exam- 
ined (221).— COLORADO: Crowley County: 
3 mi N Fowler, 4400 ft, 7 (KU); Olney ( = 
Olney Springs), 12 (USNM). El Paso County: 
1.5 mi SW Fountain, 5700 ft, 2 (KU); 2.5 mi 
SW Fountain, 5700 ft, 1 (KU); 3 mi S, 2 mi 
W Fountain, 5600 ft, 1 (KU). Kit Carson 
County: Tuttle, 2 (USNM). Yuma County: 
Wray, 5 (1 USNM, 4 AMNH); 1 mi S Wray, 
3550 ft, 3 (KU); 2 mi W Hale, 1 (KU); 1 mi 
S, 3 mi W Hale, 1 (KU). 

KANSAS: Decatur County: 5 mi S, 8 mi 
W Oberlin, 1 (KU). Ellis County: 16 mi N 
Hays, 13 (KU); 13 mi N, 1 mi W Hays, 1 
(MHP); SE % sec. 28, T. 11 S, R. 18 W (13 mi 
N Hays), 6 (MHP); NW % sec. 31, T. 13 S, R. 
18 W (2 mi W Hays), 3 (MHP); Hays, 7 
(USNM); 0.5 mi S, 3.5 mi W Hays, 1 (KU); 

2 mi S Hays, 1 ( MHP); 7 mi S, 10 mi W Hays, 

3 (KU); NW Yi sec. 11, T. 15 S, R. 20 W (8 
mi S, 10 mi W Hays), 2 (MHP); SW % sec. 
16, T. 15 S, R. 19 W (9 mi S, 6 mi W Hays), 

1 (MHP). Finney County: 19 mi S Dighton, 
7 (KU); 23 mi S Dighton, 2 (KU). Gove 
County: Castle Rock, 9 (KU). Hodgeman 
County: 4 mi S, 0.5 mi W Jetmore, 2 (KU). 
Lane County: 1 mi N Pendennis, 10 (KU); 
Pendennis, 29 (6 AMNH, 23 USNM); 12 mi 
SW Pendennis, 2 (KU); unspecified, 2 (KU). 
Logan County: NE )i sec. 8, T. 13 S, R. 35 W 
(2.5 mi N, 2.5 mi W Russell Springs), 1 
(MHP); NE % sec. 27, T. 13 S, R. 35 W (1 
mi S, 1 mi W Russell Springs), 1 (MHP); I 
mi S Russell Springs, 6 (KU); 5 mi SE Elkader, 

2 (KSTC); 5 mi S Elkader, 4 (KU); un- 
specified, 4 (KU). Ness County: 1 mi S, 16 
mi W Ness City, 4 (KU). Rawlins County: 
7 mi N, 16.5 mi W Atwood, 1 (KU). Rooks 
County: 1.5 mi S, 1 mi W Stockton, 6 (MHP); 

3 mi S, 3 mi W Stockton, 1 (MHP); 6 mi SW 
Woodston, 3 (KU); 20 mi N Hays, 1 (MHP); 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



15 



SW J£ sec. 34, T. 10 S, R. 17 W (7 mi S, 4.5 
mi E Plainville), 1 (MHP). Russell County: 
NE % sec. 34, T. 12 S, R. 11 W (6 mi S, 1 
mi E Lucas), 1 (MHP); NW % sec. 8, T. 13 
S, R. 11 W (8 mi S, 2 jni W Lucas), 1 (MHP); 
NE % sec. 17, T. 13 S, R. 11 W (9 mi S, 1 
mi W Lucas), 4 (MHP); SE % sec. 13, T. 13 
S, R. 11 W (10 mi S, 3 mi E Lucas), 1 (MHP); 
0.5 mi W Russell, 1 (KSTC); NW % sec. 34, 
T. 13 S, R. 12 W (11 mi E Russell), 1 (MHP); 
2 mi W Wilson, 1 (KU); 6 mi S, 4 mi E Russell, 
18 (KU). Scott County: State Park, 1 (KU); 
12 mi N, 3 mi W Scott City, 2 (MHP). Thomas 
County: unspecified, 1 (MHP). Trego County: 
sec. 29, T. 13 S, R. 25 W (Banner), 6 (KU); 
unspecified, 1 (USNM). Wallace County: 
Lacey Ranch (9 mi S, 4.5 mi E Wallace), 
1(KU). 

NEBRASKA: Dundy County: 5 mi N, 2 
mi W Parks, 8 (KU); Haigler, 1 (USNM). 

Additional records.— COLORADO (Finley, 
1958:318, unless otherwise noted): Rent 
County: Fort Lyon. Elbert County: 8 mi NE 
Agate; Cedar Point, 6 mi NW Limon. El Paso 
County: 7 mi SSE Colorado Springs, 5900 ft; 
10 mi S Colorado Springs; 16 mi W Wigwam 
(Armstrong, 1972). Kit Carson County: South 
Fork Republican River, near Flagler (Cary, 
1911:114). Lincoln County: Big Sandy Creek, 
near Hugo (Cary, 1911:115). Pueblo County: 
N of Pinon (Warren, 1942:209); Chico Basin, 
20 mi N Pueblo (ibid.); Pueblo. Yuma County: 
Dry Willow Creek, Boyce Ranch. 

NEBRASKA (Jones, 1964:219): Chase 
County: 5 mi S Imperial. Dawson County: 
10 mi S Gothenburg. Frontier County: vicinity 
Curtis. Hays County: 0.5 mi S Hamlet. Lin- 
coln County: North Platte; sec. 10, T. 11 N, 
R. 27 W (5 mi S, 2.5 mi W Brady). Red 
Willow County: McCook. 

Distribution and habitat. — Locality- 
records for Neotoma floridana campestris 
are shown in figures 2, 3, and 4. Several 
localities listed by Finley (1958:318) 
and one reported by Jones (1964:219) 
are based on observations of dens by 
collectors and laymen. Of the undocu- 
mented reports I have traced, I accept 
the following: 5 mi S Imperial, Chase 
Co., Nebraska (Jones, 1964:215); near 
Flagler, Kit Carson Co., Colorado, and 
near Hugo, Lincoln Co., Colorado (Cary, 
1911:114, 115); Chico Basin, 20 mi N 
Pueblo, Pueblo Co., Colorado, and N of 
Pinon, Pueblo Co., Colorado (Warren, 
1942:209). I have disregarded the follow- 
ing records pending their documentation 
by specimens: 6 mi N, 12 mi W Pueblo, 
Pueblo Co., Colorado — this is a den rec- 



ord reported by Finley (1958:318) and, 
although the den most likely was con- 
structed by N. f. campestris, it is con- 
ceivable that both N. mexicana (disre- 
garded by Finley as constructing dens 
unlike the one he observed) and N. 
albigula occur at this locality; 10 mi N 
Arlington, Kiowa Co., Colorado — Cary 
(1911:114) entered this record on the 
strength of reports by "stockmen" that a 
few woodrats occurred in the area, 
which, if true, probably represented N. 
f. campestris but could have been N. 
micropus; along the Arkansas River, 
south of Chivington, in Prowers Co., 
Colorado — this is another "stockmen" re- 
port cited by Cary (loc. cit.), but because 
micropus now is known on the north side 
of the Arkansas River both east and west 
of this locality, it is more likely that the 
observed woodrat dens were those of 
that species; Arkansas River bottom, near 
Holly, Prowers Co., Colorado — originally 
reported by Warren ( 1910:112), this rec- 
ord of woodrat dens clearly should be 
removed from localities included in the 
distribution of campestris because micro- 
pus has been collected approximately six 
miles east in adjacent Kansas (Coolidge) 
and the general habitat near Holly is 
more like that of micropus than that of 
campestris. 

One other locality of record for 
campestris is worthy of comment. Finley 
(1958:318) discussed a specimen repre- 
sented only by a skull with incomplete 
data (USNM 6301) and Armstrong 
(1972) reported another (USNM 6320) 
of N. floridana from Denver, Colorado, 
both collected by E. Palmer. Both au- 
thors agree, as do I, that Denver is cer- 
tainly not within the present distribu- 
tional range of campestris and, although 
the identity of the skulls is not in ques- 
tion, they probably are from some lo- 
cality (ies) to the east of Denver. 

Considering only the records ac- 
cepted, the distribution of campestris in 
Colorado extends from just north of the 
Arkansas River (Fort Lyon, 3 mi N 
Fowler, and Olney Springs) to the foot- 
hills of the Rockies (several localities 



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107 



105 



103 



40 



38 




40 



50 



100 Miles 



33 



107 



105 



103 



Fig. 3. Selected locality records for Neototna floridana campestris (symbols solid below) and N. 
micropus canescens (solid symbols) in Colorado. 




39- 



38 






38 



100 



97 



Fig. 4. Selected locality records for Neotoma floridana campestris (symbols solid below), N. f. 
attwateri (symbols solid above), and N. micropus canescens ( solid symbols ) in Kansas. Circles rep- 
resent records accompanied by specific locality data; squares denote records specific only to county. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



17 



south and southeast of Colorado Springs), 
thence northeastward at least as far as 
Wray and in Nebraska as far as North 
Platte. In Kansas, the race occurs east 
to the line (discussed above) between 
Russell and Ellsworth counties, where 
bampestris intergrades with attwateri. I 
have not attempted to determine the 
northern limit of range of campestris 
through field investigations, but Ander- 
sen and Fleharty (1967:39) did not find 
woodrats in Jewell County, Kansas, and 
neither Jones (1964) nor Choate and 
Genoways (1967) reported finding them 
in southern Nebraska east of Red Willow 
County. The first specimens to be asso- 
ciated with the name campestris in Ne- 
braska were reported by Jones (1954: 
485), although Goldman (1910:25) 
earlier listed a specimen from Haigler 
under the name baileyi. 

The southern extension of the species 
in western Kansas seems to correlate well 
with the southern extent of the Ogallala 
limestone formations north of the Arkan- 
sas River. I have searched for woodrats 
throughout the area between the Arkan- 
sas River and the southernmost locality 
records for campestris. Specimens of 
campestris from the Pawnee River in 
northern Finney County are from only 
about 20 miles north of a locality (just 
north of the Arkansas River) where I 
have collected Neotoma micropus. The 
distributional status of floridana and mi- 
cropus in those areas where the two 
might come into contact is discussed in 
the account of N. m. canescens. 

A detailed and extensive ecological 
account of N. f. campestris in Colorado 
is given by Finley (1958:499-514). He 
found that this rat is one of the most 
versatile species of the genus in utilizing 
available materials, rocks, tree cactus, 
trees, or bushes for the construction of 
dens. Type of vegetation available is 
apparently of little importance, with the 
exception that unsculptured shortgrass 
prairie is insufficient for the fulfillment 
of denning requirements. In Kansas and 
Nebraska the situation is undoubtedly 
much the same. In Dundy County, Ne- 



braska, I have seen houses of campestris 
constructed in sagebrush in a manner 
that rendered them indistinguishable 
from houses of micropus in southwestern 
Kansas. At several localities in Kansas 
(e.g. 19 mi S Dighton, Finney County, 
and 4 mi S and 0.5 mi W Jetmore, Hodge- 
man County) I have collected this wood- 
rat from rock outcrops in otherwise open 
grasslands. In many cases the nearest 
outcrops or river systems were several 
miles distant. At two localities ( 16 mi 
N Hays, Ellis County, and 6 mi S and 4 
mi E Russell, Russell County ) large pop- 
ulations of campestris were observed in 
eastern red cedar windbreaks not far 
from major rivers (the Saline River and 
the Smoky Hill River, respectively). 
Most nests in the windbreaks were on 
the ground at the bases of trees, partially 
shielded by overhanging boughs. A few 
nests, however, were two to about 10 feet 
above the ground, supported solely by 
the trees. Along the Pawnee River in 
Finney County and the Smoky Hill River 
in Logan County, woodrats were living 
in piles of flood debris. In some cases the 
debris served as a skeleton upon which 
the rats had amassed large superstruc- 
tures, but in others the only outward 
signs of the presence of woodrats were 
fecal droppings and faint runways. 

Throughout the range of A7. /. cam- 
pestris, the distributional pattern is one 
of apparent disjunctness, with most pop- 
ulations almost certainly at least semi- 
isolated. Such a pattern probably re- 
sults from inability of these woodrats to 
permanently occupy shortgrass prairie 
between river systems, rock outcrops, 
and stands of trees. A study of long- 
range dispersal habits of the race would 
be enlightening in revealing how iso- 
lated populations are founded and how 
much (if any) interpopulational gene 
flow takes place (see Wiley, 1971). 

Neotoma floridana attwateri M earns 

Neotoma attwateri Mearns, 1897:721 [Holotype 
— USNM 11964/10402 from Lacey's Ranch, 
Turtle Creek, Kerr Co., Texas]. 

[Neotoma floridana] attwateri — Elliot, 1901: 
157. 



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MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



Neotoma floridana osagensis Blair, 1939:5 
[Holotype— UNMZ 76070 from Okesa, 
Osage Co., Oklahoma]. 

Remarks. — Relegation of the name 
Neotoma floridana osagensis to the syn- 
onymy of N. f. attwateri extends the dis- 
tribution of attwateri north to Kansas 
and Missouri. Total geographic varia- 
tion within the subspecies is increased as 
a result of this change. As discussed be- 
yond, the pattern of variation northward 
through Texas and in southern Oklahoma 
is clearly clinal, and lacking in abrupt 
changes that might indicate either re- 
stricted gene flow or secondary inter- 
gradation. I have not examined speci- 
mens from the area between Hill and 
Robertson counties, Texas, but according 
to Strecker (1924:16 and 1929:220) 
woodrats are common in that area, at 
least along the Brazos River, Tehuacana 
Creek, and White Rock Creek. These 
reports indicate that although docu- 
mentary specimens may be lacking, 
woodrats are more or less continuously 
distributed throughout the area in which 
the ranges of attwateri and osagensis 
were alleged to meet; therefore, no rea- 
son exists to suspect reduced gene flow. 

The pattern of variation at the zone 
of contact between attwateri and campes- 
tris is discussed in the remarks of the 
previous account. On the east, the range 
of attwateri meets that of A 7 . /. illinoensis 
in Missouri and Arkansas and that of N. 
f. rubida in southeastern Texas. I have 
only superficially studied woodrats from 
Missouri and Arkansas, and cannot com- 
ment in detail on the relationships of 
illinoensis to attwateri. These two races 
seemingly resemble each other to a 
greater degree than either resembles 
rubida, but detailed study might not 
support this supposition. I have exam- 
ined specimens of rubida from Texas and 
found woodrats assignable to that name 
relatively distinct from those represent- 
ing attwateri. One specimen from Harris 
County, Texas (SFA 2312), appears to 
be an intergrade between the two sub- 
species, but herein is assigned to attica- 
teri on the basis of its comparatively 



small size and the absence of reddish 
coloration typical of rubida. 

Records of occurrence. — Specimens examined 
(680).— KANSAS: Allen County: 2 mi N, 0.5 
mi W Neosho River Bridge, Humbolt, 2 ( KU ) . 
Anderson County: 3.7 mi S Garnett, 1 (KU); 
4.5 mi NNE Welda, 1 (KU). Chase County: 
9 mi E Lincolnville, 1 (KU); 1.5 mi S Safford- 
ville, 1 (KSTC). Chautauqua County: Cedar 
Vale, 8 (USNM); 1 mi N, 2.5 mi W Elgin, 

1 (KU). Cowley County: 3.75 mi S, 1.5 mi W 
Udall, 1 (KU); 6 mi N, 12 mi E Arkansas City, 

2 (KU); 3 mi W Cedar Vale, 1 (KU); 8.6 
mi E Arkansas City, 2 (KU); 3 mi SE Ar- 
kansas City, 2 (KU). Crawford County: Mul- 
berry, 1 (KU). Douglas County: 7 mi N 
Lawrence, 1 (KU); 5 mi N, 2 mi W Law- 
rence, 1 (KU); 6 mi NW Lawrence, 1 (KU); 

1 mi N Midland, 2 (KU); 1 mi NW Midland, 
5 (KU); 1 mi W Midland, 2 (KU); within 3 
mi radius of Lawrence, 17 (KU); 1 mi N, 5 
mi W Lawrence, 1 ( KU ) ; 7 mi W Lawrence, 

2 (SM); 8 mi SW Lawrence, 1 (KU); 8.5 mi 
SW Lawrence, 2 (KU); 10 mi SW Lawrence, 

3 (KU); Lone Star Lake, 6 (KU); 9 mi S, 
9 mi W Lawrence, 1 (KU); 10 mi S, 9 mi W 
Lawrence, 1 (KU); 2 mi S, 2 mi W Pleasant 
Grove, 1 (KU); unspecified. 1 (KU). Elk 
County: 1.12 mi S, 1.75 mi W Moline, 1 (KU). 
Ellsworth County: 3 mi S Wilson, 2 (KU); 
3.5 mi SE Ellsworth, 8 (KU); 5 mi SW 
Ellsworth, 3 (KU). Geary County: Fort Riley, 
2 (USNM). Greenwood County: within 5 mi 
radius of Hamilton, 32 (KU); 15 mi W Hamil- 
ton, 9 (1 AMNH, 8 KU); 12 mi W Hamilton, 
1 (AMNH); 4 mi S, 17 mi W Hamilton, 3 
(1 AMNH, 2 KU); 4 mi S, 14 mi W Hamilton, 
1 (KU); 12 mi SW Hamilton, 4 (KU); 8 mi 
SW Toronto, 7 (KU); 8.5 mi SW Toronto, 17 
(KU); unspecified, 1 (AMNH). Jackson 
County: 6 mi S, 10 mi W Holton, 1 (KU). 
Jefferson County: 13 mi NE Lawrence, 2 (KU). 
Leavenworth County: 5 mi NE Lawrence, 1 
(KSTC); unspecified, 10 (KU). Lyon County: 
Ross Natural History Reservation, 2 (KSTC); 
Emporia, 1 (KSTC); unspecified, 1 (KSTC). 
Marshall County: 1 mi W Vermillion, 2 (KU). 
Montgomery County: 17 mi NNE Sedan, 1 
(KU). Morris County: 4.12 mi S, 6 mi W 
Council Grove, 1 (KU). Rice County: 2 mi 
N, 2 mi E Little River, 1 (KSTC). Riley 
County: 3.25 mi S, 2 mi E Randolph, 1 
(MHP); Manhattan, 9 (4 AMNH, 5 USNM). 
Shawnee County: 1 mi N, 1 mi W Big Springs, 
1 (KU). Wabaunsee County: 1 mi N Alma, 

4 (KU). Wilson County: 2 mi N, 3 mi E 
Benedict, 1 (KSTC). Woodson County: State 
Lake, 2 (KSTC). 

OKLAHOMA: Adair County: 5 mi SE 
Flint, 1 (OSU); 3 mi NNE Chewey, 5 (SM); 
7 mi W Stihvell, 1 (KU); Stilwell, 8 (USNM). 
Blaine County: Canton Public Hunting Area 
and Lake — vicinity of Longdale, 17 ( 1 FWCM, 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



19 



11 OSU, 5 USNM); Salt Creek Canyon, 2 
(KU); 2 mi N, 9 mi W Okeene, 1 (KSTC); 

2 mi N, 2 mi W Okeene, 1 (KSTC); Roman 
Nose State Park, 9 (OSU); 2 mi W Watonga, 

3 (OSU). Bryan County: 10 mi SE Benning- 
ton, 1 (TNHC); 5 mi N Colbert, 2 (TNHC); 
0.5 mi NW Colbert, 3 (TNHC). Caddo 
County: 5 mi W Cogar, 3 (SM); Fort Cobb, 
2 (USNM). Canadian County: Methodist 
Church Camp, sec. 18, T. 11 N, R. 10 W, 

1 (SM); 5.5 mi SE Hinton, 1500 ft, 1 (KU). 
Carter County: 3 mi N Springer, 3 (USNM). 
Cherokee County: 2.5 mi NW Chewey, 2 

SM). Choctaw County: 1.5 mi N Hugo, 1 

OSU); 1 mi N, 3 mi E Hugo, 1 (OSU). 

Cleveland County: 9 mi N, 2 mi E Norman, 

2 (SM); within 5 mi radius of Norman, 18 (6 
SM, 1 USNM, 11 KU); 1 mi N, 9 mi E 
Norman, 1 (SM); 0.5 mi N, 6 mi E Norman, 
1 (SM); 6 mi E Norman, 1 (SM); 8 mi E 
Norman, 1 (SM); 9 mi E Norman, 1 (SM); 

3 mi NE Noble, 1 (SM); 1 mi N, 3 mi E 
Lexington, 1 (OSU); 4 mi SE Lexington, 1 
(OSU); unspecified, 2 (SM). Comanche 
County: Wichita Mountains Wildlife Refuge, 
24 (10 OSU, 6 SM, 8 USNM); 19 mi NW 
Cache, 1 (SM); Mt. Scott, 7 (USNM); 9 mi 
NW Cache, 1 (SM); Chattanooga, 1 (USNM); 
unspecified, 1 (SM). Cotton County: 5 mi SE 
Taylor, 3 (SM). Creek County: Sapulpa, 4 

KU). Dewey County: 2 mi N, 6 mi W Long- 
dale, 4 (KSTC); NE corner Canton Public 
Hunting Area, 1 (OSU); 2 mi S, 2 mi W 
Seiling, 1 (KU); 6 mi S, 2 mi W Seiling, 2 
(KU); 5 mi W Canton, 2 (KU); 6.5 mi S, 
3 mi W Seiling, 2 (KU); 7 mi S, 2.5 mi W 
Seiling, 3 (KU); 8 mi S, 5 mi W Seiling, 2 
(KU). Garfield County: 1 mi S, 2 mi E Enid, 
1 (OSU). Haskell County: 8.5 mi S Stigler, 

1 (SM). Johnston County: Tishomingo Na- 
tional Wildlife Refuge, 1 (USNM). Kay 
County: 1 mi S, 7 mi E Ponca City, 1 (OSU); 
Ponca Agency, 1 (USNM). Latimer County: 
5 mi N Wilburton, 1 (KU); 3.5 mi N Wilbur- 
ton, 8 (SM); Red Oak, 1 (USNM); Wilburton, 

2 (OSU). Le Flore County: 5 mi S Wister, 

1 (SM); 2 mi NE Zoe, 2 (SM); 0.75 mi N 
Zoe, 4 (SM). Lincoln County: 3.5 mi S 
Perkins, 1 (OSU); 5 mi W Stroud, 1 (OSU). 
Major County: 15 mi S Waynoka (see remarks 
in account of N. m. canescens), 1 (OSU); 1.5 
mi N, 0.25 mi W Cleo Springs, 8 (KSTC); 5 
mi S, 2.5 mi E Cleo Springs, 2 (KSTC); 3 mi 
S Chester [ = 1.5 mi N Seiling] (see remarks 
in account of N. m. canescens), 16 (8 KSTC, 
8 KU); 3 mi S, 0.5 mi E Chester, 4 (KU); 3 
mi S, 1 mi E Chester, 1 (KU). Marshall 
County: 6 mi N Willis, 1 (SM); 5 mi S, 1 
mi W Shay, 1 ( OSU ) ; 0.5 mi E Willis, 1 ( SM ) ; 

2 mi E Willis, 4 (MWU); 1 mi S, 2 mi W 
Willis, 1 ( SM ) ; University of Oklahoma Biolog- 
ical Station, including Engineering Tract and 
Paul's Landing, 19 (2 OSU, 17 SM); unspec- 
ified, 4 (1 MWU, 2 OSU, 1 SM). Mayes 



County: 1 mi S Spavinaw, 6 (KU). McCurtain 
County: 2 mi N Smithville, 1 (SM); 2.5 mi 
W Smithville, 3 (SM); 2 mi W Smithville, 2 
(SM); Beavers Bend State Park, 4 (2 SM, 
2 KU); 15 mi SE Broken Bow, 1 (SM). Mur- 
ray County: Sulphur, 1 (OSU); 1.5 mi S 
Dougherty, 1 (MWU); unspecified, 1 (OSU). 
Muskogee County: 4 mi below [=SW] Fort 
Gibson Dam, 1 (OSU); 6 mi SE Fort Gibson, 
1 (OSU). Okmulgee County: 3 mi S Okmul- 
gee, 1 (OSU). Osage County: 10 mi NE 
Pawhuska, 1 (TNHC); Osage Hills State Park, 
6 (OSU); 10 mi WSW Fairfax, 3 (SM); 
McClintock Boy Scout Camp, 1 (USNM); 
Heartwood Mountain, 1 (OSU). Pawnee 
County: 7.5 mi N, 2.75 mi W Pawnee, 1 (KU). 
Payne County: 2 mi N, 15 mi W Stillwater, 

1 ( OSU );lmiN,9miW Stillwater, 2 ( OSU ) ; 
vicinity of Lake Carl Blackwell, 36 (34 OSU, 

2 USNM); 11 mi W Stillwater, 1 (OSU); JO 
mi W Stillwater, 8 (2 OSU, 6 TT); 8 mi W 
Stillwater, 1 (OSU); 5.5 mi W Stillwater, 1 
( OSU );4miW Stillwater, 1 ( OSU ) ; Stillwater, 

1 (OSU); 2 mi E Stillwater, 1 (OSU); 4 mi 
E Stillwater, 1 (OSU); 5 mi E Stillwater, 1 
(OSU); 1 mi S, 3 mi W Stillwater, 2 (OSU); 
4.25 mi SW Stillwater, 1 (OSU); 2.5 mi S, 
0.25 mi W Stillwater, 1 (OSU); 1 mi S, 3 
mi W Mehan, 1 (OSU); 10.5 mi S Stillwater, 

2 (OSU); unspecified, 7 (OSU). Pittsburg 
County: 4 mi NW McAlester, 1 (OSU); 2 mi 
E McAlester, 1 (OSU); Savanna, 1 (USNM). 
Pontotoc County: 4 mi S Ada, 1 (OSU); un- 
specified, 2 (OSU). Pottawatomie County: 1 
mi W Pink, 3 (SM); 7 mi SE Tecumseh, 2 
(KU). Pushmataha County: 4 mi SE Clayton, 
1 (SM); 1 mi S Nashoba, 4 (TNHC). Rogers 
County: 0.5 mi E Chelsea, 1 (OSU). Stephens 
County: unspecified, 1 (SM). Tulsa County: 
8 mi W Red Fork, 2 (USNM); Red Fork, 2 
(USNM); unspecified, 1 (SM). Woodward 
County: unspecified (see remarks in account 
of N. m. canescens), 2 (SM). 

TEXAS: Brazos County: 3 mi W Bryan, 
1 (TCWC); 7 mi W College Station, 1 
(TCWC); within 5 mi radius of College Sta- 
tion, 19 (TCWC); 7 mi SW College Station, 

1 (TCWC); 10 mi SE College Station, 1 
(TCWC). Collins County: 1 mi NE Wylie, 

2 (MWU). Colorado County: Eagle Lake, 1 
(TCWC). Cooke County: Marysville, 2 
(USNM); 2 mi S Marysville, 2 (TCWC); 
8 mi W Gainsville, 2 (MWU); Gainsville, 1 
(USNM); unspecified, 2 (USNM). Gonzales 
County: Palmetto State Park, 1 (TNHC). 
Gregg County: 3.2 mi E Gladewater, 1 (TT). 
Grimes County: Navasota, 3 (USNM). Harris 
County: 22 mi N Houston, 1 (SFA). Hender- 
son County: 2 mi NE Malakoff, 1 (SFA); 12 
mi SE Athens, 1 (SFA). Hill County: 4 mi 
N Blum, 2 (KU). Jack County: 7 mi SE 
Jacksboro, 1 (MWU). Kaufman County: 19 
mi SE Dallas, 2 (TT). Kerr County: Lacey's 
Ranch, Turtle Creek, 11 (5 AMNH. 1 TNHC, 



20 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



5 USNM); Ingram, 9 (USNM). Lavaca 
County: 3 mi W Hallettsville, 1 (TCWC); 
0.5 mi W Hallettsville, 1 (TCWC); 14 mi WSW 
Hallettsville, 1 (TCWC). Montague County. 
2 mi W Nocona, 1 ( MWU ) ; 3 mi E Nocona, 

1 (MWU); 4 mi E Stoneburg, 1 (MWU). 
Navarro Comity: Barry, 1 (SFA). Parker 
County: 8.9 mi S Aledo, 13 (FWCM). Rob- 
ertson County: 2 mi W Hearne, 2 (TCWC). 
Tarrant County: Lake Worth Area, 1 
(FWCM); Fort Worth, 1 (FWCM); 6.5 mi 
S, 4 mi W Benbrook, 2 (FWCM). Victoria 
County: Victoria, 1 (USNM); unspecified, 1 
(USNM). Williamson County: 3 mi N Mc- 
Neil, 1 (TNHC). 

Additional records : KANSAS ( Rainey, 
1956): Dickinson County: 15 mi E Talmage 
(Pi. 9). Greenwood County: 7 mi E Eureka 
(Pi. 2, Fig. 2). Lyon County: 6 mi N Madison 
(PI. 3, Fig. 1). Marshall County (p. 634): 

2 mi S Marysville; 5.5 mi S Beattie. Riley 
County: 7 mi S Manhattan (p. 551). 

OKLAHOMA (Blair, 1939b: 124, unless 
odierwise noted): Adair County: 5 mi S 
Kansas. Bryan County: 5 mi SW Colbert ( Mc- 
Carley, 1952:108). Cleveland County: Noble. 
McClain County: 7 mi SW Normaii (Hays, 
1958:235, 238). Murray County: Dougherty. 
Osage County: Conway Springs; Okesa (Blair, 
1939a:7); 2 mi SW Okesa. Rogers County 
(Blair, 1939a:7): 3 mi W Catoosa; Garnett. 

TEXAS: Cooke County (Russell, 1953: 
461 ) : 13 mi NE Gainsville; 7 mi N Gains- 
ville; 4 mi NNE Myra; 4 mi NE Rosston; 3 
mi NE Leo. Hunt County: 5 mi N Greenville 
(Baker, 1942:343). McLennan County: vi- 
cinity of Waco (Strecker, 1929:220). 

Distribution and habitat. — Figures 4, 



5, and 6 show localities of occurrence of 
Neotoma jioridana attwateri in Kansas, 
Oklahoma, and Texas, respectively. This 
subspecies also is known from adjacent 
parts of Missouri and Arkansas. The dis- 
tribution of attwateri extends from north- 
central and northeastern Kansas and cen- 
tral Missouri southward through Okla- 
homa, western Arkansas, and eastern 
Texas to the Gulf of Mexico. In extreme 
southeastern Texas it is replaced by the 
larger, reddish-colored N. f. rubida. 
Goldman (1910:26) listed two speci- 
mens as attwateri from the Edwards 
Plateau at Rocksprings, Kerr Co., Texas. 
I examined two specimens (USNM 
117552-53) from 7 mi S Rocksprings that 
were collected in 1902; I do not doubt 
that they are the same specimens studied 
by Goldman. The identity of these and 
other woodrats, and resultant ramifica- 
tions as regards distribution of several 
species will be discussed elsewhere; it is 
only necessary to indicate here that both 
specimens are best referred to Neotoma 
albigida. Neotoma jioridana, therefore, 
is not known to have occurred on the 
Edwards Plateau in Recent times (see 
Dalquest et at, 1969:250). The south- 
westernmost locality of record for the 
species is Ingram, Kerr County. 




Fig. 5. Selected locality records for Neotoma jioridana attwateri (symbols solid above) and N. 
micropus canescens (solid symbols) in Oklahoma. The encircled symbol denotes the single known 
locality of sympatric occurrence of the two species; for explanation of symbols see figure 4. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



21 



Distributional relationships of N. f. 
attwateri at the western limit of its range, 
where it abuts the range of N. m. canes- 
cens, will be discussed in the account of 
the latter. Neotoma floridana attwateri 
has not been found in Nebraska; factors 
possibly limiting its range to the north 
are discussed by Rainey (1956:632-637) 
and Jones (1964:218). 

The literature is replete with ecolog- 
ical accounts of N. f. attwateri in Kansas 
and northern Oklahoma but the habits 
of this rat in southern Oklahoma and 
Texas are not well known. Rainey (1956: 
549), in one of the better ecological 
studies of the species, summarized the 
habitat in eastern Kansas as follows: 
'habitat of the woodrat in eastern Kansas 
is divisible into two principal types; the 
osage orange, Madura pomifera (Raf. ), 
hedge-row habitat type, which is the 
more widespread, and the rock outcrop 
type of habitat. Stone fences, upland 
woods, wooded stream-courses, shrubby 
hillsides, and uninhabited buildings con- 
stitute habitat types of less importance." 
Fitch and Rainey ( 1956 ) contributed 
significantly to a general understanding 
of the ecology of woodrats in eastern 
Kansas, but found them only in the 
habitats reported by Rainey (loc. cit.). 
My observations of attwateri in eastern 
Kansas also fit the pattern outlined by 
Rainey. In Ellsworth County, this wood- 
rat was trapped in two markedly differ- 
ent habitats. At a locality 3.5 mi SE 
Ellsworth, woodrats were living in crev- 
ices and around large boulders of a 
steep rocky hillside just south of the 
Smoky Hill River, but 5.5 mi SW Ells- 
worth I found a sparsely distributed, and 
apparently small, population of wood- 
rats occupying what appeared to be mar- 
ginal habitat along the banks of a dry 
creek. Most houses were in small piles 
of flood debris, but one small, active nest 
was on the ground partially concealed 
by the dead stems of annual weeds in 
the corner of a recently harvested milo 
field. A few scattered trees near the 
creek may have afforded some cover and 
building materials, but no dens were 



observed directly associated with the 
trees. 

Murphy (1952:205) concluded that 
woodrats in north-central Oklahoma pre- 
fer postoak-blackjack oak ravines and 
fringed forest ravines. Goertz (1970:96- 
98) studied attwateri in the same area 
and found them in various types of 
woodlands, brushy areas, riparian asso- 
ciations along stream banks, and to a 
lesser extent in small rock outcrops in 
relatively open prairie. Spencer (1968: 
38) reported collecting attwateri in a 
mesquite-prickly pear cactus association 
in gypsum rock outcrops near the west- 
ern edge of the range in Oklahoma. 

A colony of woodrats in thick wood- 
land along the banks of a sandy gully in 
Brazos County, Texas, was studied by 
Lay and Baker (1938). Rats variously 
occupied surface dens in the wooded 
area, burrows and root crevices in the 
gully bank, and an underground burrow 
in a nearby pasture. Farther north in 
Texas, Strecker (1929:220) reported at- 
twateri common along rocky and wooded 
river banks. Bailey (1905:110) stated 
that "near Ingram, in the valley of the 
Guadalupe River, a few of these wood 
rats were caught in the cliffs and rocks 
bordering the river valley, but they were 
more common under the great heaps of 
driftwood and rubbish along the river 
bottoms." 

As expressed or implied by most of 
the authors cited and as observed by 
me, the most important factor of the 
habitat of Neotoma floridana (including 
this subspecies and the two previously 
discussed) is the availability of cover to- 
gether with materials and structural ele- 
ments for construction of dwellings. 
Neotoma floridana seems to be extremely 
versatile as regards food requirements 
and relatively opportunistic in terms of 
habitat selection so long as minimal re- 
quirements for cover and nesting ma- 
terials are available. 

Neotoma floridana rubida Bangs 

Neotoma floridana mbida Bangs, 1898:185 
[Holotype — collection of E. A. and O. Bangs 



22 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 




Fig. 6. Selected locality records for Ncotoma floridana attwateri (symbols solid above), N. f. 
rubida (symbols solid below), and N. micropus canesccns (solid symbols) in Texas. For explana- 
tion of symbols see figure 4. 



2872 from Gibson, Terrebonne Parish, 
Louisiana]. 

Remarks. — The systematic status of 
Neotoma floridana rubida was not a pri- 
mary concern of this study, but was con- 
sidered to determine the eastern extent 
of the distribution of N. f. attwateri in 
southern Texas. My findings agree with 
those of McCarley (1959:411), except 
that specimens from Nacogdoches and 
Panola counties (although herein as- 
signed to rubida) are much less reddish 
than specimens of rubida from farther 
south in Texas and those (LSU) exam- 
ined from Louisiana. This may be an 
area of intergradation between N. f. 
rubida and N. f. attwateri or N. f. illi- 



noensis (or among all three). Kelson 
(1952:236) referred a specimen, pre- 
viously assigned to rubida (Goldman, 
1910:23), from Texarkana, Bowie 
County, to N. f. illinoensis, but indicated 
it resembled N. f. osagensis (= IV. /. 
attwateri) in certain characters. I have 
not seen the specimen in question and 
therefore follow Kelson. Goldman (1910: 
26) assigned two specimens from 
Kountze, Hardin County, to attwateri 
and 22 specimens from nearby Sourlake, 
Hardin County, to rubida (p. 23). That 
portion of Texas was mapped by him as 
within the range of rubida (p. 21). I 
regard the specimens from Kountze as 
rubida on geographic grounds. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



23 



Records of occurrence. — Specimens exam- 
ined (25).— TEXAS: Anderson County: 5.5 
mi SE Slocnm, 1 (SFA). Angelina County: 
Diboll, 1 (SFA). Cherokee County: 0.5 mi 
N Forest, 1 (SFA); 3 mi W Forest, 1 (SFA). 
Nacogdoches County: 1 mi N Nacogdoches, 2 
(TT); Nacogdoches, 3 (SFA); 5 mi S Nacog- 
doches, 1 ( SFA ) ; 8 mi S Nacogdoches, 1 
(SFA). Panola County: 2 mi S, 5 mi W 
Carthage, 1 (SFA). Polk County: 14 mi N 
Camden, 4 (TCWC); 12 mi W Camden, 1 
(TCWC). Trinity County: 1 mi E Trinity, 
1 (TCWC). Walker County: 17 mi WNW 
Huntsville, 1 (TCWC); Hnntsville, 2 (TCWC); 
4 mi E Huntsville, 1 (TCWC); 2 mi SW Hunts- 
ville, 1 (TCWC); 6 mi S Huntsville, 1 
(TCWC); 11 mi NW New Waverhj, 1 
(TNHC). 

Additional records: TEXAS: Hardin 
County: Konntze (Goldman, 1910:26); Sonr- 
lake (Goldman, 1910:23). 

Distribution and habitat. — The dis- 
tribution of N. f. rubida in Texas is shown 
in figure 6. I have not studied woodrats 
of this subspecies in the field, but Mc- 
Carley (1959:411) indicated that their 
habits are not markedly different from 
those of N. f. attwateri in Texas. Davis 
(1960:192) reported that in some areas 
of eastern Texas woodrats live in bur- 
rows and do not construct surface nests. 
If true, this would be a departure from 
the usual habits of N. floridana in north- 
ern and western portions of the range. 

Neotoma micropus 

Three nominal subspecies of Neo- 
toma micropus are recognized herein; 
this is a reduction by two in the number 
heretofore regarded as valid. In com- 
parison with most other species of wood- 
rats, the biological attributes (including 
geographic variation and taxonomy) of 
micropus have received relatively little 
attention from mammalogists. As indi- 
cated previously, I studied micropus 
throughout its geographic range, but less 
intensively in New Mexico than in other 
areas. 

Recent studies have shown that 
Neotoma micropus and Neotoma albigula 
are more closely related than previously 
was thought. The two species have been 
found together at many localities and at 
some of these they apparently hybridize. 



Finley ( 1958 ) first reported specimens 
from Colorado that appeared to be pos- 
sible hybrids and Anderson ( 1969 ) re- 
searched this problem in Chihuahua and 
Coahuila. I have examined the material 
studied by Finley as well as additional 
material from Texas and New Mexico. 
Elucidation of the micropus-albigula 
problem eventually will affect the total 
understanding of the systematics of the 
woodrats of both of these species and of 
Neotoma floridana. In this report, how- 
ever, I have concentrated on micropus 
and floridana. 

The patterns of geographic variation 
in micropus are such that I considered 
three alternative schemes with regard to 
the assignment of subspecific names. Ir- 
respective of the alternatives, it seems 
clear that the woodrats from White 
Sands, New Mexico, are only slightly 
more pallid ecomorphs of populations of 
the species in adjacent areas and do not 
warrant recognition at the subspecific 
level. However, one of the alternatives 
discussed and rejected below would re- 
quire use of the name leucophea for all 
populations of the species in western 
Texas, New Mexico and adjacent Chi- 
huahua, Coahuila, and Nuevo Leon. 

The first alternative was to leave ex- 
isting names (with the exception of 
leucophea) unchanged and simply de- 
scribe geographic variation within that 
system. The only advantage seemed to 
be that of nomenclatural stability. Rec- 
ognition of a darker eastern subspecies 
(micropus) and a generally paler western 
subspecies (canescens) would obscure 
some trends in variation in color and in 
external and cranial sizes. This alterna- 
tive also would result in continued rec- 
ognition of the name N. m. littoralis, 
even though woodrats previously as- 
signed to that name differ appreciably 
from specimens of N. m. micropus from 
farther north in Tamaulipas only in be- 
ing somewhat more brownish. 

The second alternative involved rec- 
ognition of seven subspecies to denote 
each general kind of variant seen. 
Neotoma micropus littoralis and N. m. 



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MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



planiceps would continue to be recog- 
nized. Neotoma micropus micropus 
would be restricted to the small, dark, 
coastal woodrats of central and northern 
Tamaulipas. A new name would be pro- 
posed for the large, intermediate-colored 
woodrats of the Texas Coast and adjacent 
inland areas. The available name N. m. 
surberi would be applied to the large, 
dark woodrats of south-central Kansas 
and western Oklahoma (not including 
the panhandle of that state). The name 
canescens would be restricted to the 
large, pale-colored woodrats of the Okla- 
homa Panhandle, southwestern Kansas, 
and southeastern Colorado; and the 
name leucophea would be applied to the 
small, pallid woodrats of New Mexico, 
western Texas, and Mexico, exclusive of 
coastal Tamaulipas and the vicinity of 
Rio Verde, San Luis Potosi. 

The third alternative, and the one 
adopted, involves provisional retention of 
the name N. m. planiceps (pending ac- 
quisition of specimens that elucidate the 
distributional and morphological rela- 
tionships of this woodrat, which pres- 
ently is known only by the holotype). 
The name N. m. littoralis is placed in the 
synonymy of N. m. micropus, a subspe- 
cies of small, dark-colored ( often brown- 
ish) woodrats of coastal Tamaulipas. All 
other populations of the species, includ- 
ing those previously known as N. m. 
micropus from localities other than 
coastal Tamaulipas, are referred to a 
single subspecies, N. m. canescens. Be- 
cause variation both in size and color is 
gradually clinal throughout the distribu- 
tion of canescens, no clearcut areas of 
demarcation separate local populations. 
However, to recognize only a single 
taxon results in assignment of woodrats 
that are quite different (especially from 
the extremes of the clines) to the same 
subspecies. Total geographic variation 
within the subspecies N. m. canescens as 
thus conceived exceeds that in any of 
the other races considered in this study. 

Neotoma micropus canescens J. A. Allen 
Neotoma micropus canescens J. A. Allen, 1891: 



285 [Lectotype— AMNH 3030/2350 from 
North Beaver (=North Canadian River), 
Indian Territory ( Cimarron Co., Okla- 
homa), near the boundary line between the 
Indian Territory and New Mexico]. 

Neotoma macropus [sic] surberi Elliot, 1899: 
279 [Holotype— Field Mus. Nat. Hist. 6755 
from 3 mi W Aha, Oklahoma Territory 
( Woods Co., Oklahoma ) ] . 

Neotoma micropus leucopJiea Goldman, 1933: 
472 [Holotype— USNM 251057 from White 
Sands, 10 mi W Point of Sands, White Sands 
National Monument, Otero Co., New 
Mexico]. 

Remarks. — Confusion exists concern- 
ing the proper lectotype of Neotoma 
micropus canescens. Although I would 
have resolved this question differently, I 
follow Finley (1958:310-312) in 'the 
above synonymy to avoid belaboring a 
controversial point. Considerations ger- 
mane to the taxonomic status of this sub- 
species are discussed above, including 
nomenclatorial alternatives that might be 
used to reflect patterns of geographic 
variation within the samples of woodrats 
here treated as N. m. canescens. 

Records of occurrence. — Specimens exam- 
ined ( 1102).— COLORADO: Baca County: 14 
mi N, 4 mi E Springfield (Two Buttes Reser- 
voir), 2 (KU); 5 mi S, 2 mi W Pritchett, 22 
(KU); 2 mi N, 7 mi W Regnier, 4 (KU). Bent 
County: 2 mi S, 2 mi E Hasty, 11 (KU). Las 
Animas County: 11 mi N, 8 mi E Branson, 
5600 ft, 4 (KU). Prowers County: 16 mi N, 
1 mi E Springfield, 1 (KU); 1 mi N Two Buttes 
Reservoir, 4350 ft, 1 (KU). 

KANSAS: Barber County: 5 mi S Sun City, 
1 (KU); 15 mi W Medicine Lodge, 1 (KSTC); 
10 mi W Medicine Lodge, 16 (KU); 8 mi 
S\V Medicine Lodge, 2 (KU); 6 mi N Aetna, 
1 (KU); 7 mi N, 7 mi W Kiowa, 2 (KSC); 
7 mi N, 6 mi W Kiowa, 1 (KSC); 1 mi N 
Aetna, 1 (KSC); 1 mi SW Aetna, 1 (KU); 
3 mi S Aetna, 1 (KU); 3,5 mi S Aetna, 1 
(KU); Marty Ranch, 5 (KU); unspecified, 2 
(SM). Clark County: 7 mi S Kingsdown, 3 
(KU); 11 mi S, 1 mi W Kingsdown, 3 (KU). 
Comanche County: 7 mi S Coldwater, 3 
(KSTC); 11.5 mi S, 16 mi E Coldwater, 6 
(KU); Cave Creek, 1 (KU). Finney County: 
1 mi S Pierceville, 2 (KU); 15 mi S, 4 mi W 
Garden City, 1 (KU). Gray County: 2 mi 
NW Ingalls, 1 (KU). Hamilton County: 
Coolidge, 1 (KU); State Lake, 5 (2 MHP, 3 
KU); 2.5 mi N Syracuse, 1 (KU); 1 mi N, 3 
mi W Syracuse, 4 (KSTC); 1 mi S, 6 mi W 
Syracuse, 1 (MHP). Haskell County: 2 mi 
S, 4 mi W Satanta, 30 (KU); 3 mi S, 1 mi 
W Satanta, 11 (KU); 5 mi S, 4 mi W 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



25 



Satanta, 8 (KU). Kiowa County: 5 mi N 
Belvidere, 31 (17 AMNH, 14 KU); Rezeau 
Ranch, N of Belvidere, 1 (KU). Meade 
(Bounty: 0.5 mi S, 4 mi E Fowler, 7 (KU); 
11.5 mi E Meade, 2 (KU); 11 mi SW Meade, 

2 (AMNH); vicinity of State Park (12-17 mi 
SW Meade), 67 (21 AMNH, 3 MHP, 43 KU); 
unspecified, 1 (KU). Morton County: 9 mi 
N, 3 mi E Elkhart, 13 (KU); 8 mi N Elkhart, 

3 (KSTC); 7 mi N, 2 mi W Elkhart, 2 (KU); 
7 mi N Elkhart, 2 (MHP); unspecified, 4 (3 
KU, 1 UNAM). Seward County: unspecified, 

1 (KSTC). StaiUon County: 1 mi N, 8 mi 
W Manter, 5 (KU); J mi N, 7.5 mi W Manter, 

2 (KU); 1 mi N, 6 mi W Manter, 2 (KU); 3 
mi S, 14 mi W Johnson, 7 (MHP). Stevens 
County: 4 mi E Moscow, 4 (KU). 

NEW MEXICO: Eddy County: 3.25 mi 
NE Carlsbad, 2 (LSU); 24 mi E Carlsbad, 
3500 ft, 1 (KU); 5 mi SW Carlsbad, 1 (KU); 

2 mi NE Black River Village, 1 (KU); Carls- 
bad Cavern, 1 (KU); Rattlesnake Spring, 30 
mi SW Carlsbad, 1 (KU). Hidalgo County: 
6 mi SSE Lordsburg, 4200 ft, 1 (KU). Luna 
County: 3 mi N Deming, 4300 ft, 2 (KU). 
Otero County: 13 mi W Tularosa, 1 (TNHC); 

3 mi SW Alamogordo, 2 (TNHC); 3 mi S 
Alamogordo, 3 (TNHC); 10 mi W Point of 
Sands, White Sands National Monument, 3 
(USNM). San Miguel County: 1 mi S, 2 mi 
W Conchas Dam, 2 (KU). Santo Fe County: 
0.5 mi NW Santa Fe Municipal Airport, 1 
( KU ) ; 1 mi W Santa Fe Municipal Airport, 
1 (KU); 8 mi SW Santa Fe, 4 (KU); Santa 
Fe Field Station, 1 ( KU ) . 

OKLAHOMA: Beaver County: 21 mi S 
Meade, Kansas, 1 (KU); 8 mi NE Gate, 1 
(KU); 1.5 mi NE Beaver, 2 (KU); 3 mi NE 
Slapout, 1 (SM). Blaine County: Canton 
Reservoir (see remarks below), 1 (OSU). 
Cimarron County: Regnier, 4375 ft, 1 (KU); 
3 mi SE Regnier, 4350 ft, 1 (KU); 6 mi N 
Kenton, 3 (OSU); 4 mi N Kenton, 1 (OSU); 
1 mi S, 2 mi E Kenton, 1 (SM); 3 mi S, 2 
mi E Kenton, 1 (OSU); 7.5 mi S, 10 mi W 
Boise City, 3 (KU); 9 mi W Griggs, 3900 ft, 

1 (KU). Greer County: Granite, 1 (OSU); 
5 mi NE Reed, 1700 ft, 1 (SM); 1 mi S, 1 mi 
W Reed, 1 (SM); 10 mi SE Mangrum, 1 
(MWU). Harmon County: 3 mi W Reed, 6 
(SM); 1 mi S, 6 mi E Vinson, 1700 ft, 9 
(SM); 1 mi S, 2 mi W Madge, 1 (SM); 6.5 
mi SE Vinson, 1 (SM); 13 mi N Hollis, 1 
(OSU); 11 mi N Hollis, 2 (FWCM); 6 mi N, 

2 mi W Hollis, 2 (OSU); 6 mi N Hollis, 13 
(FWCM); 5.5 mi S Hollis, 5 (FWCM). 
Harper County: Beaver River, Southern Great 
Plains Experiment Range, 15 (OSU); 3.4 mi 
N Fort Supply, 2 (USNM); 3 mi N Fort 
Supply, 43 (USNM). Jackson County: 14 mi S 
Olustree, 4 (TNHC). Kiowa County: 2 mi S 
Lugert, 1 (OSU). Major County: 5.5 mi S 
Waynoka, 2 (SM); 6 mi S, 3 mi E Waynoka, 
1 (OSU); 16 mi NW Orienta, 1 (OSU); 1 mi 



N, 7 mi W Orienta, 3 (KSTC); 16 mi W 
Orienta, 8 (OSU); 5 mi W Orienta, 4 (2 SM, 
2 USNM); 3 mi W Orienta, 1 (OSU); 3 mi 
N, 9 mi W Fairview, 1 (OSU); 3 mi S Chester 
[ = 1.5 mi N Seiling] — (see remarks below), 
37 (8 KSTC, 29 KU); 3 mi S, 0.5 mi E 
Chester, 2 (KU); unspecified, 2 (OSU). Roger 
Mills County: 7 mi N Cheyenne, 2000 ft, 2 
(SM). Texas County: 5.5 mi N Guymon, 3100 
ft, 1 (SM); 4.5 mi N Guymon, 3100 ft, 3 (SM); 
2 mi N Guymon, 3000 ft, 3 (SM). Tillman 
County: 5.5 mi S Grandfield, 1 (SM). Woods 
County: Alva, 7 (USNM); 2 mi W Edith, 6 
(5 SM, 1 USNM); 4 mi S, 12 mi W Alva, 3 
(KU) ; Waynoka Dunes, 1 (OSU); 3 mi S 
Waynoka, 2 (SM); 5 mi S Waynoka, 1400 ft, 

6 ( SM ) . Woodward County: Alabaster Cav- 
erns, 4 (3 OSU, 1 SM); Boiling Springs State 
Park, 6 (1 KSTC, 5 SM); 2 mi NNW Wood- 
ward, 1900 ft, 4 (SM); Woodward, 3 (USNM); 
unspecified, 3 (SM). 

TEXAS: Andrews County: 10 mi NW 
Andrews, 1 (TCWC); 14 mi S Andrews, 1 
(OSU). Aransas County: Aransas National 
Wildlife Refuge, 3 (TCWC); 4.6 mi NE 
Rockport, 3 (TNHC); 6 mi W Rockport, 1 
(TNHC); Rockport, 1 (TNHC). Archer 
County: 20 mi N Archer City, 1 (MWU); 6 
mi W Holliday, 1 (MWU); within 5 mi radius 
of Hollidat/, 4 (MWU); within 4 mi radius of 
Mankins, ±7 (MWU); 7 mi SW Wichita Falls, 

1 (MWU); 6 mi S Wichita Falls, 1 (MWU); 
11 mi SW Wichita Falls, 1 (MWU); vicinity 
of Lake Kickavoo, 9 ( MWU ) ; 1 mi W Scotland, 

2 (MWU); 12 mi N Archer City, 1 (MWU); 

9 mi N Archer City, 1 (MWU); 14 mi S 
Holliday, 2 (MWU); 4 mi W Archer City, 1 
(MWU); 4 mi S Archer City, 1 (MWU); 5 
mi S Archer City, 1 (MWU); 7 mi S Archer 
City, 1 (MWU); 7 mi NE Olney, 1 (MWU). 
Atascosa County: 7 mi SE Lytle, 1 (TNHC); 

7 mi SW Somerset, 1 (TNHC); 8 mi SW 
Somerset, 1 (TNHC); 12 mi W Floresville, 1 
(TNHC). Baylor County: 12 mi NW Seymour, 

1 (MWU); Bomarton, 1 (MWU). Bee County: 
12.5 mi N Beeville, 2 (TNHC). Bexar County: 
San Antonio, 2 (TNHC); unsvecified, 1 (KU). 
Borden County: 16 mi W Gail, 1 (MWU). 
Brewster County: 11 mi N Alpine, 1 (MWU); 

2 mi W Alpine, 2 (AMNH ) ; 7.4 mi S Marathon, 
1 (AMNH ) ; 5 mi S Terlingua, 2 ( KU ) ; Tornillo 
Creek, 12 mi N Government Springs, 2700 ft, 
1 (AMNH); Government Springs, 3950 ft, 
Chisos Mountains, 2 (AMNH); East base 
Chisos Mountains, 2 (USNM); Bumham 
Ranch, 3950 ft, 2 (AMNH). Callahan County: 
30 mi SE Abilene, 1 (SFA). Cameron County: 

10 mi E Rio Hondo, 4 (LSU); 8 mi NW Bay- 
side, 1 (LSU); 2 mi W Port Isabel, 1 (TNHC); 
Brownsville, 5 (2 KU, 1 TNHC, 2 USNM); 
14.7 mi E Broivnsville, 5 (KU). Childress 
County: 18 mi N Childress, 1 (MWU); 15 
mi N Childress, 1 (MWU); 5 mi N Childress, 



26 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



1 (TNHC); 5 mi S Childress, 1 (TNHC). 
Clay County: 7 mi SE Wichita Falls, 2 
(MWU); 2 mi NE Bellevue, 1 (MWU). 
Cottle County: 13 mi N Paducah, 3 (TNHC). 
Crane County: 20 mi NNW Crane, 1 (MWU). 
Crosby County: Home Creek Canyon, 1 
(AMNH); unspecified, 2 (AMNH). Culberson 
County: 25 mi N Van Horn, 1 (MWU); 16 mi 
E Van Horn, 5 (TCWC); 16 mi SE Van Horn, 

8 (TCWC). Dawson County: 10 mi E Lamesa, 

4 (TNHC); 12 mi NW Patricia, 1 (TNHC). 
Dickens County: 7 mi NE Dickens, 1 ( MWU ) ; 

5 mi NW Spur, 2 (MWU). Eastland County: 

9 mi S Ranger, 2 (TNHC). El Paso County: 
15 mi N El Paso, 2 (USNM); JO mi N El Paso, 
7 ( USNM ) ; East El Paso, 1 ( USNM ) ; near El 
Paso, 3 (USNM). Fisher County: 12 mi E 
Hermleigh, 6 (TNHC). Floyd County: 6 mi 
S, 2 mi W Quitaque, 1 (OSU). Foard County: 
1 mi N, 12 mi E Crowell, 1 (MWU). Frio 
County: 2 mi N Dilley, 1 (TNHC). Garza 
County: 4 mi W Post, 1 (OSU). Goliad 
County: 3.5 mi N Goliad, 2 (TCWC). Hans- 
ford County: 6 mi S, 3 mi W Grnver, 1 (KU); 

6 mi S, 2 mi W Gruver, 1 (KU). Hardeman 
County: 3 mi N Quanah, 1 (MWU); 3 mi SE 
Lazare, 1 (MWU); 7 mi SW Quanah, 2 
(MWU); 13.5 mi S Quanah, 1 (MWU). 
Hartley County: Romero, 5 (AMNH). Haskell 
County: 6 mi N, 11 mi E Haskell, 3 (MWU); 
12 mi SW Haskell, 1 (MWU). Hemphill 
County: 6 mi E Canadian, 4 (TCWC); 9 mi 
NNE Miami, 1 (MWU). Hidalgo County: 4 
mi WSW Hargill, 1 (LSU); 17 mi NW Edin- 
hurg, 3 (TNHC); Alamo, 1 (LSU); 5 mi S 
Mission, 1 (LSU); 6 mi S McAllen, 7 (TNHC). 
Howard County: 7 mi E Vealmoor, 2 (TNHC); 
Big Spring, 1 (USNM). Hudspeth County: 
Fort Hancock, 2 (1 AMNH, 1 USNM); W 
slope Sierra Diablo, 1 (FWCM). Hutchinson 
County: 1 mi S, 10 mi E Pringle, 2 (KU); 9 
mi E Stinnett, 14 (TNHC). Jeff Davis County: 

7 mi NW Toyahvale, 2 (MWU); 16 mi NE 
Fort Davis, 3 (TCWC); Mouth of Madera 
Canyon, 1 (TCWC). Jim Hogg County: 20 
mi S Hebbronville, 9 (TNHC). Jim Wells 
County: Alice, 1 (LSU). Karnes County: 2 
mi SW Kenedy, 2 (TNHC). Knox County: 

4 mi SE Vera, 1 (MWU); 5 mi NW Knox City, 
1 (MWU). La Salle County: 2 mi S Wood- 
ward, 1 (TCWC); 8 mi NE Los Angeles, 5 
(TCWC); 3 mi NE Los Angeles, 1 (TCWC); 

5 mi W Cotulla, 2 (TCWC); 25 mi E Cotulla, 
1 (KU); 8 mi E Encinal, 3 (TCWC). Lynn 
County: 2 mi W Tahoka, 1 (MWU). Martin 
County: Stanton, 4 (USNM). Maverick 
County: Eagle Pass, 1 (TCWC). McMullen 
County: 21 mi W Three Rivers, 3 (TNHC); 
20 mi W Three Rivers, 1 (TNHC); 10 mi W 
Simmons, 2 (TNHC); 18 mi SE Tilden, 1 
(LSU); 21 mi SW Three Rivers, 1 (TNHC). 
Medina County: 7 mi N Castorville, 3 (KU). 
Midland County: 9 mi S Stanton, 1 (TCWC). 
Mitchell County: Colorado City, 2 (USNM). 



Montague County: 5 mi S Ringgold, 1 
(MWU); 3 mi N Stoneburg, 1 (MWU); 2 mi 
N Stoneburg, 1 (MWU). Motley County: 6 
mi N Flomot, 2 (MWU). Nueces County: 
1 mi S Bishop, 2 (TNHC). Palo Pinto County: 
Brazos, 1 (USNM). Presidio County: 7 mi W 
Valentine, 7 (TNHC); 1.5 mi SE Buford Well, 
Miller Ranch, 1 (TNHC); unspecified, 1 
(USNM). Reeves County: 20 mi S Pecos, 4 
(KU). Roberts County: 6 mi N Miami, 4 
(MWU). San Patricio County: 8 mi NE 
Sinton, 4 (LSU). Scurry Countt/: 4 mi SW 
Synder, 1 (MWU); 20 mi NW Colorado City, 

1 (USNM). Starr County: Garciaville, 2 
(MWU). Taylor County: 6 mi W View, 4 
(MWU). Terrell County: Lozier, 1 (USNM). 
Terry County: 8 mi N Tokio, 1 (TNHC). 
Throckmorton County: 18 mi SW Throckmor- 
ton, 2 (TNHC); 20 mi SW Throckmorton [ = 
Lamhshead Ranch], 2 (TNHC). Uvalde 
County: Montell, 2 (KU); 3 mi N Sabinal, 

2 (TNHC); 20 mi E Uvalde, 1 (TCWC). 
Vol Verde County: Comstock, 1 (USNM); Del 
Rio, 2 (USNM). Ward County: 4 mi NW 
Royalty, 3 (TNHC). Webb County: 45 mi 
NW Laredo, 10 (KU); 40 mi NW Laredo, 1 
(TNHC); 40 mi SW Catarina, 3 (TNHC); 
15 mi NE Laredo, 1 (TNHC); Islitas, 10 mi 
NNW Laredo, 3 (KU). Wichita County: 4 
mi SE Electra, 2 (MWU); within 6 mi radius 
of Ioiva Park, 25 (MWU); within 2 mi radius 
of Wichita Falls, 11 (MWU); 5 mi NNW 
Wichita Falls, 1 (MWU); 6 mi E Wichita 
Falls, 1 (MWU); 1.5 mi N Oliversion Lake, 
1 (MWU); 0.5 mi W Lake Wells, 1 (MWU). 
Wilbarger County: 8 mi S, 2 mi W Vernon, 
1 (MWU); 9 mi S Vernon, 1 (MWU); 15 mi 
S Vernon, 2 (TNHC); 7 mi S Harrold, 2 
(MWU); unspecified, 2 (MWU). Willacy 
County: 10 mi NW Raymondville, 1 (TNHC); 
28 mi E Raymondville, 3 ( 1 KU, 2 TCWC). 
Young County: 7 mi SW Graham, 1 (MWU). 
Zapata County: 16 mi N San Ygnacio (=1.8 
mi from Webb County line on highway 83), 

3 (TNHC); 6 mi NW San Ygnacio, 1 (TCWC); 
5 mi N Zapata, 1 (TNHC); 3,5 mi NE 
Zapata, 2 (TNHC); 5 mi E Zapata, 6 (TNHC). 
Zavala County: 29 mi S Uvalde, 4 (TNHC); 
14 mi W Crystal City, 1 (KU); unspecified, 
3 (TNHC). 

CHIHUAHUA: San Isidro, 10 mi SE 
Zabagoza, 2 (KU); 7 mi W Porvenir, 1 (KU); 
3.5 mi ESE Los Lamentos, 420 m, 1 (KU). 

COAHUILA: 1 mi S, 9 mi W Villa Acuna, 
8 (6 KU, 2 UNAM); 10 mi SE Villa Acuna, 
1 (TNHC); Canon del Cochino, 3200 ft, 16 
mi N, 21 mi E Piedra Blanca, 1 (KU); 11 mi 
S Hacienda San Miguel, 2200 ft, 1 (KU); 15 
mi N, 8 mi W Piedras Negras, 5 (KU); 2 mi 
S, 11 mi E Nava, 810 ft, 4 (KU); Ciudad 
Allende, 1 (TNHC); 10 mi SE Guerrero, 7 
(TNHC); 29 mi N, 6 mi E Sabinas, 10 (KU); 10 
mi E Hacienda La Mariposa, 300a ft, 1 (KU); 
Mariposa Ranch, 1 mi E Nacimiento, 27 mi 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



27 



NE Ciudad Muzquiz, 1 (TNHC); La Gacha 
[=La Concha], 1600 ft, 1 (KU); La Lajita, 
Rancho de la Golondrina, 13 mi NE Ciudad 
Muzquiz, 1 (TNHC); 10 mi N Ciudad Muz- 
quiz, 2 (TNHC); 2 mi S, 3 mi E San Juan 
de Sabinas, 1160 ft, 1 (KU); Sabinas, 4 
(TNHC); 10 mi ESE Sabinas, 2 (KU); 9 
mi NW Don Martin, 2 (KU); Don Martin, 800 
ft, 2 (KU); Base of Don Martin Dam, 2 (KU); 
8 mi N Hermanas, 1500 ft, 2 (KU); Hermanas, 
1205 ft, 2 (KU); 1 mi S Hermanas, 1200 ft, 

1 (KU); Cuatrocienegas, 1 (TNHC); 5 mi N, 

2 mi W Monclova, 1 (KU); 0.5 mi E San 
Antonio de Jaral, 4400 ft, 1 (UNAM); 3 mi 
N, 5 mi W La Rosa, 3600 ft, 3 (KU). 

NUEVO LEON: 15 mi N, 2 mi W Anahuac 
[=Rodriguez], 1 (KU); 5 mi N, 3 mi W La 
Gloria, 1 (KU); 5 mi WSW [General] Zuazua, 
1 (UNAM); Rancho 14 de Mayo, 1 km E 
Casa Principal, 1 (UNAM); 7 mi NW Provi- 
densia, 1 (KU). 

TAMAULIPAS: 4 mi SW Nuevo Laredo, 
900 ft, 14 (KU); 4.5 mi S Nuevo Laredo, 1 
(KU). 

Additional records: COLORADO (Finley, 
1958:315, unless otherwise noted): Baca 
County: Monon, Bear Creek; Furnish Canyon; 
Craugh Ranch, Cimarron River. Otero County: 
18 mi S La Junta. Prowers County: 15 mi S 
Lamar (Armstrong, 1972). 

KANSAS: Barber County: Sun [City] 
(Goldman, 1910:28). Grant County: 10 mi 
S, 8 mi E Ulysses (record of unoccupied wood- 
rat dwellings, see text beyond in this account). 

NEW MEXICO (marginal records only): 
Luna County: 8 mi E Deming (Goldman, 
1910:29). Rio Arriba County: Rinconada 
(Goldman, 1910:29). Valencia County: 8 mi 
SE Grants (Hooper, 1941:32). 

OKLAHOMA (Blair, 1939b: 125): Harper 
County: 4 mi N Laverne. Woods County: 

3 mi W Alva; White Horse Spring; Waynoka. 

TEXAS (Goldman, 1910:28, unless other- 
wise noted): Bee County: Beeville. Bexar 
County: Adams. Brewster County: Alpine; 
Altuda; Marathon. Cameron County: 11 mi 
E Brownsville (Baker and Mascarello, 1969: 
196). Clay County: Henrietta. Concho County: 
unspecified. Culberson County: Kent. Dimmit 
County: Blocker Ranch. Duval County: San 
Diego. Ector County: 9 mi N Odessa (Baker 
and Mascarello, 1969:196). Garza County: 
Post (Baker and Mascarello, 1969:196). Hall 
County: Newlin. Hudspeth County: Sierra 
Blanca. Jeff Davis County: Valentine. Kinney 
County: Fort Clark. Lamb County: 3 mi N 
Fieldton. La Salle County: Cotulla. Lipscomb 
County: Lipscomb. Lynn County: 2.5 mi S, 
1 mi W Tahoka. Maverick County: Moras 
Creek; Pinto Creek. Nueces County: Corpus 
Christi; Nueces Bay. Presidio County: 7 mi 
NE Marfa, 4900 ft (Blair, 1940:32). Reeves 
County: Toyah; Toyahvale. Roberts County: 
Miami. San Patricio County: 7 mi NE Sinton 



(Raun, 1966:2). Starr County: Roma; Rio 
Grande City. Taylor County: Tebo. Terrell 
County: Dryden. Tom Green County: San 
Angelo. Ward County: Monohans. Webb 
County: Dos Hermanos; Laredo; Santo Tomas. 
Wheeler County: Mobeetie; 5.5 mi S, 2.5 mi 
W Old Mobeetie (Shekel and Stickel, 1948: 
292). Wilbarger County: Vernon. Winkler 
County (Baker and Mascarello, 1969:196): 2 
mi N Wink; 8 mi SSE Kermit. 

CHIHUAHUA: Monument 15, Boundary 
Line (Anderson, 1969:29). 

COAHUILA (Goldman, 1910:21, 29, un- 
less otherwise noted ) : 3 mi NW Cuatrocienegas 
(Baker, 1953:253); 7 mi E Las Vacas; Sabinas; 
Monclova (also see Anderson, 1969:43); Saltillo 
(probably N. albigida, see Anderson, 1969:43). 

NUEVO LEON (Goldman, 1910:28, unless 
otherwise noted ) : Rodriguez; 70 mi S Nuevo 
Laredo (Booth, 1957:15); Doctor Cos; 16 mi 
S China; Allende (Jimenez— G., 1966:187); 
Linares. 

TAMAULIPAS (Goldman, 1910:28, unless 
otherwise noted): Nuevo Laredo; 10 mi S 
Nuevo Laredo (Booth, 1957:15); Camargo. 

Distribution and liabitot. — Locality 
records for Neotoma micropus canescens 
are shown in figures 3, 4, 5, 6, and 7. On 
the west, the range of this primarily 
Lower Sonoran subspecies corresponds 
roughly with the foothills of the Rocky 
Mountain-Sierra Madre Oriental Cordil- 
lera and associated extensions. The Rio 
Grande and Canadian rivers have served 
as corridors into the Rio Grande and 
Pecos valleys of New Mexico ( see Bailey, 
1932:171) as far north as Rinconada and 
possibly as far as the San Jose River 
Valley near Grants. A single juvenile 
tentatively identified as this subspecies 
by Hooper (1941:32) extends the distri- 
bution to the latter valley. In northern 
Mexico, N. m. canescens extends into the 
lower mountainous areas in the natural 
breaks between various mountain ranges 
(Baker, 1956:129). In the watershed of 
the Rio Salado, for example, canescens 
is known to occur as far west as Cuatro- 
cienegas. Distributional relationships of 
A7. m. canescens and the geographically 
contiguous subspecies, N. m. micropus, 
are discussed beyond in the account of 
that subspecies. 

In southeastern Colorado, southwest- 
ern Kansas, western Oklahoma, and east- 
central Texas, the range of N. micropus 



28 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



105 



99 



30 — 



50 



150 



S 



Miles 




24 



Fig. 7. Selected locality records in Mexico for Neotoma angustipalata (symbols solid right), N. 
micropus canescens (solid symbols), A 7 , m. micropus (symbols solid above), and N. m. planiceps 
(symbol solid below). 



abuts that of N. ftoridana. Spencer (1968) 
reported the single locality of known 
sympatry, which is on the North Cana- 
dian River in extreme southwestern Ma- 
jor County, Oklahoma (Figs. 1 and 5). 
The distributional relationships of the 



two species along the zone of potential 
abutment, with special emphasis on the 
area of sympatry, is considered below 
following a review of habitat types used 
by N. m. canescens. 

In comparison with Neotoma flori- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



29 



dana, N. micropus occurs in more xeric 
habitats, is associated less often with 
either trees or rocks, and usually occurs 
in areas marked by a high incidence of 
one or more species of cactus (genus 
Opuntia). In western Kansas (Haskell 
County), I have found canescens com- 
mon in overgrazed shortgrass pastures, 
especially where prickly pear cactus (O. 
polyacantha) is locally abundant. In pas- 
tures that also have soapweed (Yucca) 
or sagebrush (Artemisia), large dens of 
cactus stems and cow dung are con- 
structed in and around these plants. 
However, in pastures having abundant 
cactus and lacking soapweed and sage- 
brush, dens are built over clumps of cac- 
tus, and are characterized by an exten- 
sive underground system of tunnels and 
usually a low superstructure of cactus 
and cow dung. In this situation the 
woodrat dwellings appear to be small 
dome-shaped protrusions in an otherwise 
gently rolling sea of buffalo grass and 
cactus. On August 11, 1968, approxi- 
mately 30 houses of this type were exam- 
ined in a pasture 10 mi S and 8 mi E 
Ulysses in Grant County. The dwellings 
were in good repair, some even contained 
green cactus stems and well-formed grass 
nests, but none was occupied at that 
time. 

Farther east in Kansas (Barber 
County), this woodrat utilizes the crev- 
ices and caves formed by gypsum out- 
crops and often constructs dens around 
trees and brush in wooded draws. In 
such habitats the dwellings are not un- 
like those of floridana; in fact, much of 
the habitat in southern Barber County 
seems to me more like that normally oc- 
cupied by floridana than by micropus. 

In Baca and Prowers counties, Colo- 
rado, dens of N. m. canescens often are 
constructed in tree cactus (Opuntia ar- 
borescens). Finley (1958:494) reports 
that tree cactus also is the most important 
food plant of the species in Colorado, 
but where other species of cactus and 
Yucca are available, tree cactus is not 
essential. 

In New Mexico the habitat of this 



woodrat is apparently similar to that in 
Colorado. Bailey (1932:171) stated that 
these rats "are abundant in open arid 
valleys where cactus abounds and are 
usually found associated with either cac- 
tus or some of the thorny desert shrubs. 
Their favorite location for a house is in 
the midst of a bed of large prickly-pears 
or thorny bushes . . . where an abundance 
of cactus can be found for building ma- 
terial." Blair (1943a, 1943b) studied 
canescens in the Tularosa basin near 
Alamogordo, New Mexico, where it was 
common in a mesquite association in 
which cactus apparently was either ab- 
sent or scarce. 

Published reports of the habits of IV. 
m. canescens in Oklahoma and northern 
and western Texas are scarce. Glass 
(1949:29) found these rats nesting in 
canyons along with N. mexicana and IV. 
albigula in the Black Mesa region of 
extreme western Oklahoma. Blair (1939b: 
125) stated that "its bulky nests of sticks, 
liberally augmented by the remains of 
prickly pear plants, often are built 
around mesquite or other thorny shrubs." 
In Major County, Oklahoma, I have col- 
lected this rat along the North Canadian 
River where it comes into contact with 
Neotoma floridana. This unique area is 
discussed in more detail below. Blair 
(1954:252) studied canescens in north- 
ern Texas and adjacent Oklahoma, and 
reported that "these rats show a remark- 
able amount of variation in their ecolog- 
ical preference ... at some stations they 
are found only on rock bluffs; at other 
stations they live on the level plains and 
away from rocks." In the Davis Moun- 
tains of southwestern Texas, Blair ( 1940: 
32 ) collected woodrats of this subspecies 
from nests constructed in the bases of 
thorny shrubs in shortgrass-yucca, mes- 
quite-cholla, and shortgrass-mesquite as- 
sociations. In similar habitat in south- 
western Texas, Blair and Miller (1949: 
18) noted that in some cases old dens of 
Dipodomys spectabilus were utilized. In 
one of the more complete ecological 
studies of Neotoma micropus, Rami 
(1966) reported the species common in 



30 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



a shortgrass-cactus-mesquite association 
in San Patricio County, Texas. Blair 
(1952:224) characterized micropus as 
one of the commonest and widely dis- 
tributed mammals in the southern part 
of Texas. 

In Coahuila, N. m. canescens has 
been reported (Baker, 1956:285) to 
avoid rocky areas and densely vegetated 
arroyos. Houses are constructed most 
commonly in prickly pear cactus. At one 
locality (vicinity of Nava) rats lived in 
oak thickets, and at another (La Bosa) 
near houses constructed in short vegeta- 
tion on desert flats. 

In the summer of 1969, N. m. canes- 
cens first was collected from north of the 
Arkansas Biver in Colorado. This lo- 
cality, near Hasty in Bent County, is 
only about 10 miles from the nearest 
locality record, (Fort Lyon) for N. flori- 
dana. (The single specimen from Fort 
Lyon was collected about 80 years ago 
and the species probably does not occur 
at that locality today.) Southeastern 
Colorado, especially in the area of the 
Arkansas Biver, is undoubtedly one of 
the critical areas in which members of 
the two species are likely to come into 
contact. If they are in contact at this 
time or should come together at some 
future time, study of the two together 
would be most interesting because sym- 
patry of N. f. campestris and N. m. 
canescens is not known now. 

Neotoma micropus canescens is 
known from four localities north of the 
Arkansas Biver in western Kansas (Fig. 
4), but floridana is known from no 
nearer than 20 miles to any of these 
record stations. I have searched the in- 
tervening areas intensively; most are 
presently either cultivated or shortgrass 
patsureland devoid of habitat likely to 
support either species. Farther east in 
Kansas, the hiatus between the ranges 
of the two species widens appreciably 
and in the south-central portion of that 
state is roughly 80 miles in width. In the 
upland areas of much of the hiatus, land 
utilization is primarily for cultivation of 
erain and the fields are not habitable for 



woodrats. Intervening lowland areas, 
however, are often at least sparsely 
wooded, planted hedgerows are common 
but discontinuous, and several small 
tributaries of the Arkansas Biver extend 
riparian communities into the zone. The 
watershed of the Arkansas Biver is 
heavily wooded along most of its course. 
In September of 1967, I searched for 
several days, walking long sections of the 
Arkansas Biver and many likely-looking 
hedgerows, but neither woodrats nor any 
evience of their presence was seen. I am 
not convinced that this area is devoid of 
woodrats, but, if present, they are un- 
common; thus, the chance of the two 
species occurring together in south-cen- 
tral Kansas seems negligible. 

In northern Oklahoma, the haitus be- 
tween the ranges of the two species nar- 
rows rapidly and specimens of both spe- 
cies are known from localities separated 
by less than three miles along the Cimar- 
ron Biver just west of Orienta. South 
and west of Orienta on the north side of 
the North Canadian Biver on either side 
of U.S. Highway 281, micropus and 
floridana occur together. This unique 
area of sympatry was reported by Spen- 
cer ( 1968 ) and subsequently was visited 
by me in June, 1968, and January, 1969. 
Specimens from this area in the collec- 
tion at Kansas State Teachers College 
(collected by Spencer) are labeled 1.5 
mi N Seiling, in Major Co., Oklahoma, 
whereas those collected by me ( all KU ) 
are labeled 3 mi S Chester, Major Co., 
Oklahoma. 

West of highway 281, woodrats occur 
in two distinct areas. Immediately ad- 
jacent to the river, vegetation is dense 
and shrubby with occasional trees and 
fallen trees in an area varying in width 
from 30 to 80 feet. Superficially this ap- 
pears to be habitat typical of floridana. 
A cultivated field approximately an 
eighth to a quarter of a mile in width 
separates the river-edge habitat from an 
area roughly an eighth of a mile wide 
where yucca, cactus, sparse grass, and 
scattered large trees grow on semi-stabi- 
lized sand dunes. This area is super- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



31 



ficially like that often inhabited by mi- 
cropus. East of the highway, the river 
edge ( 50 to 100 feet wide ) was densely 
wooded in 1968 with a dense layer of 
leaf-litter and a canopy that permitted 
little ground vegetation. Woodrats were 
not found in this habitat. Bordering the 
dense trees to the south was a pasture of 
relatively stable, vegetated sand dunes. 
Small stands of large trees were scattered 
throughout the pasture, primarily at the 
bases of the dunes. Vegetation on the 
sides and tops of the dunes consisted of 
grass and cactus. The area extended ap- 
proximately three-eighths of a mile north 
and half a mile east. Farther to the east, 
the density and sizes of trees increased, 
density of cactus decreased, and the area 
became more typical of the habitat of 
floridana. In 1969, the dense woods bor- 
dering the river east of the highway were 
uprooted and piled in a huge windrow 
bordering the sand dunes on the south. 
x\t that time the windrow already har- 
bored several woodrat dens. 

Of eighteen woodrats collected at this 
locality in 1965 and 1966 by Spencer 
(196S), six were identified as N. flori- 
dana, three as N. micropus, and nine as 
probable hybrids or intergrades. I have 
examined 16 of these specimens and 
identified seven as floridana, three as mi- 
cropus, and six as being of mixed parent- 
age. Using my identifications, six flori- 
dana, one micropus, and four "hybrids" 
were collected east of the highway and 
one floridana, two micropus, and two 
"hybrids" were obtained west of the high- 
way. Four of seven animals trapped west 
of the highway in 1968 were identified as 
micropus and three were considered to 
be of mixed parentage; of 16 specimens 
taken at that time from the east side, six 
were identified as micropus, three as 
floridana, and seven as "hybrids." No 
traps were set west of the highway in 
1969, but traps set within half a mile 
east of the highway yielded four mi- 
cropus and eight "hybrids." No wood- 
rats identified as N. floridana were taken 
from the place defined by Spencer 
(1968) as the area of sympatry. How- 



ever, another series of traps set in an 
area 100 to 200 yards farther east caught 
one floridana, one micropus, and four 
"hybrids." Although these findings are 
inconclusive, it appears that the hybrid 
zone may have shifted eastward at least 
a quarter of a mile between 1965 and 
1969, although remaining about three 
fourths of a mile in length. The destruc- 
tion of trees and formation of the wind- 
row may have significantly altered the 
ecological balance of the two species in 
the area of sympatry; if so, the alteration 
likely will favor N. floridana. A single 
specimen trapped one mile east of the 
highway in 1968 was clearly referable to 
floridana; it showed no characteristics of 
micropus or of hybrids. 

Four specimens from Major and 
Woodward counties are worthy of spe- 
cial comment with respect to the dis- 
tributional relationship of the two spe- 
cies. The first (OSU 3891), is a skin 
and skull that is referable to floridana 
on the bases of pelage (color) and 
cranial characters. This specimen bears 
the following information on the data 
label: "15 miles south of Waynoka, Okla., 
southside of Cimmarron [sic] River, Ma- 
jor Co." Fifteen miles south of Waynoka is 
no closer than nine miles to the Cimarron 
River and all other specimens examined 
by me from within 15 miles of Waynoka, 
in any direction, are N. micropus. Be- 
cause these two species hybridize at the 
one known locality of sympatry, and be- 
cause the locality in question here clearly 
is in error as stated above, I have not 
plotted this specimen on figure 5; I sus- 
pect it is from some locality east of 
Waynoka. Another specimen, OSU 4063, 
also is not plotted because of probable 
error in locality data; a skin alone, it is 
from "Canton Res. Blaine Co., Okla." 
Canton Reservoir is approximately 15 
miles east along the North Canadian 
River from the locality of sympatry and 
hybridization. This rat is gray in color 
like micropus, but slightly atypical in be- 
ing buffy on the shoulders and sides. 
However, the color variation is so slight 
that if this specimen was not otherwise 



32 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



in question, it readily would be identified 
as micropus. I have examined several 
specimens from near the Canton Reser- 
voir and all seem to be typical representa- 
tives of floridana. Three explanations 
seem possible: (1) both species occur 
at this locality, but floridana is commoner 
than micropus; (2) this is a hybrid pop- 
ulation most like floridana, but occa- 
sional genetic combinations result in in- 
dividuals colored as in micropus; (3) 
the locality data are incorrect and the 
specimen is from some more western 
locality. I regard the last alternative as 
the most plausible and the first as the 
least plausible. Both specimens appar- 
ently were collected by beginning stu- 
dents ( field catalog numbers of both are 
below 10). OSU 3891 bears a collection 
date of 26 October 1958 and OSU 4063 
is dated 28 October 1958. Although not 
prepared by the same student, it is pos- 
sible that the labels were somehow 
switched in preparation. The other two 
noteworthy specimens are SM 4980 and 
4981, preserved only as skins. Both spec- 
imens clearly were prepared some years 
ago (date of collection not on specimen 
labels) and are typical dark brown rep- 
resentatives of floridana. The specimen 
labels read "Woodward Co., Oklahoma." 
The southeastern corner of Woodward 
County is two miles west of the area of 
sympatry and all other specimens exam- 
ined from that county are micropus. If 
the zone of contact is shifting gradually 
eastward and has been doing so for many 
years, it is possible that floridana may 
have occurred in Woodward County in 
the not too distant past. It also is pos- 
sible that these specimens were not from 
the North Canadian River, but are from 
some locality elsewhere in Woodward 
County that once supported or still sup- 
ports a population of N. floridana. 

Farther south in Oklahoma, speci- 
mens of the two species are known from 
localities at a minimum of 20 miles from 
each other. The Red River, 5.5 mi S 
Grandfield, Tillman, Co., Oklahoma, is 
the locality of capture for SM 3602, a 
N. m. canescens. This locality is nearly 



straight south of Chattagnooga, Coman- 
che County, where N. f. attwateri has 
been taken. It is west along the Red 
River from another floridana locality, 5 
mi SE Taylor, Cotton County. South of 
Taylor, in adjacent Clay and Wichita 
counties, Texas, micropus is known from 
several localities. 

Dalquest (1968:19) stated that "the 
ranges of N. floridana and N. micropus 
meet in Clay and Montague counties 
[Texas] but the two species do not inter- 
breed." In actuality, floridana is not 
known from Clay County and micropus 
is known only from the extreme western 
edge of Montague County. Neotoma 
micropus canescens has been collected 2 
mi N Stoneburg and N. f. attwateri is 
known from a locality 4 mi E Stoneburg, 
a distance of 4.47 miles. Continued field 
work in northern Texas and along the 
Red River likely will result in the loca- 
tion of a zone of contact between the 
two species, but none presently is known 
in northern Texas. 

A specimen of attwateri (MWU 
5256) obtained 7 mi SE Jacksboro, Jack 
County, is from west of known micropus 
localities both to the north and to the 
south, but N. m. canescens has not been 
taken at any nearby localities. Another 
area in Texas that would be worthy of 
additional field work is along the Brazos 
River in Parker and Hood counties. 
Neotoma micropus canescens is known 
from the Brazos River just west of Parker 
County in Palo Pinto County. A series 
of 13 N. f. attwateri from 8.9 mi S Aledo. 
Parker County, is suspiciously grayish- 
brown in color, but cranially members 
of the series are more or less typical of 
floridana. Possibly this population con- 
tains some introgressed genetic material 
derived from micropus, but more likely 
the color is the result of adaptation to 
the local environment on the western 
edge of the range of the species. 

There are few records of museum 
specimens of woodrats from the central 
portion of Texas. Strecker (1929:220) 
reported N. f. attwateri from near Waco. 
West of Waco, the nearest locality of 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



33 



record for N. m. canescens is approxi- 
mately 175 miles distant in Concho 
County. On a north-south axis there is 
an apparent hiatus of some 200 miles in 
the distribution of micropus along the 
eastern edge of the range of the species 
in central Texas. The Colorado River 
and many smaller waterways traverse 
this area. Insofar as I am aware, there 
are no physiographic factors that would 
be expected to prevent woodrats from 
inhabiting this sizable portion of central 
Texas, which is surrounded by areas 
known to support foridana on the east 
and micropus on the north, west, and 
south. 

Museum specimens indicate that the 
two species are in close proximity in 
southeastern Texas adjacent to the Gulf 
Coast. However, no localities of sym- 
patry are known; the nearest localities 
are in Victoria County (N. f. attwateri) 
and Goliad County (N. m. canescens). 

Neotoma micropus micropus Baird 

Neotoma micropus Baird, 1855:333 [Lectotype 

— USNM 1676/554 from Charco Escondido, 

Tamaulipas]. 
Neotoma micropus littoralis Goldman, 1905:31 

[Holotype— USNM 92952 from Altamira, 

Tamaulipas]. 

Remarks. — When Baird named Neo- 
toma micropus he had specimens from 
both Charco Escondido, Tamaulipas, and 
Santa Rosalia ( =Ciudad Camargo), Chi- 
huahua. Unfortunately no holotype was 
designated by Baird. Merriam (1894b: 
244 ) pointed out that the specimen from 
Santa Rosalia is "somewhat aberrant" 
and that because "the original descrip- 
tion is based wholly on the Charco Es- 
condido specimen . . . [it] must be taken 
as the type of this species." The speci- 
men from Santa Rosalia, not seen by me, 
is assignable on geographic grounds to 
Neotoma albigula (see Anderson, 1969), 
but Merriam's designation of the Charco 
Escondido specimen as a lectotype firmly 
reserved the name for the woodrats to 
which it is applied. 

The decision to consider the name N. 
m. littoralis as a junior synonym of N. 



m. micropus was not an easy one. How- 
ever, when analyzed by both univariate 
and multivariate statistics, the samples of 
woodrats from northern and southern 
Tamaulipas are consistently more alike 
than either is to any other sample of the 
species. From north to south in Tamauli- 
pas, these rats tend to become less gray- 
ish and more brownish. One extreme in 
this trend is reached in southern Tamau- 
lipas to the south of the Sierra de Tamau- 
lipas; it is the woodrats at this end of the 
range that formerly were recognized as 
littoralis. Alvarez ( 1963 ) studied mi- 
cropus in Tamaulipas and chose to rec- 
ognize two subspecies within the state. 
He (p. 453) concluded that micropus 
and littoralis intergraded in the vicinity 
of Soto la Marina, and assigned speci- 
mens from that locality to IV. m. micropus 
and those from localities farther south in 
Tamaulipas to N. m. littoralis. 

Woodrats throughout the coastal 
plain of Tamaulipas have relatively 
longer tails than specimens of micropus 
from other localities and tend to be some- 
what brownish in coloration ( rather than 
grayish), especially on the hind legs 
where the dorsal coloration meets the 
"white" of the feet. Although specimens 
of micropus from southern Texas are ap- 
preciably larger than those from Tamau- 
lipas and are assignable to N. m. canes- 
cens, an occasional specimen from the 
general area of Brownsville resembles 
N. m. micropus. 

Woodrats from just south of the Rio 
Grande near Nuevo Laredo, Tamaulipas, 
are somewhat intermediate between mi- 
cropus and canescens but have been as- 
signed to the latter. Conversely, speci- 
mens from Matamoros, Tamaulipas, have 
some characteristics of woodrats from 
farther north and west, but I have in- 
cluded these with N. m. micropus. 

Specimens from the type locality of 
N. m. micropus, Charco Escondido, prob- 
ably are intergrades between the small, 
brownish, long-tailed coastal woodrats 
and the equally small, but grayish short- 
tailed woodrats in Nuevo Leon and 
Coahuila. It is always somewhat incon- 



34 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



venient when specimens from a type 
locality appear to be intergrades. To 
consider specimens from Charco Escon- 
dido to be of the same subspecies as 
those from Nuevo Leon and Coahuila 
would result in all the woodrats herein 
referred to as N. m. canescens being ar- 
ranged as N. m. micropus, and those from 
coastal Tamaulipas being regarded as N. 
m. littoralis. Although specimens from 
Charco Escondido and adjacent localities 
in northwestern Tamaulipas could be 
placed about equally well with either the 
coastal population or with the inland and 
northern populations, I concluded that 
they best represent those nearer the 
coast. Specimens from Tamaulipas north 
to approximately Reynosa and south to 
the vicinities of Ciudad Victoria ( on the 
southwest) and Altamira (on the coast) 
are here assigned to the subspecies N. 
m. micropus, with the type locality being 
Charco Escondido, Tamaulipas; the 
name N. m. littoralis thus becomes a sub- 
jective junior synonym of N. m. micropus. 

Records of occurrence. — Specimens exam- 
ined (66).— TAMAULIPAS: 3 mi SE Reynosa, 
1 (KU); 3 mi S Matamoros, 2 (KU); Charco 
Escondido, 2 (1 UNAM, 1 USNM); 33 mi S 
Washington Beach, 1 (KU); San Fernando, 
180 ft, 3 (KU); 7 km S, 2 km W San Fer- 
nando, 2 (KU); 12 mi NW San Carlos, 1300 
ft, 4 (KU); 9.5 mi SW Padilla, 800 ft, 3 (KU); 
3 mi NE Guemes, 1 (KU); 3 mi N Soto la 
Marina, 3 (KU); Soto la Marina, 500 ft, 13 
(12 KU, 1 LSU); 4 mi N La Pesca, 3 (KU); 
La Pesca, 2 (KU); 1 mi E La Pesca, 1 (KU); 
7 mi NE Ciudad Victoria, 1 (KU); Ciudad 
Victoria, 6 (KU); Sierra de Tamaulipas, 2 
mi S, 10 mi W Piedra, 1200 ft, 6 (KU); 
Manuel, 1 (AMNH); 6 mi W Altamira, 8 
(KU); Altamira, 100 ft, 5 (USNM). 

Additional records: TAMAULIPAS (Gold- 
man, 1910:28, unless otherwise noted): Mata- 
moros; Bagdad; 40 mi S Matamoros (Hooper, 
1953:9); Sierra San Carlos [=E1 Malato, 
Tamaulipeca] (Dice, 1937:254); 16 km N 
Ciudad Victoria (Hsu and Benirschke, 1968); 
Forlon. 

Distribution and habitat. — The dis- 
tribution of N. m. micropus is essentially 
the coastal plain of Tamaulipas, extend- 
ing north to the Rio Grande River and 
south to Altamira, Tamaulipas (Fig. 7). 
Possibly the subspecies occurs in north- 



ern coastal Veracruz, but specimens from 
that state are not presently available ( see 
Hall and Dalquest. 1963). Distributional 
relationships of N. m. micropus and N. 
m. canescens in western Tamaulipas, 
eastern Nuevo Leon, and across the 
lower Rio Grande are discussed in re- 
marks above. 

With respect to ecological habits, N. 
m. micropus probably differs little from 
N. m. canescens. According to Alvarez 
(1963:453), the subspecies occurs 
throughout the Tamaulipas Biotic Prov- 
ince and is most common in brushy areas. 
Specimens have been obtained from the 
beach near La Pesca and in rocky areas 
on the Sierra de Tamaulipas. 

Neotoma micropus planiceps Goldman 

Neotoma micropus planiceps Goldman, 1905:32 
[Holotype— USNM 82105 from Rio Verde, 
San Luis Potosi]. 

Remarks.— Dalquest (1953:158) re- 
ported that no specimens of this woodrat 
were collected during his investigation 
of the mammals of San Luis Potosi, but 
did not indicate if specimens were sought 
near Rio Verde. He suggested (loc. cit.) 
that the holotype of N. m. planiceps 
might be "an aberrant specimen, not 
fully adult, of Neotoma albigula leu- 
codon." I have examined the holotype 
and concur that it is not fully adult but 
concluded unequivocally that it is not a 
Neotoma albigula. I think it possible 
that Neotoma angustipalata, discussed in 
the following account, may be the same 
taxon as N. m. planiceps; however, spec- 
imens are not presently available to re- 
solve this problem. 

Record of occurrence. — Specimen examined 
(1).— SAN LUIS POTOSI: Rio Verde, 1 

(USNM). 

Distribution and habitat. — This sub- 
species is known only from the type lo- 
cality, which is shown in figure 7. 
Goldman (1905:32) did not contribute 
ecological comments in the original de- 
scription of N. m. planiceps, but presum- 
ably it is an inhabitant of the plains im- 
mediately west of the Sierra Madre 
Oriental. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



35 



Neotoma angustipalata 

Neotoma angustipalata is one of the 
least well-known members of the genus. 
The species was described in 1951, long 
after most species of Neotoma were at 
least moderately well studied. The dis- 
tributional relationship of N. angusti- 
palata and N. micropus might appear to 
be that of two subspecies; Hooper (1953) 
and Alvarez ( 1963 ) both suggested that 
angustipalata is probably no more than 
a subspecies of micropus. However, re- 
sults of analyses presented beyond indi- 
cate that angustipalata is best regarded 
as a distinct species, albeit in the same 
species-group as floridana and micropus. 

Neotoma angustiplata Baker 

Neotoma angustipalata Raker, 1951:217 [Holo- 
type — KU 36976 from 70 km (by highway) 
S Ciudad Victoria and 6 km W of the ( Pan- 
American) highway (at El Carrizo), 
Tamaulipas]. 

Remarks. — As pointed out previously, 
the systematic affinities of this woodrat 
are poorly known. They have been con- 
sidered to be with Neotoma mexicana 
(Baker, 1951:217), N. albigula (Hall, 
1955:329), and N. micropus (Hooper, 
1953:10; Alvarez, 1963:453). I suggested 
in the previous account that N. angusti- 
palata may be identical to the rat that 
bears the name N. micropus planiceps. 
Had I synonymized the two, the name 
angustipalata would have been placed as 
a junior synonym of planiceps, and the 
latter would have been elevated to spec- 
ific status. 

I agree with Hooper and Alvarez that 
N. angustipalata is much like N. mi- 
cropus, but have found that it shares a 
nearly equal number of characters with 
N. floridana in addition to having some 
characters unique unto itself. These char- 
acteristics are treated in detail in the 
discussion of quantitative and qualitative 
morphological comparisons beyond. 

The three specimens from San Luis 
Potosi to which Dalquest (1951:363) 
gave the name Neotoma ferruginea 
griseoventer ( placed in the species mexi- 
cana by Hall, 1955:330) were examined 



to determine if this woodrat and N. 
angustipalata also might represent the 
same taxon. The type locality of N. 
mexicana griseoventer is Xilitla, San Luis 
Potosi; two of the specimens (LSU 3193, 
3194) are from the type locality and one 
(LSU 3191) is from El Salto, San Luis 
Potosi. The two specimens from Xilitla 
appear to be referable to N. mexicana, 
but LSU 3191 is indistinguishable from 
N. angustipalata and is best assigned to 
that species. The similarities between N. 
angustipalata and N. m. griseoventer are 
many and the two may yet prove to be 
synonymous. However, in all specimens 
of N. angustipalata (including LSU 
3191), the vomer is solid beyond the 
leading edge of the palate, whereas all 
N. mexicana examined by me have a 
deep notch in the vomer anterior and 
dorsal to the palate; the vomers of the 
two specimens from Xilitla are distinctly 
notched. Specimens of both species have 
a deep anteroreentrant angle on Ml, the 
character long used to distinguish N. 
mexicana from other species of Neotoma, 
but several authors have commented on 
the variability in depth of this angle both 
in N. mexicana and N. micropus (see 
especially Hooper, 1953:10). 

Records of occurrence. — Specimens exam- 
ined (12).— TAMAULIPAS: 70 km [by high- 
way] S Ciudad Victoria, 6 km W [Pan-Ameri- 
can] highway [at El Carrizo], 2 (KU); 10 km 
N, 8 km W El Encino, 400 ft, 1 (KU); 12 km 
S Ciudad Mante, 1 (UNAM); 2 km S Quintero, 
250 m, 2 (UNAM); 4 km SSE Quintero, 2 
(UNAM). SAN LUIS POTOSI: El Salto, 1 
(LSU); 5 mi W El Naranjo, 1 (TT); 30 km 
W Valles, edge of plateau, 1 (MWU). 

Additional records.— TAMAULIPAS: Ran- 
cho del Cielo, 1050 m [6 km NW Gomez 
Farias] (Hooper, 1953:9; Goodwin, 1954:14; 
Koopman and Martin, 1959:7); Infernillo (= 
Inferno), 1320 m [7 km W Gomez Farias] 
(Koopman and Martin, 1959:6); Paraiso, 420 
m [13 km SW Gomez Farias] (ibid.); El Pachon 
(Hooper, loc. cit.; Goodwin, loc. cit.) . 

Distribution and habitat. — Booth 
(1957:15) first reported Neotoma an- 
gustiplata from San Luis Potosi; reas- 
signment of a specimen previously as- 
signed to the species N. mexicana (see 
remarks) and assignment of TT 9769 



36 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



and MWU 3055 to this species further 
elucidate the known geographic range 
of angustiplata in the state. 

All locality records for N. angustiplata 
are either in or near the eastern slopes of 
the Sierra Madre Oriental (Fig. 7). 
Koopman and Miller (1959:2-3) de- 
scribed the localities from whence their 
material (owl pellets) probably origi- 
nated as Tropical Evergreen Forest and 
Cloud Forest. Goodwin (1954:2) de- 
scribed Rancho del Cielo as being "on 



the first ridge of the Sierra Madre Orien- 
tal at 1150 meters. Humid, oak and 
sweet gum, cloud forest (humid upper 
tropical life zone) surrounding the ranch 
has been thoroughly lumbered since 
1952." The specimens on which the name 
originally was based were trapped "in 
rocks and crevices at the base of a small 
hill in thick vegetation growing in deep 
humus" (Baker, 1951:218). All speci- 
mens reported by Hooper (1953:9) were 
collected in limestone caves. 



COMPARATIVE MORPHOLOGICAL ANALYSES 



In view of the ubiquity of woodrats 
in the United States and Mexico, it is 
interesting that relatively little attention 
has been devoted to generic variation in 
Neotoma as compared with that given 
other cricetine genera such as Peromi/scus 
(King, 1968). Hooper (1938 and 1940) 
studied geographic variation in N. 
fuscipes and N. cinerea. Hoffmeister and 
de la Torre ( 1960 ) assessed variation in 
N. stephensi, comparing it to N. lepida. 
The systematica of N. goldmani were 
considered by Rainey and Baker ( 1955 ) . 
Size and physiological attributes of sev- 
eral species of Neotoma (not including 
N. floridana or N. micropus) were cor- 
related with selected environmental fac- 
tors by Brown and Lee ( 1969 ) . 

Geographic variation in six eastern 
subspecies of Neotoma floridana was 
studied by Schwartz and Odum ( 1957 ) , 
but it has not been assessed in western 
races of the species or in N. micropus. 
Cockrum (1952:188) shifted the sub- 
species boundary between N. m. mi- 
cropus (herein restricted to coastal 
Tamaulipas) and N. m. canescens east- 
ward in Kansas from that proposed by 
Goldman (1910:27), but Cockrum did 
not study patterns of variation in mi- 
cropus outside of Kansas. Baker (1956: 
286) regarded all specimens of the spe- 
cies from Coahuila as N. m. micropus, 
whereas Goldman (loc. cit.) considered 
those from western localities in the state 
as N. m. canescens. 

Although the above studies either 



lacked statistical treatment of data or 
were limited to univariate analyses of 
morphological characters, Anderson 
( 1969 ) employed multivariate statistics 
in comparisons of Neotoma micropus 
with N. albigtda from Chihuahua and 
Coahuila. Multivariate statistics have 
been used widely in studies of members 
of the genus Canis ( Jolicoeur, 1959; Law- 
rence Bossert, 1967, 1969) and recently 
have been employed in studies of geo- 
graphic variation in bats (Smith, 1972), 
shrews (Choate, 1970), and spiny mice 
(Genoways, 1971). Geographic variation 
in western subspecies of N. floridana and 
all subspecies of N. micropus is consid- 
ered here by means of a combination of 
univariate and multivariate analyses. 

MATERIALS AND METHODS 

Age determination. — Age of speci- 
mens examined was determined by use 
of a modification of the scheme devised 
by Hoffmeister and de la Torre (1960: 
479) for Neotoma stephensi. They rec- 
ognized four age-groups based on degree 
of eruption of upper molars and subse- 
quent wear on these teeth. The oldest 
and youngest categories in my arrange- 
ment correspond in a general way to 
those two groups as defined by Hoff- 
meister and de la Torre. However, pre- 
liminary calculations indicated that vari- 
ance of mensural characters of rats in the 
intermediate groups exceeded that ex- 
pected. Age groups then were recon- 
sidered and eight age classes were rec- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



37 



Ognized as follow: Group I. — immature 
rats iu which M3 is not occlusal and 
often not erupted. Group II. — immature 
rats iu which M3 is occlusal, but with 
the posterior loph of the tooth still iso- 
lated. Group III. — rats with the dentine 
of the posterior loph on M3 continuous 
with that of the anterior loph and with 
the labial reentrant angles of M2 and M3 
continuing out of view into the alveolus; 
the proximal termination of the labial 
reentrant angles of Ml often is visible. 
Group IV. — rats characterized by visible, 
proximal terminations of reentrant angles 
on all upper molars; the reentrant angles 
of Ml are more than three-fourths as 
long as the exposed portion of that tooth. 
Group V. — young adults in which the 
reentrant angles of Ml are shorter than 
defined for group IV, but less than half 
as long as the height of Ml. Group VI. 
— adults with the reentrant angles of Ml 
between a third and a half as long as 
the height of the tooth. Group VII. — 
rats with visible reentrant angles on Ml 
that are less than a third as long as the 
height of the tooth. Group VIII.— old 
adults with no visible reentrant angles 
on Ml but often with short reentrant 
angles on M2 and M3. For reasons dis- 
cussed beyond (see variation with age), 
only specimens of age groups VI, VII, 
and VIII were included in studies of 
geographic variation when such speci- 
mens were available, and males and fe- 
males were treated separately (see sec- 
ondary sexual variation). In two in- 
stances it was necessary to include spec- 
imens of age group V (the holotypes of 
N. m. planiceps and N. m. leucophea 
both are males of this age and older in- 
dividuals were not available). 

Molars of woodrats that had been 
reared or maintained in the laboratory 
were less worn than those of woodrats 
that had not been in captivity. As a re- 
sult, aging criteria described above were 
not applicable in separating laboratory 
animals into age groups comparable to 
those of non-laboratory rats. Laboratory 
specimens known to be more than two 
years of age frequently were placed in 



groups IV and V. Results of growth and 
development studies, which will be pub- 
lished elsewhere, indicated that labora- 
tory woodrats essentially had ceased 
growth by 30 weeks of age; this age then 
was used as the critical age and only 
laboratory woodrats more than 30 weeks 
old were used in comparisons or treated 
statistically. As discussed beyond, it was 
found that laboratory woodrats were 
larger in some measurements than their 
non-laboratory counterparts from the 
same localities. Thus, woodrats that had 
been maintained in the laboratory in ex- 
cess of one month were not included in 
studies of geographic variation employ- 
ing univariate analyses or in multivariate 
analyses using CLSNT; a few were in- 
cluded in MULDIS when other speci- 
mens from critical areas were not avail- 
able. 

Pelage variation. — A Photovolt Photo- 
electric Reflection meter (Model 610), 
which yields values that are percentages 
of reflection of pure white, was employed 
to quantify color variation of woodrats. 
Readings made for each of three reflec- 
tions (red, green, and blue) were taken 
from the lumbar region of museum spec- 
imens of age groups VI-VIII character- 
ized by unworn or relatively unworn 
pelage. Analyses of adult molts and 
pelages were made on museum skins. 
The number and sequence of matura- 
tional molts were studied on live wood- 
rats in the laboratory; these data will be 
included elsewhere in a discussion of 
growth and development. 

Qualitative cranial characters. — Three 
cranial characters (Fig. 10) that have 
been used as "taxonomic characters" 
(Finley, 1958:248) were found to be 
more variable than previously recorded. 
The anterior palatal spine may be 
pointed and nonbifurcate or distally 
bifurcate. The presence and size of the 
bifurcation was scored from one to five, 
with "one" denoting absence of the fork. 
The posterior margin of the hard palate 
varies from having a relatively well-de- 
fined medial indentation to having a 
well-developed projecting medial con- 



38 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



vexity. Variation in this character was 
scored one to eight, with one being as- 
signed to specimens with the deepest 
indentation and eight to those with the 
largest convexity. Size of sphenopalatine 
vacuities was found to vary from nearly 
closed in a few individuals to a large 
opening extending anterior beyond the 
posterior edge of the hard palate in 
others; variation in this character was 
scored one to six, from smallest to largest. 
None of these characters lends itself to 
precise measurements without more 
sophisticated equipment than usually is 
available. To insure consistency in scor- 
ing, exemplary skulls were selected and 
used for comparison in scoring other 
specimens. 

Bacular variation. — Bacula of selected 
adult male woodrats in the Museum of 
Natural History of The University of 
Kansas were prepared and stained ac- 
cording to the method described by 
Lidicker (1960:496), and subsequently 
removed from phalli. Measurements of 
bacula were taken to the nearest tenth 
of a millimeter with the aid of a Wild 
Heerbrugg Stereomicroscope, graph pa- 
per, and dial calipers. 

External and cranial size variation. — 
External measurements (total length, 
length of the tail, length of the hind foot, 
and length of the ear from the notch) 
were recorded from data on specimen 
labels. These data were omitted if ob- 
viously erroneous as recorded. Ten 
cranial measurements were taken to the 
nearest tenth of a millimeter. Seven of 
the measurements were taken as illus- 
trated and described by Hooper (1952: 
9-11); these include greatest length of 
skull, zygomatic breadth, least interor- 
bital constriction ( interorbital breadth), 
length of rostrum, breadth of rostrum, 
alveolar length of maxillary toothrow 
(length of molar row), and length of 
palatal bridge (length of palate). The 
remaining three measurements were 
taken as follow: condylobasilar length — 
midline length of the skull from anterior- 
most extensions of the premaxillae to the 
posterior surface of the condyles; breadth 



at mastoids — the distance, perpendicular 
to the longitudinal axis of the skull, from 
the most lateral extension on one mastoid 
to the same point of the other; and length 
of nasals — the distance from the anterior 
edge of the longest nasal to the most 1 
posterior extension of either nasal. 

Selection of samples. — Because there 
were so few adults of each sex for statis- 
tical treatment of specimens from indi- 
vidual localities it was necessary to in- 
clude those from adjacent localities in 
pooled samples. Decisions for grouping 
specific localities and establishing size of 
geographic areas to include in each sam- 
ple were based on several criteria. In no 
case were specimens of different nominal 
taxa, as recognized at the onset of the 
study, included together in a single sam- 
ple. In areas of suspected intergradation 
or possible contact between species and 
subspecies, an attempt was made to keep 
size of geographic areas as small as pos- 
sible. Whenever practical, localities were 
grouped so that at least three and pre- 
ferably no fewer than five adults of each 
sex were available. Whenever the above 
criteria could be met and there was no 
cause to suspect biologically-based rea- 
sons for doing otherwise, locality group- 
ings often were made with consideration 
to political boundaries merely to facili- 
tate menial tasks such as sorting of orig- 
inal data. 

The thirty-two aggregate localities 
(samples) and their identifying symbols 
are shown in figure 8 and briefly outlined 
below. When all available specimens of 
a species or subspecies are included in a 
single sample, the geographic area is not 
described (exact localities were listed 
previously under specimens examined). 
Grouped localities of Neotoma floriclana 
were coded with numeric symbols and 
those of N. micropus and the single sam- 
ple of N. angustipalata were given alpha 
symbols. Names given below in paren- 
theses are those by which the woodrats 
previously were recognized. 

Sample 1. — Neotoma floridana bai- 
leyi. 

Sample 2. — N. f. campestris from all 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



39 



localities in Colorado and Nebraska. 

Sample 3. — N. f. campestris from all 
localities in Kansas west of a north-south 
line extended from the boundary be- 
tween Trego and Ellis counties. 

Sample 4. — IV. /. campestris from all 
localities in Kansas east of the line de- 
scribed for sample 3 and west of a paral- 
lel line extended from the boundary be- 
tween Russell and Ellsworth counties. 

Sample 5. — IV. /. attwateri (N. f. 
osagensis) from all localities in Kansas 
east of the line described for sample 4 
and west of a parallel line extended from 




Fig. 8. Sketch map of region in which 
woodrats were studied showing general geo- 
graphic areas of grouped localities, indicated by 
identifying code symbols. All samples of Neo- 
toma floridana (1-13) are represented by nu- 
meric symbols and those of N. micropus (A-P) 
and N. angustipalata ( R ) are represented by 
alpha symbols. Solid lines separate the distri- 
butions of species and dashed lines the distribu- 
tions of subspecies. The solid dot labeled S in 
Oklahoma marks the single known locality of 
sympatry between two of the species. See text 
for precise definitions of the area included in 
each grouped locality. 



the boundary between Saline and Dick- 
inson counties. 

Sample 6. — IV. /. attwateri (N. f. 
osagensis) from all localities in Kansas 
east of the line described for sample 5 
and north of a perpendicular line ex- 
tended from the boundary between Lyon 
and Greenwood counties. 

Sample 7.—N. f. attwateri (N. f. 
osagensis) from all localities in Kansas 
south of the line described for sample 6. 

Sample 8. — N. f. attwateri (N. f. 
osagensis) from all localities in Okla- 
homa west of a line extended from the 
boundary between Major and Garfield 
counties. 

Sample 9. — IV. /. attwateri (N. f. 
osagensis) from all localities in Oklahoma 
east of the line described for sample 8 
and north of a perpendicular line ex- 
tended from the boundary between 
Lincoln and Pottawatomie counties. 

Sample 10. — N. f. attwateri (N. f. 
osagensis) from all localities in Oklahoma 
east of the line described for sample 8 
and south of the line described for sam- 
ple 9. 

Sample 11. — N. f. attwateri (N. f. 
osagensis) from all localities in Texas 
north of a line extended from the boun- 
dary between Navarro and Limestone 
counties and west of a perpendicular line 
extended from the boundary between 
Harrison and Gregg counties. 

Sample 12. — N. f. attwateri from all 
localities in Texas south of the east-west 
line described for sample 11 and south- 
west of a line extended from the south- 
western border of Walker County where 
it abuts Montgomery County. 

Sample 13. — N. f. rubida from all lo- 
calities in Texas. 

Sample A. — IV. micropus canescens 
from all localities in Colorado, and in 
Cimarron County, Oklahoma. 

Sample B. — N. m. canescens from all 
localities in Kansas northwest of U.S. 
highway 54, and in Beaver and Texas 
counties, Oklahoma. 

Sample C. — IV. m. canescens from all 
localities in Meade and Clark counties, 



40 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



Kansas, and in Harper County, Okla- 
homa. 

Sample D. — N. m. canescens (N. m. 
micropus) from all localities in Barber, 
Comanche, and Kiowa counties, Kansas. 

Sample E. — N. m. canescens from all 
localities in New Mexico except the 
White Sands National Monument. 

Sample F. — N. m. canescens from all 
localities in Texas north of a line ex- 
tended from the boundary between An- 
derson and Winkler counties and west 
of a perpendicular line extended from 
the boundary between Fisher and Curry 
counties. 

Sample G. — N. m. canescens (N. m. 
micropus) from all localities in Oklahoma 
north of the South Canadian River, ex- 
clusive of localities in samples A, B, 
and C. 

Sample H. — N. m. canescens (N. m. 
micropus) from all localities in Oklahoma 
south of the South Canadian River. 

Sample I. — N. m. canescens (N. m. 
micropus) from all localities in Texas 
north of the east-west line described for 
sample F, and east of the north-south line 
described for that sample. 

Sample J. — N. m. canescens from all 
localities in Chihuahua and those in 
Texas south of the east-west line de- 
scribed for sample F and west of a line 
extended from the boundary between 
Reagan and Irion counties. 

Sample K. — N. m. canescens (N. m. 
micropus) from all localities in Texas east 
of the line described for sample J, south 
of the east-west line described for sample 
F, west of a line extended from the 
boundary between Medina and Bexar 
counties, and north of the Webb-Zapata 
County boundary. 

Sample L. — N. m. canescens (N. m. 
micropus) from all localities in Texas 
south of the east-west line described for 
sample F and the Webb-Zapata County 
boundary, and east of a north-south line 
extended south to the southern Webb 
County boundary from the boundary be- 
tween Medina and Bexar counties. 

Sample M. — N. m. canescens (N. m. 
micropus) from all localities in Coahuila 



and Nuevo Leon and those in Tamaulipas 
north of an east- west line passing through 
Reynosa. 

Sample N. — N. m. micropus from all 
localities in Tamaulipas south of the line 
described for sample M and north of 23° 
30' N latitude. 

Sample O. — N. m. canescens (N. m. 
leucophea) from White Sands National 
Monument in New Mexico. 

Sample P. — N. m. micropus (N. m. 
littoralis) from all localities in Tamaulipas 
south of 23° 30' N latitude. 

Sample Q. — N. m. planiceps. 

Sample R. — N. angustipalata . 

Sample S. — Neotoma fJoridana, N. 
micropus, and their natural hybrids from 
3 mi S Chester, Major Co., Oklahoma. 

Statistical analyses. — Statistical anal- 
yses were selected for their appropriate- 
ness, ease of interpretation, and avail- 
ability at The University of Kansas Com- 
putation Center. Standard statistics 
(mean, range, standard deviation, stand- 
ard error of the mean, variance, and 
coefficient of variation) were calculated, 
after which group-means were simul- 
taneously tested for significant differ- 
ences at the 0.95 level of confidence ( 0.05 
level of significance) by single classifica- 
tion analysis of variance (univariate 
ANOVA). If significant variation was 
present among the group-means and if 
more than two samples were being com- 
pared, the Sums of Squares Simultaneous 
Testing Procedure (SS-STP) described 
by Gabriel ( 1964 ) was employed to de- 
termine maximal non-significant subsets. 
Calculations involved in the SS-STP were 
outlined by Sokal and Rohlf (1969:582), 
and use of the procedure in studies of 
geographic variation was considered by 
Gabriel and Sokal (1969). All of the 
above calculations were computed by 
Power's UNIVAR program (Power, 1970). 

Univariate analyses first were con- 
ducted to compare males and females by 
selecting samples of woodrats considered 
to be adults that were from the same geo- 
graphic areas ( ideally, animals from a 
single locality would be used, but no suf- 
ficiently large samples were available). 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



41 



When it was clear that significant sexual 
dimorphism existed, samples of the pre- 
viously described age groups were com- 
pared separately within each sex. Re- 
sults indicated that animals of age groups 
V and younger frequently were signifi- 
cantly smaller than those in groups VI 
or older. Although animals in group VI 
occasionally were significantly smaller 
^than those of groups VII and VIII, these 
three age groups were considered to- 
gether with sexes being treated separ- 
ately in analysis of geographic variation. 
So-called Dice-grams (Dice and Leraas, 
1936) have been employed frequently to 
illustrate a general array of variation. 
For reasons discussed by Sokal and 
Rinkel ( 1963 ) , Dice-grams are not ap- 
propriate for determination of statistical 
significance when more than two samples 
i are being compared; therefore, all deter- 
minations of significance or the absence 
thereof were based on SS-STP tests. 

Because the sample of specimens from 
each locality usually exhibited various 
subset relationships with samples from 
other localities when different characters 
were considered, it was necessary to use 
multivariate analyses to determine rela- 
tionships based on all characters exam- 
ined. This was accomplished by means 
of two programs (CLSNT- Version 2, and 
MULDIS) available in the Numerical 
Taxonomy System at the Computation 
Center of The University of Kansas. 
CLSNT was used to compare samples of 
populations for geographic variation by 
considering the sample of specimens 
from each aggregate locality as an Oper- 
ational Taxonomic Unit (OTU) and 
sample means as characters. When only 
a single individual was available, as for 
Neotoma micropus planiceps, the char- 
acters of that specimen were treated as 
means. Discriminant function analysis 
(MULDIS) was employed to compare 
individuals from various samples and to 
analyze for hybridization and intergrada- 
tion. 

Among other sets of values, CLSNT 
and optional subroutines as employed by 
me computed matrices of Pearson's prod- 



uct moment correlations and matrices of 
taxonomic distance coefficients (see 
Sokal, 1961, and Sokal and Sneath, 1963). 
Each matrix was then subjected to clus- 
ter analyses using UPGMA (unweighted 
pair group method using arithmetic aver- 
ages), and a two-dimensional phenogram 
was generated from each. A coefficient 
of cophenetic correlation (Sokal and 
Sneath, 1963) was computed to express 
the reliability of the phenogram based 
on comparisons with the respective 
matrices. Moss (1968) discussed rela- 
tionships of the two phenograms and ex- 
perimentally studied general types of 
variation affecting each. I have consid- 
ered both matrices and both phenograms 
in all analyses, but because coefficients 
of cophenetic correlation usually were 
higher between the distance matrix and 
phenogram, these have been given 
greatest consideration. All computations 
for CLSNT were conducted on stand- 
ardized data, which was derived by con- 
verting the mean for each character to 
zero and the variance and standard devi- 
ation to one so that the value for each 
character was expressed in terms of 
standardized deviates (see Sokal and 
Rohlf, 1969:109). 

A principal components analysis also 
was conducted on the among-characters 
correlation matrix to "condense" or "com- 
press" the variation in the characters con- 
sidered into a smaller number of "new" 
characters, the first few principal com- 
ponents. At least the first three com- 
ponents were extracted in all cases and 
the first five components frequently were 
considered, especially when the number 
of characters for each OTU was large. 
The percentage of the total variation ac- 
counted for by each principal component 
also was calculated. OTU's were pro- 
jected onto the principal components, and 
bivariate scatter diagrams were made by 
plotting projections of OTU's on all 
combinations of components. Projection 
of OTU's into three-dimensional draw- 
ings was accomplished with a PROJ-3D 
program whereby the first three prin- 
cipal component scores of each OTU 



42 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



were transferred to a magnetic tape from 
which a Benson-Lehner incremental plot- 
ter made the perspective drawings. The 
shortest minimally connected network 
between OTU's was computed from the 
matrix of distance coefficients and in- 
cluded on the three-dimensional models. 
Discriminant function analysis 
(MULDIS) employs variance-covariance 
mathematics to differentially weight each 
character relative to the variance within 
and between groups of that character 
when two reference samples are con- 
sidered. A discriminant multiplier (dis- 
criminant function) was calculated for 
each variable; then each discriminant 
multiplier was multiplied by the value of 
its respective variable and summed for 
all variables to yield a discriminant score 
for each OTU. The discriminant scores 
then were plotted on a frequency histo- 
gram to compare the individuals of two 
populations, with or without additional 
comparisons of a test sample of geo- 
graphic intermediates or suspected and 
known (laboratory-bred) hybrids. 

NON-GEOGBAPHIC VABIATION 

In order to undertake a meaningful 
assessment of geographic variation, it is 
necessary to understand the non-geo- 
graphic variation that exists in popula- 
tions of the organisms to be compared. 
I have analyzed variation with respect 
to age, secondary sexual characteristics, 
individual differences, and effects of hav- 
ing been held in captivity. Variation in 
pelages resulting from age and molts was 
considered and was found to vary sea- 
sonally. Because seasonal timing of molt 
and certain characteristics of pelage in 
woodrats vary geographically, these as- 
pects are considered beyond with dis- 
cussion of geographic variation in color. 

Variation with Age 

Variation in size correlated with age 
differences was analyzed for samples of 
Neotoma floridana campestris (Table 1), 
N. f. baileyi, N. f. attwateri, and N. mi- 
cropus canescens (Birney, 1970). Be- 



cause age-groups and sexes were sepa- 
rated sample size frequently was small, 
especially for baileyi. As a result, some 
age-groups were strikingly different in 
size, but the differences were not always 
statistically significant. 

Dimensions of two external charac- 
ters (length of hind foot and length of 
ear) and those of two cranial characters 
(least interorbital constriction and alve- 
olar length of the maxillary toothrow) 
were influenced less by age than were 
those of other characters. Growth and 
development studies of laboratory wood- 
rats demonstrate that the hind foot and 
ear grow at a disproportionately faster 
rate than the body and tail. Also, varia- 
tion in external measurements of museum 
specimens is high ( see discussion of indi- 
vidual variation) because of inconsis- 
tencies in techniques used to measure 
these characters by various collectors. 

Alveolar length of the maxillary tooth- 
row does not increase with age after the 
molars have become occlusal, because 
individual teeth of woodrats do not in- 
crease in diameter after eruption. There 
is a tendency for the molar row to be 
slightly longer in rats of age-groups III 
and IV than in older animals. The alve- 
olar tissue in cleaned skulls of older 
woodrats usually is separated slightly 
from the base of the teeth and in some 
senile rats the molar roots extend to the 
alveolus. These factors tend to result in 
smaller measurements, and a decrease in 
accuracy of the measurement. Least 
interorbital constriction shows a general 
increase in size up to age-groups III and 
IV. Sequence of means varied noticeably 
in the older age-groups, indicating that 
the constriction changes little with age 
after the early period of rapid growth. 

Dimensions of other cranial charac- 
ters indicated that animals in age-groups 
VII and VIII do not differ significantly 
in size. Although the mean of a sample 
in age-group VI frequently was less than 
that of older woodrats, this difference 
seldom was significant. Highest F, 
values and the greatest number of non- 
significant subsets frequently were com- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



43 



TABLE 1. Variation with age in 14 external and cranial measurements of Neotoma floridana 
campestris. F s was calculated by single classification analysis of variance. Tabular F values 
are at the P 0.05 level of significance; ns indicates no significant difference within a group of 
means. Nonsignificant subsets (as calculated by the Sums of Squares Simultaneous Testing 
Procedure) of significantly different groups of means are shown in the last column. 



Measurement, 




















sex, and 












F s 








age class 


N 


Mean 


± 2SE 


Range 


cv 


F 




SS-STP 


Total length 




















Females 




















VIII 


15 


370.8 


8.70 


(340.0-402.0) 


4.54 


22.88 


I 






VI 


16 


369.6 


8.88 


(340.0-409.0) 


4.81 


2.21 


I 






VII 


10 


268.7 


11.39 


(344.0-395.0) 


4.88 




I 






V 


20 


353.5 


6.72 


(325.0-377.0) 


4.25 




I 


I 




IV 


14 


337.0 


8.91 


(303.0-365.0) 


4.94 






I 


I 


III 


13 


314.2 


13.15 


(291.0-374.0) 


7.55 








I I 


II 


2 


284.0 


24.00 


(272.0-296.0) 


5.98 








I 


Males 




















VIII 


7 


399.7 


15.56 


(371.0-434.0) 


5.15 


30.90 


I 






VI 


11 


382.8 


9.84 


(350.0-408.0) 


4.26 


2.15 


I 






V 


17 


377.6 


13.19 


(325.0-424.0) 


7.20 




I 


I 




VII 


9 


373.9 


10.30 


(341.0-395.0) 


4.13 




I 


I 


I 


IV 


13 


347.8 


12.54 


(307.0-383.0) 


6.50 






I 


I 


III 


7 


332.3 


21.00 


(288.0-365.0) 


8.38 








I 


I 


3 


264.7 


33.17 


(232.0-286.0) 


10.85 








I 


II 


6 


264.3 


17.82 


(240.0-287.0) 


8.26 








I 


Length of tail 


vertebrae 
















Females 




















VI 


16 


156.6 


4.54 


(144.0-172.0) 


5.80 


13.65 


I 






VIII 


15 


154.5 


4.85 


(136.0-175.0) 


6.07 


2.21 


I 






VII 


10 


154.5 


7.46 


(138.0-172.0) 


7.63 




I 


I 




V 


20 


148.4 


4.86 


(131.0-167.0) 


7.33 




I 


I 




IV 


14 


142.2 


3.35 


(133.0-152.0) 


4.41 






I 


I 


III 


13 


130.8 


5.48 


(115.0-154.0) 


7.56 








I I 


II 


2 


122.5 


25.00 


(110.0-135.0) 


14.43 








I 


Males 




















VIII 


7 


164.4 


6.38 


(151.0-175.0) 


5.13 


17.39 








VI 


11 


161.0 


8.33 


(130.0-178.0) 


8.58 


2.15 








V 


17 


155.9 


6.53 


(132.0-177.0) 


8.64 










VII 


9 


151.6 


9.17 


(120.0-164.0) 


9.07 






I 




IV 


13 


146.8 


6.08 


(129.0-168.0) 


7.47 






I 




III 


7 


132.7 


9.77 


(107.0-147.0) 


9.73 






I 


I 


I 


3 


113.0 


21.94 


(92.0-129.0) 


16.81 








I 


II 


6 


108.5 


8.53 


(98.0-124.0) 


9.63 








I 


Length of hindfoot 


















Females 




















IV 


14 


39.9 


1.10 


(36.0-43.0) 


5.15 


<1.00 


n< 






VI 


16 


39.7 


0.60 


(38.0-42.0) 


3.01 


2.21 








V 


20 


39.4 


0.69 


(36.0-41.0) 


3.90 










VIII 


16 


39.2 


0.71 


(36.0-41.0) 


3.64 










VII 


10 


39.1 


1.28 


(36.0-42.0) 


5.18 










III 


13 


38.8 


1.13 


(35.0-41.0) 


5.24 










II 


2 


38.0 


4.00 


(36.0-40.0) 


7.44 











44 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 1.— Continued. 



Measurement, 
















sex, and 












Fs 




age class 


N 


Mean 


± 2SE 


Range 


CV 


F 


SS-STP 


Males 
















VII 


4 


40.8 


0.88 


(39.0-43.0) 


3.43 


4.84 




VIII 


8 


40.8 


1.50 


(36.0-44.0) 


6.38 


2.14 




V 


10 


40.6 


0.90 


(36.0-44.0) 


4.73 






VI 


5 


40.4 


1.24 


(37.0-44.0) 


5.11 






IV 


7 


40.0 


1.01 


(35.0-42.0) 


4.56 




I I 


III 


5 


38.9 


1.34 


(37.0-41.0) 


4.56 




I I 


II 


5 


36.7 


1.52 


(35.0-40.0) 


5.08 




I 


I 


3 


36.7 


0.67 


(36.0-37.0) 


1.57 




I 


Length of ear 
















Females 
















VIII 


8 


28.0 


1.07 


(26.0-30.0) 


5.40 


1.36 


ns 


VI 


12 


27.8 


1.18 


(25.0-32.0) 


7.32 


2.31 




VII 


5 


27.2 


1.47 


(25.0-29.0) 


6.04 






IV 


9 


27.2 


1.19 


(25.0-30.0) 


6.57 






V 


6 


27.0 


0.89 


(25.0-28.0) 


4.06 






III 


9 


26.4 


1.11 


(25.0-30.0) 


6.30 






II 


2 


25.0 


4.00 


(23.0-27.0) 


11.31 






Males 
















VI 


5 


29.0 


2.28 


(26.0-33.0) 


8.79 


1.70 


ns 


IV 


7 


28.9 


1.60 


(26.0-32.0) 


7.33 


2.26 




VIII 


8 


28.6 


2.28 


(26.0-33.0) 


8.79 






VII 


4 


28.5 


0.58 


(28.0-29.0) 


2.03 






V 


8 


28.5 


1.00 


(26.0-30.0) 


4.96 






III 


5 


26.0 


1.41 


(24.0-28.0) 


6.08 






II 


5 


25.6 


1.36 


(24.0-28.0) 


5.92 






I 


3 


25.0 


1.15 


(24.0-26.0) 


4.00 






Greatest length 


of skull 














Females 
















VIII 


14 


49.9 


0.69 


(48.3-52.1) 


2.57 


24.01 


I 


VI 


13 


49.4 


0.87 


(47.0-53.3) 


3.18 


2.23 


I 


VII 


8 


49.3 


0.86 


(47.5-51.8) 


2.45 




I I 


V 


19 


47.3 


4.19 


(45.8-49.5) 


1.93 




I I 


IV 


14 


46.7 


0.57 


(44.4-48.1) 


2.28 




I I 


III 


10 


44.9 


1.51 


(42.5-48.3) 


5.31 




I I 


II 


2 


41.8 


2.90 


(40.4-43.3) 


4.90 




I 


Males 
















VIII 


10 


51.8 


1.13 


(49.5-55.2) 


3.44 


32.64 


I 


VII 


6 


51.6 


1.30 


(49.0-53.4) 


3.08 


2.17 


I 


V 


20 


49.8 


0.76 


(47.3-53.7) 


3.40 




I 


VI 


9 


49.7 


1.52 


(46.0-52.7) 


4.60 




I I 


IV 


13 


46.8 


0.95 


(43.3-49.6) 


3.66 




I I 


III 


4 


44.4 


2.25 


(42.3-47.4) 


5.06 




I 


I 


1 


40.9 


____ 


(40.9-40.9) 


.._ 




I I 


II 


5 


39.2 


2.19 


(37.1-42.7) 


6.26 




I 


Condylobasilar 


length 














Females 
















VIII 


15 


48.4 


0.75 


(46.9-51.6) 


2.98 


36.40 


I 


VII 


8 


48.3 


0.90 


(46.4-50.9) 


2.63 


2.23 


I 


VI 


10 


47.3 


0.67 


(45.2-48.9) 


2.25 




I I 


V 


20 


45.7 


0.45 


(44.0-48.2) 


2.21 




I I 


IV 


14 


44.6 


0.57 


(42.7-46.3) 


2.37 




I 


III 


12 


42.4 


1.27 


(39.9-45.6) 


5.19 




I 


II 


2 


39.3 


2.60 


(38.0-40.6) 


4.68 




I 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



45 



TABLE 1.— Continued. 



Measurement, 


















sex, and 












F, 






age class 


N 


Mean 


± 2SE 


Range 


CV 


F 


SS-STP 


Males 


















VIII 


12 


50.6 


1.07 


(48.1-54.3) 


3.66 


36.44 


I 




VII 


7 


49.6 


1.63 


(46.6-52.3) 


4.32 


2.17 


I 




VI 


9 


48.3 


1.47 


(44.5-52.3) 


4.57 




I 




V 


20 


48.2 


0.82 


(45.3-52.8) 


3.82 




I 




IV 


13 


44.7 


0.95 


(41.1-46.8) 


3.81 






I 


III 


4 


42.0 


2.94 


(39.6-46.1) 


6.99 






I 


I 


1 


38.6 




(38.6-38.6) 









I I 


II 


5 


36.7 


2.09 


(34.8-40.1) 


6.38 






I 


Zygomatic bit 


adth 
















Females 


















VIII 


14 


27.4 


0.52 


(26.0-29.6) 


3.54 


34.92 


I 




VII 


6 


26.8 


0.54 


(26.0-27.7) 


2.46 


2.23 


I 




VI 


14 


26.3 


0.41 


(25.1-28.0) 


2.88 




I 


I 


V 


19 


25.6 


0.36 


(24.5-27.1) 


3.09 






I I 


IV 


14 


24.7 


0.33 


(23.6-25.9) 


2.54 






I I 


III 


13 


23.7 


0.54 


(22.6-25.5) 


4.15 






I I 


II 


2 


22.5 


0.60 


(22.2-22.8) 


1.89 






I 


Males 


















VIII 


11 


28.2 


0.51 


(27.0-29.9) 


2.99 


49.56 


I 




VII 


7 


27.3 


0.72 


(26.1-28.5) 


3.47 


2.17 


I 


I 


VI 


8 


26.7 


0.54 


(25.4-28.1) 


2.85 




I 


I 


V 


19 


26.6 


0.44 


(25.3-28.7) 


3.57 






I 


IV 


13 


24.8 


0.49 


(23.4-26.4) 


3.56 






I 


III 


6 


24.3 


1.13 


(22.9-26.1) 


5.69 






I 


I 


3 


20.6 


1.64 


(19.0-21.7) 


6.88 






I 


II 


5 


20.5 


1.30 


(18.9-22.6) 


7.07 






I 


Least interorbital constriction 














Females 


















VI 


15 


6.8 


0.19 


(6.1-7.5) 


5.55 


2.01 


ns 




VII 


9 


6.7 


0.17 


(6.2-7.0) 


3.78 


2.21 






VIII 


16 


6.6 


0.13 


(6.2-7.1) 


3.92 








V 


20 


6.6 


0.12 


(6.1-7.1) 


4.07 








IV 


14 


6.6 


0.12 


(6.1-6.9) 


3.49 








III 


14 


6.5 


0.18 


(6.0-7.3) 


5.15 








II 


2 


6.2 


0.10 


(6.1-6.2) 


1.15 








Males 


















VII 


10 


7.0 


0.23 


(6.5-7.7) 


5.19 


5.97 






VIII 


12 


6.8 


0.13 


(6.5-7.1) 


3.32 


2.14 






VI 


10 


6.8 


0.18 


(6.4-7.1) 


4.20 








V 


20 


6.7 


0.11 


(6.2-7.2) 


3.60 








III 


7 


6.6 


0.20 


(6.3-6.9) 


3.97 








IV 


13 


6.5 


0.18 


(6.1-7.1) 


4.90 








II 


6 


6.4 


0.31 


(5.9-6.9) 


5.87 








I 


3 


6.2 


0.20 


(6.1-6.4) 


2.79 








Breadth at mastoids 
















Females 


















VIII 


15 


19.4 


0.36 


(18.3-21.0) 


3.55 


7.96 


I 




VI 


11 


19.3 


0.40 


(18.1-20.2) 


3.42 


2.23 


I 


I 


VII 


10 


19.2 


0.38 


(18.1-20.0) 


3.12 




I 


I I 


V 


19 


18.7 


0.20 


(17.9-19.7) 


2.32 






I I I 


IV 


13 


18.7 


0.20 


(17.9-19.2) 


1.91 






I I 


III 


12 


18.3 


0.30 


(17.7-19.5) 


2.82 






I 


II 


2 


17.9 


0.60 


(17.6-18.2) 


2.37 






I 



46 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 1.— Continued. 



Measurement, 




















sex, and 










F s 










age class N 


Mean 


± 2SE 


Range 


CV 


F 




SS-STP 


Males 




















VIII 11 


20.5 


0.51 


(19.3-22.4) 


4.15 


16.91 


I 








VII 10 


19.6 


0.33 


(18.7-20.2) 


2.66 


2.15 


I 


I 






V 20 


19.6 


0.37 


(18.3-20.8) 


4.20 




I 


I 


I 




VI 8 


19.1 


0.73 


(17.4-20.3) 


5.43 






I 


I 




IV 13 


18.7 


0.27 


(17.6-19.6) 


2.59 






I 


I 




III 5 


18.6 


0.36 


(18.1-19.0) 


2.17 








I 


I 


II 6 


17.0 


0.48 


(16.3-17.7) 


3.45 










I 


I 1 


16.9 


-— 


(16.9-16.9) 


— 










I 


Length of rostrum 




















Females 




















VII 10 


19.5 


0.51 


(18.2-21.0) 


4.11 


19.25 


I 








VIII 15 


19.4 


0.29 


(18.6-20.5) 


2.92 


2.21 


I 








VI 16 


19.0 


0.44 


(17.3-21.1) 


4.62 




I 


I 






V 19 


18.3 


0.26 


(17.5-19.8) 


3.14 






I 






IV 15 


18.1 


0.36 


(16.7-19.4) 


3.84 






I 


I 




III 12 


17.2 


0.61 


(15.9-18.6) 


6.11 








I 


I 


II 2 


15.8 


0.90 


(15.3-16.2) 


4.04 










I 


Males 




















VIII 11 


20.5 


0.64 


(19.4-22.9) 


5.19 


37.51 


I 








VII 8 


20.4 


0.44 


(19.3-21.2) 


3.08 


2.14 


I 








V 20 


19.7 


0.43 


(18.0-21.7) 


4.92 




I 








VI 11 


19.2 


0.51 


(18.0-20.9) 


4.38 




I 


I 






IV 13 


18.2 


0.49 


(16.4-19.6) 


4.88 






I 






III 6 


17.5 


0.95 


(16.1-18.8) 


6.66 






I 






I 3 


14.7 


1.92 


(12.8-15.9) 


11.32 








I 




II 6 


14.4 


0.94 


(13.2-15.6) 


7.99 








I 




Breadth of rostrum 




















Females 




















VIII 16 


8.5 


0.17 


(8.0-9.4) 


4.10 


8.62 


I 








VII 9 


8.5 


0.21 


(8.0-9.0) 


3.64 


2.21 


I 


I 






VI 15 


8.2 


0.12 


(7.7-8.5) 


2.84 




I 


I 


I 




V 20 


8.1 


0.15 


(7.3-8.5) 


4.11 






I 


I 


I 


IV 15 


7.9 


1.16 


(7.4-8.4) 


3.89 








I 


I 


III 13 


7.8 


0.23 


(7.3-8.5) 


5.20 








I 


I 


II 1 


7.6 




(7.6-7.6) 


— 










I 


Males 




















VIII 12 


8.9 


0.14 


(8.6-9.3) 


2.64 


17.51 


I 








VII 9 


8.6 


0.24 


(8.2-9.2) 


4.10 


2.14 


I 


I 






V 20 


8.4 


0.17 


(7.8-9.4) 


4.54 




I 


I 


I 




VI 11 


8.2 


0.46 


(6.1-8.8) 


9.35 






I 


I 




IV 13 


8.1 


0.20 


(7.5-9.0) 


4.58 






I 


I 


I 


III 7 


7.7 


0.23 


(7.2-8.1) 


3.90 








I 


I I 


II 6 


7.0 


0.44 


(6.3-7.6) 


7.79 










I I 


I 3 


7.0 


0.46 


(6.6-7.4) 


5.71 










I 


Alveolar length of maxillary toothrow 
















Females 




















IV 15 


9.9 


0.17 


(9.3-10.5) 


3.31 


2.32 










VII 10 


9.8 


0.17 


(9.4-10.3) 


2.75 


2.21 










V 20 


9.7 


0.14 


(9.1-10.3) 


3.15 












VI 16 


9.7 


0.17 


(9.3-10.5) 


3.49 












III 13 


9.7 


0.13 


(9.4-10.1) 


2.41 












II 2 


9.6 


0.50 


(9.3-9.8) 


3.70 












VIII 16 


9.5 


0.18 


(8.9-10.0) 


3.82 













WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



47 



TABLE 1.— Concluded. 



Measurement, 






















sex, and 












F 9 










age class 


N 


Mean 


± 2SE 


Range 


CV 


F 




SS-STP 




Males 






















V 


20 


9.9 


0.12 


(9.2-10.4) 


2.64 


2.13 


ns 








IV 


13 


9.9 


0.19 


(9.3-10.6) 


3.43 


2.14 










III 


7 


9.8 


0.19 


(9.6-10.3) 


2.55 












VIII 


12 


9.7 


0.26 


(9.0-10.4) 


4.68 












VII 


10 


9.7 


0.26 


(8.9-10.2) 


4.22 












VI 


11 


9.6 


0.23 


(9.1-10.3) 


4.05 












I 


3 


9.5 


0.18 


(9.3-9.6) 


1.61 












II 


6 


9.4 


0.28 


(8.9-9.8) 


3.66 












Length of palatal bridg 


e 


















Females 






















VII 


10 


8.6 


0.20 


(8.0-9.1) 


3.72 


4.91 


I 








VIII 


16 


8.5 


0.25 


(7.8-9.4) 


5.96 


2.21 


I 


I 






VI 


16 


8.2 


0.17 


(7.5-8.8) 


4.13 




I 


I 






V 


20 


8.2 


0.15 


(7.4-8.7) 


4.15 






I 






IV 


15 


8.1 


0.19 


(7.3-8.6) 


4.44 






I 






III 


13 


8.1 


0.16 


(7.6-8.8) 


3.67 












II 


2 


7.6 


0.10 


(7.6-7.7) 


0.92 












Males 






















VII 


9 


9.0 


0.44 


(7.9-9.8) 


7.47 


14.27 


I 








VIII 


12 


9.0 


0.21 


(8.5-9.7) 


4.05 


2.14 


I 


I 






VI 


11 


8.5 


0.25 


(7.6-9.0) 


4.81 




I 


I 


I 




V 


20 


8.4 


0.23 


(7.4-9.5) 


6.15 






I 


I I 




III 


6 


8.1 


0.33 


(7.6-8.7) 


4.96 








I I 




IV 


13 


7.9 


0.18 


(7.4-8.4) 


4.07 








I I 


I 


I 


2 


7.4 


0.60 


(7.1-7.7) 


5.73 








I 


I 


II 


6 


7.1 


0.41 


(6.5-7.9) 


7.02 










I 


Length of nasals 






















Females 






















VIII 


15 


19.4 


0.30 


(18.7-20.4) 


3.03 


20.54 


I 








VII 


10 


19.3 


0.36 


(18.4-20.4) 


2.96 


2.21 


I 








VI 


16 


18.9 


0.44 


(17.6-20.3) 


4.70 




I 


I 






V 


19 


18.1 


0.25 


(17.2-19.3) 


3.04 






I 


I 




IV 


15 


17.9 


0.42 


(16.2-19.2) 


4.55 








I I 




III 


12 


16.8 


0.61 


(15.4-18.5) 


6.26 








I 


I 


II 


2 


16.0 


2.00 


(15.0-17.0) 


8.84 










I 


Males 






















VII 


8 


20.3 


0.42 


(19.1-21.0) 


2.94 


29.19 


I 








VIII 


11 


20.2 


0.83 


(18.3-23.3) 


6.77 


2.14 


I 








V 


20 


19.5 


0.43 


(18.3-21.5) 


4.90 




I 


I 






VI 


11 


19.0 


0.60 


(17.7-20.5) 


5.20 




I 


I 


I 




IV 


13 


18.1 


0.52 


(16.0-19.5) 


5.21 






I 


I 




III 


6 


17.0 


1.12 


(15.5-19.0) 


8.06 








I I 




I 


3 


14.8 


2.07 


(12.8-16.2) 


12.10 








I 


I 


II 


6 


14.4 


0.91 


(13.3-15.7) 


7.69 










I 



puted for measurements involving di- 
mensions of the anterior portions of 
skulls. In studies of Neotoma micropus, 
Allen (1894a: 240) noticed that relative 
growth of the preorbital region exceeded 
that of the postorbital area in post- 
partum development. Hall (1926:396) 



observed similar relative rates of growth 
for Spermophihis beecheyi and con- 
sidered them a common feature of mam- 
malian development. Therefore, it was 
expected that measurements such as 
length of rostrum and length of nasals 
would be most critical in terms of group- 



48 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



ing animals of different ages for other 
analyses. Animals of age-group V usu- 
ally were significantly different from 
animals of older groups, thus indicating 
that specimens of age-group V should 
not be included with older woodrats. Al- 
though this resulted in reduction of the 
sizes of available samples, comparisons 
of smaller, more homogeneous samples 
are more reliable than those involving 
heterogeneous samples. 

Secondary Sexual Variation 

Although no detailed analytical tests 
comparing woodrats of different sexes 
from the same geographic areas are avail- 
able, males and females generally have 
been treated separately in studies of 
geographic variation (Hooper, 1938, 
1940; Hoffmeister and de la Torre, 1960) . 
However, Schwartz and Odum (1957) 
apparently treated both sexes of N. flori- 
clana in the same samples. Using only 
specimens of age groups VI, VII, and 
VIII, males and females were tested by 
single classification ANOVA to deter- 
mine if secondary sexual variation was 
present in external and cranial dimen- 
sions of N. f. baileyi, N. f. campestris, N. 
f. atticateri, N. m. micropus, and N. m. 
canescens ( Table 2) . 

In one sample, N. f. campestris, size 
variation attributable to sex was ob- 
served in most measurements. Samples 
of campestris generally included more 
individuals than other samples. Means 
for males were larger at the 0.01 level 
of significance ( P < 0.01 ) in eight of the 
14 measurements, and significantly larger 
( P < 0.05 ) in two of the remaining six. 
Only in length of ear did the mean for 
females exceed that for males. In N. m. 
micropus, the taxon represented by few- 
est individuals, no significant differences 
in means were detected, but means of 
measurements for males were larger than 
those for females in nine characters. This 
suggests that non-significant results were 
a function of the small samples rather 
than absence of real differences between 
sexes. Males of baileyi were found to be 
larger than females in only six measure- 
ments and the difference was significant 



only in one (least interorbital constric- 
tion). Size of females exceeded that of 
males in three characters, but the dif- 
ference was significant in none. Means 
accurate to the nearest tenth of a milli- 
meter were identical in five dimensions 
considered. Although larger samples 
might alter the results, it appears that 
baileyi has less secondary sexual varia- 
tion than other taxa considered. Samples 
of canescens and atticateri were rela- 
tively large. Seven significant differences 
( one at the 0.01 level and six at the 0.05 
level) apparently resulting from secon- 
dary sexual variation were observed for 
atticateri, whereas only four (one at the 
0.01 level and three at the 0.05 level) 
were exhibited by canescens. 

Significant secondary sexual variation 
was not demonstrated for length of tail 
vertebrae, length of ear, breadth of ros- 
trum, and alveolar length of maxillary 
toothrow. Total length, condylobasilar 
length, and length of nasals varied sig- 
nificantly between the sexes in all of the 
taxa having samples of more than 10 
individuals of each sex. 

When all taxa and characters are 
considered, it is seen that sufficient sec- 
ondary sexual variation exists to discour- 
age treatment of males and females as 
a single sample. Therefore, the sexes 
were treated separately in geographic 
considerations of mensural data. Spec- 
imens of both sexes were treated as a 
single sample in only one set of analyses 
that included mensural data (discrim- 
inant function analysis). Because dis- 
criminant function analysis was used in 
comparisons of individuals and not in 
comparisons of sample means, the sex 
of each individual could be considered 
when interpreting results. 

As discussed beyond (comparative 
reproduction), it was observed in the 
laboratory that males capable of phys- 
ically dominating females in breeding 
cages were the more successful breeders 
and, conversely, females that were phys- 
ically subordinate were more successful 
breeders than large dominant females. 
Thus secondary sexual variation in size 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



49 



TABLE 2. Secondary sexual variation in 14 external and cranial measurements of selected 
samples of adult Neotoma floridana and N. micropus. F s was calculated by single classification 
analysis of variance. Tabular F values are given at the level of significance or at P<0.05 if not 
significant. One asterisk and two asterices indicate significance at P<0.05 and P<0.01, re- 
spectively, whereas ns indicates no significant difference. 



Measurements 

and sex N 


Mean 


± 2SE 


Range 


CV 


F s 
F 




Sample 


1 (Neotoma floridana baileyi) 






Total length 

Females 9 
Males 7 


374.4 
381.3 


9.87 
10.04 


(350.0-393.0) 
(361.0-398.0) 


3.95 
3.48 


<1.00 
4.60 ns 


Length of tail vertebrae 
Females 9 
Males 7 


161.7 
159.7 


9.00 
10.20 


(136.0-180.0) 
(138.0-176.0) 


8.35 
8.44 


<1.00 
4.60 ns 


Length of hind foot 
Females 11 
Males 8 


39.1 
39.8 


0.51 
0.60 


(38.0-41.0) 
(38.0-41.0) 


2.14 
2.12 


3.00 
4.45 ns 


Length of ear 

Females 5 
Males 2 


26.6 
27.5 


1.20 
3.00 


(25.0-28.0) 
(26.0-29.0) 


5.04 

7.71 


<1.00 
6.61 ns 


Greatest length of skull 
Females 11 
Males 7 


48.8 
48.4 


0.44 
1.11 


(47.5-49.7) 
(46.5-50.7) 


1.51 
3.03 


<1.00 

4.49 ns 


Condylobasilar length 
Females 1 1 
Males 7 


47.4 
47.4 


0.55 
1.17 


(46.0-48.9) 

(45.7-49.8) 


1.92 
3.27 


<1.00 

4.49 ns 


Zygomatic breadth 

Females 11 
Males 7 


26.1 
25.9 


0.27 
0.61 


(25.4-26.6) 

(24.8-27.1) 


1.72 
3.10 


<1.00 
4.49 ns 


Least interorbital constriction 

Females 11 6.7 
Males 9 6.9 


0.15 
0.17 


(6.3-7.0) 
(6.6-7.4) 


3.63 
3.68 


6.34 
4.41* 


Breadth at mastoids 
Females 11 
Males 8 


19.0 
19.0 


0.13 
0.51 


(18.2-19.6) 
(18.0-20.4) 


2.35 

3.79 


<1.00 
4.45 ns 


Length of rostrum 

Females 1 1 
Males 8 


18.8 
18.9 


0.32 
0.43 


(17.5-19.4) 
(17.8-19.6) 


2.86 
3.22 


<1.00 
4.45 ns 


Breadth of rostrum 
Females 1 1 
Males 9 


7.9 
7.9 


0.13 
0.17 


(7.5-8.2) 
(7.5-8.2) 


2.76 
3.26 


<1.00 
4.41 ns 


Alveolar length of maxillary 
Females 11 
Males 9 


toothrow 
9.4 
9.5 


0.17 
0.20 


(8.8-9.9) 
(9.2-10.0) 


3.07 
3.10 


<1.00 
4.41 ns 


Length of palatal bridge 
Females 11 
Males 9 


8.7 
8.7 


0.34 
0.33 


(7.3-9.2) 
(8.2-9.6) 


6.42 
5.66 


<1.00 
4.41 ns 


Length of nasals 

Females 1 1 
Males 8 


18.7 
18.7 


0.33 
0.43 


(18.0-20.2) 
(17.6-19.4) 


2.96 

3.22 


<1.00 
4.45 ns 



50 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 2.— Continued. 



Measurements 

and sex N 


Mean 


± 2SE 


Range 


cv 


F. 

F 




Samp 


les 2, 3, 


and 4 (Scotoma 


floridana campestris) 








Total length 

Females 41 
Males 27 


369.8 
384.2 


5.33 

7.47 


(340.0-409.0) 
(341.0-434.0) 


4.61 
5.05 


10.42 

7.04 


o O 


Length of tail vertebrae 
Females 41 
Males 27 


155.3 
158.7 


3.03 
5.12 


(136.0-175.0) 
(120.0-178.0) 


6.24 
8.37 


1.48 
3.99 


ns 


Length of hind foot 
Females 42 
Males 33 


39.4 
40.6 


0.46 
0.72 


(36.0-42.0) 
(36.0-44.0) 


3.80 
5.07 


9.71 
7.01 


© © 


Length of ear 

Females 25 
Males 17 


27.8 
28.7 


0.71 
0.82 


(25.0-32.0) 
(26.0-33.0) 


6.35 

5.88 


3.02 
4.08 


ns 


Greatest length of skull 
Females 35 
Males 25 


49.6 
51.0 


0.46 
0.84 


(47.0-53.3) 
(46.0-55.2) 


2.76 
4.12 


10.02 
7.12 


© © 


Condylobasilar length 
Females 33 
Males 28 


48.1 
49.6 


0.47 
0.83 


(45.2-51.6) 
(44.5-54.3) 


2.82 
4.43 


11.84 
7.12 


© © 


Zygomatic breadth 
Females 34 
Males 26 


26.8 

27.5 


0.32 
0.42 


(25.1-29.6) 
(25.4-29.9) 


3.53 
3.85 


6.53 
4.02 


» 


Least interorbital constriction 

Females 40 6.7 
Males 32 6.9 


0.09 
0.10 


(6.1-7.5) 
(6.4-7.7) 


4.56 
4.29 


7.44 
7.01 


© o 


Breadth at mastoids 
Females 36 
Males 29 


19.3 
19.8 


0.22 
0.37 


(18.1-21.0) 

(17.4-22.4) 


3.35 
4.97 


5.96 
4.00 


* 


Length of rostrum 

Females 41 
Males 30 


19.3 
20.0 


0.24 
0.38 


(17.3-21.1) 
(18.0-22.9) 


3.98 
5.26 


11.40 
7.04 


O 


Breadth of rostrum 
Females 40 
Males 32 


8.4 
8.6 


0.10 
0.20 


(7.7-9.4) 
(6.1-9.3) 


3.97 
6.77 


3.35 
3.98 


ns 


Alveolar length of maxillary 
Females 42 
Males 33 


toothrow 

9.6 0.11 

9.7 0.14 


(8.9-10.5) 
(8.9-10.4) 


3.60 
4.21 


<1.00 
3.98 


ns 


Length of palatal bridge 
Females 42 
Males 32 


8.4 
8.8 


0.13 
0.18 


(7.5-9.4) 
(7.6-9.8) 


5.06 
5.83 


12.48 
7.01 





Length of nasals 

Females 41 
Males 30 


19.2 
19.8 


0.23 
0.44 


(17.6-20.4) 

(17.7-23.3) 


3.84 
6.03 


7.91 
7.04 


© 


Sam 


ales 5, 6 


and 7 (Neotom 


a floridana attwateri) 








Total length 

Females 20 
Males 18 


364.6 
386.9 


8.89 
13.02 


(329.0-397.0) 
(345.0-450.0) 


5.45 
7.14 


8.28 
7.39 


O 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



51 



TARLE 2.— Continued. 



Measurements 
and sex 



N 



Mean 



± 2SE 



Range 



CV 



F 



Length of tail vertebrae 



Females 20 


157.2 


Males 18 


160.1 


Length of hind foot 




Females 21 


38.1 


Males 19 


39.4 


Length of ear 




Females 15 


27.1 


Males 15 


26.7 


Greatest length of skull 




Females 21 


49.4 


Males 18 


50.7 


Condylobasilar length 




Females 21 


48.1 


Males 18 


49.6 


Zygomatic breadth 




Females 22 


26.9 


Males 17 


27.7 


Least interorbital constriction 




Females 23 


6.5 


Males 20 


6.7 


Rreadth at mastoids 




Females 23 


19.2 


Males 18 


19.9 


Length of rostrum 




Females 21 


19.2 


Males 20 


19.7 


Rreadth of rostrum 




Females 21 


8.1 


Males 19 


8.3 



Alveolar length of maxillary toothrow 
Females 23 9.4 

Males 20 9.6 



Length of palatal bridge 
Females 23 

Males 20 



Length of nasals 
Females 
Males 



Total length 
Females 
Males 



20 
19 



31 

23 



Length of tail vertebrae 
Females 31 

Males 23 

Length of hind foot 
Females 30 

Males 25 



8.5 

8.7 

19.1 
19.8 



355.8 
370.0 

147.1 
152.6 

38.4 

39.2 



4.23 


(142.0-170.0) 


4.18 


(139.0-175.0) 


0.96 


(34.0-42.0) 


0.69 


(36.0-42.0) 


1.79 


(23.0-38.0) 


0.93 


(25.0-30.0) 


0.70 


(47.0-52.2) 


0.80 


(47.4-53.5) 


0.77 


(45.6-51.7) 


0.87 


(46.1-52.2) 


0.39 


(25.6-29.1) 


0.55 


(25.7-29.2) 


0.13 


(6.1-7.2) 


0.18 


(6.0-7.8) 


0.31 


(17.8-20.4) 


0.49 


(16.9-21.0) 


0.32 


(18.1-20.6) 


0.43 


(17.9-21.5) 


0.11 


(7.7-8.5) 


0.21 


(7.5-9.1) 


1.54 


(8.7-10.1) 


1.62 


(9.0-10.2) 


1.60 


(7.6-9.3) 


1.98 


(7.9-9.6) 


0.36 


(17.8-21.3) 


0.37 


(18.0-21.6) 


Neotom 


a micropus canesi 


5.97 


(310.0-382.0) 


9.46 


(334.0-411.0) 


3.70 


(130.0-165.0) 


5.10 


(131.0-175.0) 


0.54 


(36.0-41.0) 


1.01 


(35.0-45.0) 



6.02 
5.54 


<1.00 
4.11 ns 


5.75 
3.81 


4.51 

4.10 • 


12.76 
6.70 


<1.00 
4.20 ns 


3.23 
3.36 


5.49 
4.11 * 


3.68 
3.74 


5.90 
4.11 * 


3.42 
4.12 


5.61 

4.11 ° 


4.81 
6.01 


2.67 
4.08 ns 


3.84 
5.23 


5.98 
4.10 * 


3.77 
4.85 


3.17 
4.10 ns 


3.24 
5.45 


3.31 
4.10 ns 


3.95 
3.78 


2.63 
4.08 ns 


4.50 
5.08 


2.27 
4.08 ns 


4.17 
4.12 


6.03 
4.11 ° 


4.67 
6.13 


7.11 
4.03 * 


7.01 
8.01 


3.22 
4.03 ns 


3.85 
6.46 


1.95 
4.03 ns 



52 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 2.— Continued. 



Measurements 

and sex N 


Mean 


± 2SE 


Range 


CV 


F, 

F 




Length of ear 

Females 24 
Males 16 


27.1 
27.1 


0.56 
0.72 


(25.0-30.0) 
(25.0-29.0) 


5.10 
5.31 


<1.00 

4.10 


ns 


Greatest length of skull 
Females 27 
Males 25 


48.8 
49.5 


0.70 
0.63 


(44.2-51.8) 
(46.4-52.9) 


3.75 
3.17 


1.89 
4.03 


ns 


Condylobasilar length 
Females 29 
Males 24 


47.0 
48.3 


0.58 
0.66 


(42.8-50.0) 
(44.6-50.9) 


3.34 
3.33 


8.72 
7.17 


*# 


Zygomatic breadth 
Females 30 
Males 26 


26.5 
26.7 


0.39 
0.36 


(24.7-29.1) 
(25.1-28.8) 


4.06 

3.47 


<1.00 

4.03 


ns 


Least interorbital constriction 

Females 32 6.3 
Males 27 6.3 


0.10 
0.11 


(5.8-7.0) 
(5.8-6.9) 


4.72 
4.39 


<1.00 
4.02 


ns 


Breadth at mastoids 
Females 27 
Males 24 


19.1 
19.3 


0.23 

0.28 


(17.9-20.3) 
(18.0-20.8) 


3.10 
3.58 


1.86 
4.04 


ns 


Length of rostrum 

Females 30 
Males 26 


18.9 
19.4 


0.27 
0.28 


(17.2-20.2) 
(17.8-20.7) 


3.98 
3.67 


7.13 
4.03 


* 


Breadth of rostrum 
Females 32 
Males 27 


8.3 
8.3 


0.14 
0.14 


(7.2-9.3) 
(7.5-9.2) 


4.92 

4.41 


<1.00 
4.02 


ns 


Alveolar length of maxillary toothrow 
Females 32 9.4 
Males 27 9.3 


0.14 
0.12 


(8.5-10.1) 
(8.7-10.1) 


4.35 
3.47 


<1.00 
4.02 


ns 


Length of palatal bridge 
Females 31 
Males 26 


7.9 
8.1 


0.19 
0.18 


(7.1-9.5) 
(6.8-8.9) 


6.56 
5.72 


<1.00 
4.02 


ns 


Length of nasals 

Females 30 
Males 26 


19.2 
19.8 


0.35 
0.32 


(16.7-21.2) 
(18.0-21.1) 


5.04 
4.11 


6.03 
4.03 


* 




Sample P (Neotoma n 


icropus micropus) 








Total length 

Females 4 
Males 3 


354.5 
364.3 


24.84 
24.04 


(333.0-377.0) 
(362.0-366.0) 


7.01 
5.71 


<1.00 
6.61 


ns 


Length of tail vertebrae 
Females 4 
Males 3 


173.5 
169.7 


19.77 
4.06 


(155.0-193.0) 
(166.0-173.0) 


11.40 
2.07 


<1.00 
6.61 


ns 


Length of hind foot 
Females 4 
Males 3 


36.5 
38.0 


1.29 
1.15 


(35.0-38.0) 
(37.0-39.0) 


3.54 
2.63 


2.76 
6.61 


ns 


Length of ear 

Females 4 
Males 2 


28.2 
28.0 


2.22 
2.00 


(25.0-30.0) 
(27.0-29.0) 


7.85 
5.05 


<1.00 
7.71 


ns 


Greatest length of skull 
Females 4 
Males 3 


45.8 
46.6 


1.49 
0.42 


(43.9-47.1) 
(46.2-46.9) 


3.25 
0.77 


1.21 
6.61 


ns 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



53 



TABLE 2.— Concluded. 



Measurements 
and sex 



Y 



Mean 



2SE 



Range 



Condylobasilar leng 
Females 


th 
4 


43.2 


1.44 


(41.7-44.5) 


Males 


3 


44.2 


0.75 


(43.6-44.9) 


Zygomatic breadth 
Females 


4 


24.0 


0.38 


(23.5-24.4) 


Males 


3 


25.0 


1.17 


(24.4-26.2) 


Least interorbital constriction 








Females 


4 


6.3 


0.36 


(6.0-6.8) 


Males 


3 


6.0 


0.29 


(5.8-6.3) 


Breadth at mastoids 










Females 


4 


18.2 


0.48 


(17.6-18.6) 


Males 


3 


18.3 


0.44 


(18.0-18.7) 


Length of rostrum 










Females 


4 


17.6 


0.91 


(16.4-18.5) 


Males 


3 


17.4 


0.47 


(17.0-17.8) 


Breadth of rostrum 










Females 


4 


7.4 


0.25 


(7.2-7.8) 


Males 


3 


7.5 


0.12 


(7.4-7.6) 


Alveolar length of maxillary toothrow 
Females 4 8.9 


0.34 


(8.6-9.4) 


Males 


3 


9.1 


0.41 


(8.8-9.5) 


Length of palatal bridge 
Females 


7.8 


0.42 


(7.5-8.4) 


Males 


3 


7.5 


0.81 


(6.8-8.2) 


Length of nasals 
Females 


4 


17.1 


0.80 


(16.3-18.2) 


Males 


3 


17.9 


0.35 


(17.6-18.2) 



cv 



F, 
F 



3.32 
1.47 


1.24 
6.61 


ns 


1.57 
4.04 


3.88 
6.61 


ns 


5.68 
4.17 


1.42 
6.61 


ns 


2.64 
2.07 


<1.00 
6.61 


ns 


5.19 
3.33 


<1.00 
6.61 


ns 


3.38 
1.33 


<1.00 
6.61 


ns 


3.82 
3.84 


<1.00 
6.61 


ns 


5.39 
9.33 


<1.00 
6.61 


ns 


4.70 
1.68 


2.42 
6.61 


ns 



(with males being larger than females) 
might convey a selective advantage. 
However, the laboratory breeding cage 
was clearly an unnatural situation. In 
the natural environment, domination of 
females by males may not be important 
if females tolerate males only during 
estrus but are willing to accept any male 
at that time. Considering the habit of 
solitary occupancy of dens and competi- 
tion for den sites during times of high 
population density (see Fitch and Rainey, 
1956:517), females that are large enough 
to protect choice dens for maternity pur- 
poses may rear more young than less 
robust females. On the other hand, most 
adult male N. micropus collected in west- 
ern Kansas in June, 1967, had what ap- 
peared to be fresh wounds in the region 
of the lower back, but no "battle scars" 



were noted for females at that time (see 
Fitch and Rainey, 1956:521, for similar 
comments pertaining to N. floridana) . 
Perhaps in the natural environment, 
physical competition and fighting is most 
common between males, which would 
cause selection for large size to be more 
intense in males than females. 

Brown ( 1968 ) and Brown and Lee 
( 1969 ) studied various physiological and 
morphological responses of woodrats to 
differing thermal regimes. It was found 
that body size was related to tempera- 
ture, and although no comparisons of 
sexes were reported, it is clear that selec- 
tive responses to temperature and other 
environmental factors play a major role 
in determination of size of woodrats. 
Such factors probably act similarly on 
animals of both sexes, tending to reduce 



54 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



secondary sexual variation. The magni- 
tude of secondary sexual variation prob- 
ably is controlled by several interacting 
forces, some of which favor secondary 
sexual differences while others operate to 
minimize such differences. The result is 
as seen in Table 2; perceptible differences 
exist, but these appear to be more pro- 
nounced in some taxa (campestris, for 
example) than in others (such as 
baileyi). 

Individual Variation 

Of more than 2000 woodrats exam- 
ined during this investigation, only five 
had obviously atypical coloration that I 
assumed to be genetically based. Three 
of these, Neotoma micropus canescens 
that were previously reported by Baker 
(1956:286), are from near Sabinas, 
Coahuila; all were collected on the same 
day. One is a young adult female that 
was lactating and the other two are 
juveniles nearing completion of the post- 
juvenal molt. Most hairs of the venter 
are white to the base on all three, and 
white hairs extend onto the sides and 
lower rump. The female probably is the 
mother of the two juveniles. The status 
of the color pattern in the population 
from which these specimens originated 
would be of interest. The other two 
abnormally colored specimens are Neo- 
toma floridana attwateri. One (OSU 
4541) is a young adult female from 
northeastern Dewey County, Oklahoma; 
dorsal coloration is a uniform creamy tan 
and the ears are nearly white. The other 
(KU 18682), from Anderson County, 
Kansas, is an albino in fresh winter 
pelage. The ears, plantar surfaces of the 
feet, hair, and underlying skin are de- 
void of pigment; written on the data 
label are the words "eyes pink." 

A specimen of Neotoma micropus 
obtained in western Kansas in June 1967 
and another from Prowers County, Colo- 
rado captured in April 1968 were dis- 
tinctly reddish dorsally, at the time of 
capture. Both were in old pelage and the 
one from Colorado was still in reddish 
pelage when sacrificed about six weeks 



after capture. The other was molting at 
the time of capture and eventually com- 
pleted molt into a gray pelage lacking 
the reddish coloration. This reddish 
coloration is not considered to be ge- 
netically based, but probably was the 
result of chemical alterations of pigment 
in old pelage and likely caused by ex- 
trinsic factors such as high concentra- 
tions of ammonia in the nest. 

Because coefficients of variation re- 
flect the ratio of the standard deviation 
to the mean, the statistic is useful in 
comparing the degree of variation be- 
tween populations of a single species or 
between populations of different taxa. 
The coefficient of variation can be used 
also to compare the relative reliability 
of different measurements of a single 
sample. Long ( 1968, 1969) recently sum- 
marized patterns of individual variation 
and comparative variation of measure- 
ments commonly used in taxonomic in- 
vestigations. 

Coefficients of variation for each sex 
of three samples of floridana and three 
samples of micropus are shown in figure 
9. The coefficients are superimposed on 
Dice-grams illustrating the trends of vari- 
ation among the measurements taken. 
Size of all samples except the two (one 
male, one female) for canescens from 
Coahuila ( M ) are given in table 2. Sam- 
ple M consisted of 12 females and 13 
males. Length of tail vertebrae and 
length of ear are the most variable di- 
mensions considered, and also are two 
of the four recorded from specimen 
labels. Length of hind foot and total 
length were recorded from specimen 
labels. The former shows about average 
variability, whereas total length is more 
variable than all except one cranial mea- 
surement, but less variable than lengths 
of tail and ear. 

Of the 10 cranial measurements, 
length of the palatal bridge is the most 
variable. This measurement varies in 
part with the shape of the posterior mar- 
gin of the palate (see beyond under 
geographic variation of qualitative cra- 
nial characters), which is relatively vari- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



55 



N 

M 

L 

K 

J 
in 

£ I 
01 

E H 

I c 
n 

•r 

E 
D 
C 

B - 
A - 



'2 ,9 »> 3 



6 * i ■> 



3 "ll 



J lil «. '"7 



2 |U 76 | ^ n 12., ,Q 

1 11 2 12 8 4 7 l 6 9 3 _5 

lii io i yn if s 



11 2 4 10 l 7 ■» 6 5 3 



1 11 7 9 -t 4 



J2_L 



-t=5 2 » 



_6_4 8, l! 31 



I 2__, 4? 1Q 3 6911 7 125 



00 



5 6 70 8 

Coefficients of Variation 



Fig. 9. Coefficients of variation for 14 external and cranial measurements showing variability of 
that statistic in each. Measurements are as follows: A — total length; B — length of tail vertebrae; 
C — length of hind foot; D — length of ear; E — greatest length of skull; F — condylobasilar length; 
G — zygomatic breadth; H — least interorbital constriction; I — breadth at mastoids; J — length of ros- 
trum; K — breadth of rostrum; L — alveolar length of maxillary toothrow; M — length of palatal bridge; 
N — length of nasals. Numbers plotted on the horizontal lines are individual coefficients of variation 
for each sample of adult woodrats, as defined below; odd numbers are males, and even numbers are 
females (see figure 8 for geographic areas included within the coded localities indicated in paren- 
theses): 1 and 2, Neotoma floridana baileiji (1); 3 and 4, N. f. campestris (2, 3, and 4); 5 and 6, 
N. f. attwateri (5, 6, and 7); 7 and 8, N. micropus canescens (B and C); 9 and 10, N. m. canescens 
(M); 11 and 12, N. m. micropus (P). The apex of the darkened triangle is the arithmetic mean of 
the coefficients of variation of the 12 samples, and the thick horizontal bar is plus and minus two 
standard errors of the mean; the thin horizontal bar is plus and minus one standard deviation of the 
mean, and the horizontal line is the range. 



able even at the intra populational level. 
All cranial measurements were recorded 
only to the nearest tenth of a millimeter 
and length of palatal bridge is one of 
the smaller dimensions; thus, the pre- 
cision of data recorded relative to size 
of the character measured would be only 
about one-fifth of that for, say, greatest 
length of skull. Least interorbital con- 
striction was the next most variable cra- 
nial measurement and also is one of the 
smaller dimensions; however, other char- 
acters measured having means of less 
than 10 (alveolar length of maxillary 
toothrow and breadth of rostrum) dem- 
onstrate near average variability. Great- 
est length of skull, condylobasilar length, 
zygomatic breadth, and mastoid breadth 
are the least variable characters mea- 



sured; all having average coefficients of 
variation less than 4.0. 

To compare the relative variation of 
the 14 characters simultaneously between 
the 12 groups, three simple tallies were 
made. When only extreme coefficients 
were considered, one or the other of the 
two samples of baileiji is least variable in 
six of the 14 measurements and one or 
the other of the samples of attwateri is 
most variable in five instances. This tally 
also shows that a sample of males is most 
variable in 10 of the 14 characters con- 
sidered. Each pair of samples from each 
locality next was compared for all mea- 
surements to determine if males were in 
fact more highly variable than females. 
Of the 84 comparisons (six localities 
times 14 measurements ) made, males are 



56 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



more variable than females in 49 in- 
stances and less variable in 35, a differ- 
ence not significant at P < 0.05 as tested 
by Chi-square. Lastly, the coefficients of 
variation for each character were as- 
signed values on a rank-order basis so 
that the lowest coefficient for a character 
accrued one unit and the highest accrued 
12 units to the respective taxa. These 
scores then were totaled for each sample 
by summing the 14 rank-order scores; 
thus a low total implies less variation and 
a high total more variation. As deter- 
mined by this crude technique, the sam- 
ple of baileyi females is least variable 
(41.5) and the sample of campestris 
males is most variable (134.0). Males 
were shown to be more variable than 
their female counterparts at four lo- 
calities (N. m. micropus from locality P, 
and N. m. canescens from combined lo- 
calities B and C being the two excep- 
tions); they have a rank-order total of 
587 compared to 504 for females ( differ- 
ent at P < 0.05, as tested by Chi square). 
When scores of the sexes were summed 
for each locality, the sample of baileyi 
is least variable (106.5) and that of 
atticateri is most variable (215.5). Coef- 
ficients of variation in the sample of 
7nicropus is intermediate (158.0) be- 
tween baileyi and the four samples of 
widely distributed taxa (201.5-215.5); 
but in micropus the distribution of coef- 
ficients is erratic, probably reflecting the 
small sample size available. 

The tendency for samples of males 
to be more variable than those of females 
is indicated by all three methods of anal- 
ysis that I employed. Long (1969:298) 
found males of domestic mammals more 
variable than conspecific females, but 
indicated that no basis presently exists 
for attributing greater variation to males. 
The apparent presence of relatively less 
individual variation in the isolated sub- 
species, baileyi, as compared to widely 
distributed taxa is not surprising; small, 
isolated populations are prone to loss of 
variation by chance or "drift." Addition- 
ally, they lack one of the most important 
means of acquiring "new" genetic varia- 



tion, i.e. immigration. Mayr (1963:177) 
suggested that a reasonable estimate of 
"new" genes normally acquired by a local 
population through immigration is at 
least 90 percent and possibly exceeds 99 
percent. 

It was expected a priori that individual 
variation in the samples of cajnpestris 
would be more pronounced than in other 
taxa. In part the prediction was correct; 
the sample of campestris males is more 
variable than other samples, but only 
baileyi females and micropus males are 
less variable than campestris females. 
Possibly selection acting on populations 
that live in similar environments main- 
tains the observed degree of homogeneity 
(Ehrlich and Raven, 1969), or perhaps 
there is more interpopulational gene flow 
in campestris than my observations have 
indicated. 

Variation Resulting from Captivity 

The most striking differences ob- 
served between a specimen that had 
been reared, or at least maintained, in 
the laboratory for an extended period of 
time and one that had been killed at the 
time of capture were in the teeth. The 
cheekteeth of woodrats fed on laboratory 
chow did not wear at a rate comparable 
to that in natural populations. The molars 
of cleaned skulls of laboratory rats often 
are as much as a third or a half longer 
than those of non-laboratory animals. 
Furthermore, the reentrant angles of lab- 
oratory-reared woodrats extend much 
nearer to the alveolus than do those of 
comparably aged non-laboratory rats. Al- 
though this may be the result of reduced 
tooth growth to compensate reduced 
wear, the stimulus that stops or slows 
growth is unknown. In some laboratory 
specimens, alveolar tissue near the base 
of the molars appeared reduced and 
slightly porous. If the alveolar tissue of 
laboratory rats grows abnormally slow or 
if it is resorbed, the molar may undergo 
normal growth but have higher crowns. 

The incisors of woodrats living in the 
laboratory frequently are broken, result- 
ing in abnormal occlusion and the ab- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



57 



sence of wear on the opposing incisor. 
The frequency of abnormal growth of 
incisors is relatively high in laboratory 
animals, whereas woodrats living in the 
natural environment and having maloc- 
cluding incisors probably are destined to 
early death. 

Comparisons of size of woodrats 
reared in the laboratory with non-labora- 
tory animals from the same geographic 
areas are shown in table 3. Only speci- 
mens at least 30 weeks of age that either 
were born in the laboratory or were cap- 
tured before they had completed the 
postjuvenal molt were included in lab- 
oratory samples. After specimens meet- 
ing these criteria were separated by sex, 
only three samples, Neotoma micropus 
canescens ( localities B and C ) males and 
females, and Neotoma floridana cam- 
pestris (localities 3 and 4) females, con- 
tained enough specimens ( 10 or more ) 
for conducting the tests. Non-laboratory 
comparative samples included all avail- 
able specimens of age groups VI, VII, 
and VIII from the grouped localities in- 
dicated above. 

Differences in two measurements, 
total length and alveolar length of maxil- 
lary toothrow, are highly significant 
(P<0.01) between the two samples of 
N. f. campestris females; no highly sig- 
nificant differences were observed for N. 
m. canescens. Significant differences 
( P < 0.05 ) were observed for two other 
characters (length of hind foot and 
length of nasals) in floridana, one mea- 
surement (total length) of micropus fe- 
males, and five measurements (length of 
hind foot, length of ear, greatest length 
of skull, condylobasilar length, and 
breadth of rostrum) for N. m. canescens 
males. Total length of micropus females 
is the only dimension significantly larger 
in the non-laboratory or "wild" sample. 
On the average, laboratory samples are 
slightly larger in most measurements that 
are not significantly different. 

Increased size of laboratory animals 
may be the result of a more nutritious 
diet or it may reflect differences in age. 
Many animals in the laboratory samples 



were near two years of age. It is doubt- 
ful that the average age of non-labora- 
tory animals equals that of the laboratory 
sample. 

GEOGRAPHIC VARIATION 

In the discussion beyond, I will in- 
terpret patterns of both qualitative and 
quantitative variation of morphological 
characteristics primarily from an evolu- 
tionary point of view in an attempt to 
elucidate the relationships of woodrats. 
If it can be determined whether patterns 
of variation are concordant or discordant, 
and clinal or abrupt, one can surmise 
which patterns have resulted from pri- 
mary intergradation, secondary intergra- 
dation, or from present restrictions to 
gene flow. Also, I will attempt to ascer- 
tain if natural hybridization is introgres- 
sive in N. floridana and N. micropus. 

Pelage, Molt, and Color 

Finley (1958:232) described the suc- 
cession of molts and pelages of woodrats 
as juvenal pelage, postjuvenal molt, sub- 
adult pelage, second molt, first autumn 
pelage, third molt, first winter pelage, 
annual molt. My observations agree in a 
general way with this scheme. Animals 
born late in summer or early in autumn, 
however, do not undergo the complete 
sequence, but spend the first winter in 
either the subadult pelage or first autumn 
pelage. 

Remarkably little published informa- 
tion pertaining to molt in adult Neotoma 
is available. Goldman (1910:12) sum- 
marized his understanding of molt on 
adults as follows: "The molting season 
is somewhat irregular, especially in the 
southern part of the range of the group. 
The northern species molt once a year, 
toward the end of summer or fall. The 
southern forms usually molt in early 
winter, but individuals in worn and in 
fresh pelage may often be seen together." 
Linsdale and Tevis (1951:450-458) de- 
scribed and discussed molt in Neotoma 
fuscipes, and Finley (1958) studied it 
in those species of woodrats that occur in 



58 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 3. Size comparisons of woodrats reared in the laboratory and those killed at the time 
of initial capture (wild). Statistics given are sample size, mean, two standard errors of the 
mean, range, coefficient of variation, F s (F value calculated by single classification ANOVA), 
and F (tabular F value at level of significance or at P<0.05 if not significant). One asterisk 
and two asterices indicate significance at the 0.05 and 0.01 levels, respectively, whereas ns 

indicates no significant difference. 



Measurement 
and treatment 



.V 



Mean 



± 2SE 



Range 



CV 



Neotoma floridana campestris females (Samples 3 and 4) 



Total length 

Wild 33 
Laboratory 10 


370.8 
394.2 


6.23 
17.94 


(340.0-409.0) 
(331.0-421.0) 


Length of tail vertebrae 
Wild 33 
Laboratory 10 


154.9 
162.7 


3.59 
8.93 


(136.0-175.0) 
(129.0-178.0) 


Length of hind foot 
Wild 34 
Laboratory 10 


39.3 
40.7 


0.55 
0.45 


(36.0-42.0) 
(39.0-43.0) 


Length of ear 

Wild 19 
Laboratory 10 


2.8 
2.9 


0.72 
0.13 


(25.0-32.0) 
(24.0-31.0) 


Greatest length of skull 
Wild 29 
Laboratory 12 


5.0 
5.0 


0.52 

1.17 


(47.0-53.3) 

(46.2-52.4) 


Condvlobasilar length 
Wild 26 
Laboratory 12 


48.2 
49.1 


0.56 
0.99 


(45.2-51.6) 
(45.2-51.2) 


Zygomatic breadth 
Wild 27 
Laboratory 12 


27.0 

27.2 


0.38 
0.63 


(25.1-29.6) 
(25.7-29.0) 


Least interorbital constriction 

Wild 32 6.7 
Laboratory 12 6.7 


0.11 
0.21 


(6.1-7.5) 
(6.2-7.5) 


Breadth at mastoids 
Wild 29 
Laboratory 12 


19.4 
19.6 


0.24 
0.35 


(18.1-21.0) 
(18.5-20.5) 


Length of rostrum 
Wild 33 
Laboratory 12 


19.4 
19.8 


0.25 
0.72 


(17.8-21.1) 
(17.4-21.2) 


Breadth of rostrum 
Wild 32 
Laboratory 11 


8.5 
8.6 


0.12 
0.25 


(7.9-9.4) 
(7.8-9.2) 


Alveolar length of maxillarv 
Wild 34 
Laboratory 12 


toothrow 

9.7 

10.0 


0.09 
0.09 


(9.1-10.3) 
(9.6-10.3) 


Length of palatal bridge 
Wild 34 
Laboratory 12 


8.5 
8.6 


0.14 
0.25 


(7.8-9.4) 
(8.2-9.6) 


Length of nasals 

Wild 33 
Laboratory 12 


19.2 
19.8 


0.26 
0.57 


(17.6-20.4) 
(18.0-21.1) 



4.83 
7.20 


9.86 
7.31 *° 


6.66 
8.68 


3.70 
4.07 ns 


4.09 

3.48 


5.94 

4.07 * 


5.53 
7.01 


<1.00 
4.21 ns 


2.81 
4.05 


<1.00 
4.10 ns 


2.97 
3.49 


2.83 
4.11 ns 


3.68 

4.03 


<1.00 
4.11 ns 


4.72 
5.31 


<1.00 
4.07 ns 


3.31 
3.13 


<1.00 
4.10 ns 


3.70 
6.35 


1.85 
4.07 ns 


3.85 
4.81 


1.34 
4.08 ns 


2.84 
1.61 


11.27 

7.24 oa 


4.72 
5.09 


<1.00 
4.06 ns 


3.93 
4.97 


5.30 
4.07 * 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 
TABLE 3.— Continued. 



59 



Measurement 
and treatment 



N 



Mean 



± 2SE 



Range 



CV 



F R 
F 



Neotoma micropus canescens females (Samples B and C) 



Total length 
Wild 
Laboratory 



31 
11 



Length of tail vertebrae 
Wild 31 

Laboratory 11 

Length of hind foot 
Wild 30 

Laboratory 13 



Length of ear 
Wild 

Laboratory 



24 
13 



355.8 
351.8 

147.1 
146.2 

38.4 
39.2 



27.1 
28.1 



Greatest length of skull 
Wild 27 

Laboratory 14 

Condylobasilar length 
Wild 29 

Laboratory 15 

Zygomatic breadth 
Wild 30 

Laboratory 14 

Least interorbital constriction 
Wild 32 

Laboratory 15 

Breadth at mastoids 
Wild 27 

Laboratory 14 

Length of rostrum 
Wild 30 

Laboratory 14 



48.8 
48.9 



47.0 
47.4 



26.5 
26.7 



6.3 
6.2 



19.1 
19.4 

18.9 

18.8 



5.97 
11.25 



3.70 
8.32 



0.54 
0.69 

0.56 
0.86 

0.70 
0.86 



0.58 
0.71 



0.39 
0.43 



0.11 
0.15 



0.23 
0.17 



0.27 
0.39 



(310.0-382.0) 
(326.0-382.0) 



(130.0-165.0) 
(126.0-171.0) 

(36.0-41.0) 
(37.0-41.0) 



(25.0-30.0) 
(25.0-30.0) 

(44.2-51.8) 
(46.2-51.4) 

(42.8-50.0) 
(45.0-49.4) 



(24.7-29.1) 
(25.2-30.0) 



(5.8-7.0) 
(5.7-6.6) 

(17.9-20.3) 
(18.9-19.9) 

(17.2-20.2) 
(17.8-20.2) 



Breadth of rostrum 
Wild 
Laboratory 


32 
15 


8.3 
8.4 


0.14 
0.21 


(7.2-9.3) 
(7.9-9.3) 


Alveolar length of 
Wild 
Laboratory 


maxillary 
32 
15 


toothrow 
9.4 
9.3 


0.14 
0.19 


(8.5-10.1) 
(8.4-9.9) 


Length of palatal bridge 
Wild 31 
Laboratory 15 


8.0 
8.0 


0.19 
0.18 


(7.1-9.5) 
(7.4-8.5) 


Length of nasals 
Wild 
Laboratory 


30 
14 


19.2 
19.4 


0.35 
0.43 


(16.7-21.2) 
(18.0-20.9) 




Neotom 


a micropus canescens 


males ( Samples B 


Total length 
Wild 
Laboratory 


23 

8 


370.1 
383.0 


9.46 
11.84 


(334.0-411.0) 
(354.0-398.0) 



4.67 
5.30 


4.47 
4.08 * 


7.01 
9.43 


<1.00 

4.08 ns 


3.85 
3.15 


2.90 
4.08 ns 


5.10 

5.53 


4.00 
4.13 ns 


3.75 
3.31 


<1.00 
4.10 ns 


3.34 
2.92 


<1.00 

4.07 ns 


4.06 

3.04 


<1.00 
4.07 ns 


4.72 
4.73 


2.80 
4.06 ns 


3.10 
1.65 


3.21 
4.08 ns 


3.98 
3.93 


<1.00 
4.07 ns 


4.92 
4.87 


<1.00 
4.06 ns 


4.35 
3.92 


<1.00 
4.06 ns 


6.56 
4.38 


<1.00 
4.06 ns 


5.04 
4.15 


<1.00 
4.07 ns 



and C ) 



6.13 

4.37 



2.16 
4.18 ns 



60 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 3.— Concluded. 



Measurement 

and treatment N 


Mean 


± 2SE 


Range 


cv 


F 




Length of tail vertebrae 
Wild 23 
Laboratory 8 


152.6 
154.8 


5.10 
7.52 


(131.0-175.0) 
(142.0-172.0) 


8.01 

6.87 


<1.00 
4.18 


ns 


Length of hind foot 
Wild 25 
Laboratory 10 


39.2 
41.3 


1.01 
0.79 


(35.0-45.0) 
(39.0-43.0) 


6.46 

3.03 


6.18 
4.15 


» 


Length of ear 

Wild 16 
Laboratory 11 


27.1 
28.7 


0.72 
1.05 


(25.0-29.0) 

(27.0-32.0) 


5.31 
6.05 


7.39 
4.24 


« 


Greatest length of skull 
Wild 25 
Laboratory 1 


49.5 
50.6 


0.63 
0.43 


(46.4-52.9) 
(49.4-51.9) 


3.17 
1.35 


4.79 
4.15 


* 


Condylobasilar length 
Wild 24 
Laboratory 10 


48.3 
49.5 


0.66 
0.44 


(44.6-50.9) 
(48.3-50.6) 


3.33 
1.39 


5.24 
4.15 


* 


Zygomatic breadth 
Wild 26 
Laboratory 1 1 


26.7 
26.9 


0.36 
0.39 


(25.1-28.8) 
(26.1-28.2) 


3.47 
2.42 


<1.00 
4.13 


ns 


Least interorbital constriction 

Wild 27 6.3 
Laboratory 1 1 6.4 


0.11 
0.13 


(5.8-6.9) 
(6.1-6.9) 


4.39 
3.38 


<1.00 
4.11 


ns 


Breadth at mastoids 
Wild 24 
Laboratory 11 


19.3 
19.4 


0.28 
0.10 


(18.0-20.8) 
(19.2-19.8) 


3.58 
0.87 


<1.00 
4.15 


ns 


Length of rostrum 
Wild 26 
Laboratory 10 


19.4 
19.5 


0.28 
0.40 


(17.8-20.7) 
(18.3-20.4) 


3.67 
3.23 


<1.00 
4.13 


ns 


Breadth of rostrum 
Wild 27 
Laboratory 1 1 


8.4 
8.6 


0.14 
0.22 


(7.5-9.2) 
(8.0-9.2) 


4.41 
0.22 


4.86 
4.11 


# 


Alveolar length of maxillarv 
Wild 27 
Laboratory 1 1 


toothrow 
9.3 
9.5 


0.12 
0.22 


(8.7-10.1) 
(9.0-10.0) 


3.47 
3.81 


2.19 
4.11 


ns 


Length of palatal bridge 
Wild 26 
Laboratory 10 


8.1 
8.4 


0.18 
0.13 


(6.8-8.9) 
(7.9-8.6) 


5.73 
2.54 


3.37 
4.13 


ns 


Length of nasals 

Wild 26 
Laboratory 10 


19.8 
19.9 


0.32 
0.35 


(18.0-21.1) 
(19.0-20.7) 


4.11 
2.79 


<1.00 

4.13 


ns 



Colorado. In both studies it was con- 
cluded that only a single annual molt 
occurs in adult woodrats. 

Seasonal occurrence of molt in se- 
lected samples of N. floridana and N. 
micropus is shown in table 4. Specimens 
of age-groups V-VIII were included in 
these tabulations. With one exception, 



animals were considered to be molting if 
new pelage appeared to have been re- 
placing old pelage regardless of whether 
the replacement was symmetrical or in- 
volved a complete replacement of hair. 
Many woodrats have a varying number 
of tiny spots of actively growing hair. 
These probably are areas in which hair 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



61 



lost while fighting or in other ways not 
directly associated with seasonal molt is 
replaced. Specimens with such "spots" 
that were not molting elsewhere were not 
considered to be molting. 

As can be seen in table 4, some wood- 
rats obtained in eveiy month were molt- 
ing. It was thought that possibly only 
animals of age-groups V and VI (which 
still might have been in some stage of 
maturational molt) were molting at 
times other than late summer and au- 
tumn as has been reported previously. 
However, when only specimens of age- 
groups VII and VIII were considered, 
the seasonal array of molting and non- 
molting individuals remained approxi- 
mately the same. 

In northern populations of the two 
species studied, adults are almost in vari- 
ably in a dense, luxuriant winter pelage 
by late November or early December. 
Beginning in late winter or early spring, 
the winter pelage of many individuals 
begins to deteriorate; it becomes thinner, 
less luxuriant, has many broken tips, and 
appears "scruffy." In other rats, the 
winter pelage seems to be well main- 
tained into late May or early June. When 
the pelage begins to deteriorate, it gen- 
erally is replaced erratically over the 
body, usually beginning in those areas 
where the winter pelage is thinnest or 



most worn. This "molt" has little or no 
symmetry of pattern. In occasional indi- 
viduals, the winter pelage is nearly or 
completely replaced by a shorter, usually 
darker "summer" pelage. Some rats have 
only localized spots of this pelage and 
others show no sign of replacement until 
July or August. At this time they appar- 
ently begin the "annual molt" and molt 
the old winter pelage directly into a new 
winter pelage. Those individuals that re- 
placed some or all of the pelage earlier 
also molt into a new winter pelage in 
late summer and autumn. 

The molting sequence in southern 
populations of both species is less clear. 
Even the new winter pelage of southern 
woodrats is shorter than "summer pelage" 
of those from northern populations, and 
the "annual molt" (molt into winter pel- 
age) is only weakly synchronized among 
animals of the same population. Usually 
this molt occurs anytime from June to 
October, and generally is complete by 
November. 

Whether one wishes to consider the 
replacement of worn winter pelage prior 
to the attainment of new winter pelage 
as a "vernal molt" and the resultant pel- 
age as a "summer pelage" is primarily a 
question of semantics. Almost certainly 
the only molt that is consistently com- 
plete and common to all adults is the 



TABLE 4. Seasonal distribution of molt in selected samples of Neotoma floridana and N. 
micropus. See figure 8 for geographic areas included in coded localities. 

Jan. Feb. Mar. April May June July Aug. Sept. Oct. Nov. Dec. 

Sample 1 (Neotoma floridana baileyi) 
Females 

Molting ___. __ _ .._ __ 1 2 

Examined ____ __ 1 1 3 

Males 

Molting .___ ___ 1 2 

Examined .... ____ ___. .... 1 .___ 2 



Molting 
Examined 

Molting 
Examined 



Samples 2, 3, and 4 (Neotoma floridana campestris) 
Females 
3 2 .- 2 5 

3 1 3 _ 3 5 

Males 
1 5 -- 1 3 

1 5—13 



2 





__ 


2 


— 


— 




1 





- 


2 


9 







1 




2 


11 



62 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 

TABLE 4.— Concluded. 
Jan. Feb. Mar. April May June July Aug. Sept. Oct. Nov. Dec. 



Molting 

Examined 2 



Molting 
Examined 



Molting 
Examined 



Molting 
Examined 



Molting 
Examined 



Molting 1 

Examined 8 



Molting 
Examined 

Molting 
Examined 



Molting 1 

Examined 1 



Molting 

Examined 3 



Molting 
Examined 

Molting 

Examined 1 



Molting 
Examined 

Molting 
Examined 



5 

I 1 

1 
2 



Samples 5, 6, and 7 (Neotoma floridana attwateri) 
Females 

2 1 _ _ -- 1 1 

12 2 _ .... 1 1 

Males 

.... .... .... 3 1 

8 4 .... .... .... 3 1 

Samples 8, 9, 10 (Neotoma floridana attwateri) 
Females 

2 .... 1 1 

1 2 _.- 3 1 .... 2 

Males 

.... 3 
6 3 .... 3 

Samples 11 and 12 (Neotoma floridana attwateri) 
Females 

1 .... .... .._ .... .... 

1 .... .... ___ .... _.. 1 

Males 
.... _ .._ .- __ 2 

2 .._ .... .... .... _ 2 



Samples A, B, C, and F (Neotoma micropus canescens) 
Females 

18 3 12 

1 1 10 7 6 2 

Males 

1 3 2 6 

1 115 4 6 

Samples D, G, H, and I (Neotoma micropus canescens) 
Females 
1 6 .... 1 

_ 1 3 7 _.. 1 

Males 
.... .... 3 2 

2 3 3 

Samples J, K, L, and M (Neotoma micropus canescens) 

Females 

3 10 11 

12 4 12 12 1 

Males 

14 11 .... 1 

1 6 1 1 3 _.. 1 

Samples N and P (Neotoma micropus micropus) 
Females 

2 112 

4 4 112 

Males 

3 2 2 4 

1 4 2 4 5 



1 


6 


1 


2 


11 


12 


2 


5 





2 


9 


6 



4 


3 


2 


6 


6 


9 


5 


3 


1 


5 


4 


6 



3 








3 


1 


9 













10 



4 





12 


1 


10 




16 





2 




1 


3 





9 


2 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



63 



autumn molt or in Finley's (1958) ter- 
minology, the annual molt. The "vernal 
molt" apparently is primarily a mechan- 
ism to maintain the pelage and may be 
complete, abbreviated, or absent. For 
Uany years it was thought that members 
of the genus Peromijscus molted only 
once a year (see Layne, 1968:141, for 
review), but recent studies have shown 
that at least in some species molting also 
Occurs at other times of the year ( Brown, 
11963; Lawlor. 1965). Possibly the sea- 
sonal molting regimes of members of the 
two genera are similar, but characterized 
by much more individual and geographic 
(variation than previously has been 
thought. 

An attempt was made to correlate re- 
productive data from specimen labels 
kvith molt in females. Pregnant or lactat- 
ing females that were collected in spring 
|or early summer usually were in the old 
winter pelage; however, pregnant and 
lactating females collected in late sum- 
mer often were actively molting. An 
adult female N. f. campestris (KU 
120844) was captured in December in a 
relatively new winter pelage. She was 
maintained in the laboratory until late 
March without having been placed with 
a male. At that time she was undergoing 
what probably would have been a nearly 
complete molt from her typical winter 
pelage, which was in remarkably good 
repair, to a new shorter darker "summer 
pelage." On 20 March she was placed 
with a male and on 26 April she gave 
birth to a litter. Insofar as I could deter- 
mine, the molt had progressed very little 
between those dates and remained with- 
out change until she was killed on 10 
June. The specimen shows no line of 
"current" activity between the two pel- 
ages, which are markedly different in 
length, color, and general texture. Ap- 
parently molt of woodrats is influenced 
by the hormones of reproduction and 
shortly after this female became preg- 
nant the molt was arrested. 

Other factors that probably influence 
the timing and degree of completeness 
of the "vernal molt" include age, condi- 



tion of health, and condition of the ex- 
isting pelage. Although exchange of pel- 
ages clearly is necessary, especially in 
northern woodrats preparing for winter, 
molt may be one of the body processes 
that is under a relatively loose genetic 
control and easily altered when it is 
physiologically advantageous for an in- 
dividual to divert energy or reserves 
elsewhere. 

The variation in molts and pelages 
of woodrats in spring and summer re- 
sulted in some difficulty selecting speci- 
mens for color measurements. Ideally, 
only adults in fresh winter pelage would 
be considered in analyses of geographic 
variation in color. However, sufficient 
samples from the various aggregate lo- 
calities were not available when samples 
were thus limited. It was necessary to 
include all specimens whose pelage was 
in relatively good repair, regardless of 
season. 

The effect of including animals col- 
lected at different times of the year was 
tested for each of the three reflectance 
readings and for the total (value ob- 
tained by summing the three individual 
reflectance readings for each individual) 
by pooling readings of animals from lo- 
calities 5 through 11 (all Neotoma flori- 
dana atticaieri) and separating the indi- 
viduals into four seasonal samples. Each 
sample included animals killed during a 
three-month period so that four samples 
corresponding roughly to winter (De- 
cember-February), spring (March-May), 
summer (June- August), and autumn 
(September-November) were available. 
Seasonal variation is not significantly dif- 
ferent in reflectance of blue or green, 
but is significantly different ( 0.05 > P > 
0.01 ) for reflectance of red and for total 
reflectance. These data were separated 
by sex to test males against females. 
Males were significantly paler ( 0.05 > P 
> 0.01 ) as indicated by reflectance of 
red, but F s values were less than unity 
for blue and green, and less than F for 
total reflectance. 

Explanation of the slight seasonal 
variation is commensurate with the above 



64 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



discussion of molt and pelages. Most 
woodrats are darkest in fresh winter pel- 
age and palest in old pelage just before 
undergoing molt into winter pelage, 
which is the only more or less synchro- 
nous molt of adults. This molt usually 
occurs in September, October, or early 
November; thus most animals in the au- 
tumn sample recently had molted or 
were molting. The high coefficients of 
variation for this sample are attributable 
to the fact that all specimens were not in 
the same pelage. The three seasonal sam- 
ples involving mostly animals in winter 
pelage were not significantly different in 
color, and even the sample composed 
mostly of summer specimens was not sig- 
nificantly different from the spring or 
winter samples. 

Specimens of both sexes and from 
all seasons were pooled for each locality 
for studies of geographic variation. Re- 
sults of univariate analyses of intra- 
specific color variation in Neotoma flori- 
dana are shown in table 5. Highly 
significant ( P < 0.01 ) differences exist in 
comparisons of group-means for all re- 
flectance readings. In no case, however, 
are animals from localities 5-13 (all sam- 
ples of N. f. attwateri and the single 
sample of N. f. rubida) significantly dif- 
ferent from each other with respect to 
color. Specimens from localities 12 
(southern Texas), 6 (northeastern Kan- 
sas), and 11 (northern Texas) tend to 
be slightly paler in color than other spec- 
imens. Samples 5 (north-central Kan- 
sas), 10 (southeastern Oklahoma), and 
13 (N. f. rubida) generally are darkest. 
Within the subspecies N. f. campestris, 
a rather clear trend exists from paler 
animals in the west (localities 2 and 3) 
to darker ones in the east (locality 4) 
where the range of campestris meets that 
of attwateri. In no case is the difference 
between animals from localities 2 and 3 
significant, but those from locality 4 are 
significantly darker than those from 2 in 
all reflectance readings. Specimens in 
sample 4 also are significantly paler in 
all readings from those of attwateri from 
adjacent locality 5. Only in reflectance 



of blue are differences between samples 
3 and 4 shown to be significantly differ- 
ent. The darker color of specimens from 
locality 4 as compared to those in sam- 
ples 2 and 3 probably has resulted from 
intergradation with the darker attwateri 
population to the east. With respect to 
color, the zone of intergradation would 
appear to have been assigned largely to 
campestris, although in size (see be- 
yond) animals from locality 5 are more 
like those from locality 4 than from 
locality 6. 

Neotoma floridana bailey i (locality 1) 
is paler than all samples of attwateri, and 
significantly darker than campestris 
(with the exception of the sample of 
campestris from the narrow zone where 
campestris intergrades with attwateri at 
locality 4 ) . The pale coloration of bailey i 
is less tannish than that of campestris, 
and although most specimens of baileyi 
are distinctly paler than specimens of 
attwateri, their coloration more closely 
resembles that of attwateri, than that of 
campestris. The habitat in which baileyi 
occurs resembles that where attwateri is 
found, but most adjacent habitat types 
in northern Nebraska, which thus far 
have not been found to support wood- 
rats, are mostly shortgrass pasture ( more 
like the habitat of campestris) . The pale 
color seen in baileyi and campestris 
probably signifies convergence, which 
has resulted from adaptation to an arid 
environment, from a darker common an- 
cestor. 

Table 6 contains results of univariate 
analyses of intraspecific color variation 
for Neotoma micropus. As opposed to 
the pattern of color variation in floridana, 
that in micropus is clearly clinal and 
lacks noticeable steps. Specimens from 
locality E (New Mexico) are paler on 
the average than those from White Sands 
National Monument (locality O, pre- 
viously N. m. leucophea). Therefore, 
there seems to be no sound reason for 
recognizing the name leucophea. (If 
larger samples separable by season had 
been available, the White Sands popula- 
tion might have averaged paler, but cer- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



65 



tainly the differences are slight.) When 
all samples of micropus are considered, 
specimens from localities in New Mexico 
( E and O ) and western Texas ( F and J ) 
generally are palest in color as evinced 
by higher reflectance readings. 

Those from localities D, G, H, K, L, 



N, and P generally are darker than those 
from A, B, C, I, and M, which tend to be 
intermediate. Darkest populations gen- 
erally occur at localities in the eastern 
parts of the range of the species, and 
palest populations are from the more 
arid western localities. As shown bv the 



TARLE 5. Geographic variation in color of selected samples of Neotoma floridana. F H was 
calculated by single classification analysis of variance. Tabular F values are at the P<0.05 
level of significance; ns indicates no significant difference within a group of means. Nonsig- 
nificant subsets (as calculated by the Sums of Squares Simultaneous Testing Procedure) of 
significantly different groups of means are shown in the last column. See figure 8 for geographic 
areas included within each coded locality. 



Color reflectance 














measured, and 












F 8 


coded localities 


N 


Mean 


± 2SE 


Range 


CV 


F SS-STP 


Red 














2 


2 


19.2 


0.50 


(19.0-19.5) 


1.84 


12.78 I 


3 


19 


17.0 


1.06 


(13.0-20.5) 


13.66 


1.83 I 


1 


23 


15.6 


0.88 


(12.0-20.0) 


13.56 


I I 


4 


16 


15.5 


0.97 


(12.0-19.5) 


12.52 


I I I 


12 


16 


14.1 


0.92 


(11.5-17.0) 


12.96 


I I I 


9 


7 


13.1 


1.18 


(12.0-16.5) 


11.98 


I I I 


6 


12 


13.0 


0.85 


(10.0-14.5) 


11.33 




11 


7 


12.7 


0.69 


(11.5-14.0) 


7.13 




7 


28 


12.7 


0.53 


(10.0-17.0) 


11.07 




13 


5 


12.6 


1.66 


(10.5-15.0) 


14.69 




8 


4 


12.5 


0.82 


(11.5-13.5) 


6.53 




10 


5 


12.2 


0.93 


(10.5-13.0) 


8.50 




5 


6 


11.2 


1.09 


(10.0-13.5) 


11.90 




Rlue 














2 


2 


10.5 


2.00 


(9.5-11.5) 


13.47 


41.62 I 


3 


19 


9.6 


0.45 


(7.5-11.5) 


10.20 


1.83 I 


4 


16 


8.3 


0.42 


(7.0-10.5) 


9.96 


I 


1 


23 


8.0 


0.32 


(6.5-9.5) 


9.61 


I 


12 


16 


6.6 


0.28 


(5.5-7.5) 


8.49 




5 


6 


6.5 


0.52 


(6.0-7.5) 


9.73 




11 


7 


6.5 


0.65 


(5.5-8.0) 


13.32 




8 


4 


6.5 


0.00 


(6.5-6.5) 


0.00 




6 


12 


6.4 


0.45 


(5.0-7.5) 


12.12 




9 


7 


6.3 


0.37 


(5.5-7.0) 


7.76 




7 


28 


6.0 


0.19 


(5.5-7.0) 


8.41 




13 


5 


5.6 


0.37 


(5.0-6.0) 


7.47 




10 


5 


5.3 


0.75 


(4.0-6.0) 


15.79 




Green 














2 


2 


12.0 


2.00 


(11.0-13.0) 


11.79 


39.62 I 


3 


19 


10.5 


0.52 


(8.5-12.5) 


10.85 


1.83 I I 


4 


16 


9.4 


0.49 


(8.0-11.5) 


10.40 


I I 


1 


23 


8.3 


0.28 


(7.5-9.5) 


8.10 


I I 


6 


12 


7.3 


0.40 


(6.5-8.5) 


9.35 


I I 


8 


4 


7.2 


0.65 


(6.5-8.0) 


8.90 


I I 


5 


6 


7.2 


0.43 


(6.5-8.0) 


7.23 


I I 


12 


16 


7.2 


0.36 


(6.0-9.0) 


10.11 




11 


7 


7.2 


0.61 


(6.5-9.0) 


11.22 




7 


28 


6.9 


0.20 


(5.5-8.0) 


7.65 




9 


7 


6.9 


0.29 


(6.5-7.5) 


5.51 




13 


5 


6.5 


0.32 


(6.0-7.0) 


5.44 




10 


5 


6.2 


0.68 


(5.0-7.0) 


12.23 





66 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 
TABLE 5.— Concluded. 



Color reflectance 




















measured, and 












F s 








coded localities 


N 


Mean 


± 2SE 


Range 


CV 


F 


SS-STP 




Total 




















2 


2 


41.8 


4.50 


(39.5-44.0) 


7.62 


29.51 


I 






3 


19 


37.1 


1.90 


(29.0-44.5) 


11.19 


1.83 


I I 






4 


16 


33.2 


1.66 


(28.0-41.5) 


9.96 




I 


I 




1 


23 


31.7 


1.21 


(26.0-35.5) 


9.14 






I I 




12 


16 


28.0 


1.40 


(23.0-33.5) 


10.00 






I 


I 


6 


12 


26.8 


1.44 


(22.5-30.5) 


9.31 








I 


11 


7 


26.4 


1.77 


(23.5-31.0) 


8.84 








I 


8 


4 


26.2 


0.87 


(25.5-27.5) 


3.30 








I 


9 


7 


26.2 


1.41 


(24.0-30.0) 


7.12 








I 


7 


28 


25.7 


0.79 


(22.0-31.5) 


8.18 








I 


5 


6 


24.9 


1.85 


(22.5-29.0) 


9.10 








I 


13 


5 


24.7 


2.14 


(22.0-28.0) 


9.67 








I 


10 


5 


23.7 


2.20 


(19.5-25.5) 


10.40 








I 



sequence of means and arrangement of 
maximal non-significant subsets in table 
6, however, the trends in color variation 
in N. micropus take the form of gradual 
clines. 

Qualitative Cranial Characters 

Finley (1958:248-252) discussed sev- 
eral cranial features of woodrats that 
vary among taxa. Three cranial charac- 
ters can be employed to distinguish skulls 
of Neotoma angustipalata, N. floridana, 
and IV. micropus, although none is diag- 
nostic. A fourth varies greatly with sex 
and age but is useful in skull identifica- 
tion. The three most useful characters, 
the anterior palatal spine, the posterior 
margin of the bony palate, and the 
sphenopalatine vacuities (Fig. 10), are 
discussed individually below and anal- 
yzed geographically. The fourth, shape 
of the interorbital region, was assessed 
in the measurement of least interorbital 
constriction. In micropus, the supraor- 
bital region tends to be narrower and 
more ridged than in floridana. Espe- 
cially in mature micropus males (less 
frequently in females ) , ridging is so pro- 
nounced that a structure resembling a 
postorbital shelf is formed. In floridana 
such a "shelf" is never present and the 
interorbital region usually is nearly level. 
Ridging between the orbits and presence 
of the "shelf" generally are distinctive to 



micropus, but because of variation withi 
sex and age, absence of these characters 
is not distinctive to floridana. The num- 
ber of adult N. angustipalata available 
for analysis of normal variation in the 
interorbital region is small; however, 
specimens examined tend to be more like 
micropus than floridana in this character. 
Berry and Searle (1963) discussed 
occurrence and frequency in several 
rodent species of characters similar to 
the three considered below. Hedges 
( 1969 ) studied such characters inter- 
specifically and geographically in two 
species of Apodemus. These authors, and 
others, referred to such characters as 
"epigenetic characters." Berry and Searle 
(1963:607) stated that "many genes are 
concerned in the determination of each 
character, while environmental factors 
are also very important, so that the ef- 
fects of individual genes cannot be iso- 
lated." I am not presently prepared to 
comment on the relative genetic versus 
environmental control of the germane 
characters, but planned study of these 
through several generations of labora- 
tory-bred woodrats should be elucidat- 
ing. Although the term "epigenetic" may 
well apply to characters such as these, 
I prefer to avoid use of the term until 
more is known about their developmental 
control and functional importance. How- 
ever, "qualitative characters" is also 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



67 



TABLE 6. Geographic variation in color of selected samples of Neotoma micropus. F s was 
calculated by single classification analysis of variance. Tabular F values are at the P<0.05 
level of significance; ns indicates no significant difference within a group of means. Non- 
significant subsets (as calculated by the Sums of Squares Simultaneous Testing Procedure) of 
significantly different groups of means are shown in the last column. See figure 8 for geographic 
areas included within each coded locality. 



Color reflectance 
















measured, and 












F s 




coded localities 


iV 


Mean 


± 2SE 


Range 


CV 


F 


SS-STP 


Red 
















E 


5 


17.1 


0.97 


(16.5-19.0) 


6.34 


5.44 I 




O 


2 


16.8 


0.50 


(16.5-17.0) 


2.11 


1.76 I 




J 


2 


16.8 


2.50 


(15.5-18.0) 


10.55 






F 


2 


16.8 


0.50 


(16.5-17.0) 


2.11 






B 


18 


16.2 


0.98 


(13.0-19.5) 


12.87 






C 


17 


15.6 


0.88 


(13.5-19.5) 


11.56 






M 


32 


15.1 


0.78 


(10.5-20.5) 


14.69 






A 


5 


14.9 


0.73 


(14.0-16.0) 


5.51 






I 


3 


14.5 


0.58 


(14.0-15.0) 


3.45 






G 


2 


14.2 


2.50 


(13.0-15.5) 


12.41 






H 


18 


13.9 


0.72 


(11.5-17.0) 


10.94 






L 


3 


13.7 


2.40 


(12.0-16.0) 


15.18 






P 


10 


13.4 


1.09 


(11.5-17.0) 


12.81 






N 


23 


13.1 


0.66 


(11.0-16.5) 


12.11 






D 


12 


13.1 


0.81 


(10.0-14.5) 


10.79 






K 


13 


13.0 


1.08 


(8.5-15.5) 


14.97 






Blue 
















F 


2 


12.2 


3.50 


(10.5-14.0) 


20.20 


11.62 I 




E 


5 


10.5 


1.18 


(9.0-12.5) 


12.60 


1.76 I 




O 


2 


10.2 


1.50 


(9.5-11.0) 


10.35 






J 


2 


10.0 


2.00 


(9.0-11.0) 


14.14 






B 


18 


10.0 


0.56 


(8.0-12.5) 


11.88 






C 


17 


9.4 


0.42 


(8.0-11.0) 


9.21 






A 


5 


9.1 


0.66 


(8.0-10.0) 


8.15 






M 


32 


8.9 


0.52 


(7.0-13.0) 


16.69 






I 


3 


8.8 


0.67 


(8.5-9.5) 


6.54 






G 


2 


8.2 


1.50 


(7.5-9.0) 


12.86 






H 


18 


8.2 


0.42 


(7.0-10.0) 


10.88 






D 


12 


7.9 


0.46 


(7.0-9.5) 


10.02 






L 


3 


7.5 


1.00 


(7.0-8.5) 


11.55 






K 


13 


7.3 


0.56 


(5.0-9.0) 


13.84 






N 


23 


7.3 


0.34 


(6.0-9.5) 


11.26 






P 


10 


6.8 


0.44 


(5.5-7.5) 


10.35 






Green 
















F 


2 


15.0 


1.00 


(14.5-15.5) 


4.71 


11.44 I 




J 


2 


12.8 


7.50 


(9.0-16.5) 


41.59 


1.76 I 




E 


5 


10.7 


1.21 


(9.5-13.0) 


12.63 


I 




B 


18 


10.4 


0.68 


(8.5-13.5) 


13.83 






O 


2 


10.0 


1.00 


(9.5-10.5) 


7.07 






C 


17 


9.6 


0.44 


(8.0-11.0) 


9.41 






A 


5 


9.5 


0.63 


(8.5-10.5) 


7.44 






M 


32 


9.2 


0.57 


(6.5-13.5) 


17.45 






H 


18 


8.7 


0.47 


(7.0-11.0) 


11.53 






G 


2 


8.5 


1.00 


(8.0-9.0) 


8.32 






I 


3 


8.5 


1.00 


(8.0-9.5) 


10.19 






L 


3 


8.3 


1.20 


(7.5-9.5) 


12.49 






D 


12 


8.2 


0.57 


(7.0-10.5) 


12.06 






K 


13 


7.7 


0.60 


(5.5-9.5) 


14.18 






N 


23 


7.6 


0.35 


( 6.0-9.5 ) 


10.86 






P 


10 


7.2 


0.58 


(6.0-8.5) 


12.76 







68 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 
TABLE 6— Concluded. 



Color reflectance 


















measured, and 












F s 






coded localities 


N 


Mean 


± 2SE 


Range 


CV 


F 


SS-STP 


Total 


















F 


2 


44.0 


2.00 


(43.0-45.0) 


3.21 


8.93 ! 






J 


2 


39.5 


12.00 


(33.5-45.5) 


21.48 


1.76 ] 


[ I 




E 


5 


38.3 


3.20 


(35.5-44.5) 


9.35 




[ I 




O 


2 


37.0 


3.00 


( 35.5-38.5 ) 


5.73 




[ I 


I 


B 


18 


36.0 


2.21 


(27.5-43.5) 


13.03 




[ I 


I 


C 


17 


34.6 


1.53 


(29.5-40.5) 


9.11 




[ I 


I I 


A 


5 


33.5 


1.70 


( 30.5-35.5 ) 


5.68 


] 


[ I 


I I 


M 


32 


33.1 


1.77 


(24.5-46.5) 


15.13 




I 


I I I 


I 


3 


31.8 


1.33 


(30.5-32.5) 


3.63 




I 


I I I I 


G 


2 


31.0 


5.00 


(28.5-33.5) 


11.40 




I 


I I I I 


H 


18 


30.8 


1.47 


(26.5-36.5) 


10.10 






I I I I 


L 


3 


29.5 


1.53 


(28.0-30.5) 


4.48 






I I I I 


D 


12 


29.2 


1.67 


(25.0-34.5) 


9.92 






I I I 


N 


23 


28.0 


1.22 


(24.0-34.0) 


10.41 






I I 


K 


13 


28.0 


2.16 


(19.0-33.5) 


13.90 






I 


P 


10 


27.5 


1.74 


(23.5-33.0) 


10.00 






I 




\J 



12 3 4 5 



wa w^\ ^m w*$ 

n n n n 

1 2 3 < 

r ] h n n 




Fig. 10. Semidiagrammatic drawing of a 
skull of Neotoma floridana showing: A — ante- 
rior palatal spine; B — posterior margin of the 
bony palate; and C — sphenopalatine vacuities. 
Enlargements of A-C (scale at bottom applies 
to all) to the right illustrate the range of vari- 
ation seen in these characters in N. floridana and 
A 7 , micropus. Numbers represent sequential 
scoring values assigned to each character. KU 
numbers of skulls from which enlargements 
were drawn are: A— (1) 53908, (2) 3094, 

(3) 117335, (4) 117325, (5) 119707; B— (1) 
119615, (2) 117786, (3) 117783, (4) 117324, 
(5) 119797, (6) 119796, (7) 119804, (8) 
53906; C— (1) 16111, (2) 117774, (3) 117786, 

(4) 117324, (5) 119804, (6) 38922. 



somewhat of a misnomer because the 
variation is nearly continuous and, as 
noted by Berry and Searle (loc. cit.), 
must be treated by statistics rather than 
Mendelian methods. 

Another important characteristic of 
woodrat skulls involves the relative de- 
velopment of the vomer within the narial 
passage and the resultant absence or 
presence and relative size of a maxillovo- 
merine notch (Finley, 1958:249). In 
four species of Neotoma, the three dis- 
cussed herein and N. palatina ( Hall and 
Genoways, 1970), the vomerine septum 
is solid anterior to the palate (see also 
Anderson, 1969:47, Fig. 7). None of the 
specimens of N. angustipalata, N. flori- 
dana, or N. micropus from the Central 
Plains examined by me exhibit a maxil- 
lovomerine notch, but all specimens of 
N. f. magister in the Museum of Natural 
History of The University of Kansas have 
a deep notch and also lack a fork on the 
anterior palatal spine discussed below 
(but see Schwartz and Odum, 1957). 

Anterior Palatal Spine. — Geographic 
variation in the morphology of the an- 
terior palatal spine is shown graphically 
in figure 11 and in percent frequency of 
occurrence of the five categories (Fig. 
10) in table 7. Calculations for making 
the pie diagrams (Fig. 11) were as fol- 
low: 1) the percent frequency of each 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



69 



category was multiplied by the score 
shown (Table 7) for that category; 2) 
these values were summed for each 
grouped locality; 3) the lowest total was 
subtracted from each total; and 4) this 
value then was divided by the largest 
remaining value and converted to per 
cent development of the fork relative to 
the sample having the largest fork. This 
percentage value is represented by the 
darkened areas in the symbols of figure 
11. Thus, circles that are most darkened 
represent samples having a greater fre- 
quency of occurrence and larger size of 
the fork on the palatal spine than samples 
from localities with more open circles. 
Morphology of the anterior palatal 



spine varies geographically in both N. 
floridana and N. micropus. In N. f. 
baileyi, the bifurcate condition is ob- 
served in more than 91 percent of the 
specimens examined and in more than 
40 percent of these the spine is classified 
as "large." As a result, baileyi represents 
100 percent development for this charac- 
ter and the percent development for all 
other samples is relative to this situation 
in baileyi. Of the two specimens of N. 
m. canescens from White Sands National 
Monument, New Mexico (locality O, 
previously N. m. leucophea), examined 
for this character, neither has a fork; 
thus, that sample represents zero percent 
relative to the condition seen in baileyi. 



TABLE 7. Percent frequency of occurrence of five morphological categories of the anterior 
palatal spine in 31 grouped samples of Neotoma floridana, N. micropus, and N. angustipalata. 
See figure 10 for illustrations of morphological categories and figure 8 for geographic areas 

included within each coded locality. 









Spatu- 


Small 


Medium 


Large 


Locality 




Pointed 


late 


fork 


fork 


fork 


code 


N 


(1) 


(2) 


(3) 


(4) 


(5) 


1 


49 


8.16 




8.16 


40.82 


42.86 


2 


43 


9.30 




55.82 


25.58 


9.30 


3 


79 


10.13 


5.06 


48.10 


26.58 


10.13 


4 


69 


8.70 


11.60 


33.33 


31.88 


14.49 


5 


12 






58.33 


33.34 


8.33 


6 


67 


13.43 


4.48 


55.23 


19.40 


7.46 


7 


63 


11.11 


11.11 


34.92 


31.75 


11.11 


8 


73 


24.66 


4.11 


41.09 


17.81 


12.33 


9 


93 


6.45 




13.98 


47.31 


32.26 


10 


63 


17.46 




28.57 


33.33 


20.64 


11 


27 


14.82 


14.82 


33.33 


33.33 


3.70 


12 


50 


38.00 


6.00 


46.00 


8.00 


2.00 


13 


17 


41.18 


5.88 


47.06 


.... 


5.88 


A 


37 


97.30 




2.70 








B 


98 


76.53 


7.14 


16.33 








C 


117 


94.02 


1.71 


3.42 


0.85 


____ 


D 


69 


92.75 


1.45 


4.35 





1.45 


E 


23 


82.61 


4.35 


13.04 








F 


55 


89.09 


1.82 


9.09 








G 


37 


89.19 





10.81 








H 


43 


86.05 





13.95 








I 


108 


89.81 


1.85 


5.56 


2.78 





J 


45 


95.56 





4.44 








K 


35 


94.28 




2.86 


2.86 





L 


50 


94.00 


2.00 


4.00 








M 


71 


73.24 


8.45 


18.31 








N 


44 


86.36 





13.64 








O 


2 


100.00 













P 


16 


87.50 


6.25 





6.25 





Q 


1 






100.00 








R 


9 


22.22 


22.22 


44.45 


11.11 





S 


55 


60.00 


3.64 


23.64 


5.45 


7.27 



70 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



Only one sample of N. micropus (N. 
m. planiceps, locality Q) demonstrates 
a higher percentage than some samples 
of N. floridana. Because planiceps is 
known only by the holotype, which has 
a small fork on the spine, this sample is 
not necessarily indicative of the condi- 
tion in the population. With the excep- 
tion of planiceps, however, percent 
morphological development of the fork 
in micropus is consistently below 15, and 
populations geographically adjacent to 
floridana show no apparent increase 
either in the frequency of occurrence of 
a fork or in size of the fork as compared 
to those not geographically adjacent to 
floridana. A fork classified "large" is 
seen only in one specimen of micropus 
(KU 69604), but five other specimens 
from the same locality (Comanche 
County, Kansas) do not have forked 
spines. Medium-sized forks are uncom- 
mon in micropus, but all samples repre- 



\ 







Fig. 11. Geographic variation in morphol- 
ogy of anterior palatal spine in three species ot 
Neotoma. See figure 8 for geographic areas 
represented by each symbol and text for discus- 
sion of variation and calculations. 



sented by more than 16 specimens have 
at least one individual with a bifurcated 
palatal spine. Grouping of samples was 
not conducive to demonstrating local 
populational variation; only one series of 
specimens from a single locality deviates 
noticeably in frequency of the palatal 
spine as compared to that of other speci- 
mens from the aggregate locality. Six 
of seven micropus ( MHP 3377-81, 4634- 
35) collected on the same date from 3 
mi S and 14 mi W Johnson, Stanton Co., 
Kansas, have small terminal forks on the 
anterior palatal spine. Two of five ani- 
mals from other localities in Stanton 
County also have small forks. Therefore, 
although less than 10 percent of the 
other specimens from locality B have 
forked spines, 66.7 percent of those from 
Stanton County demonstrate the char- 
acter. 

Considering intraspecific variation in 
Neotoma floridana, samples of both 
campestris and att water i from Colorado 
and Kansas are similar, ranging from 
near 65 percent to 80 percent develop- 
ment. Of the three samples from Okla- 
homa, specimens from locality 10 ( south- 
eastern part of the state) have an aver- 
age similar to that of samples of floridana 
from Kansas. Frequency of the fork is 
noticeably lower in specimens from lo- 
cality 8, and even when present the forks 
tend to be relatively smaller. Many of 
the specimens in this sample originated 
from Blaine, Dewey, and Major counties, 
Oklahoma, all of which are near the 
known area of sympatry and natural 
hybridization of floridana with micropus. 
It should be reiterated that specimens 
from the locality of sympatry were not 
pooled with those from adjacent locali- 
ties, but were treated separately as a 
single sample (S). The intermediacy of 
this sample is evident in figure 11. 

Intermediacy of sample S was ex- 
pected. If considered alone, the ten- 
dency toward intermediacy in sample 8 
might lead to the conclusion that hy- 
bridization of the two species in central 
Oklahoma is introgressive. This observa- 
tion must not be disregarded in evalua- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



71 



tion of the specific integrity of floridana 
and micropus. The importance of the 
reduced frequency and size of forks on 
the anterior palatal spine of specimens 
from sample 8 may be even more sig- 
nificant when considered in view of the 
high frequency of the fork on specimens 
from adjacent sample 9. When only spec- 
imens from Oklahoman localities 8 and 
9 and the two adjacent localities for 
micropus (G and H) are considered, 
those from locality 8 appear almost per- 
fectly intermediate. If these findings are 
interpreted as being the result of intro- 
gression, the flow of genetic materials 
then would appear to be eastward and 
not westward. However, Key ( 1968 : 19 ) 
has shown that in some instances hybrid 
suture zones are in a manner analogous 
to semipermeable membranes. If so, they 
probably allow flow of some genes in 
only one direction, others in the opposite 
direction, and still others to move in 
both directions. Lewontin and Birch 
( 1966) have hypothesized, with support- 
ing evidence, that a species may actually 
become better fit to expand its distribu- 
tion as a result of having introgressed 
certain desirable genes from a closely 
related species. In neither case discussed 
did the original hybridizing taxa merge 
to form a single species. 

Samples of floridana from Texas dem- 
onstrate the lowest percent scores of sam- 
ples of that species. The sample of N. f. 
rubida (locality 13) shows least develop- 
ment of the spine and is not geograph- 
ically adjacent to a population of micro- 
pus. Localities 11 and 12, however, are 
geographically adjacent to the range of 
micropus and the reduction in frequency 
and development of the fork in these 
populations could be interpreted as dis- 
cussed above for specimens from locality 
8. On the other hand, sample 8 and the 
Texas samples may represent no more 
than a geographic cline toward reduc- 
tion and loss of the fork. Further inter- 
pretation must await additional material 
from Oklahoma and Texas as well as 
study of this character in eastern popula- 
tions of floridana. 



Morphology of the anterior palatal 
spine in N. angustipalata is highly vari- 
able (see Hooper, 1953:9-10, for notes 
on apparent excessive variation within 
this species ) , but is more similar to flori- 
dana than micropus. The presence of a 
small fork and the deep reentrant angle 
of Ml on the holotype of N. m. planiceps 
(both characters unlike typical micropus 
and resembling angustipalata) support 
my earlier suggestion that rats of these 
two nominal taxa may actually represent 
a single taxon. Additional specimens of 
angustipalata from localities in northern 
San Luis Potosi and more planiceps from 
near Rio Verde should elucidate this 
question. 

Because the anterior palatal spines of 
other species of Neotoma are not forked 
(Finley, 1958:252, reported the presence 
of a fork on one specimen of N. albigula), 
it seems logical to assume that the forked 
condition is derived, and that a pointed 
spine represents the original or "primi- 
tive" grade. A solid vomer is also the 
exception rather than the rule for Neo- 
toma. Both characters apparently 
evolved together in the precursor of the 
angustipalata-floridana-micropus com- 
plex. Subsequently, evolution either has 
favored the solid vomer equally in all 
three species or the character was al- 
ready "fixed" before speciation within 
the complex occurred. In the case of the 
forked spine, it appears that at least some 
members of the precursory species must 
have possessed the character but selec- 
tion has favored it more strongly in 
floridana and angustipalata than in mi- 
cropus. Alternatively, the frequency of 
occurrence may have been dispropor- 
tionately in favor of the direct ancestors 
of angustipalata and floridana at the 
time of isolation. 

Posterior Margin of Bony Folate. — 
Calculations of percent development of 
the posterior margin of the palate were 
conducted in a manner similar to those 
described for the palatal spine. Deter- 
mination of sequence for scoring varia- 
tion in the posterior margin of the palate 
was more difficult. On the palate, the 



72 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



plain or rounded condition of the palatal 
margin probably is intermediate (primi- 
tive?) with the deep notch being one 
extreme (advanced?) and the large con- 
vexity being the other ( also advanced? ) . 
The decision concerning which extreme 
to designate one and which to designate 
eight was arbitrary and does not imply 
evolutionary direction. Less arbitrary 
and more troublesome was the decision 
of scoring condition four (Fig. 10), in 
which two convexities form a median 
notch. Variation in morphology of the 
margin results from the manner in which 
the right and left halves of the develop- 
ing hard palate adjoin. When a single 
projection is present, approximately half 
of the bone involved was contributed by 
each side of the palate. Conversely, 
when an indentation is present, it is be- 
cause the two halves of the palate fuse 
anterior to the posterior margin. When 
two projections are present, each con- 
sists only of bone originating from a 
single half of the palate; the resultant 
"notch" between the projections clearly 
is homologous with the notch present in 
the absence of projections. Thus, two 
projections are homologous to the single 
projection characteristic of other animals. 
Because most ( if not all ) other species of 
woodrats tend to have either a rounded 
palatal margin or one with a convexity, 
is is most parsimonious to conclude that 
the notch is derived and that the double 
projection is an evolutionary grade in 
N. f. baileyi. It may be a condition 
derived from the single notch seen fre- 
quently in N. floridana. If the latter is 
the case, this condition probably should 
have been scored as one and placed at 
the left of the series. In any event, it 
apparently is more closely allied to the 
indentation than to the single convexity, 
and therefore, was scored as intermediate 
between the rounded margin and the 
smallest indentation. 

On the average, the sample of Neo- 
toma micropus canescens (locality E) 
from New Maxico exhibited greatest de- 
velopment of the posterior palatal con- 
vexity. Nearly 75 percent of specimens 



in that sample have convexities classified 
as medium or large. Therefore, this sam- 
ple was established as 100 percent de- 
velopment of the palatal convexity. The 
palatal margins of specimens of N. f. 
rubida (locality 13) show the least ten- 
dency toward a convexity, with 11 of 12 
specimens having an indentation and 
none having a convexity. Thus, sample 
13 is considered zero percent relative to 
sample E for this character (see Table 
8, and Fig. 12). 

Geographic variation in the morphol- 
ogy of the posterior margin of the bony 
palate in micropus is slight, ranging from 
the established 100 percent in sample E 
to 75.9 percent for sample G. Intra- 
specific variation in floridana is greater 
than for micropus, ranging from the es- 
tablished zero percent at locality 13 to 
53.7 percent at locality 5. In most sam- 
ples of floridana, percent development of 
a convexity is between 10 and 30, but in 
three samples (1, 5, and 11) it exceeds 
40 percent. In sample 1 (baileyi), the 
high frequency (49 percent) of the 
double convex palatal margin discussed 
above accounts for the high index of de- 
velopment, but in samples 5 and 11, the 
frequency of this morph is not especially 
high. Both of these populations are char- 
acterized by a relatively high incidence 
of animals with rounded palatal margins. 
Bounded margins are common in labo- 
ratory hybrids having a floridana parent 
with an indentation and a micropus par- 
ent with a convexity. Locality 5, al- 
though adjacent in the broad sense to 
localities C and D, is situated geograph- 
ically so that woodrats from there are 
not currently in contact with any popula- 
tion of micropus. If the two species oc- 
curred together in the vicinity of the 
Arkansas Biver at some date in the past 
(prior to settlement of the area by Euro- 
pean man), it seems plausible that the 
intermediacy of population 5 could be 
the result of previous hybridization be- 
tween the two species. However, speci- 
mens from locality 5 demonstrate no 
morphological or other proclivities to- 
ward micropus in other characters, and 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



73 



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74 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



the sample is relatively small ( 13 indi- 
viduals). Probably it is best not to 
attribute the deviation seen in this pop- 
ulation to past or present hybridization, 
but rather to interpret it either as a local 
population phenomenon or an artifact of 
the small sample. 

Interpretation of palatal morphology 
in sample 11 is more difficult and may 
represent one result of hybridization of 
floridana and micropus in north-central 
Texas. Specimens of this sample also 
tend toward micropus with respect to 
the anterior palatal spine discussed 
above. As mentioned elsewhere, a sam- 
ple of floridana from southwest of Dallas, 
Texas, was nearly intermediate in color 
between the two species (see beyond 
under discussion of results of discrim- 
inant function analysis ) . Specimens from 
locality 8, which show a marked ten- 
dency toward micropus in morphology 



i . 



ex 










Fig. 12. Geographic variation in morphol- 
ogy of the posterior margin of the bony palate 
in three species of Neotoma. See figure 8 for 
geographic areas represented by each symbol 
and text for discussion of variation and calcu- 
lations. 



of the anterior palatal spine, do not differ 
noticeably in morphology of the posterior 
palatal margin from specimens from lo- 
calities remote from the range of mi- 1 
cropus. Specimens from the locality of 
sympatry (sample S) are approximately 
intermediate between the adjacent pop- 
ulations of the two species in average 
morphology, but demonstrate a range of 
variation from medium indentations to 
large convexities. Increased variation in 
a hybrid population is, of course, to be 
expected. With respect to this character, 
specimens of the species angustipalata 
are more like micropus than floridana. 

Sphenopalatine Vacuities. — Variation 
in form and size of the sphenopalatine 
vacuities was scored and treated in a 
manner similar to that explained pre- 
viously. The range of observed variation 
and values assigned to each category are 
shown in figure 10; percent frequency of 
each category for each sample is shown 
in table 9, and the relative size of the 
vacuities for each population is shown 
geographically in figure 13. On the aver- 
age, vacuities in specimens from locality 
G are largest. That sample was set as 
the standard of 100 percent development. 
Vacuities of specimens from locality 4 
are smallest on the average, and were set 
at zero percent relative to the vacuities 
of animals from sample G. 

The average size of the sphenopala- 
tine vacuities is markedly different in 
samples of micropus as compared to that 
of floridana; samples of the former range 
from 60.3 percent (N. m. planiceps) to 
100 percent (sample G), whereas those 
of floridana range from zero percent ( lo- 
cality 4) to 50.6 percent for sample 1 
(N. f. baileyi). Neotoma angustipalata is 
highly variable with respect to morphol- 
ogy of the vacuities; it is clearly flori- 
dana-hke when averages are considered. 
Specimens from the locality of sympatry 
(sample S) are intermediate (58.6 per- 
cent), but on the average nearer micro- 
pus than floridana. 

Size of the sphenopalatine vacuities 
in specimens of baileyi is appreciably 
larger on the average than those of other 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 75 

TABLE 9. Percent frequency of occurrence of six morphological categories of the spheno- 
palatine vacuities in 31 grouped samples of Ncotoma floridana, N. micropus, and IV. angusti- 
palota. See figure 10 for illustrations of morphological categories and figure 8 for geographic 
areas included within each coded locality. 

















Very 


Locality 




Closed 


Minute 


Small 


Medium 


Large 


large 


code 


N 


(1) 


(2) 


(3) 


(4) 


(5) 


(6) 


1 


47 






44.68 


38.30 


17.02 




2 


38 




23.68 


44.74 


23.68 


7.90 




3 


63 




23.81 


55.56 


15.87 


4.76 




4 


44 




72.73 


27.27 




___. 




5 


12 




25.00 


66.67 


8.33 







6 


59 


1.70 


22.03 


67.80 


8.47 







7 


56 


1.79 


41.07 


51.78 


5.36 






8 


27 




18.52 


59.26 


22.22 




__ 


9 


13 




15.38 


84.62 








10 


12 




8.33 


75.00 


16.67 






11 


16 




25.00 


75.00 








12 


41 




36.58 


53.66 


9.76 






13 


12 


8.33 


33.33 


41.67 


16.67 






A 


34 






5.88 


44.12 


41.18 


8.82 


B 


87 






2.30 


29.88 


66.67 


1.15 


C 


78 






1.28 


12.82 


79.49 


6.41 


D 


43 






2.33 


41.86 


43.48 


2.33 


E 


14 






14.29 


50.00 


28.57 


7.14 


F 


16 




_.__ 


12.50 


56.25 


31.25 




G 


14 









21.43 


42.86 


35.71 


H 


30 







10.00 


23.33 


63.34 


3.33 


I 


2 




__._ 




50.00 


50.00 




J 


18 




.... 


5.56 


50.00 


38.88 


5.56 


K 


19 





____ 


.___ 


36.84 


42.11 


21.05 


L 


10 








20.00 


60.00 


10.00 


10.00 


M 


55 








21.82 


76.36 


1.82 


N 


37 


.... 




16.22 


56.75 


27.03 




O 


3 








66.67 


33.33 




P 


15 


____ 





20.00 


26.67 


33.33 


20.00 


Q 


1 





.... 




100.00 




___. 


R 


8 


12.50 


25.00 


25.00 


25.00 


12.50 




S 


40 


— 


5.00 


20.00 


50.00 


25.00 


.... 



members of the species. The presence 
of relatively large vacuities, two marginal 
convexities on the palate, and a large 
palatal fork is more or less characteristic 
of members of the subspecies, and gen- 
erally will suffice to distinguish the skull 
of a specimen of baileyi from skulls of 
campestris or atticateri. The relative dis- 
tinctiveness of baileyi undoubtedly has 
resulted from the present state of isola- 
tion. It is possible that these cranial 
characters of baileyi are indicative of the 
more primitive condition of the species 
at the time baileyi became established in 
north-central Nebraska. However, it is 
equally plausible that the subspecies has 
differentiated during isolation and that 



the present state of these characters rep- 
resents a derived condition. The well- 
developed fork on the anterior palatal 
spine would appear to be the latter situa- 
tion, but the unique ( possibly intermedi- 
ate) palatal margin and intermediate- 
sized vacuities likely are the former. 

Other samples of N. floridana do not 
differ appreciably from each other. Both 
samples 8 and 11, which deviate notice- 
ably in one and both, respectively, of the 
characters discussed above, are below 
20 percent in total development and 
show no noticeable tendency toward the 
adjacent populations of N. micropus. 

Intraspecific variation in the size of 
the sphenopalatine vacuities in micropus 



76 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 




Fig. 13. Geographic variation in morphol- 
ogy of the sphenopalatine vacuities in three 
species of Neotoma. See figure 8 for geographic 
areas represented by each symbol and text for 
discussion of variation and calculations. 

also is minor. When the sample of one 
individual for N. m. planiceps is disre- 
garded, the sample most like floridana 
is sample L (63.8 percent). This sample 
is from an area geographically adjacent 
to part of the range of floridana. How- 
ever, percent values of other samples, 
such as N (64.1 percent) and F (66.9 
percent), are not appreciably higher than 
that of specimens from locality L. There- 
fore, I do not think that the 63.8 percent 
value calculated for sample L can be 
interpreted as evidence of hybridization 
or introgression. It also is noteworthy 
that sample G, set at 100 percent, is geo- 
graphically adjacent to the hybrid zone 
in Oklahoma and to locality 8, which is 
somewhat micropus-Hke in other char- 
acters, and yet by definition is the sam- 
ple least foridana-\\ke for this character. 
In summation for all characters la- 
beled as qualitative cranial characters, it 
is noted that some samples from localities 



geographically adjacent to those of the 
other species deviate sufficiently toward 
the other species morphologically in one 
or at most two characters to warrant con- 
sideration of introgressive hybridization. 
However, these deviate samples can be 
interpreted without invoking introgres- 
sion. Thus it probably is best to inter- 
pret these data otherwise until additional 
evidence clearly indicates that hybrid- 
ization between floridana and micropus 
is or has been introgressive. In no case 
did all three characters vary in a manner 
that would indicate random gene flow, 
but the possibility of limited or direc- 
tional gene flow was considered and left 
open. All three characters serve well to 
distinguish the skulls of the three species, 
but none is diagnostic. The three char- 
acters considered together usually suffice 
to distinguish N. f. bailei/i from other 
subspecies of N. floridana. 

Baculum 

Burt and Barkalow (1942:290-295) 
first described the bacula of N. floridana 
and N. micropus, and compared the 
bacula of these two species with that of 
N. albigula. On the basis of their con- 
clusion that the baculum of micropus is 
intermediate between the bacula of the 
other two species, these authors removed 
micropus from the floridana species- 
group and established a micropus spe- 
cies-group. 

Burt (1960:60) later indicated that 
the bacula of micropus and floridana are 
similar and not distinguishable with cer- 
tainty. Hooper ( 1960:4-6) described and 
compared the phalli and bacula of flori- 
dana, micropus, and albigula and found 
them similar, but reported "fewer dis- 
tinctions between floridana and micro- 
pus." He further considered floridana to 
be intermediate in this character between 
the other two species. Alvarez (1963: 
452) found that although the baculum 
of N. angustipalata is narrower and 
longer on the average, it resembles that 
of N. micropus. 

The baculum of albigula is not con- 
sidered here, but those of angustipalata, 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



77 



floridana, and micropus were compared. 
Although the bacula of all three differ 
little, that of floridana usually can be 
distinguished from those of the other 
two species by its rectangular base as 
compared to a triangular base in both 
angustipalata and micropus. Individual 
variation of size and morphology over- 
laps among individuals of the three spe- 
cies. When measurements for several in- 
dividuals (two to five in all samples 
except that of angustipalata, which was 
represented by the bone of a single in- 
dividual) were averaged and the width 
of the base plotted against the length of 



the base, a separation obtains among the 
species (Fig. 14). The baculum of N. 
m. micropus from southern Tamaulipas 
(locality P, formerly N. m. littoralis) 
tends more toward that of floridana than 
do the bacula of specimens of micropus 
from any other locality. In all dimen- 
sions, the two bacula available from 
sample P are the largest studied. Besides 
the minor differences in color, the dif- 
ferences in size and to a lesser extent 
shape of the bacula were the only ways 
in which animals from locality P (pre- 
viously N. m. littoralis) were found to 
differ from those from locality N. 



■* 
^ 



CN 



o 



00 
ro 



ro ro 

m 

•^ 
o 

ro 



"O 



m' 



o 

ro' 



CO 
CN 



O 

CN 











o p 




o c 


o N 








o D 


o B 


# 7 




© R 


o A 


1 


6XD 








% S1 


• 


• 3 


o M 






• • 

• 


• S2 

s 


o E 











2.0 



2.2 



2.4 



2.6 



2.8 



30 



32 



3.4 



36 



3.8 



4.0 



Length of Base 



Fig. 14. Scatter diagram comparing bacular measurements of selected samples of Neotoma an- 
gustipalata, N. floridana, and N. micropus. See figure 8 for areas included within coded localities. 
"SI" and "S2" represent samples of micropus-like and floridana-like vvoodrats, respectively, from 
the same locality; "6 X D" is a sample of laboratory bred Fi hybrids whose parents were from 
localities 6 and D. 



78 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



The bacula of four adult Fi hybrids 
between micropus from locality D and 
floridana from locality 6 also were mea- 
sured, averaged, and plotted in the dia- 
gram. This sample was plotted in a posi- 
tion nearly intermediate between the 
parental populations, but more like flori- 
dana if all localities are considered. The 
intermediacy in the bacula of hybrids 
demonstrates the assumed genetic basis 
for determination of the shape of the 
bone. 

Because woodrats from the locality 
of sympatry, 3 mi S Chester, Major Co., 
Oklahoma, were identified by charac- 
ters of the skin and skull, but not the 
baculum, the three specimens most like 
floridana (SI) were averaged indepen- 
dently from the five most like micropus 
(S2). When plotted as above, the SI 
sample appears to be typical of floridana 
and gives no indication of effects of hy- 
bridization. Sample S2 plots in a posi- 
tion marginal to other samples of mi- 
cropus, but clearly more like micropus 
than floridana. Bacular measurements of 
woodrats from other localities do not 
indicate any obvious intraspecific or geo- 
graphic trends nor do they seem to be 
noticeably correlated to any of the other 
measurements and characters studied. In 
most instances the baculum of floridana 
can be distinguished from that of micro- 
pus or angustipalata, but no completely 
diagnostic differences exist in the mor- 
phology or size of the bone. 

Univariate Analyses of Mensural 
Characters 

The four external and ten cranial 
measurements described previously were 
analyzed by Powers' UNIVAR Program 
in univariate assessment of geographic 
variation. This was done separately for 
each sex and each species, then sepa- 
rately for each sex with samples of both 
species treated simultaneously. These re- 
sults are discussed below, in a considera- 
tion of general trends of geographic vari- 
ation. A more detailed evaluation that 
includes discussion of each measurement 
and subset relationships of group-means 



as determined by SS-STP (as included 
exemplarily below for total length) may 
be found elsewhere (Birney, 1970). 

Neotoma floridana. — Standard statis- 
tics computed on measurements of spec- 
imens from the 13 pooled localities of 1 
Neotoma floridana are shown in table 10 
Interlocality variation in the measure- 
ments of total length is significantly 
(P < 0.01) different for both sexes. For 
males, localities are separated into two 
broadly overlapping, non-significant sub- 
sets ( hereafter called subsets ) indicating 
that animals from southeastern Texas ( N. 
f. rubida, locality 13) and from south- 
eastern Kansas (locality 7) are signifi- 
cantly larger than those from localities 
6 (northeastern Kansas) and 9 (north- 
eastern Oklahoma). Males from locality 
12 (southern Texas), adjacent on the 
west to locality 13, also are large. Males 
from sample 7 are significantly larger 
than those from both adjacent localities 
(6 and 9), but not significantly larger 
than those from non-adjacent localities. 
In females, variation in total length is 
similar to that for males, but group- 
means separated into five subjects with 
females from locality 5 being signifi- 
cantly larger than those from localities 
8, 6, 10, and 9 (hereafter written as 
locality 5 > 8, 6, 10, 9), locality 13 > 6, 
10, 9 and locality 12 > 9. The only ad- 
jacent localities showing significant dif- 
ferences are 5 and 6, the two samples 
from north-central and northeastern 
Kansas. 

Hind foot length in both sexes is 
greatest in N. f. campestris and the sam- 
ple of N. f. attwateri (5) that is geo- 
graphically contiguous with campestris. 
Ear length is not significantly different 
for group-means in either sex. Coeffi- 
cients of variation for external measure- 
ments are high compared to those for 
cranial measurements. Although analy- 
ses of these characters are indicative of 
total size relationships, they probably 
are less reliable than analyses of cranial 
dimensions. Differences that may ac- 
tually exist in external size are difficult 
to document statistically because unre- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



79 



TABLE 10. Geographic variation in 14 external and cranial measurements of Neotoma floridana 
from Nebraska, Colorado, Kansas, Oklahoma, and Texas. See figure 8 for geographic areas 

included within each coded locality. 



Locality 

Code N 



Mean 



Males 
± 2SE 



Range 



N Mean 



Females 
± 2SE 



Range 











Total length 








1 


7 


381.3 


10.04 


(361.0-398.0) 


9 


374.4 


9.88 


(350.0-393.0) 


2 


9 


379.6 


11.04 


(350.0-398.0) 


8 


365.8 


9.40 


(344.0-382.0) 


3 


12 


385.1 


10.25 


(341.0-408.0) 


19 


376.4 


6.57 


(349.0-409.0) 


4 


9 


379.4 


18.10 


(345.0-434.0) 


14 


363.2 


10.65 


(340.0-402.0) 


5 


2 


386.5 


21.00 


(376.0-397.0) 


2 


397.0 


26.00 


(384.0-410.0) 


6 


5 


357.4 


11.60 


( 342.0-370.0 ) 


8 


354.0 


14.83 


(329.0-395.0) 


7 


14 


394.3 


14.22 


(349.0-450.0) 


12 


371.8 


9.41 


(340.0-397.0) 


8 


15 


380.0 


11.99 


( 350.0-425.0 ) 


9 


357.1 


10.87 


(334.0-379.0) 


9 


20 


359.5 


7.70 


(323.0-397.0) 


17 


349.3 


12.05 


(308.0-392.0) 


10 


12 


377.0 


11.29 


(334.0-400.0) 


13 


352.1 


9.82 


(320.0-374.0) 


11 


8 


369.4 


20.56 


(328.0-420.0) 


8 


374.1 


19.55 


(322.0-340.0) 


12 


7 


388.0 


25.61 


(317.0-414.0) 


8 


384.6 


11.96 


(356.0-412.0) 


13 


4 


407.0 


18.20 


(387.0-430.0) 
Length of tail \ 


5 
ertebrae 


396.0 


27.33 


(368.0-442.0) 


1 


7 


159.7 


10.20 


(138.0-176.0) 


9 


161.7 


9.00 


(136.0-180.0) 


2 


9 


155.0 


8.76 


(130.0-167.0) 


8 


157.2 


4.81 


(146.0-168.0) 


3 


12 


161.3 


8.94 


(120.0-178.0) 


19 


158.5 


4.06 


(144.0-175.0) 


4 


9 


156.1 


6.34 


(139.0-174.0) 


14 


149.9 


5.54 


(136.0-172.0) 


5 


2 


159.5 


29.00 


(145.0-174.0) 


2 


164.5 


17.00 


(156.0-173.0) 


6 


5 


148.6 


6.65 


(139.0-156.0) 


8 


150.8 


6.16 


(142.0-169.0) 


7 


14 


162.9 


3.74 


(153.0-175.0) 


12 


161.5 


4.32 


(148.0-170.0) 


8 


15 


160.7 


6.79 


(149.0-185.0) 


9 


154.4 


6.07 


(137.0-165.0) 


9 


20 


155.8 


5.39 


(132.0-176.0) 


16 


150,3 


5.52 


(136.0-170.0) 


10 


12 


162.2 


5.30 


(143.0-172.0) 


13 


151.0 


4.59 


(138.0-163.0) 


11 


9 


153.7 


13.65 


(130.0-195.0) 


8 


162.9 


9.01 


(138.0-174.0) 


12 


7 


168.4 


9.08 


(147.0-181.0) 


8 


173.2 


6.48 


(156.0-185.0) 


13 


3 


174.0 


21.63 


(159.0-195.0) 


5 


188.2 


11.30 


(175.0-207.0) 










Length of hind foot 








1 


8 


39.8 


0.60 


(38.0-41.0) 


11 


39.1 


0.51 


(38.0-41.0) 


2 


10 


41.8 


1.26 


(39.0-44.0) 


8 


39.5 


0.65 


(38.0-41.0) 


3 


15 


39.9 


1.12 


(36.0-43.0) 


19 


39.8 


0.77 


(36.0-42.0) 


4 


11 


40.1 


1.06 


(36.0-42.0) 


15 


38.7 


0.67 


(36.0-40.0) 


5 


3 


41.0 


1.15 


(40.0-42.0) 


2 


42.0 


0.00 


(42.0-42.0) 


6 


6 


39.3 


1.91 


(36.0-42.0) 


10 


36.8 


1.36 


(34.0-40.0) 


7 


15 


39.3 


0.64 


(37.0-42.0) 


11 


39.3 


0.90 


(37.0-42.0) 


8 


14 


39.5 


1.75 


(36.0-49.0) 


10 


37.5 


1.31 


(35.0-42.0) 


9 


20 


38.2 


0.74 


(35.0-41.0) 


13 


37.2 


0.82 


( 35.0-40.0 ) 


10 


10 


38.6 


1.53 


(35.0-43.0) 


13 


38.2 


1.14 


(35.0-42.0) 


11 


9 


38.0 


1.37 


(34.0-41.0) 


8 


38.5 


1.65 


(35.0-42.0) 


12 


7 


39.1 


1.41 


(37.0-42.0) 


11 


39.3 


1.01 


(36.0-42.0) 


13 


4 


38.8 


1.50 


(38.0-41.0) 

Length of 


4 
ear 


38.0 


2.58 


(35.0-41.0) 


1 


2 


27.5 


3.00 


(26.0-29.0) 


5 


26.6 


1.20 


(25.0-28.0) 


2 


4 


27.8 


1.71 


(26.0-30.0) 


6 


26.0 


0.89 


(25.0-28.0) 


3 


6 


28.8 


1.89 


(26.0-33.0) 


9 


28.7 


1.05 


(27.0-32.0) 


4 


10 


28.0 


1.26 


(25.0-31.0) 


10 


28.0 


0.99 


(25.0-30.0) 


5 


3 


26.3 


2.40 


(24.0-28.0) 


2 


29.0 


0.00 


(29.0-29.0) 


6 


6 


26.7 


1.33 


(25.0-29.0) 


7 


25.9 


1.54 


(23.0-28.0) 


7 


11 


27.0 


1.14 


( 25.0-30.0 ) 


8 


28.2 


2.95 


(25.0-38.0) 


8 


11 


27.7 


0.66 


(26.0-30.0) 


4 


26.2 


2.06 


(24.0-29.0) 


9 


16 


27.9 


0.97 


(25.0-32.0) 


11 


27.4 


1.91 


(25.0-36.0) 


10 


10 


27.2 


1.07 


(25.0-30.0) 


12 


26.8 


0.96 


(25.0-29.0) 


11 


8 


28.5 


1.00 


(27.0-30.0) 


5 


27.0 


3.03 


(21.0-29.0) 



80 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 10. — Continued. 



Locality 






Males 








Females 




Code 


N 


Mean 


± 2SE 


Range 


JV 


Mean 


± 2SE 


Range 


12 


3 


27.7 


5.33 


(25.0-33.0) 


3 


26.7 


3.33 


(25.0-30.0) 


13 


3 


31.7 


2.91 


(29.0-34.0) 
Greatest length' 


3 
of skull 


30.3 


2.91 


(28.0-33.0) 


1 


7 


48.4 


1.11 


(46.5-50.7) 


11 


48.8 


0.44 


(47.5-49.7) 


2 


7 


49.6 


2.06 


(46.0-53.8) 


6 


48.9 


0.87 


(47.5-50.6) 


3 


12 


51.1 


0.81 


(48.9-53.4) 


18 


49.7 


0.72 


(47.0-53.3) 


4 


9 


51.4 


1.41 


(48.4-55.2) 


11 


49.7 


0.74 


(48.3-52.1) 


5 


3 


51.3 


2.66 


(49.1-53.7) 


2 


51.2 


1.20 


(50.6-51.8) 


6 


5 


50.1 


1.58 


(48.0-51.7) 


10 


48.6 


0.94 


(47.0-52.2) 


7 


15 


50.8 


0.91 


(47.4-53.5) 


11 


50.2 


0.79 


(48.6-52.1) 


8 


15 


50.5 


1.13 


(47.1-54.0) 


8 


48.6 


1.00 


(46.8-50.7) 


9 


16 


50.2 


0.82 


(47.1-52.9) 


14 


48.2 


0.84 


(45.3-51.4) 


10 


13 


50.2 


0.69 


(48.2-52.4) 


13 


48.3 


1.01 


(45.0-50.8) 


11 


9 


49.6 


1.75 


(44.4-53.0) 


8 


50.7 


0.70 


(49.5-51.9) 


12 


9 


51.6 


1.09 


(49.8-54.0) 


8 


50.4 


1.27 


(47.9-53.2) 


13 


5 


53.0 


1.39 


(50.7-54.5) 


4 


52.3 


1,31 


(51.0-54.1) 










Condylobasilar length 








1 


7 


47.4 


1.17 


(45.7-49.8) 


11 


47.4 


0.55 


(46.0-48.9) 


2 


9 


48.6 


1.71 


(44.5-52.9) 


7 


47.6 


0.77 


(46.4-48.9) 


3 


13 


49.5 


0.89 


(47.3-52.3) 


14 


47.8 


0.73 


(45.2-50.9) 


4 


9 


50.6 


1.47 


(47.6-54.3) 


12 


48.6 


0.81 


(47.4-51.6) 


5 


3 


49.3 


3.27 


(47.7-52.6) 


2 


50.1 


1.20 


(49.5-50.7) 


6 


5 


49.3 


1.61 


(47.1-51.1) 


10 


47.2 


0.99 


(45.6-51.2) 


7 


15 


49.5 


0.99 


(46.1-52.2) 


11 


49.0 


0.93 


(47.3-51.7) 


8 


16 


49.2 


1.15 


(45.2-53.2) 


8 


47.2 


0.93 


(44.9-48.8) 


9 


19 


48.8 


0.81 


(45.5-52.4) 


13 


46.9 


0.87 


(50.0-54.0) 


10 


13 


48.9 


0.74 


(47.1-51.0) 


11 


46.7 


1.26 


(42.9-49.3) 


11 


10 


48.0 


1.50 


(43.2-50.9) 


8 


49.0 


0.72 


(47.6-50.5) 


12 


9 


50.1 


1.29 


(48.1-52.4) 


10 


48.4 


1.04 


(46.3-51.2) 


13 


5 


50.6 


1.63 


(47.4-52.0) 


5 


49.4 


1.98 


(46.4-52.6) 










Zygomatic breadth 








1 


7 


25.9 


0.61 


(24.8-27.1) 


11 


26.1 


0.27 


(25.4-26.6) 


2 


8 


26.9 


0.72 


(25.4-28.6) 


7 


26.4 


0.49 


(25.2-27.0) 


3 


12 


27.4 


2.14 


(26.2-28.3) 


15 


26.8 


0.44 


(25.1-28.0) 


4 


10 


27.8 


1.02 


(25.5-29.9) 


12 


27.1 


0.67 


(25.9-29.6) 


5 


2 


27.4 


2.00 


(26.4-28.4) 


2 


27.4 


0.70 


(27.1-27.8) 


6 


6 


27.0 


1.03 


(25.7-28.9) 


10 


26.5 


0.51 


(25.6-28.3) 


7 


13 


27.9 


0.53 


(25.9-29.2) 


12 


27.3 


0.49 


(26.2-29.1) 


8 


16 


26.9 


0.68 


(24.4-29.0) 


6 


26.6 


0.91 


(25.4-28.1) 


9 


18 


26.9 


0.51 


(24.4-28.9) 


15 


26.1 


0.58 


(24.0-27.9) 


10 


13 


27.1 


0.55 


(25.2-28.5) 


14 


26.1 


0.51 


(23.3-27.1) 


11 


9 


27.1 


1.20 


(22.8-29.3) 


8 


27.6 


0.54 


(26.1-28.3) 


12 


8 


27.0 


0.86 


(25.5-28.7) 


10 


26.9 


0.63 


(25.5-29.2) 


13 


4 


27.7 


0.80 


(26.6-28.5) 


5 


26.8 


1.15 


(25.5-28.4) 










Least interorbital constriction 






1 


9 


6.9 


1.70 


(6.6-7.4) 


11 


6.6 


0.15 


(6.3-7.0) 


2 


10 


6.9 


0.24 


(6.4-7.7) 


8 


6.6 


0.17 


(6.2-6.9) 


3 


14 


7.0 


0.15 


(6.4-7.5) 


19 


6.8 


0.16 


(6.1-7.5) 


4 


12 


6.7 


0.13 


(6.4-7.0) 


13 


6.6 


0.13 


(6.2-6.9) 


5 


3 


6.8 


0.07 


(6.8-6.9) 


2 


6.6 


0.10 


(6.5-6.6) 


6 


6 


6.6 


0.16 


(6.4-7.0) 


11 


6.5 


0.15 


(6.2-6.9) 


7 


16 


6.7 


0.22 


(6.0-7.8) 


12 


6.6 


0.21 


(6.1-7.2) 


8 


18 


6.8 


0.18 


(6.2-7.6) 


10 


6.7 


0.24 


(6.1-7.2) 


9 


22 


6.7 


0.14 


(5.8-7.2) 


17 


6.5 


0.15 


(6.1-7.3) 


10 


15 


6.9 


0.16 


(6.5-7.5) 


13 


6.6 


0.14 


(6.2-7.2) 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



81 



TARLE 10.— Continued. 



Locality 






Males 








Females 




Code 


N 


Mean 


± 2SE 


Range 


N 


Mean 


± 2SE 


Range 


11 


10 


6.7 


0.26 


(6.0-7.2) 


9 


6.9 


0.16 


(6.5-7.2) 


12 


9 


6.8 


0.23 


(5.2-7.5) 


11 


7.0 


0.24 


(6.4-7.7) 


13 


5 


7.0 


0.19 


(6.8-7.3) 


5 


6.9 


0.24 


(6.7-7.3) 










Breadth at mastoids 








1 


8 


19.0 


0.51 


(18.0-20.4) 


11 


19.0 


0.27 


(18.2-19.6) 


2 


8 


19.2 


0.83 


(17.4-20.7) 


7 


18.9 


0.37 


(18.1-19.3) 


3 


13 


19.7 


0.30 


(18.7-20.5) 


15 


19.2 


0.30 


(18.1-20.2) 


4 


11 


20.3 


0.63 


(18.5-22.4) 


14 


19.7 


0.34 


(18.7-21.0) 


5 


2 


19.8 


0.70 


(19.5-20.2) 


2 


20.0 


0.50 


(19.7-20.2) 


6 


5 


19.5 


0.76 


(18.5-20.6) 


11 


19.0 


0.44 


(17.8-20.1) 


7 


15 


20.0 


0.55 


(16.9-21.0) 


12 


19.4 


0.42 


(18.2-20.4) 


8 


18 


19.6 


0.31 


(18.2-20.7) 


8 


19.2 


0.41 


(18.5-20.2) 


9 


18 


19.3 


0.22 


(18.7-20.2) 


14 


18.8 


0.39 


(16.5-19.6) 


10 


15 


19.8 


0.31 


(19.0-20.9) 


13 


19.0 


0.28 


(18.1-19.6) 


11 


8 


19.6 


0.72 


(17.4-20.6) 


8 


19.8 


0.18 


(19.4-20.1) 


12 


8 


20.0 


0.49 


(19.0-21.0) 


10 


19.8 


0.51 


(18.8-21.6) 


13 


5 


20.5 


0.68 


(19.5-21.6) 
Length 


5 
af rostrum 


19.4 


0.55 


(18.5-20.0) 


1 


8 


18.9 


0.43 


(17.8-19.6) 


11 


18.8 


0.32 


(17.5-19.4) 


2 


8 


19.5 


0.91 


(18.0-21.9) 


8 


18.9 


0.65 


(17.3-20.0) 


3 


14 


19.9 


0.41 


(18.7-21.2) 


19 


19.3 


0.39 


(17.8-21.1) 


4 


12 


20.3 


0.69 


(17.9-22.9) 


14 


19.4 


0.28 


(18.7-20.5) 


5 


3 


20.1 


1.10 


(19.2-21.1) 


2 


20.6 


0.30 


(20.4-20.7) 


6 


6 


19.2 


0.99 


(17.7-20.5) 


10 


18.8 


0.40 


(18.1-20.0) 


7 


16 


19.8 


0.46 


(18.1-21.5) 


11 


19.5 


0.39 


(18.6-20.6) 


8 


17 


20.0 


0.49 


(18.4-21.6) 


9 


19.1 


0.51 


(18.2-20.4) 


9 


19 


19.6 


0.42 


(18.2-21.1) 


17 


18.7 


0.35 


(17.3-19.9) 


10 


15 


19.5 


0.36 


(18.2-20.4) 


13 


18.6 


0.50 


(16.4-19.5) 


11 


9 


19.3 


0.81 


(17.0-21.0) 


9 


19.9 


0.43 


(19.0-20.6) 


12 


9 


20.3 


0.58 


(19.1-21.7) 


8 


19.7 


0.50 


(18.9-20.7) 


13 


5 


21.2 


0.61 


(20.1-21.9) 
Breadth 


4 
of rostrum 


20.4 


0.34 


(19.9-20.7) 


1 


9 


7.9 


0.17 


(7.5-8.2) 


18 


7.9 


0.13 


(7.5-8.2) 


2 


9 


8.2 


0.58 


(6.1-9.0) 


8 


8.1 


0.16 


(7.7-8.4) 


3 


15 


8.7 


0.15 


(8.3-9.2) 


17 


8.4 


0.18 


(7.9-9.4) 


4 


12 


8.5 


0.36 


(7.6-9.3) 


15 


8.5 


0.14 


(7.9-9.0) 


5 


3 


8.3 


0.35 


(8.0-8.6) 


2 


8.5 


0.00 


(8.5-8.5) 


6 


6 


8.1 


0.36 


(7.6-8.7) 


10 


8.0 


0.15 


(7.7-8.3) 


7 


15 


8.4 


0.22 


(7.5-9.1) 


11 


8.2 


0.14 


(7.8-8.5) 


8 


18 


8.2 


0.21 


(7.6-9.0) 


10 


8.0 


0.20 


(7.5-8.5) 


9 


22 


8.0 


0.15 


(7.4-8.7) 


17 


7.8 


0.14 


(7.3-8.2) 


10 


15 


7.9 


0.17 


(7.3-8.5) 


13 


7.8 


0.17 


(7.4-8.3) 


11 


10 


8.0 


0.24 


(7.1-8.4) 


9 


8.2 


0.21 


(7.7-8.7) 


12 


8 


8.2 


0.31 


(7.5-8.7) 


10 


8.4 


0.33 


(7.5-9.2) 


13 


5 


8.2 


0.34 


(7.8-8.6) 


5 


8.3 


0.27 


(7.9-8.7) 










Length of ma 


xillary toothrow 






1 


9 


9.5 


0.20 


(9.2-10.0 


11 


9.4 


0.17 


(8.8-9.9) 


2 


10 


9.3 


0.23 


(8.9-10.0 


8 


9.4 


0.38 


(8.9-10.5) 


3 


15 


9.9 


0.18 


(9.4-10.4 


19 


9.7 


0.12 


(9.2-10.0) 


4 


12 


9.6 


0.19 


(9.1-10.0 


15 


9.7 


0.16 


(9.1-10.3) 


5 


3 


9.6 


0.64 


(9.0-10.0 


2 


9.8 


0.40 


(9.6-10.0) 


6 


6 


9.7 


0.28 


(9.3-10.0 


11 


9.3 


0.21 


(8.8-9.9) 


7 


16 


9.5 


0.18 


(9.0-10.2 


12 


9.4 


0.23 


(8.7-10.1) 


8 


19 


9.6 


0.15 


(8.7-10.2 


1 10 


9.4 


0.26 


(8.9-10.1) 


9 


22 


9.3 


0.15 


(8.8-9.9) 


17 


9.2 


0.14 


(8.7-9.6) 



82 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 10.— Concluded. 



Locality 






Males 








Females 




Code 


N 


Mean 


± 2SE 


Range 


N 


Mean 


± 2SE 


Range 


10 


15 


9.2 


0.20 


(8.5-9.8) 


14 


9.4 


0.14 


(9.0-9.9) 


11 


8 


9.4 


0.26 


(8.8-9.9) 


9 


9.4 


0.24 


(8.9-10.0) 


12 


9 


9.0 


0.28 


(8.3-9.4) 


11 


9.1 


0.22 


(8.4-9.7) 


13 


5 


9.6 


0.19 


(9.4-9.9) 


5 


9.4 


0.43 


(8.8-9.9) 










Length of palatal bridge 








1 


9 


8.7 


0.33 


(8.2-9.6) 


11 


8.7 


0.34 


(7.3-9.2) 


2 


9 


8.5 


0.30 


(7.6-9.0) 


8 


8.1 


0.28 


(7.5-8.7) 


3 


15 


8.8 


0.23 


(7.9-9.6) 


19 


8.4 


0.15 


(7.8-9.0) 


4 


12 


8.9 


0.37 


(7.9-9.8) 


15 


8.6 


0.24 


(8.0-9.4) 


5 


3 


8.7 


0.74 


(8.2-9.4) 


2 


8.8 


0.40 


(8.6-9.0) 


6 


6 


8.5 


0.35 


(7.9-9.0) 


11 


8.4 


0.27 


(7.6-9.0) 


7 


16 


8.8 


0.20 


(8.1-9.6) 


12 


8.7 


0.16 


(8.3-9.3) 


8 


18 


8.6 


0.32 


(7.2-9.6) 


10 


8.3 


0.18 


(7.8-8.7) 


9 


22 


8.5 


0.23 


(7.6-9.7) 


16 


8.2 


0.21 


(7.5-9.0) 


10 


15 


8.3 


0.12 


(7.9-8.8) 


14 


8.5 


0.21 


(7.6-9.0) 


11 


10 


8.7 


0.39 


(7.8-9.5) 


9 


8.7 


0.32 


(8.1-9.5) 


12 


9 


8.5 


0.36 


(7.7-9.4) 


10 


8.4 


0.45 


(7.3-9.8) 


13 


5 


8.7 


0.15 


(8.6-9.0) 
Length of 


5 
nasals 


8.7 


0.61 


(7.9-9.7) 


1 


8 


18.7 


0.43 


(17.6-19.4) 


11 


18.7 


0.33 


(18.0-20.2) 


2 


8 


19.3 


0.89 


(17.7-20.9) 


8 


19.0 


0.48 


(18.0-20.3) 


3 


14 


19.5 


0.45 


(18.3-20.9) 


19 


19.0 


0.37 


(17.6-20.3) 


4 


12 


20.3 


0.71 


(18.5-23.3) 


14 


19.4 


0.34 


(18.5-20.4) 


5 


3 


20.5 


1.33 


(19.3-21.6) 


2 


20.6 


0.50 


(20.3-20.8) 


6 


6 


19.4 


0.70 


(18.5-20.7) 


9 


18.7 


0.40 


(17.8-19.5) 


7 


15 


19.9 


0.42 


(18.0-21.6) 


11 


19.5 


0.47 


(18.6-21.3) 


8 


17 


20.0 


0.51 


(17.7-21.5) 


9 


19.3 


0.41 


(18.3-20.5) 


9 


19 


19.8 


0.49 


(17.8-21.6) 


17 


18.7 


0.42 


(16.7-20.2) 


10 


15 


19.7 


0.47 


(18.2-20.9) 


14 


18.8 


0.55 


(16.5-19.8) 


11 


9 


19.4 


0.99 


(17.3-21.9) 


9 


20.1 


0.49 


(18.9-21.1) 


12 


9 


20.5 


0.68 


(19.2-22.1) 


8 


19.9 


0.47 


(18.8-20.7) 


13 


5 


21.7 


0.94 


(20.4-23.3) 


4 


21.1 


0.73 


(20.2-22.0) 



lated factors contribute to within-group 
variation. Thus, trends in external char- 
acters are not shown graphically, al- 
though some of the observed trends were 
not evinced by studies of cranial di- 
mensions. 

Standard statistics and geographic 
variation in greatest length of skull are 
illustrated as a graphic example of vari- 
ation in a longitudinal cranial measure- 
ment (Fig. 15, males; Fig. 16, females). 
Results of SS-STP tests for this measure- 
ment for both sexes are shown in table 
11. Table 12 illustrates observed results 
of samples of floridana and micropus 
tested together. Also included are com- 
parisons of subset relationships involving 
additional variance between groups, and 
results of SS-STP testing for greatest 



length of skull for both species treated 
simultaneously. 

Comparisons of males show that spec- 
imens from locality 11 are the smallest 
end of a gradual north to south cline in 
greatest length of skull. Females from 
locality 11 are noticeably larger than 
those from localities immediately to the 
north and more nearly equivalent in size 
to samples 12 and 13 from farther south 
and east in Texas. Otherwise, males and 
females are more or less similar with ex- 
pected minor shifts in sequence of means. 

Condylobasilar length was expected 
to differ little from greatest length of 
skull because both are measurements of 
the long axis of the skull. However, a 
remarkable amount of shifting in se- 
quence of means is evident between the 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



83 



TABLE 11. Results of SS-STP tests comparing means of greatest length of skull for males and 

females separately from 13 localities of Neotoma floridana and 14 localities for N. micropus. 

See figure 8 for geographic areas included within each coded locality. 





Males 










Females 














M 


aximal 






M« 


iximal 


Locality 






non-significant 


Locality 


non-s 


Lgru 


ficant 


code 


Mean 




subsets 




code 


Mean 


si 


bsets 










Neotoma floridana 










13 


53.0 


I 








13 


52.3 ] 








12 


51.6 


I 


I 






5 


51.2 ] 


I 






4 


51.4 


I 


I 






11 


50.7 ] 


[ I 






5 


51.3 


I 


I 






12 


50.4 ] 


[ I 


I 




3 


51.1 


I 


I 






7 


50.2 ] 


[ I 


I 




7 


50.8 


I 


I 






4 


49.7 ] 


[ I 


I 




8 


50.5 


I 


I 






3 


49.7 ] 


[ I 


I 




9 


50.2 


I 


I 






2 


48.9 ] 


[ I 


I 




10 


50.2 


I 


I 






1 


48.8 


I 


I 




6 


50.1 


I 


I 






8 


48.6 


I 


I 




2 


49.6 


I 


I 






6 


48.6 




I 




11 


49.6 


I 


I 






10 


48.3 








1 


48.4 




I 






9 


48.2 
















Neotoma micropus 










L 


51.0 


I 








D 


49.7 ] 








H 


50.6 


I 


I 






C 


48.8 ] 


[ I 






D 


50.5 


I 


I 






B 


48.8 ] 


[ I 






C 


49.7 


I 


I ] 


I I 




L 


48.6 ] 


I 


I 




G 


49.6 


I 


I 


[ I 


I 


I 


48.5 ] 


[ I 


I 




A 


49.4 


I 


I ] 


[ I 


I 


G 


48.3 ] 


[ I 


I 


I 


B 


49.2 


I 


I ] 


[ I 


I ] 


[ F 


47.7 ] 


I 


I 


I 


K 


48.7 


I 


I 


[ I 


I 


[ H 


47.6 ] 


I 


I 


I 


I 


48.3 




I ] 


[ I 


I 


[ K 


47.1 1 


I 


I 


I 


F 


48.1 




I ] 


I 


I ] 


[ M 


46.7 


I 


I 


I 


J 


47.9 






I 


I ] 


[ A 


46.5 




I 


I 


N 


46.8 






I 


I ] 


[ J 


46.2 






I 


P 


46.6 








I ] 


[ P 


45.8 






I 


M 


46.6 










[ N 


45.7 






I 



two characters. Also, no significant dif- 
ferences were detected in group-means 
of males for condylobasilar length. 

No significant differences exist among 
group-means for zygomatic breadth of 
males. Although specimens of rubida 
( 13 ) are larger, on the average, than in- 
dividuals from more northerly samples 
of the species in the measurements of 
longitudinal axis of the skull, they are 
narrower in zygomatic breadth than 
males from localities 7 and 4 (Fig. 17). 
However, the differences are not sig- 
nificant. Highly significant ( P < 0.01 ) 
differences were detected in zygomatic 
breadth of females ( Fig. 18 ) . 

Least interorbital constriction is one 
of the least variable measurements con- 
sidered for N. floridana. Group-means 



are not significantly different for males, 
and sequence of means for this character 
(Fig. 19, males; Fig. 20, females) does 
not follow that seen in other measure- 
ments for either sex. The pattern of 
geographic variation in mastoidal 
breadth closely approximates that seen 
for zygomatic breadth. 

Woodrats from localities 3, 4, and 5 
(the two samples of campestris from 
northwestern Kansas and the sample of 
attwateri from adjacent north-central 
Kansas) are generally larger in breadth 
of rostrum than are woodrats from south- 
ern Texas ( 12 and 13 ) . In measure- 
ments of length, specimens from locality' 
13 are consistently larger than specimens 
from northern Kansas. It is visually per- 
ceptible that the skulls of specimens of 



84 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



campestris tend to be broader, more 
heavily structured and robust than those 
of rubida. To a lesser extent the same 
differences prevail between campestris 
and attwateri with the exception of spec- 
imens from locality 5. The latter are like 
other samples of attwateri in color, but in 
several aspects of overall size and general 
shape of the skull, they more closely re- 
semble campestris. 

Patterns of variation for alveolar 
length of the maxillary toothrow are 
similar to those of rostral breadth, but 
unique in certain aspects. Notably, spec- 
imens from locality 12 are smallest both 
for males and females, whereas those 
from localities 1 (baileyi) and 6 (north- 
eastern Kansas), which are among the 
smallest in most dimensions, are rela- 
tively much larger. Results of computa- 
tions for this measurement also are some- 



what unique in that more total variation 
exists between means of males than be- 
tween those of females. 

Of the dimensions analyzed, palatal 
bridge length demonstrates the least 
amount of geographic variation. Group- 
means are not significantly different for 
males and are significant only at the 
0.05 level for females. Coefficients of 
variation for measurements of this char- 
acter are noticeably larger than for other 
cranial dimensions. The reduction in 
significant geographic variation in length 
of palatal bridge may be a result of high 
within-group variation. 

Geographic variation in nasal length 
exceeds that for other cranial dimen- 
sions. Geographic trends for this de- 
mension are similar to those for length 
of rostrum. These two measurements in- 
clude the same region of the skull, but 



TABLE 12. Results of SS-STP tests comparing means of greatest length of skull for males and 
females treated separately and localities of Neotoma jloridana and A 7 , micropus tested simul- 
taneously. See figure 8 for geographic areas included within each coded locality. 





Males 












Females 




















\ 


aximal 










Maximal 




Locality 




non- 


significant Locality 






non- 


sign 


ficant 


code 


Mean 






subsets 


code 


Mean 






subsets 




13 


53.0 


I 










13 


52.3 ] 














12 


51.6 


I 


I 








5 


51.2 ] 


I 












4 


51.4 


I 


I 








11 


50.7 ] 


[ I 


I 










5 


51.3 


I 


I 








12 


50.4 ] 


[ I 


I 


I 








3 


51.1 


I 


I 








7 


50.2 ] 


[ I 


I 


I 


I 






L 


51.0 


I 


I 


I 






4 


49.7 ] 


[ I 


I 


I 


I I 






7 


50.8 


I 


I 


I 


I 




D 


49.7 ] 


[ I 


I 


I 


I I 






H 


50.6 


I 


I 


I 


I 


I 


3 


49.7 ] 


[ I 


I 


I 


I I 






D 


50.5 


I 


I 


I 


I 


I 


2 


48.9 ] 


[ I 


I 


I 


I I 


I I 




8 


50.5 


I 


I 


I 


I 


I 


C 


48.8 ] 


[ I 


I 


1 


I I 


I I 




9 


50.2 


I 


I 


I 


I 


I I 


B 


48.8 ] 


[ I 


I 


I 


I I 


I I 




10 


50.2 


I 


I 


1 


I 


I I I 


1 


48.8 ] 


[ I 


I 


I 


I I 


I I 




6 


50.1 


I 


I 


I 


I 


I I I 


8 


48.6 ] 


[ I 


I 


I 


I I 


I I 


I 


C 


49.7 


I 


I 


I 


I 


I I I 


L 


48.6 


I 


I 


I 


I I 


I I 


I 


G 


49.6 


I 


1 


I 


I 


I I I 


I 6 


48.6 


I 


I 


I 


I I 


I I 


I 


2 


49.6 


I 


I 


I 


I 


I I I 


I I 


48.5 


I 


I 


I 


I I 


I I 


I I 


11 


49.6 


I 


I 


I 


I 


I I I 


I G 


48.3 




I 


I 


I I 


I I 


I I I 


A 


49.4 


I 


I 


I 


I 


I I I 


I 10 


48.3 






I 


I I 


I I 


I I I 


B 


49.2 


I 


I 


I 


I 


I I I 


I 9 


48.2 






I 


I I 


I I 


I I I 


K 


48.7 




I 


I 


I 


I I I 


I F 


47.7 








I I 


I I 


I I I 


1 


48.4 




I 


I 


I 


I I I 


I H 


47.6 








I I 


I I 


I I I 


I 


48.3 






I 


I 


I I I 


I K 


47.1 










I I 


I I I 


F 


48.1 








I 


I I I 


I M 


46.7 










I I 


I I I 


J 


47.9 










I I I 


I A 


46.5 










I 


I I I 


N 


46.8 












I 1 


46.2 












I I I 


P 


46.6 












I P 


45.8 












I I 


M 


46.6 












I N 


45.7 












I 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



85 



differ in that rostral length is in part 
dependent on shape of the anterior end 
of the zygomatic arch. 

When all measurements are con- 
sidered, there is general agreement be- 
tween the patterns of variation as indi- 
cated by separate analyses of males and 
females except for specimens from lo- 
cality 11 (northern Texas). Males from 
that locality are smaller (as determined 
by rank-order scoring of means for the 
14 characters) than samples of males 
from all localities except northeastern 
Oklahoma (9). Rank-order scores of 
males from localities 9, 11, 6, and 1 were 
so close as to be indistinguishable by 
this method of analysis. In comparisons 
of females, however, specimens from lo- 
cality 11 were surpassed in total size only 
by those from samples 5 and 13. 

When the rank-order scores for males 
and females are summed, a general trend 
of geographic variation for floridana in 
the Central Great Plains can be seen. 
Neotoma floridana rubida is slightly 
larger than any of the samples of attica- 
teri or campestris, and appreciably larger 
than baileyi. Specimens of campestris 
from localities in Kansas are larger than 
those from Colorado and larger than 
specimens of atticateri from all except 
adjacent localities in north-central Kan- 
sas. Within the subspecies atticateri, 
there is appreciable variation in size, but 
this variation does not follow expected 
trends. Specimens from north-central 
Kansas (5) are largest, followed in se- 
quence by those from southern Texas 
(12), southeastern Kansas (7), and west- 
ern Oklahoma ( 8 ) . Specimens from east- 
ern Oklahoma (9 and 10) and northeast- 
ern Kansas (6) are the smallest examples 
of the subspecies. Neotoma floridana 
baileyi is slightly larger than the smaller 
representatives of atticateri, but smaller 
than the larger representatives of that 
subspecies. The only contiguous locali- 
ties from which samples of specimens 
frequently are significantly different in 
size are those in north-central Kansas 
( 5 ) and northeastern Kansas ( 6 ) . How- 
ever, on the basis of color, specimens 



from these localities are similar and indi- 
viduals in both samples are significantly 
darker than specimens of campestris. 

Neotoma micropus and N. angusti- 
palata. — In univariate analysis of geo- 
graphic variation in Neotoma micropus 
and N. angustipalata, specimens from lo- 
calities O (White Sands National Monu- 
ment, New Mexico) and Q (Rio Verde, 
San Luis Potosi) were not included in 
UNIVAR computations because only 
single specimens were available. Sample 
R (N. angustipalata) was not included 
because only one adult specimen of each 
sex was available at the time UNIVAR 
analyses were conducted. Subsequently, 
two additional adult females were exam- 
ined and included with calculations of 
standard statistics shown in table 13. 
Sample E (N. m. canescens from New 
Mexico ) also was omitted from UNIVAR 
analyses because New Mexico was not 
included in the study area at the time 
computations were conducted. Standard 
statistics of this sample are shown in 
table 13. In all four instances, sequence 
of means were considered for rank-order 
analysis of trends in size variation, but 
significance levels are not known for 
these four samples. 

Considering the remaining 14 sam- 
ples of IV. micropus, differences in group- 
means of total length are not significant 
for males, but they are significant ( P < 
0.05) for females. Specimens from lo- 
calities N and P (coastal Tamaulipas) 
are relatively large in this character, 
whereas those from adjacent Coahuila 
and Nuevo Leon are small. Specimens 
of both sexes from localities P and N 
(N. m. micropus) have the longest tails 
of any samples of the species. This is in 
marked disagreement with trends in cra- 
nial measurements, wherein specimens of 
N. m. micropus are among the smallest. 
Furthermore, they exhibit a marked ten- 
dency toward being unicolored, espe- 
cially in southern parts of Tamaulipas. 

Although somewhat variable and less 
reliable than cranial measurements, ex- 
ternal dimensions demonstrate certain 
overall trends. The two samples com- 



86 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 




42.5 



55.5 



Fig. 15. Dice-grams illustrating geographic variation in greatest length of skull of male Neotoma 
angustipalata, N. floridana, and N. micropus. The upper point of the triangle is the arithmetic 
mean; the darkened bar is plus and minus two standard errors of the mean; the open bar is plus 
and minus one standard deviation of the mean, and the horizontal or vertical lines indicate the 
range. See figure 8 for geographic areas included within the coded localities indicated on the ordinate. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



87 




43.0 44.0 45.0 46.0 47.0 



48.0 49.0 

mm 



50.0 51.0 52.0 53.0 54.0 



Fig. 16. Dice-grams illustrating geographic variation in greatest length of skull of female Neo- 
toma angustipalata, N. floridana, and N. micropus. See figure 15 for explanation of symbols and 
figure 8 for geographic areas included within the coded localities indicated on the ordinate. 



88 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 




Fig. 17. Dice-grams illustrating geographic variation in zygomatic breadth of male Neotoma 
angustipalata, N. floridana, and N. micropus. See figure 15 for explanations of symbols and figure 
8 for geographic areas included within the coded localities indicated on the ordinate. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



89 



1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

A 



E 
F 
G 
H 
I 
J 
K 
L 
M 
N 
P 

R \ 




23.0 23.5 24.0 24.5 25.0 



25.5 



26.0 26.5 
mm 



27.0 27.5 28.0 28.5 29.0 29.5 



Fig. 18. Dice-grams illustrating geographic variation in zygomatic breadth of female Neotoma 
angustipalata, N. floridana, and N. micropus. See figure 15 for explanation of symbols and figure 
8 for geographic areas included within the coded localities indicated on the ordinate. 



90 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



1 

2 

3 

4 

5 r 

6 

7 

8 

9 

10 

11 

12 

13 

A 
<A 

.2 B 

'■5 C 
S° 

J E 

F 
G 
H 

J 
K 
L 
M 
N 

P 
Q 
R 




mm 



5.5 



5.7 



5.9 



6.1 



6.3 



6.5 6.7 
m m 



6.9 



7.1 



7.3 



7.5 



7.7 



7.9 



Fig. 19. Dice-grams illustrating geographic variation in least interorbital constriction of male 
Neotoma angustipalata, N. floridana, and N. micropus. See figure 15 for explanation of symbols and 
figure 8 for geographic areas included within the coded localities indicated on the ordinate. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



91 




5.5 



5.7 



5.9 



6.1 



6.3 



6.5 6.7 

mm 



6.9 



7.1 



7.3 



7.5 



7.7 



Fig. 20. Dice-grams illustrating geographic variation in least interorbital constriction of female 
Neotoma angustipalata, N. floridana, and N. micropus. See figure 15 for explanation of symbols and 
figure 8 for geographic areas included within the coded localities indicated on the ordinate. 



92 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



posed of largest individuals ( exclusive of 
the tail) tend to be L and D. Locality L 
is composed of specimens from along the 
Gulf Coast of Texas and D represents 
specimens from south-central Kansas. 
Specimens from localities N and P (N. 
m. micropus) have noticeably longer tails 
than even the samples of IV. m. canescens 
characterized by large size. Specimens 
from southwestern Texas, in the general 
region of the Big Bend area (J), appear 
smallest in external characters. 

Geographic variation in greatest 
length of skull is shown graphically for 
Neotoma micropus in figures 15 (males) 
and 16 (females). Results of SS-STP 
tests illustrating maximally connected 
non-significant subsets for this dimension 
are given in table 11 for tests conducted 
only on the specimens of IV. micropus 
from grouped localities, and in table 12 
for tests made when specimens from 
grouped localities of N. floridana and N. 
micropus were tested simultaneously. 
Means of samples of the two species 
overlap broadly, but samples shown to 
be significantly different by the two 
methods are generally the same. 

The pattern of geographic variation 
seen in this measurement is typical of 
most cranial measurements. The sam- 
ples of largest woodrats are from locali- 
ties L (southern coastal Texas), C, D, 
and G (south-central Kansas and ad- 
jacent western Oklahoma inclusive of the 
panhandle). The smallest are N. m. mi- 
cropus (N and P) from Tamaulipas and 
N. m. canescens from samples J (south- 
west Texas) and M (Coahuila and 
Nuevo Leon ) . Specimens from other lo- 
calities tend to form gradual clines with 
the large and small samples listed above. 
The single exception is the marked 
change in size between specimens from 
coastal Texas (IV. m. canescens, locality 
L) and northern Tamaulipas (IV. m. 
micropus, locality N ) . 

Specimens of both sexes from locali- 
ties in Colorado, Kansas, northern Texas, 
and Oklahoma generally are larger in 
condylobasilar length than those from 
southern localities, including sample I 



(northeastern part of the range in Texas 
just south of the Red River). The only 
breaks in this trend result from the large 
size of specimens from the Gulf Coast 
of Texas and the relatively small size of 
females (A) from Colorado. Geographic 
trends in zygomatic breadth are shown 
in figures 17 (males) and 18 (females). 
Except the females from Colorado (A) 
appear larger and more nearly the size 
of females from other northern localities, 
these are comparable to those discussed 
for condylobasilar length. 

Trends in geographic variation of the 
least interorbital constriction are shown 
in figures 19 (males) and 20 (females). 
This dimension differs from other cranial 
characters of micropus in three respects. 
First, variation in group-means is not sig- 
nificant for females. Second, means of 
both sexes from locality L are relatively 
low, placing this population more nearly 
with others in the southern part of the 
distribution rather than with the larger 
northern populations. Thirdly, specimens 
from locality H, which generally are in- 
termediate in size (especially females), 
have the broadest average interorbital 
constriction. Interorbital constriction is 
consistently broader in floridana than 
micropus, and the possibility exists that 
the wide constriction in specimens of 
micropus from these localities has re- 
sulted from introgression of floridana 
genes. 

The pattern of variation for breadth 
at the mastoids is typical of most cranial 
measurements save for the unusually 
large size of specimens from localities A 
and B. Analysis of rostral length, espe- 
cially for males, exemplifies the north to 
south and east to west clines in diminish- 
ing size. The pattern of geographic vari- 
ation in rostral breadth deviates from 
this general trend of variation in the 
large size of males from locality J ( south- 
western Texas). In other characters, 
woodrats from locality J tend to be more 
like the smaller woodrats from western 
and southern parts of the range of the 
species. 

Variation in alveolar length of maxil- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



93 



TABLE 13. Geographic variation in 14 external and cranial measurements of Neotoma 
micropus and N. angustipalata. See figure 8 for geographic areas included within each coded 

locality. 



Locality 
Code N 



Mean 



Males 

± 2SE 



Range 



Females 
N Mean ± 2SE 



Range 



Locality 


















A 


3 


360.1 


10.73 


353.0-371.0) 


10 


348.5 


12.74 


(318.0-372.0) 


B 


8 


364.4 


17.76 


340.0-410.0) 


13 


357.3 


8.08 


(323.0-381.0) 


C 


15 


373.1 


11.13 


334.0-411.0) 


18 


354.8 


8.62 


(310.0-382.0) 


D 


8 


374.8 


12.45 


1 351.0-404.0) 


14 


362.3 


10.52 


(337.0-398.0) 


E 


3 


321.0 


16.04 


305.0-330.0) 


5 


329.0 


18.25 


(310.0-354.0) 


F 


7 


362.7 


10.58 


340.0-380.0) 


8 


358.5 


12.46 


(333.0-378.0) 


G 


4 


363.5 


8.89 


355.0-376.0) 


10 


353.9 


8.21 


(328.0-373.0) 


H 


5 


363.2 


12.42 


348.0-385.0) 


7 


341.7 


11.14 


(311.0-355.0) 


I 


23 


358.4 


10.21 


317.0-398.0) 


30 


345.3 


9.32 


(303.0-400.0) 


J 


4 


358.2 


10.72 


350.0-374.0) 


8 


330.1 


12.16 


(310.0-352.0) 


K 


7 


350.3 


23.44 


302.0-380.0) 


7 


351.3 


22.63 


(304.0-390.0) 


L 


6 


378.0 


22.72 


348.0-422.0) 


8 


365.9 


18.16 


(319.0-388.0) 


M 


12 


345.4 


1.12 


302.0-368.0) 


12 


339.2 


9.40 


(313.0-366.0) 


N 


9 


370.3 


9.78 


349.0-390.0) 


2 


361.5 


23.00 


(350.0-373.0) 





1 


318.0 




.... ....) 











P 


3 


364.3 


2.40 


362.0-366.0) 


4 


354.5 


24.84 


(333.0-377.0) 


Q 


1 


351.0 




.... ....) 











R 


1 


402.0 


— 


Length of tail 


3 
vertehrae 


390.3 


25.36 


(365.0-404.0) 


A 


3 


139.7 


4.81 


135.0-143.0) 


10 


139.6 


4.29 


(130.0-150.0) 


B 


8 


145.2 


7.28 


'131.0-160.0) 


13 


144.8 


4.36 


(130.0-157.0) 


C 


15 


156.6 


5.99 


'135.0-175.0) 


18 


148.8 


5.51 


(130.0-165.0) 


D 


8 


147.0 


9.19 


'120.0-164.0) 


14 


148.7 


5.77 


(126.0-168.0) 


E 


3 


127.7 


7.51 


121.0-134.0) 


5 


133.8 


7.60 


(126.0-144.0) 


F 


7 


146.3 


6.34 


'133.0-156.0) 


8 


152.9 


7.68 


(138.0-170.0) 


G 


4 


149.0 


3.74 


1145.0-154.0) 


10 


150.2 


4.99 


(136.0-162.0) 


H 


5 


147.4 


10.97 


; 136.0-165.0) 


7 


149.6 


5.40 


(138.0-159.0) 


I 


22 


146.0 


4.98 


1129.0-166.0) 


30 


144.8 


5.39 


(120.0-195.0) 


J 


4 


148.5 


8.19 


(140.0-156.0) 


8 


137.4 


10.65 


(110.0-153.0) 


K 


7 


149.7 


10.62 


'126.0-169.0) 


7 


149.9 


7.65 


(133.0-161.0) 


L 


6 


156.3 


9.53 


(150.0-180.0) 


8 


157.5 


6.29 


(147.0-173.0) 


M 


13 


141.2 


6.33 


(113.0-154.0) 


12 


140.4 


4.88 


(121.0-153.0) 


N 


9 


164.9 


7.00 


(147.0-177.0) 


2 


164.5 


15.00 


(157.0-172.0) 


O 


1 


120.0 




.... ___) 











P 


3 


169.7 


4.06 


(166.0-173.0) 


4 


173.5 


19.77 


(155.0-193.0) 


Q 


1 


167.0 




.... _..) 











R 


1 


200.0 


____ 


___) 


3 


190.7 


11.79 


(179.0-198.0) 










Length of hind foot 








A 


6 


38.0 


1.37 


(35.0-40.0) 


10 


37,3 


1.08 


(34.0-39.0) 


B 


9 


38.7 


1.76 


(36.0-45.0) 


13 


38.5 


0.89 


(36.0-41.0) 


C 


16 


39.5 


1.25 


(35.0-43.0) 


17 


38.4 


0.68 


(36.0-41.0) 


D 


9 


40.2 


0.93 


(38.0-42.0) 


15 


39.1 


0.73 


(37.0-41.0) 


E 


3 


36.3 


0.67 


(36.0-37.0) 


5 


36.6 


1.85 


(35.0-40.0) 


F 


6 


37.5 


2.35 


(33.0-41.0) 


8 


35.9 


0.80 


(34.0-37.0) 


G 


5 


38.2 


1,33 


(36.0-40.0) 


9 


38.2 


1.14 


(36.0-41.0) 


H 


7 


36.6 


1,37 


(35.0-39.0) 


8 


37.0 


1.20 


(35.0-40.0) 


I 


21 


37.3 


1.54 


(28.0-43.0) 


31 


36.7 


0.79 


(32.0-40.0) 


J 


4 


36.0 


0.82 


(35.0-37.0) 


8 


34.6 


1.25 


(33.0-38.0) 


K 


9 


39.1 


0.62 


( 38.0-40.0 ) 


7 


36.6 


2.64 


(30.5-40.0) 


L 


6 


40.3 


1.91 


(37.0-43.0) 


7 


39.9 


1.45 


(37.0-43.0) 


M 


13 


37.2 


1.49 


(32.0-41.0) 


12 


37.9 


0.87 


(36.0-41.0) 


N 


10 


37.5 


1.00 


(35.0-40.0) 


3 


37,3 


1.33 


(36.0-38.0) 


O 


1 


36.0 




( .... ....) 









( .... ....) 


P 


3 


38.0 


1.15 


(37.0-39.0) 


4 


36.5 


1.29 


(35.0-38.0) 



94 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 13.— Continued. 



Locality 
Code N 



Mean 



Males 

± 2SE 



Range 



N 



Females 
Mean ± 2SE 



Range 



Q 


1 


38.0 




( .... ....) 











R 


1 


42.0 


— 


( .... .._) 

Lenj 


3 
*th of ear 


38.7 


2.91 


(36.0-41.0) 


A 


6 


28.3 


0.42 


(28.0-29.0 


9 


27.0 


0.94 


(25.0-29.0) 


B 


9 


27.1 


1.02 


(25.0-29.0 


12 


27,3 


0.62 


(25.0-29.0) 


C 


7 


27.0 


1.07 


(25.0-29.0 


12 


26.8 


0.95 


(25.0-30.0) 


D 


6 


28.2 


0.61 


(27.0-29.0 


11 


28.1 


1.31 


(25.0-32.0) 


E 


3 


26.3 


1.76 


(25.0-28.0 


5 


28.4 


1.85 


(27.0-32.0) 


F 


4 


25.2 


3.77 


(20.0-28.0 


6 


28.2 


0.61 


(27.0-29.0) 


G 


5 


27.0 


1.10 


(25.0-28.0 


7 


26.1 


0.81 


(25.0-28.0) 


H 


6 


26.3 


0.42 


(26.0-27.0 


6 


26.7 


0.99 


(25.0-28.0) 


I 


21 


25.9 


1.15 


(20.0-30.0 


24 


25.9 


0.79 


(22.0-30.0) 


J 


4 


26.2 


3.40 


(22.0-29.0 


8 


26.1 


1.33 


(23.0-28.0) 


K 


6 


28.8 


2.39 


(25.0-34.0 


2 


23.5 


7.00 


(20.0-27.0) 


L 


6 


28.2 


1.50 


(25.0-30.0 


6 


29.1 


1.42 


(27.0-32.0) 


M 


12 


28.7 


0.92 


(26.0-31.0 


10 


28.4 


0.84 


(26.0-30.0) 


N 


10 


29.4 


0.90 


(27.0-32.0 


3 


29.0 


1.15 


(28.0-30.0) 


O 









( .... ....; 











( ) 


P 


2 


28.0 


2.00 


(27.0-29.0 


4 


28.2 


2.22 


(25.0-30.0) 


Q 










( .... __; 








— 


( .... — ) 


R 


1 


36.0 


— 


( .... .... 

Greatest 


3 
ength of skull 


28.7 


3.33 


(27.0-32.0) 


A 


6 


49.4 


1.17 


(47.9-51.4 


9 


46.5 


1.20 


(43.0-48.8) 


B 


11 


49.2 


0.78 


(47.6-51.6 


> 12 


48.8 


0.86 


(46.1-51.3) 


C 


14 


49.7 


0.95 


(46.4-52.9 


) 15 


48.8 


1.09 


(44.2-51.8) 


D 


9 


50.5 


0.95 


(48.8-53.4 


) 15 


49.7 


0.56 


(48.0-51.4) 


E 


3 


46.6 


0.53 


(46.2-47.1 


) 4 


47.0 


2.33 


(43.8-49.2) 


F 


6 


48.1 


0.61 


(47.0-49.0 


) 8 


47.7 


0.81 


(46.0-49.2) 


G 


5 


49.6 


1.65 


(47.6-52.1 


) 8 


48.3 


0.55 


(47.1-49.0) 


H 


7 


50.6 


1.15 


(48.6-53.4 


) 8 


47.6 


1.15 


(45.2-50.5) 


I 


19 


48.3 


0.86 


(43.8-51.1 


) 28 


48.5 


0.65 


(45.3-51.5) 


J 


3 


47.9 


1.58 


(46.3-48.8 


) 8 


46.2 


1.17 


(44.0-48.8) 


K 


7 


48.7 


0.86 


(47.5-50.5 


) 6 


47.1 


1.08 


(45.9-49.5) 


L 


6 


51.0 


1.50 


(47.9-53.0 


) 7 


48.6 


1.27 


(45.9-50.8) 


M 


12 


46.6 


0.92 


(42.5-48.5 


) 11 


46.7 


1.07 


(43.9-49.3) 


N 


8 


46.8 


1.58 


( 43.9-50.0 


) 2 


45.7 


1.80 


(44.8-46.6) 





1 


44.9 




( .... .... 


> 







( ) 


P 


3 


46.6 


0.42 


(46.2-46.9 


) 4 


45.8 


1.49 


(43.9-47.1) 


Q 


1 


44.9 




( .... .... 


I o 







( ) 


R 


1 


51.0 


— 


( - 
Condylo 


) 2 
basilar length 


49.8 


0.10 


(49.7-49.8) 


A 


6 


48.8 


0.95 


(47.7-50.3 


) 9 


45.1 


1.38 


(41.1-47.5) 


B 


11 


48.2 


0.75 


(46.1-49.9 


) 13 


47.0 


0.68 


(44.8-48.8) 


C 


13 


48.3 


1.06 


( 44.6-50.9 


) 16 


47.1 


0.92 


(42.8-50.0) 


D 


9 


49.1 


0.74 


(47.2-51.3 


) 15 


47.8 


0.51 


(45.7-49.2) 


E 


3 


44.8 


1.05 


(43.8-45.6 


) 5 


45.1 


1.60 


(42.3-47.0) 


F 


7 


46.9 


0.77 


( 45.4-48.3 


) 8 


46.1 


0.66 


(44.7-47.1) 


G 


5 


47.7 


0.92 


(46.6-49.2 


) 8 


46.3 


0.78 


(45.0-47.8) 


H 


8 


48.4 


0.76 


(46.7-49.7 


) 8 


45.9 


1.08 


(43.7-48.4) 


I 


22 


46.9 


0.79 


(42.6-49.6 


) 30 


46.4 


0.58 


(43.7-49.9) 


J 


3 


46.5 


1.14 


(45.4-47.2 


) 8 


44.7 


1.36 


(41.7-47.5) 


K 


7 


46.7 


0.91 


(45.0-48.8 


) 7 


45.6 


1.10 


(43.8-48.1) 


L 


6 


49.4 


1.48 


(46.1-51.1 


) 7 


46.8 


1.21 


(44.2-48.9) 


M 


11 


44.7 


0.93 


(41.3-46.2 


) 11 


44.5 


0.84 


(41.9-46.7) 


N 


8 


45.2 


1.40 


(42.7-48.5 


) 2 


44.4 


0.80 


(44.0-44.8) 


O 


1 


43.9 




( .... .... 


) o 


.... 







WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



95 



TABLE 13.— Continued. 



Locality 






Males 








Females 




Code 


N 


Mean 


± 2SE 


Range 


N 


Mean 


± 2SE 


Range 


P 


3 


44.2 


0.75 


(43.6-44.9) 


4 


43.2 


1.44 


(41.7-44.5) 


Q 


1 


44.0 




( .... ....) 











( .... _) 


R 


1 


49.6 


____ 


( .... __) 


2 


47.4 


0.30 


(47.3-47.6) 










Zygomatic breadth 








A 


6 


27.1 


0.90 


(25.4-28.5) 


8 


26.3 


0.99 


(23.8-28.2) 


B 


11 


26.5 


0.55 


(25.1-28.0) 


13 


26.7 


0.70 


(24.7-29.1) 


C 


15 


26.8 


0.48 


(25.5-28.8) 


17 


26.5 


0.45 


(24.9-28.4) 


D 


9 


27.3 


0.45 


(26.7-28.9) 


15 


26.8 


0.44 


(25.5-28.4) 


E 


3 


25.3 


0.64 


(24.7-25.8) 


5 


25.2 


0.99 


(24,3-27.1) 


F 


7 


26.5 


0.39 


(26.0-27.4) 


7 


26.1 


0.70 


(24.6-27.6) 


G 


5 


26.5 


0.75 


(25.5-27.5) 


10 


26.1 


0.60 


(24.5-27.2) 


H 


8 


27.1 


0.67 


(26.2-29.1) 


8 


25.8 


0.51 


(25.0-26.5) 


I 


23 


26.1 


0.41 


(23.7-27.4) 


32 


26.1 


0,36 


(23.0-28.1) 


J 


3 


25.3 


0.20 


(25.2-25.5) 


8 


25.1 


0.40 


(24.3-26.0) 


K 


7 


25.8 


0.81 


(25.0-28.0) 


7 


25.5 


0.58 


(24.8-26.8) 


L 


6 


27.6 


0.88 


(25.9-28.9) 


7 


25.8 


0.80 


(24.6-27.3) 


M 


13 


24.8 


0.50 


(23.2-25.7) 


11 


24.6 


0,39 


(23.6-25.3) 


N 


8 


24.9 


0.82 


(23.3-26.7) 


2 


24.9 


1.00 


(24.4-25.4) 


O 


1 


25.4 




( .... ....) 





.... 





( .... ....) 


P 


3 


25.0 


1.17 


(24.4-26.2) 


4 


24.0 


0.38 


(23.5-24.4) 


Q 


1 


23.7 




( .... ....) 









( .... ....) 


R 


1 


25.8 


— 


( -) 


2 


25.0 


2.00 


(24.0-26.0) 










Least interorbital constriction 






A 


6 


6.4 


0.23 


(6.1-6.9) 


10 


6,3 


0.21 


(5.8-6.8) 


B 


11 


6.2 


0.16 


(5.8-6.7) 


14 


6.3 


0.16 


(5.8-6.7) 


C 


16 


6.4 


0.13 


( 6.0-6.9 ) 


18 


6.3 


0.15 


(5.9-7.0) 


D 


9 


6.4 


0.12 


(6.1-6.7) 


16 


6.4 


0.14 


(5.9-7.0) 


E 


3 


6.0 


0.13 


(5.9-6.1) 


5 


6.2 


0.32 


(5.9-6.8) 


F 


7 


6.2 


0.12 


(6.0-6.4) 


8 


6.3 


0.23 


(5.8-6.7) 


G 


5 


6.4 


0.41 


( 5.9-6.9 ) 


10 


6.4 


0.21 


(5.8-6.9) 


H 


8 


6.6 


0.33 


(6.1-7.7) 


8 


6.4 


0.24 


(5.9-6.9) 


I 


24 


6.4 


0.14 


(5.7-7.0) 


33 


6.3 


0.15 


(5.5-7.2) 


J 


3 


6,3 


0.07 


(6.3-6.4) 


8 


5.9 


0.18 


(5.7-6.3) 


K 


9 


6.1 


0.19 


(5.7-6.6) 


7 


6.1 


0.16 


(5.9-6.5) 


L 


6 


6.2 


0.21 


(5.8-6.5) 


7 


6.1 


0.24 


(5.7-6.5) 


M 


13 


6.2 


0.18 


(5.8-7.0) 


12 


6.2 


0.13 


(5.9-6.8) 


N 


11 


6.1 


0.18 


(5.5-6.5) 


3 


6.0 


0.31 


(5.7-6.2) 


O 


1 


6.0 




( ) 











( ) 


P 


3 


6.0 


0.29 


(5.8-6.3) 


4 


6.3 


0.36 


(6.0-6.8) 


Q 


1 


5.6 




( ) 











( ) 


R 


1 


5.7 


-— 


( ) 


2 


6.0 


0.30 


(5.8-6.1) 










Breadth at mastoids 








A 


6 


19.9 


0.57 


(18.9-20.9) 


8 


18.9 


0.50 


(18.0-19.9) 


B 


11 


19.1 


0.40 


(18.0-20.1) 


11 


19.3 


0.35 


(18,3-20.3) 


C 


13 


19.5 


0,38 


(18.1-20.8) 


16 


18.9 


0.27 


(17.9-19.8) 


D 


8 


19.6 


0.25 


(19.1-20.1) 


14 


19.0 


0.23 


(18.2-19.5) 


E 


3 


18.4 


0.76 


(17.7-19.0) 


5 


18.3 


0.53 


(17.5-19.0) 


F 


7 


18.9 


0.59 


(17.6-20.0) 


8 


18.8 


0.29 


(18.2-19,3) 


G 


5 


19.2 


0.49 


(18.7-20.1) 


8 


18.9 


0.42 


(17.7-19.6) 


H 


8 


19.6 


0.23 


(19.0-20.0) 


7 


19.0 


0.58 


(18.2-20.1) 


I 


18 


18.9 


0.26 


(18.0-20.0) 


25 


19.0 


0.27 


(17.6-20.7) 


J 


4 


18.8 


0.46 


(18.2-19.3) 


8 


18.5 


0,32 


(17.8-19.2) 


K 


8 


19.0 


0.40 


(18.5-20.1) 


7 


18.8 


0.38 


(18.0-19.7) 


L 


6 


19.7 


0.42 


(18.9-20.5) 


8 


19.4 


0.50 


(18.4-20.6) 


M 


12 


19.0 


0.47 


(17.5-19.9) 


10 


18.6 


0.23 


(17.8-19.1) 


N 


9 


18.8 


0.71 


(17.5-20.4) 


2 


17.7 


0.20 


(17.6-17.8) 



96 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 13.— Continued. 



Locality 






Males 








Females 




Code 


N 


Mean 


± 2SE 


Range 


N 


Mean 


± 2SE 


Range 


O 


1 


18.1 




( .... _ 









( .... ....) 


P 


3 


18.3 


0.44 


(18.0-18.7 


1 4 


18.2 


0.48 


(17.6-18.6) 


Q 


1 


18.0 





( __ __ 











( _ _) 


R 


1 


19.5 


— 


( .._ _ 
Lengtl 


1 2 
i of rostrum 


18.9 


0.20 


(18.8-19.0) 


A 


6 


19.5 


0.69 


( 18.5-20.7 


9 


17.7 


0.63 


(18.8-19.0) 


B 


11 


19.2 


0.40 


( 18.2-20.2 


13 


18.8 


0.44 


(17.7-20.2) 


C 


15 


19.5 


0.37 


( 17.8-20.7 


17 


18.9 


0.36 


(17.2-20.1) 


D 


9 


19.9 


0.67 


(18.6-21.6 


16 


19.9 


0.34 


(18.6-20.8) 


E 


3 


17.9 


0.77 


(17.5-18.7 


4 


18.2 


1.13 


(16.7-18.6) 


F 


7 


18.7 


0.20 


(18.5-19.2 


8 


18.5 


0.35 


(17.7-19.2) 


G 


5 


19.0 


0.59 


( 18.2-20.0 


10 


18.8 


0.47 


(17.6-20.1) 


H 


7 


19.8 


0.49 


( 18.7-20.7 


8 


18.6 


0.52 


(17.6-19.7) 


I 


21 


18.9 


0.41 


( 16.6-20.2 


30 


18.8 


0.31 


(17.3-20.7) 


J 


4 


18.5 


0.89 


(17.2-19.2 


8 


17.7 


0.69 


(16.6-19.4) 


K 


9 


18.9 


0.46 


( 17.9-20.0 


7 


18.2 


0.51 


(17.0-19.2) 


L 


6 


19.8 


0.94 


( 17.7-20.9 


8 


18.6 


0.74 


(17.0-20.5) 


M 


13 


17.7 


0.47 


(15.7-18.6 


12 


17.5 


0.56 


(16.0-18.9) 


N 


11 


17.6 


0.63 


(16.0-19.7 


3 


17.2 


0.98 


(16.2-17.8) 


O 


1 


17.4 




( .... .... 









( .... ....) 


P 


3 


17.4 


0.47 


(17.0-17.8 


4 


17.6 


0.91 


(16.4-18.5) 


Q 


1 


17.1 




( .... .... 









( .... ....) 


R 


1 


20.7 


— 


( .... .... 

Breadtl 


1 3 
i of rostrum 


19.1 


0.50 


(18.8-19.6) 


A 


6 


8.6 


0.47 


(8.1-9.3) 


9 


7.9 


0.30 


(7.0-8.5) 


B 


11 


8.3 


0.26 


(7.5-9.2) 


14 


8.2 


0.23 


(7.2-8.9) 


C 


16 


8.4 


0.16 


(7.8-9.0) 


18 


8.3 


0.18 


(7.7-9.3) 


D 


9 


8.5 


0.23 


(8.1-9.1) 


16 


8,3 


0.17 


(7.7-9.1) 


E 


3 


7.9 


0.12 


(7.8-8.0) 


5 


8.1 


0.36 


(8.2-8.4) 


F 


7 


8.2 


0.18 


(7.8-8.5) 


8 


7.9 


0.11 


(7.7-8.2) 


G 


5 


8.3 


0.20 


(8.0-8.6) 


10 


8.1 


0.23 


(7.6-8.6) 


H 


8 


8.2 


0.23 


(7.7-8.7) 


8 


7.9 


0.24 


(7.5-8.5) 


I 


24 


8.0 


0.17 


(7.4-8.9) 


32 


8.0 


0.11 


(7.4-8.8) 


J 


3 


8.4 


0.18 


(8.2-8.5) 


8 


7.8 


0.25 


(7.2-8.4) 


K 


9 


7.8 


0.19 


( 7.5-8.4 ) 


7 


7.9 


0.31 


(7.4-8.5) 


L 


6 


8.3 


0.41 


(7.8-8.9) 


7 


8.0 


0.39 


(7.6-9.1) 


M 


13 


7.7 


0.20 


(7.1-8.0) 


12 


7.8 


0.19 


(7.3-8.5) 


N 


11 


7.9 


0.26 


(7.0-8.7) 


3 


7.4 


0.35 


(7.1-7.7) 


O 


1 


8.0 




( ) 









( ) 


P 


3 


7.5 


0.12 


(7.4-7.6) 


14 


7.4 


0.25 


(7.2-7.8) 


Q 


1 


7.6 




( ) 









( ) 


R 


1 


8.1 


— 


( ) 


3 


8.1 


0.18 


(7.9-8.2) 








Alveolar length 


3f maxillary toothrow 






A 


6 


9.0 


0.37 


(8.5-9.6) 


10 


8.7 


0.27 


(8.2-9.4) 


B 


11 


9.3 


0.19 


(8.7-9.8) 


14 


9.5 


0.21 


(8.8-10.0) 


C 


16 


9.4 


0.17 


(8.7-10.1 


18 


9.3 


0.20 


(8.5-10.1) 


D 


9 


9.4 


0.24 


(8.6-9.8) 


16 


9.3 


0.22 


(8.6-10.1) 


E 


3 


9.0 


0.58 


(8.5-9.5) 


5 


8.6 


0.36 


(8.2-9.1) 


F 


7 


9.0 


0.25 


(8.5-9.4) 


8 


8.9 


0.26 


(8.1-9.2) 


G 


5 


9.1 


0.45 


(8.6-9.9) 


10 


9.2 


0.26 


(8.7-9.9) 


H 


8 


9.1 


0.20 


(8.7-9.6) 


8 


9.1 


0.31 


(8.4-9.7) 


I 


22 


9.4 


0.20 


(8.6-10.3 


9 


9.1 


0.17 


(8.0-10.1) 


J 


4 


9.1 


0.19 


(9.0-9.4) 


8 


8.9 


0.22 


(8.4-9.4) 


K 


8 


9.3 


0.27 


(8.8-9.8) 


7 


9.1 


0.28 


(8.6-9.5) 


L 


6 


9.7 


0.34 


(9.0-10.1 


8 


9.4 


0.34 


(8.6-9.9) 


M 


13 


8.5 


0.25 


(8.0-9.5) 


12 


8.7 


0.33 


(7.9-10.0) 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



97 



TABLE 13.— Concluded. 



Locality 






Males 








Females 




Code 


N 


Mean 


± 2SE 


Range 


N 


Mean 


± 2SE 


Range 


N 


10 


8.7 


0.27 


(8.1-9.4) 


3 


8.5 


0.75 


(7.8-9.1) 


O 


1 


9.2 


____ 


( _ ._) 









( ) 


P 


3 


9.1 


0.41 


(8.8-9.5) 


4 


9.0 


0.34 


( 8.6-9.4 ) 


Q 


1 


9.4 


__.. 


( ) 









( ) 


R 


1 


9.9 




(- -) 


3 


9.8 


0.58 


(9.3-10.3) 










Length of palatal bridge 








A 


6 


8.6 


0.25 


(8.3-9.1) 


10 


7.9 


0.24 


(7.1-8.4) 


B 


11 


8.2 


0.33 


(6.8-8.9) 


13 


7.9 


0.23 


(7.1-8.3) 


C 


15 


8.0 


0.19 


(7.3-8.5) 


18 


8.0 


0.28 


(7.1-9.5) 


D 


9 


8.3 


0.35 


(7.7-9.0) 


16 


8.0 


0.18 


(7.4-8.5) 


E 


3 


7.9 


0.23 


(7.7-8.1) 


5 


7.7 


0.20 


(7.6-8.1) 


F 


7 


7.8 


0.43 


(6.9-8.4) 


8 


8.0 


0.20 


(7.5-8.4) 


G 


5 


8.2 


0.60 


(7.0-8.7) 


10 


8.0 


0.34 


(7.1-8.9) 


H 


7 


7.9 


0.19 


(7.7-8.4) 


8 


7.9 


0.32 


(7.4-8.4) 


I 


24 


8.1 


0.17 


(7.4-9.0) 


33 


8.0 


0.14 


(7.1-8.9) 


J 


3 


7.9 


0.70 


(7.2-8.3) 


8 


7.4 


0.60 


(7.0-7.9) 


K 


8 


7.8 


0.23 


(7.2-8.2) 


7 


7.8 


0.35 


(7,3-8.5) 


L 


6 


8.4 


0.51 


(7,3-9.0) 


7 


8.2 


0.32 


(7.8-9.1) 


M 


13 


7.6 


0.19 


(7.0-8.1) 


13 


7.5 


0.22 


(6.9-8.1) 


N 


11 


8.1 


0.26 


(7.2-8.9) 


3 


7.6 


0.76 


(7.0-8.3) 


O 


1 


8.6 


__ 


( ) 









( ) 


P 


3 


7.5 


0.81 


(6.8-8.2) 


4 


7.8 


0.42 


(7.5-8.4) 


Q 


1 


8.6 




( ) 









( ) 


R 


1 


9.3 




(_ ___) 


3 


8.7 


0,31 


(8.5-9.0) 










Length of nasals 








A 


6 


19.9 


0.64 


( 18.8-20.8 


) 9 


18.4 


0.61 


(16.9-19.4) 


B 


11 


19.7 


0.46 


( 18.0-20.7 


1 13 


19.2 


0.55 


(17.9-20.7) 


C 


15 


19.9 


0.45 


(18.5-21.1 


I 17 


19.3 


0.48 


(16.7-21.2) 


D 


9 


20.1 


0.55 


(18.9-21.4 


I 16 


20.3 


0,30 


(19.3-21.6) 


E 


3 


18.3 


1.21 


(17.6-19.5 


1 4 


18.7 


1.51 


(16.9-20.4) 


F 


7 


19.6 


0.43 


( 18.5-20.2 


) 8 


18.8 


0.41 


(18.0-19.7) 


G 


5 


19.7 


0.77 


(18.8-21.1 


) 10 


19.2 


0.54 


(17.5-20.8) 


H 


7 


20.5 


0.68 


( 19.5-22.0 


8 


19.1 


0.65 


(17.6-20.6) 


I 


21 


19.3 


0.46 


(16.6-20.8 


30 


19.2 


0,35 


(17.8-21.0) 


J 


4 


19.0 


1.15 


( 17.4-20.0 


8 


18.0 


0.80 


(16.4-19.8) 


K 


9 


19.0 


0.44 


(17.8-19.7 


7 


18.4 


0.55 


(17.6-19.4) 


L 


6 


20.5 


1.00 


( 18.6-22.0 


8 


19.0 


0.54 


(17.8-19.9) 


M 


13 


18.1 


0.51 


(16.3-19.2 


12 


17.9 


0.60 


(16.2-19.3) 


N 


11 


18.0 


0.76 


( 16.1-20.3 


3 


17.2 


0.19 


(15.4-18.7) 


O 


1 


17.9 




( _ __; 





.... 




( .... ....) 


P 


3 


17.9 


0.35 


(17.6-18.2 


4 


17.1 


0.81 


(16.3-18.2) 


Q 


1 


17.9 




( .... ..... 









( .... ....) 


R 


1 


19.6 


-- 


( .... .... 


3 


19.0 


1,39 


(17.9-20.3) 



lary toothrow deviates noticeably from 
the anticipated trends. For example, sam- 
ples such as L and D, are large and M 
and N are smaller. Specimens from other 
localities, such as P and K, have propor- 
tionately longer toothrows, whereas those 
from locality A are atypically short. The 
patterns of variation in palatal bridge 
length shown by sequence of means are 
similar to those of toothrow length ex- 



cept that specimens from locality P are 
among the smallest. The pattern of vari- 
ation in nasal length is similar to that 
of rostral length. 

The rank-order system of scoring 
means described above was employed to 
search for trends in size variation in N. 
micropus. Specimens from localities D 
(south-central Kansas) and L (coastal 
Texas ) were thus calculated to be larger 



98 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



than other specimens in the range of the 
species. Moving away from locality D, 
size decreases gradually but consistently 
in specimens to the south (localities G, 
H, and I ) and west ( localities C, B, and 
A). Specimens from localities southwest 
(localities F, E, O, and J) of the above- 
listed seven localities decrease in size 
clinally. The large area in central Texas 
from which specimens of N. micropus 
are absent (see Fig. 6 and discussion of 
distribution for N. m. canescens ) lies be- 
tween locality I and the two in southern 
Texas ( K and L ) . It is possible that the 
only route for gene flow between locality 
L and I is through western Texas; or in 
other words, animals from locality L may 
be effectively isolated from the northern 
populations of woodrats that they re- 
semble in size. Specimens from locality 
K are considerably smaller than those 
from L, slightly smaller than those from 
I and slightly larger than those from J. 
Specimens from Coahuila (locality M) 
are probably smallest of N. m. canescens, 
but if so, they are only slightly smaller 
than those from New Mexico and the 
Big Bend area (J) of Texas. Specimens 
of N. m. micropus from coastal Tamauli- 
pas have proportionately longer tails, 
and thus have high means for total length 
and tail length. Cranially they are as 
small or possibly smaller than those from 
adjacent locality M. The single break in 
the gradual cline in size is across the 
lower Bio Grande Biver. Locality L, 
having among the largest specimens of 
the species, is contiguous with locality 
N, which supports small woodrats having 
relatively long and often unicolored tails 
(TV. m. micropus). The steepness of this 
"step" in the cline decreases to the north- 
west along the Bio Grande. For exam- 
ple, specimens from locality K are con- 
siderably smaller than those from L, but 
considerably larger than those from M. 
Farther west, specimens from Chihuahua 
are indistinguishable from those in south- 
west Texas. 

Size relationships between specimens 
of N. m. micropus from northern Tamau- 
lipas and southern Tamaulipas (pre- 



viously N. m. littoralis) demonstrate that 
rats from the two localities are similar, 
especially with respect to external and 
cranial dimensions and, to a lesser extent, 
color. I detect no real basis for con- 
tinuing to recognize littoralis as a sub- 
species. 

Because the only available "adult" 
specimens from Bio Verde, San Luis 
Potosi (planiceps, locality Q) and from 
White Sands, New Mexico (canescens, 
sample O, previously known as leu- 
cophea) are of age-group V, comments 
on size of these groups must be tentative. 
However, woodrats from White Sands 
appear to be nearly the same size as 
other specimens from New Mexico. The 
holotype of planiceps is similar in size to 
other specimens of N. micropus from 
Mexico. 

On the basis of the four adult speci- 
mens (one male, three females) of N. 
angustipalata examined, it appears that 
individuals of this species are much 
larger than those of N. micropus from 
all localities in Mexico. The only areas 
from which specimens of N. micropus 
compare favorably in size to individuals 
of angustipalata are localities D and L. 
The external measurements of angusti- 
palata far exceed those of all samples of 
micropus, and measurements of lengths 
of all or parts of the skull are generally 
larger. In measurements of breadth, 
however, several samples of micropus 
are larger than angustipalata (see table 
13 for comparative measurements). 

Comparisons of sequence of means 
and subset relationships from SS-STP 
computations including the 13 samples 
of N. floriclana and 14 of N. micropus 
together, reveal that floriclana generally 
is the larger (see Table 12 and Figs. 
15-20). Samples of -floriclana from north- 
western (campestris) and north-central 
(attwateri) Kansas and those from south- 
eastern Texas (rubida) are larger on the 
average in most dimensions than samples 
of micropus. Samples of attwateri from 
southeastern Kansas and from both lo- 
calities in Texas usually are larger than 
samples of micropus; however, in some 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



99 



dimensions, samples of micropus from 
South-central Kansas and coastal south- 
ern Texas are larger than one or more 
of the floridana samples. Specimens of 
micropus from the above two localities 
and from localities in western Kansas 
and northern Oklahoma are usually 
larger than samples of baileyi, campestris 
from Colorado, and attwateri from north- 
eastern Kansas and eastern Oklahoma. 
Specimens of micropus from Colorado, 
extreme southwestern Kansas, southwest- 
ern Oklahoma, and northern Texas are 
nearly equal in size to specimens of the 
last-mentioned samples of floridana. The 
micropus from southern and western lo- 
calities are consistently smaller than 
woodrats of either species from other 
localities. The single exception is tail 
length in N. m. micropus, which exceeds 
that of all other samples of N. micropus 
and most samples of N. floridana. Wood- 
rats from the panhandle of Texas, south- 
western Texas, and non-coastal southern 
Texas are intermediate in size between 
specimens from farther to the south and 
west and those from localities to the 
north and east. 

The general trends noted above are 
less well marked in certain dimensions 
than others; for example, least interor- 
bital constriction is broader in all sam- 
ples of floridana females than in any 
sample of micropus females. The only 
samples of micropus that occasionally 
average larger than N. angustipalata are 
those from south-central Kansas and 
southern coastal Texas. However, cer- 
tain samples of floridana (rubida, cam- 
pestris from Kansas, and attwateri from 
north-central Kansas) are larger than 
angustipalata in many dimensions. 

In conclusion, univariate analyses in- 
dicate that the range of size variation 
within the species micropus exceeds that 
in the populations of floridana studied. 
Also, variation in micropus tends to be 
clinal and relatively consistent geograph- 
ically. The single major exception is the 
large size of specimens from coastal 
southern Texas. Specimens of micropus 
from western and southern localities gen- 



erally are smaller than those from north- 
ern and eastern localities, but those from 
coastal Texas are larger on the average 
than all samples of micropus from con- 
tiguous localities and larger than most 
samples from northern parts of the range 
of the species. This phenomenon could 
have resulted from one or more of three 
distinct possibilities. The samples from 
this locality consisted of less than 10 in- 
dividuals of each sex, and the apparent 
large size of these woodrats might be 
the result of sampling error. I consider 
this possibility relatively unlikely, how- 
ever, because large size was evinced by 
specimens of both sexes. The proba- 
bility of sampling error involving two 
samples from the same locality is much 
lower than when only one sample is 
involved. Secondly, specimens of flori- 
dana from southern Texas are large; pos- 
sibly the large size of micropus from 
contiguous localities is the result of in- 
trogression of genetic material from flori- 
dana. Thus, the robustness of animals 
from coastal Texas perhaps should be 
interpreted as evidence for hybridiza- 
tion. Thirdly, there is the possibility that 
whatever selective forces have resulted 
in large individuals of floridana in south- 
ern Texas also are operating on adjacent 
populations of micropus, resulting in the 
unexpected large size. Evaluation of the 
latter two possibilities is difficult and 
must remain speculative until additional 
data are available. If hybridization is 
the answer, it might be expected that 
specimens of floridana from southern 
Texas would be slightly smaller than, 
instead of slightly larger than, specimens 
from northern Texas and southern Okla- 
homa. However, it also must be remem- 
bered that certain qualitative cranial 
characters discussed previously indicated 
that specimens of floridana from locali- 
ties in southern Texas were relatively 
more micropus-\ike than are those in 
most other populations of floridana. 

Multivariate Analyses of Mensural 
Characters 

Moss (1968) and Sokal and Michener 



100 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



( 1967 ) have shown that standardization 
of character states to equally weight 
characters greatly influences the cluster- 
ing of OTU's in correlation phenograms 
and further tends to reduce the degree of 
isolation of "aberrant" OTU's. The dis- 
tance phenogram usually is less influ- 
enced by standardization of character 
states. Comparisons by correlation and 
by distance augment one another, and 
must be considered simultaneously in the 
interpretation of phenograms. Correla- 
tions are relatively independent of size 
(totally independent with unstandard- 
ized character states ) and cluster OTU's 
primarily on the basis of relative propor- 
tions. On the other hand, distances are 
less dependent on relative proportions, 
and cluster primarily on the basis of ab- 
solute differences between the numerical 
values of characters. For example, when 
Moss (1968:38) multiplied continuous 
characters by a factor of two to create 
hypothetical "giant" OTU's and com- 
pared original and "giant" OTU's using 
unstandardized data, the normal and 
"giant" OTU's clustered in the correla- 
tion phenogram at the 1.0 level. How- 
ever, in the distance phenogram based 
on unstandardized data, there was com- 
plete separation of normal and "giant" 
OTU's with comparable clustering within 
each major cluster. Standardization of 
the data resulted in a high frequency of 
group clustering (a cluster of normal 
OTU's joined its respective cluster of 
giant OTU's) in the correlation pheno- 
gram, but the distance phenogram was 
altered very little by standardization. 

As previously mentioned, character 
states were standardized for all computa- 
tions by CLSNT. In most cases I have 
illustrated distance phenograms, and in 
all cases the clustering relationships of 
correlation phenograms are discussed to 
emphasize proportional relationships and 
absolute differences among the woodrats. 
When woodrats from grouped localities 
were compared using all of the available 
characters, both correlation and dis- 
tance phenograms are presented. A 
certain amount of distortion results in the 



clustering process from a multidimen- 
sional correlation or distance matrix to a 
two-dimensional phenogram. The coef- 
ficients of cophenetic correlation, calcu- 
lated to express correlation between the 
original matrices and the resultant phe- 
nograms, are given beyond for all phe- 
nograms. This coefficient is normally 
about 10 percent higher for distance 
phenograms than for correlation pheno- 
grams. Rohlf (1968) discussed various 
relationships between results of cluster 
analyses and those of principal compo- 
nents. He recommended (1968:254) that 
"numerical taxonomic studies should use 
both cluster analyses and 3-D models in 
order to extract and present as much in- 
formation as is possible from the raw 
data." In all cases, I have analyzed prin- 
cipal components in conjunction with 
cluster analyses. Additionally, for each 
projection of OTU's onto the three prin- 
cipal components, a minimally intercon- 
nected network ( Cavalli-Sforza and Ed- 
wards, 1967) was computed from the 
among-OTU distance matrix. When the 
number of OTU's was low, these have 
been included on the 3-D drawings. 
Models are presented as perspective 
drawings; thus, with respect to the left 
rear corner of a square platform, the 
viewer is 0.3 units (one unit is equal to 
the length of one side of the platform) 
to the right, 3.0 units toward the front, 
and at a height ( the third principal com- 
ponent) even with the OTU projected 
farthest from the platform. 

Neotoma foridana. — A correlation 
phenogram was computed from among- 
OTU correlations for Neotoma floriclana 
females using means of the four external 
and 10 cranial dimensions as character 
states; the coefficient of cophenetic cor- 
relation is 0.714. The 13 OTU's (corre- 
sponding to the 13 grouped localities 
shown in figure 8 ) cluster into five major 
groups, which are separated by correla- 
tions of zero or negative values. Clusters 
grouped females as follow: 1) localities 
1 (N. f. baileyi) and 10 (N. f. attwateri 
from southeastern Oklahoma); 2) local- 
ities 2 and 3 (N. f. campestris); 3) local- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



101 



ities 4 (campestris), 5, 6, and 7 (attwa- 
teri from Kansas); 4) localities 8, 11, and 
12 (attwateri from western Oklahoma 
and Texas); and 5) localities 9 (attwa- 
teri from northeastern Oklahoma) and 13 
(A 7 . /. rubida from southeastern Texas). 
The coefficient of cophenetic correlation 
between the distance phenogram and the 
respective matrix is 0.831 for the 13 sam- 
ples of florid ana females. As shown in 
figure 21, four major clusters emerged; 
the least distance between two major 
clusters is 1.35. 

The proportional relationships of 
campestris females indicate that speci- 
mens from Colorado and Nebraska are 
most like other campestris from western 
Kansas; but because of differences in size, 
they are placed with attwateri in the dis- 
tance phenogram. The large size of fe- 
males from north-central Kansas (local- 
ity 5) results in the separation of these 
rats from other attwateri females in the 
distance phenogram. The correlation in 
size between sample means of attwateri 
females from northeastern Oklahoma and 



those of rubida from southeastern Texas 
was unexpected. 

The correlation phenogram for flori- 
dana males has a coefficient of cophenetic 
correlation of only 0.699. Four major 
clusters are separated from each other 
by correlations of -0.02 or less. N. f. 
campestris from localities 2 and 3 are in 
the same cluster with Ijaileyi. The sec- 
ond cluster includes attwateri from Kan- 
sas, campestris from locality 4, and 
attwateri from the western sample in 
Oklahoma. The two samples of attwateri 
from eastern Oklahoma (9 and 10) are 
placed in the third cluster with samples 
12 (southern locality of attwateri in 
Texas) and 13 (rubida). The sample of 
attwateri from locality 11 is alone in the 
fourth group, but anastomoses with clus- 
ter three before these join the first two 
clusters. The distance phenogram, which 
has a coefficient of cophenetic correlation 
of 0.816, has four clusters separated by 
a distance of 1.25 or more (Fig. 21). 

The most noteworthy differences in 
the two phenograms for floridana males 



1 

2 

6 

8 

9 

10 

3 

4 

7 

11 

12 

■ 5 

13 



B 



r 



-10 



rC 



3 

4 

5 

8 

- 7 

-12 

-13 



1.89 



1.29 



0.69 



2.01 



1.41 



0.89 



Fig. 21. Phenograms of UPGMA cluster analyses based on distance coefficients comparing stand- 
ardized means of 14 mensural characters for 13 grouped localities of Neotoma floridana: A — females; 
B — males. See text for coefficients of cophenetic correlation and see figure 8 for geographic areas 
included within the coded localities. 



102 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



involves the placement of rats from local- 
ities 3, 11, and 13. Based on correlations, 
sample 3 is most like samples 1 and 2, 
sample 11 is most distinctive, and sample 
13 is similar to sample 12. When the 
emphasis is on differences (distance), 
sample 3 is most like the larger attwateri, 
sample 11 is similar to sample 9 and 
other small attwateri; sample 13 is unlike 
any other sample. 

The first three principal components 
account for 84.4 percent and 78.1 percent 
of the total variation for females and 
males, respectively. Percent variation in 
each component for females and males, 
respectively, is 63.4 and 48.6 in the first, 
14.5 and 15.8 in the second, and 6.5 and 
15.7 in the third. The 3-D perspective 
drawings of projections of OTU's (the 
13 samples ) onto the first three principal 
components are shown in figure 22 for 
both sexes. 

The 3-D projection for females is 
reminiscent of the cluster relationships 
seen in the distance phenogram; the same 
four basic groups obtain. Samples 5 and 
13 are relatively isolated. Large campes- 
tris (3 and 4) and large attwateri (7, 11, 
and 12) are situated relatively close, and 
baileyi and smaller campestris are near 
the samples of small attwateri. The mini- 
mally connected network shows the three 
samples of campestris (2-4) intercon- 
nected and connecting to the cluster of 
smaller-sized females through sample 2 
and the cluster of larger-sized females 
through sample 4. Within the cluster of 
"small" rats, baileyi is most distinct and 
is connected to the rest of the samples 
in the cluster through sample 10. 

The 3-D projection of floridana males 
also bears a strong resemblance to the 
respective distance phenogram. In the 
projection, sample 1 (baileyi) connects 
through sample 2 to the cluster of large 
attivateri and campestris. The group of 
smaller attwateri connects to the "large" 
group through sample 8. IV. /. rubida is 
farthest separated from other OTU's and 
connects to the group of larger rats 
through sample 12, which is connected 
to sample 8. Thus, sample 8 appears to 



be more or less intermediate, serving to 
interconnect the various clusters. 

On the basis of mensural characters, 
sample 13 (rubida) is the only sample 
that clearly and consistently is distinct. 
The females in sample 5 (north-central 
Kansas) evince distinct differences from 
either attwateri or campestris, and ap- 
pear to be nearly as distinct as rubida; 
this relationship is not seen in the com- 
parison of males. The three samples of 
campestris do not form a closely allied 
group. In attwateri, a tendency exists 
toward one cluster of smaller woodrats 
and a second of larger woodrats. Geo- 
graphically, however, localities from 
which specimens of the two "groups" 
originated are such that populations of 
"small" and "large" rats are interspersed. 
Animals from locality 12 (previously the 
only locality from which specimens were 
assigned attwateri) are much like mem- 
bers of the "large" group of other attwa- 
teri (previously osagensis) and do not 
resemble rubida. 

Neotoma micropus and Neotoma an- 
gustipalata. — Neotoma angustipalata is 
treated with samples of N. micropus in 
all CLSNT analyses. These two taxa 
were combined because, on geographic 
grounds, it appeared that angustipalata 
might be a subspecies of micropus 
(Hooper, 1953:10; Alvarez, 1963:453) 
and that N. angustipalata and N. m. 
planiceps might best be considered as a 
single taxon. 

The coefficient of cophenetic correla- 
tion between the correlation phenogram 
and matrix for the 15 samples of N. mi- 
cropus and one sample of N. angusti- 
palata females is 0.835. Two major clus- 
ters are formed. The first consists of one 
subcluster of samples A (Colorado and 
Cimarron County, Oklahoma), F (Texas 
panhandle) and E (New Mexico) and a 
second subcluster that joins the first at 
a correlation of 0.05. This subcluster in- 
cludes samples J (Big Bend area of 
Texas), K (non-coastal southern Texas), 
H (southwestern Oklahoma), I (north- 
eastern Texas), B (southwestern Kansas 
and adjacent Oklahoma panhandle), D 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



103 





Fig. 22. Three-dimensional perspective drawings of the projections of 13 samples (OTU's) of 
Neotoma floridana onto the first three principal components based on correlation among 14 mensural 
characters: A — females; B — males. Dashed lines between OTU's illustrate the minimally intercon- 
nected networks computed from the respective among-OTU distance matrices. See text for per- 
centages of variation in each component and figure 8 for geographic areas included within the 
coded localities. 



( south-central Kansas ) , C ( south-central 
Kansas just west of locality D and ad- 
jacent Oklahoma panhandle), and G 
(northwestern Oklahoma south of local- 
ity D ) . The second major cluster is com- 



posed of samples L (southern coastal 
Texas), R (N. angustipalata), M (Coah- 
uila and Nuevo Leon), N (N. m. mic- 
ropus from northern Tamaulipas) and P 
( N. m. micropus from southern Tamauli- 



104 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



pas). In essence, this phenogram places 
all samples of N. m. canescens except 
two ( M and L ) in a single major cluster 
that is not highly correlated internally. 
The other major cluster includes an array 
of taxa including N. angustipalata, both 
samples of N. m. micropus, and two sam- 
ples ( one of large woodrats and the other 
of small woodrats) of N. m. canescens. 
The distance phenogram (Fig. 23) 
for micropus and angustipalata females 
has a correlation of 0.820 with the dis- 
tance matrix. If a distance of 1.25 or 
greater is considered to separate major 
clusters, four were computed. The pat- 
tern of clustering seen in the distance 
phenogram corresponds quite well to the 
taxonomic arrangement of these two spe- 
cies. That is, angustipalata appears most 
distinct and is recognized at the specific 



level, and the two samples of N. m. mi- 
cropus are distinct from those of other 
micropus, but closer to them than to 
angustipalata. The most variable sub- 
species, canescens, consists of two groups 
that correspond, with a few exceptions, 
to the previously recognized boundaries 
of N. m. canescens and N. m. micropus. 
Nevertheless, both clusters include sam- 
ples of woodrats previously assigned to 
the two different names. 

The coefficient of cophenetic correla- 
tion for the correlation phenogram of 17 
samples of micropus males and one sam- 
ple of angustipalata males is relatively 
high (0.849) for a correlation pheno- 
gram. Of the three major clusters ( sepa- 
rated by a correlation of -0.05 or less), 
one contains the two samples from New 
Mexico (E and O); the second, joins 



B 







L- 
















— [ 










" |C 









l ~~ 



















A 

M 
E 
J 
K 
B 
C 
F 
G 



- L 
D 
N 
P 
R 



~ HI 



i-C 



C 
D 

L 
H 
B 



J 
K 
N 
P 

M 
E 
O 

Q 
R 



2.065 



1.365 



0.665 



2.20 



1.40 



0.60 



Fig. 23. Phenograms of UPGMA cluster analyses based on distance coefficients comparing stand- 
ardized means of 14 mensural characters for 16 (females) and 18 (males) grouped localities of Neo- 
toma micropus (A-Q) and N. angustipalata (R): A — females; B — males. See text for coefficients of 
cophenetic correlation and figure 8 for geographic areas included within the coded localities. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



105 



the first before these two join the third, 
and includes all samples of canescens 
from localities in the United States ex- 
cept E, O, and K. The third major 
cluster contains two distinct subgroups 
that join at a correlation of only 0.12. 
In the first subgroup are samples K and 
M (both N. m. canescens). In the other, 
samples N and P (both N. m. micropus) 
join at a correlation of 0.62, and Q (N. 
m. planiceps) joins R (N. angustipalata) 
at 0.800. These two couplets anastomose 
at a correlation of 0.45. This phenogram 
illustrates the high proportional simi- 
larities between angustipalata and plani- 
ceps, the affinities between the two sam- 
ples of the subspecies micropus, and 
the complete intermixing of samples of 
IV. micropus from the northern part of 
the range where two subspecies pre- 
viously were recognized. 

The distance phenogram for this 
series of male samples is shown in figure 
23. The coefficient of cophenetic corre- 
lation between the phenogram and its 
matrix is 0.840. There is a marked ten- 
dency in both phenograms of males for 
most samples of IV. m. canescens ( excep- 
tions were samples E, O, and M, espe- 
cially) to cluster together; the two sam- 
ples of N. m. micropus are always more 
similar to one another than either is to 
any other sample, but woodrats in sam- 
ple M appear to be as near micropus as 
canescens. The correlation between N. 
angustipalata and N. m. planiceps is re- 
markably high, indicating proportional 
similarity. Although available material 
indicates that ajigustipalata is much 
larger than planiceps, it must be remem- 
bered that the only known specimen of 
planiceps is a young adult. The simi- 
larities of samples O and E from New 
Mexico are noteworthy because speci- 
mens in sample O previously were recog- 
nized as a distinct subspecies, N. m. 
leucophea. 

Principal components analysis for fe- 
males extracted a total of 86.2 percent of 
the variation (components one to three 
composed of 55.1, 24.3, and 6.8 percent, 
respectively). The 3-D drawing of 



OTU's projected onto the first three com- 
ponents is shown in figure 24. Sample 
R, as expected, is most distinct and iso- 
lated from other OTU's, especially on 
the second component. Sample M serves 
as the intermediate through which sam- 
ples of N. m. micropus connect with 
samples of N. m. canescens. The latter 
are separated on the first component 
(which is highly correlated with size), 
but were similarly placed on the second 
component. 

The first three components for males 
contain 56.1, 27.3, and 7.6 percent of the 
total variation, respectively, for a total 
extraction of 91.0 percent. The 3-D pro- 
jection (Fig. 24) of OTU's onto these 
components placed angustipalata as the 
most distinct OTU, connected to mi- 
cropus through sample L. Neotoma mi- 
cropus planiceps is the only other rela- 
tively distinct OTU, but it is separated 
much less on component two than is 
angustipalata; planiceps connects to 
other samples of micropus through sam- 
ple P. In the projection, as in the dis- 
tance phenogram, sample M appears to 
share as many affinities with the subspe- 
cies micropus as with canescens. 

The 3-D projections of both sexes 
elucidate the distinctiveness of angusti- 
palata, and to a lesser degree, the dis- 
tinctiveness of planiceps. The affinities 
of sample L with the northern samples 
of large N. micropus are evident. Like- 
wise, the similarity of the two samples 
of IV. m. micropus from Tamaulipas, and 
the intermediacy of woodrats from 
Coahuila and Nuevo Leon between mi- 
cropus and canescens are shown. Finally, 
the projections document the absence of 
any distinct steps in the clinal variation 
in samples of N. m. canescens. 

Simultaneous Treatment of Three 
Species. — When all samples of N. flori- 
dana, N. micropus and N. angustipalata 
were treated simultaneously in a multi- 
variate analyses of 14 character states, 
the results are surprising. The correla- 
tion phenogram for the 29 samples of fe- 
males has a coefficient of cophenetic cor- 
relation of only 0.686, and is divided 



106 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 




M P 




Fig. 24. Three-dimensional perspective drawings of the projections of 16 (females) and 18 
(males) samples of Neotoma micropus (A-Q) and N. angustipalata (R) onto the first three princi- 
pal components based on correlations among 14 mensural characters: A — females; B — males. Dashed 
lines between OTU's illustrate the minimally interconnected networks computed from the respective 
among-OTU distance matrices. See text for percentages of variation in each component, and fig- 
ure 8 for geographic areas included within the coded localities. 



into two primary clusters separated by a 
negative correlation (-0.25). Most sur- 
prising is the intermixing of samples of 



micropus with those of floridana and the 
marked alteration of the clustering rela- 
tionships seen previously for samples of 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



107 



floridana. Although clustering of sam- 
ples of angustipalata and micropus is not 
exactly as discussed above, it is notice- 
ably less altered. The first major cluster 
contains A 7 . /. rubida, N. angustipalata, 
the samples of small N. micropus, and 
sample L. The two samples of N. m. 
micropus form a highly correlated coup- 
let ( 0.78 ) that anastomoses first with the 
sample of angustipalata. The other ma- 
jor cluster contains the remaining sam- 
ples of both species arranged into four 
subclusters. One of these consists only 
of sample 7 and another is made up of 
the three samples of smallest floridana 
(baileyi and attwateri samples 9 and 10). 
The two remaining subclusters include 
samples of floridana and micropus ar- 
ranged such that neither species appears 
to be distinct. 

Some geographically contiguous sam- 
ples tend to cluster together and there 
is a general tendency of samples of each 
species to cluster in the same subgroups. 
However, the deviations from these ten- 
dencies are so great as to cause this phe- 
nogram to bear little resemblance to the 
classification used herein or to the gen- 
eral conclusions based on univariate 
analyses. 

The placement of OTU's in the dis- 
tance phenogram for all samples of fe- 
males (Fig. 25) is more nearly congru- 
ent with previously discussed pheno- 
grams, 3-D projections, and the classifi- 
cation that I have proposed. Although, 
some samples of floridana and micropus 
appear together in one of the four major 
clusters, in only one instance is a sample 
of one species placed more closely to a 
sample of the other than to a conspecific 
sample. This exception was sample D. 
The coefficient of cophenetic correlation 
between phenogram and matrix is 0.736; 
the first bifurcation is at a distance of 
1.86 and each cluster thereby formed is 
composed of two major subclusters. 

The correlation phenogram for the 
31 samples of males closely resembles 
the two correlation phenograms for males 
discussed above. It has a coefficient of 
cophenetic correlation of 0.720 to the 



correlation matrix. Three clusters are 
separated from each other by negative 
correlations. The most distinct of these 
contains N. angustipalata in a couplet 
with N. m. planiceps, N. f. baileyi in a 
couplet with N. f. campestris from local- 
ity 2, a couplet with the two samples of 
N. m. micropus, and lastly a couplet with 
two geographically contiguous samples 
of N. m. canescens (K and M). The re- 
maining two clusters are more highly 
correlated than either is to the first. Sam- 
ples from the five most southern localities 
of N. floridana (9, 10, 11, 12 and 13) are 
included in one cluster with sample H 
(N. m. canescens from southwestern 
Oklahoma). In the third, sample 4 
(campestris) forms a couplet with sam- 
ple A (canescens) in a subcluster includ- 
ing sample L and northern samples of 
canescens. Samples E, J, and O (canes- 
cens from New Mexico and adjacent 
southwestern Texas) form another sub- 
cluster with sample 3 (campestris). In 
the remaining subcluster, four samples 
of attwateri (5, 6, 7, and 8) are placed 
near a sample of canescens ( I ) . 

Those OTU's that form highly corre- 
lated couplets or clusters when treated 
in the restricted samples usually tend to 
cluster when the three species are treated 
simultaneously. Similarly, samples that 
appear highly distinctive when treated in 
conspecific groupings usually retain at 
least partial distinctness when all sam- 
ples are treated together. However, 
those samples that are neither especially 
distinct nor highly correlated when 
treated conspecifically, usually are un- 
predictable in their clustering relation- 
ships when the number of samples and 
total amount of variation are increased. 

The distance phenogram for 31 sam- 
ples of males, which has a coefficient of 
cophenetic correlation of 0.765, is shown 
in figure 25. Three major clusters sepa- 
rated by a distance of 1.5 or more are 
evident. The two phenograms for all 
samples of males of both species indicate 
the distinctness of angustipalata as com- 
pared to micropus and floridana. The 
size relationships of micropus and flori- 



108 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



A 
F 
M 
E 
J 
K 
N 
P 
B 
C 
G 
H 
I — I 



C 






6 

8 

9 

10 



- 1 

- 2 

- L 
D 

- 3 

- 4 

- 7 
-11 

12 



-13 



1.925 



1.225 



0.525 



B 



rC 




2.16 



1.36 



0.56 



Fig. 25. Phenograms of UPGMA cluster analyses based on distance coefficients comparing stand- 
ardized means of 14 mensural characters for 29 (females) and 31 (males) grouped localities of Neo- 
toma floridana (1-13), N. micropus (A-Q), and N. angustipalata (R): A — females; B — males. See 
text for coefficients of cophenetic correlation, and figure 8 for geographic areas included within 
the coded localities. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



109 



dana overlap sufficiently that mensural 
characters alone do not segregate them 
into separate major clusters. The larger 
micropus tend to form eonspecific group- 
clusters which are near group-clusters of 
larger floridana; smaller micropus tend 
to cluster separately from samples of 
smaller floridana. On some occasions 
samples A, F, and K, which are from 
localities geographically intermediate be- 
tween large micropus and small micro- 
pus, clustered with the large micropus 
and smaller floridana; on other occasions, 
they clustered with the small micropus. 

The 3-D projections of all samples of 
females and of all samples of males are 
shown separately in figure 26. The mini- 
mally connected networks were com- 
puted but have been omitted from the 
drawings to enhance determination of 
relative positioning of the OTU's. Pro- 
jection of 29 OTU's on the three com- 
ponents for females results in a more 
nearly complete separation of samples of 
micropus and floridana than is seen in 
the two phenograms for females. Be- 
cause each OTU is necessarily connected 
by the network directly to at least one 
other OTU and all OTU's are intercon- 
nected, it is necessary that at least one 
connection exist between a sample of 
micropus and one of floridana. In this 
instance two such connections exist. 
Sample 9 (northeastern Oklahoma flori- 
dana ) connects to sample H ( southwest- 
ern Oklahoma micropus) , and sample D 
(south-central Kansas micropus) con- 
nects to sample 7 (southeastern Kansas 
floridana). All samples of N. micropus 
are directly or indirectly interconnected 
without involving a sample of floridana, 
but floridana samples 1, 2, 6, 8, 9, and 
10 are connected to other samples of 
floridana through a series of samples of 
micropus (9 to H to I to G to C to D 
to 7). N. angustipalata connects only to 
N. m. canescens sample L. 

In the 3-D projection of males, only 
the minimal number (two) of inter- 
specific connections were computed. 
Sample 9 is connected to sample H to 
join micropus and floridana. Neotoma 



angustipalata joins only to sample 13, 
N. f. rubida. In the unconnected draw- 
ing (Fig. 26), it can be seen that several 
samples of micropus overlapped samples 
of floridana on the first component. The 
connections of these micropus samples 
were G to A, and B to C to D to L. In 
the 3-D projections for females there are 
two distinct groups of floridana samples. 
A tendency exists toward a similar sepa- 
ration on the projections for males, but 
it is less distinctly defined. 

Multivariate Analyses of Size, Color, 
and Qualitative Cranial Characters 

Following multivariate analyses of 
the 14 mensural characters discussed 
above, similar analyses were conducted 
using the same 14 mensural characters 
together with four color reflectance 
scores and three, scored, qualitative cra- 
nial characters. Thus a total of 21 char- 
acters was available for each sex of each 
sample. Instead of analyzing sexes sepa- 
rately as above, the 21 characters for 
each were pooled and used as 42 char- 
acters for each sample. For the two sam- 
ples composed only of a single male spec- 
imen each ( O and Q ) , the 21 characters 
were treated twice, once with those for 
males and once with those for females. 
Measurements of bacula or other charac- 
ters were not included because data for 
one or more samples were not available. 

The results obtained depict the rela- 
tionships of the various OTU's in a more 
comprehensive way than do interpreta- 
tions based on separate analyses ( by sex ) 
of mensural characters alone. However, 
an understanding of the relationships 
based only on mensural characters is 
necessary to understand overall geo- 
graphic trends in size and to determine 
relative distinctness or indistinctness of 
various taxa based solely on dimensions 
and relative proportions. 

Neotoma floridana. — CLSNT based 
on 42 characters as described above us- 
ing the 13 samples of Neotoma floridana 
yielded results congruent with the pres- 
ent classification. The coefficient of co- 
phenetic correlation is 0.727 between the 



110 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 




Fig. 26. Three-dimensional perspective drawings of the projections of 29 (females) and 31 
(males) samples of Neotoma floridana (1-13), N. micropus (A-Q), and N. angtistipalata (R) onto 
the first three principal components based on correlations among 14 mensural characters: A — fe- 
males; B — males. See text for percentages of variation in each component and figure 8 for geo- 
graphic areas included within the coded localities. 



correlation phenogram ( Fig. 27 ) and the 
matrix from which the phenogram was 
computed. Two major clusters are sepa- 
rated by a correlation of -0.24. This 
phenogram, which was computed from 
data on males and females, is remarkably 
unlike the correlation phenogram dis- 
cussed above for floridana females. 
Despite several minor alterations, it re- 
sembles the correlation phenogram of 
floridana males. The relatively high cor- 
relation between N. f. attwateri and N. 
f. rubida is indicative of proportional 
similarity of the two, and possibly re- 
flects intergradation between the two in 
southeastern Texas. The two samples of 
N. f. campestris from western localities 



(2 and 3) are also relatively highly cor- 
related. Characteristics of campestris 
from locality 4 are more highly correlated 
with those of attwateri than with other 
samples of campestris. In this pheno- 
gram, balieyi appears more like cam- 
pestris than attwateri. 

The distance phenogram (Fig. 27) 
for floridana is characterized by several 
major shifts in the positioning of OTU's 
relative to that seen in the correlation 
phenogram. These shifts affect primarily 
the non-attwateri samples; samples 6, 8, 
9, and 10 remain relatively close to- 
gether and samples 7 and 11 remain to- 
gether. Sample 12, which is highly corre- 
lated to 13, is placed with two other 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



111 



samples of attwateri, 7 and 11, in the 
distance phenogram. Samples 4 and 5 
are removed from a correlation cluster 
with the "large" attwateri samples and 
placed with sample 3. Sample 3 is clus- 
tered with samples 1 and 2 in the correla- 
tion phenogram. These two samples ( 1 
and 2) remain together, but are sepa- 
rated by an appreciable distance (1.15). 
Sample 13 (rubida) is the most distinct 
sample in the distance phenogram. The 
coefficient of cophenetic correlation for 
this phenogram is 0.769. 

The first five principal components 
were extracted in computations involv- 
ing 42 characters. The percent variation 
in these is 36.6, 22.6, 12.2, 9.8, and 5.1 
for a total of 86.3 percent; 71.4 percent 
of the variation is in the first three com- 
ponents. The 3-D projection of the 13 
OTU's on the first three components 
(Fig. 28) and the minimally connected 
network ( not figured ) indicate that sam- 
ple 7 is intermediate between other sam- 
ples in many respects; five independent 
subgroups interconnect by direct attach- 
ment to sample 7. One subgroup consists 



only of sample 5 (sample 5 and 7 are 
the two most distant directly-connected 
samples of attwateri) and another only 
of sample 11. A third subgroup includes 
sample 12 relatively close and sample 
13 at a considerable distance. Another 
includes the four samples of small-sized 
attwateri and the last includes the three 
samples of campestris and one of baileyi. 
The latter "lineage" is especially interest- 
ing because neither the correlation nor 
the distance phenogram placed the three 
samples of campestris together. More- 
over, the sequence of the connections is 
4 to 3 to 2 to 1; geographically this cor- 
responds east-west for the three samples 
of campestris. The significance of the 
apparent relationship between baileyi 
and campestris will be discussed below 
with respect to zoogeographic history. 

Neotoma micropus and Neotoma 
angustipalata. — The correlation pheno- 
gram for the 18 samples of N. micropus 
and N. angustipalata (Fig. 29) has a 
coefficient of cophenetic correlation of 
0.815 and consists of three major clusters. 
Placement of the five samples of small 



- 1 
-2 

- 3 

- 6 

- 8 

- 9 
-10 
-4 

- 7 

- 5 
-11 
-12 
-13 



B 









r-C 



9 
10 

7 
11 
12 

3 
- 4 

5 
13 



-0.30 



0.10 



0.50 



1.85 



1.35 



0.85 



Fig. 27. Phenograms of UPGMA cluster analyses based on correlation (A) and distance (B) 
coefficients comparing standardized means of 42 mensural, color, and scored cranial characters for 
13 geographic localities of Neotoma floridana. See text for coefficients of cophenetic correlation, and 
figure 8 for geographic areas included within the coded localities. 



112 MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 

.0" 




II 




0' 



. Q c 



Fig. 28. Three-dimensional perspective drawings of the projections of 13 samples (OTU's) of 
Neotoma floridana (A) and 18 samples (OTU's) of N. angustipalata and N. micropus (B, com- 
pare with Fig. 30) onto the first three principal components based on correlations among 42 mensural, 
color, and scored cranial characters. Dashed lines between OTU's illustrate the minimally intercon- 
nected networks computed from the respective among-OTU distance matrices. See text for percent- 
ages of variation in each component, and figure 8 for geographic areas included within the coded 
localities. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



113 



and pallid woodrats from New Mexico, 
western Texas, Coahnila, and Nuevo 
Leon in a single cluster seems reasonable 
on an a priori visual basis. The inter- 
mediacy of specimens from locality K 
is indicated by the low correlation (0.16) 
between that sample and other samples 
from eastern and northern localities. As 
in other phenograms reflecting both cor- 
relation and distance, samples N and P 
(N. m. micropus) cluster separately from 
samples of N. m. canescens. Although 
specimens of canescens from locality L 
and specimens of angustipalata do not 
resemble each other in general appear- 
ance, these two samples are similar pro- 
portionally. However, as previously dis- 
cussed, they do not cluster together when 
distances are emphasized. 

The distance phenogram (Fig. 29) 



for these 18 samples of woodrats is some- 
what unique in that there are few small 
group-clusters anastomosing to form 
larger clusters; instead, there is a high 
incidence of individual OTU's sequen- 
tially joining clusters composed of less 
distinct OTU's. The coefficient of co- 
phenetic correlation between the pheno- 
gram and the distance matrix is 0.891. 

The distinctness of angustipalata is 
again substantiated by the distance phe- 
nogram, and N. m. planiceps appears 
more distinct than indicated by results 
of other analyses. It must be remem- 
bered, however, that the latter "sample" 
consists of a single young adult male. 
This consideration is especially important 
because characters of that one specimen 
have been used for both males and fe- 
males. Nevertheless, the results indicate 



£ 



t 



C 



E 
O 
M 
F 
J 
L 
R 
N 
P 
Q 



B 



ri 



L 
E 

F 
J 

M 

-N 

P 

Q 
R 



-0.24 



0.16 



0.56 



2.135 



1.435 



0.735 



Fig. 29. Phenograms of UPGMA cluster analyses based on correlation ( A ) and distance ( B ) co- 
efficients comparing standardized means of 42 mensural, color, and scored cranial characters for 18 
geographic localities of Neotoma micropus (A-Q) and N. angustipalata (R). See text for coeffi- 
cients of cophenetic correlation, and figure 8 for geographic areas included within the coded localities. 



114 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



that planiceps is not especially similar to 
samples of either N. m. micropus, or 
N. m. canescens and should be recog- 
nized as a distinct subspecies until more 
specimens are available. Also, planiceps 
did not cluster with angustipalata as has 
been seen in some other analyses. 

Clustering relationships indicate that 
there is slight morphological basis for 
recognizing two subspecies (as has been 
done in the past) for the woodrats that 
I have considered collectively under the 
name N. m. canescens. Of the six sam- 
ples most closely clustered, three pre- 
viously were assigned to one subspecies 
and three to another. Furthermore, 
placement of samples F, J, and K in the 
various phenograms and 3-D projections 
together with results of univariate analy- 
ses clearly indicate that any subspecies 
boundary merely would divide the wood- 
rats into two groups from some arbitrarily 
selected place within a series of partially 
discordant clines. 

Principal components analysis of 
these 18 samples considered 87.2 percent 
of the total variation when five compo- 
nents were extracted. Percents of varia- 
tion in the first five components con- 
sidered sequentially are 37.2, 30.3, 9.5, 
5.7, and 4.5. When projected onto the 
first three components (Fig. 28), which 
contain 77 percent of the total variation, 
the results are similar to those seen in 
the distance phenogram. The impression 
of close relationship among the six sam- 
ples of N. rn. canescens from northern 
and eastern localities in the range is 
maintained; samples D, L, and K con- 
nect directly to this "cluster" but do not 
connect directly to each other. Sample 
R (angustipalata) constitutes the most 
distinctive OTU and connects only to 
sample L. Sample M, which serves as 
an "intermediate", connects to sample 
K, then serves to connect samples E and 
O on one "lineage", F and J on a second, 
and N on a third. Sample N connects 
first to sample P and at a much greater 
distance to sample Q (planiceps). 

The placement of OTU's and the con- 
nections shown by the minimally con- 



nected network of the 3-D projection for 
N. micropus is congruent with the no- 
menclatorial arrangement of these wood- 
rats proposed here. Figure 30 illustrates 
the placement of OTU's on the first and 
second components better than can be 
seen in the 3-D drawing ( Fig. 28 ) . This 
figure represents a two-dimensional scat- 
ter-diagram of the OTU's on these two 
components; the three-dimensional mini- 
mally interconnected network has been 
added together with the distance coef- 
ficients from the original distance matrix 
for all directly connected OTU's. In 
viewing this figure it should be noted 
that discrepancies between apparent and 
computed distances separating OTU's 
are accounted for in the third dimension, 
which is illustrated in figure 28. 

Neotoma angustipalata, recognized as 
a distinct species, is well separated to the 
left and to the front of the plotting sur- 
face on figure 30. Furthermore, angusti- 
palata is not connected to any of the 
samples of micropus from geographically 
contiguous localities. N. m. planiceps is 
well separated from all other OTU's, 
especially on the second component, and 
connects only to a sample of N. in. mi- 
cropus from adjacent Tamaulipas. The 
two samples of N. m. micropus are 
closely placed on the first and second 
principal components and are situated in 
a position nearly intermediate between 
the nearest OTU's, representing canescens 
and planiceps. They connect directly to 
planiceps and to the sample of canescens 
from adjacent Nuevo Leon and Coahuila. 
The remaining OTU's all representing 
samples of canescens, are placed in a 
single "cluster", showing the trend to- 
ward smaller individuals in the south- 
western parts of the range (samples E, 
O, J, and M) and the intermediacy of 
samples F and K. 

Simultaneous Treatment of Three 
Species. — The correlation phenogram 
that was computed when the 42 charac- 
ter states of the 31 samples (all three 
species ) of woodrats were treated simul- 
taneously is shown in figure 31. This 
phenogram has a coefficient of cophe- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



115 



II 















0.56 


^C 42 

' .4rT /t>- 74 








0L 


0.94 


G^ ' j^A \ loo 
0.49 \^| 






/ 




. 0.66 


w 




/ 
/ 

/\ 

/ 1.58 






"-.. i/\ #° 

i - 0.81 
/ 1.07 


O'R 








N/0.66 

i 
/ 
i 
i 

/ 

i 

,' 1.31 

1/ 

i 
i 
i 
i 

i 
i 



Fig. 30. Two-dimensional drawing of the projections of 18 samples ( OTU's) of Neotoma micropus 
(A-Q) and N. angnstipalata (R) onto the first two principal components based on correlations among 
42 mensural, color, and scored cranial characters. Dashed lines between OTU's illustrate the min- 
imally interconnected networks computed from the among-OTU distance matrices. Distance coeffi- 
cients from the distance matrix are given for each pair of directly connected localities. See text 
for percentage of variation in each component, and figure 8 for geographic areas included within the 
coded localities (nominal taxa are shown with distinctive symbols). This figure should be compared 
with figure 28B. 



netic correlation of 0.863 with the corre- 
lation matrix. The major separation at a 
correlation of -0.325 separated all sam- 
ples of N. floridana into one cluster and 
all samples of JV. micropus with the 
single sample of N. angustipalata into 
the other. This phenogram corresponds 
well with results seen in 3-D projections 
and in distance phenograms for both spe- 



cies, with the obvious exception of the 
placement of N. f. rubida. 

The distance phenogram (Fig. 31) 
for computations on samples of the three 
species simultaneously has a coefficient 
of cophenetic correlation of only 0.714 
to the distance matrix. This is unusually 
low compared to the coefficient (0.863) 
for the correlation phenogram and ma- 



116 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



c: 





HZ 




HZ 1 

I — 11 

c 



HZ 



11 

12 

13 

6 

8 

9 

10 



-0.325 



0.175 



0.675 



B 



HZ 



9 
10 
• 7 
•11 
•12 
- 2 







r HZ 

























H 
D 

K 

L 
E 
M 

F 
J 
N 
P 
Q 



1.74 



1.14 



0.54 



Fig. 31. Phenograms of UPGMA cluster analyses based on correlation (A) and distance (B) co- 
efficients comparing standardized means of 42 mensural, color, and scored cranial characters for 31 
geographic localities of Neotoma ftoridana (1-13), N. micropus (A-Q), and N. angustipalata (R). 
See text for coefficients of cophenetic correlation, and figure 8 for geographic areas included within 
the coded localities. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



117 



trix; normally the highest coefficient is 
for distance. Four major clusters are 
seen in the distance phenogram. At the 
first bifurcation, all samples of micropus 
are placed together in two clusters. Neo- 
toma angustipalata forms a third "clus- 
ter" by itself that connects at a distance 
of 1.53 to the fourth major cluster ( com- 
posed of the 13 samples of N. floridana). 
Within the floridana cluster, two OTU's 
(5 and 13) are relatively distinct; this 
was expected for sample 13 (rubida) but 
I anticipated that sample 5 (attwateri 
from north-central Kansas ) would cluster 
either with other samples of attwateri or 
with samples of campestris. The three 
samples of campestris form a distinct 
cluster, and baileyi appears relatively dis- 
tinct, but joins the samples of smaller 
attwateri before they are joined by the 
samples of larger attwateri. 

Of the two major clusters of N. mi- 
cropus, one consists of the 14 samples of 
N. m. canescens and the other of the two 
samples of N. m. micropus along with 
N. m. planiceps. The two samples of 
N. m. micropus join at a distance of 0.63, 
and planiceps joins that couplet at a dis- 
tance of 1.02. In the distance phenogram 
shown in figure 29, canescens from local- 
ity M appears more like samples of N. 
m. micropus than like other samples of 
canescens; in the large phenogram, sam- 
ple M is placed with other samples of 
canescens. In both phenograms, the 
small, pallid woodrats from New Mexico, 
western Texas, and adjacent Mexico tend 
to form a relatively homogeneous and 
distinct subgroup. This relationship is 
seen also when OTU's are projected onto 
principal components. I considered the 
possibility (see introductory remarks in 
the account of N. micropus above) of 
applying the available name N. m. leu- 
cophea to those woodrats from localities 
E, F, J, M, and O. However, there are 
no indications of well marked "steps" in 
clines of variation, and no apparent past 
or present geographic or physiographic 
barriers. Because there seems to be no 
way to designate a meaningful boundary 
between the two potential taxa, this ar- 



rangement was rejected. 

Principal components analysis on the 
character correlation matrix extracted 
50.1, 15.9, 7.8, 6.6, and 3.9 percent of the 
variance for the first five principal com- 
ponents, respectively. Of this, 73.8 per- 
cent is in the first three components. A 
three-dimensional drawing of the 31 
OTU's projected onto the first three com- 
ponents is shown in figure 32. The mini- 
mally connected network has been omit- 
ted from the 3-D projection but is given 
in figure 33, which shows two two-dimen- 
sional scatter diagrams wherein the 31 
OTU's are projected onto components 
one and two (33A) and one and three 
(33B). The three drawings considered 
simultaneously show undistorted spatial 
relationships of the OTU's on the prin- 
cipal components and further elucidate 
the congruency between the results of 
these analyses and the nomenclatorial ar- 
rangement I have applied to the wood- 
rats. 

Samples of micropus and floridana 
are completely separated on the first 
component, although micropus sample 
L nearly overlaps floridana samples 1 
and 2. Also on the first component, 
angustipalata is placed with floridana 
and widely separated from micropus. 
Neotoma floridana rubida is placed to 
the left of other samples of floridana on 
that component, and the samples of small 
southwestern N. m. canescens are placed 
to the right of the samples of larger 
northern and eastern canescens. 

On the second component, samples of 
N. f. campestris are separated from other 
samples of floridana. Sample 5 (attwa- 
teri from north-central Kansas) is be- 
tween samples of campestris and those 
of other attwateri, but on a tangent rela- 
tive to the first component. This sample 
of attwateri (5) and the sample of baileyi 
( 1 ) both are connected to other samples 
of attwateri, but not to samples of cam- 
pestris or to each other. In part, this pro- 
jection implies that baileyi might best be 
considered as the same taxon as attwateri 
( baileyi is the oldest available name and 
would be the valid name for all if this 



118 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



Q 10 Q 




Fig. 32. Three-dimensional perspective drawing of the projections of 31 samples (OTU's) of 
Neotoma floridana (1-13), N. micropus (A-Q), and N. angustipalata (R) onto the first three princi- 
pal components based on correlations among 42 mensural, color, and scored cranial characters. See 
text for percentages of variation in each component, and figure 8 for geographic areas included 
within the coded localities. This figure should be compared with figure 33. 



was done). Neotoma angustipalata is 
distinctly separated from samples of flori- 
dana on the second component. When 
samples of N. micropus are considered, 
it can be seen that the second component 
separates samples P and N (N. m. mi- 
cropus) and sample Q (planiceps) in one 
direction and sample E (canescens from 
the Texas panhandle) in the other; re- 
maining samples are similarly placed on 
these two components. 

The third component further sepa- 
rates angustipalata from all samples of 
floridana and clearly demonstrates the 
distinctiveness of micropus samples D 
and L from floridana samples 1, 2, 6, and 
9. On both the first and second compo- 
nents, these six samples are placed in 
relatively close proximity. From the dis- 
tance matrix, it can be seen that the 
separation between D and 2 is 1.15, that 
between L and 8 is 1.04, that between 
L and 6 is 1.05, and that between L and 



2 (which appear especially close on the 
3-D projection) is 1.16. In the minimally 
connected network, only two intercon- 
necting lines (the minimal number) con- 
nect OTU's of different species. Neotoma 
angustipalata is connected to N. f. attwa- 
teri sample 7 at a distance of 1.58, and 
N. m. canescens sample D is connected to 
N. f. attwateri sample 8 at a distance of 
0.94. 

With the exceptions of a relatively 
high degree of distinctiveness in attwa- 
teri sample 5, the apparent affinities of 
baileyi with attwateri, and the relative 
distinctiveness of samples of canescens 
from southwestern localities, the classifi- 
cation I have employed is in accord with 
the results of this principal components 
analysis. It clearly shows that angusti- 
palata is phenetically distinct and that 
floridana and micropus are morphologi- 
cally distinct and should not be consid- 
ered conspecific. The distinctiveness of 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



119 







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120 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



N. f. campestris and N. f. ntbida as com- 
pared to contiguous samples of N. f. at- 
twateri can be seen also. Similarly, N. m. 
micropus and IV. m. planiceps are shown 
to be clearly distinct from IV. m. canes- 
cens. There appears to be some basis for 
recognition of another name (N. m. leu- 
cophea) for specimens from New Mexico, 
western Texas, and adjacent Mexico; the 
question that arises is basically a matter 
of one's concept of the limits of a sub- 
species. 

Were Neotoma floridana baileyi and 
IV. /. atticateri geographically contiguous, 
I would consider them a single taxon. 
However, baileyi clearly is isolated, and 
has been shown to share nearly equal 
affinities with campestris. Furthermore, 
it is relatively unique with respect to 
qualitative cranial characters. Therefore, 
I think it best to continue to recog- 
nize baileyi as subspecifically distinct. 
To consider those rats from locality 5 
( north -central Kansas) as a new subspe- 
cies on the basis of their uniqueness in 
the distance phenogram and 3-D projec- 
tion just discussed would be, in my esti- 
mation, a gross error. The sample from 
that area is small and there is no reason 
to believe that the population of wood- 
rats there represents a truly distinctive 
evolutionary unit. It is possible that the 
large size and apparent distinctiveness of 
woodrats from the narrow zone of sec- 
ondary intergradation between campes- 
tris and atticateri reflect some effect ( pos- 
sibly heterosis) of recent hybridization. 

There is some basis for naming as a 
distinct subspecies those large and rela- 
tively distinct populations (L) of mi- 
cropus from southern coastal Texas. They 
are different from woodrats in adjacent 
Tamaulipas (and herein are assigned to 
different subspecies), but study and sta- 
tistical analysis of all available specimens 
from southern Texas indicate that the 
pattern of variation to the north and west 
from coastal Texas is clinal and that 
woodrats from locality K (non-coastal 
southern Texas ) show varying degrees of 
intermediacy between those from locality 
L and those from localities J, I, and M. 



Discriminant Function Analysis 

Discriminant function analysis has 
been employed by Lawrence and Bossert 
( 1969 ) to distinguish dog-coyote hy- 
brids; these authors (1967) also were 
able to identify skulls of wild canids with 
this relatively sophisticated technique. 
Anderson (1969:44) conducted a pre- 
liminary discriminant analysis to dis- 
tinguish specimens of Neotoma micropus 
and N. albigula; he found that members 
of the two species could be separated 
better in this way than by factor analysis. 

I have used discriminant function 
analysis (MULDIS) to compare indi- 
vidual specimens of woodrat taxa as fol- 
lows: Neotoma floridana baileyi with N. 
f. atticateri; N. f. campestris with IV. /. 
atticateri; N. f. campestris with IV. m. 
canescens; and N. f. atticateri with N. 
m. canescens. In some cases, specimens 
from geographically intermediate sam- 
ples, suspected hybrids, or laboratory- 
bred hybrids were included as a third 
group for comparison with reference 
samples. In one instance, only the ref- 
erence samples were compared. These 
analyses were conducted to determine: 
1 ) if the nominal taxa are sufficiently and 
consistently distinctive at the level of the 
individual in the 10 cranial dimensions, 
four color reflectance scores, and three 
scored qualitative characters so that dis- 
criminant analysis could distinguish 
members of the different taxa by differ- 
entially weighting characters to accentu- 
ate existing differences; 2) if known hy- 
brids between floridana and micropus 
could be distinguished by use of the dis- 
criminant technique; 3) if discriminant 
scores of suspected hybrid individuals 
would be similar to those of known hy- 
brids; and 4) if a series of discriminant 
multipliers could be calculated from 
identified reference samples so that fu- 
ture material could be identified by mul- 
tiplying the values of the same 17 char- 
acters by the discriminant multipliers 
and then summed to compare discrim- 
inant scores. The characters used in these 
analyses have been described previously. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



121 



Males and females of Groups VI-VIII 
were treated together. In addition to 
the calculations of values previously 
mentioned, MULDIS also computed the 
"best" placement of each individual in 
the original reference samples and indi- 
cated the number, if any, that would 
"best" have been included in the other 
reference sample. 

In comparisons of N. f. boilcyi and 
A 7 . /. attwateri, 18 specimens of boileyi 
from several localities within the range 
of the subspecies were compared with 
36 specimens of attwateri from localities 
6-10. Because baileyi is geographically 
isolated, there are no suspected natural 
hybrids or geographic intermediates and 
discriminant scores for a "test" sample of 
laboratory hybrids were not computed. 
Although there is no overlap between 
the discriminant scores of the two sub- 
species (Fig. 34), one specimen of attwa- 
teri is more like the reference specimens 
of baileyi than like other specimens of 
attwateri. The mean and range (in 
parentheses) of discriminant scores from 
attwateri and baileyi, respectivelv, are 
14.20 (12.32-16.85) and 18.87 (17.47- 
20.92). When the single "wrongly 
placed" specimen of attwateri was re- 
moved, the upper extreme of that sam- 
ple was reduced to 15.82. From the list 
of discriminant multipliers computed for 
these two taxa ( Table 14 ) , it can be seen 
that measurements of interorbital con- 
striction, breadth of the rostrum, length 
of the nasals, and morphology of the 
sphenopalatine vacuities best serve to 
distinguish baileyi from attwateri. Only 
condylobasilar length and length of max- 
illary toothrow were weighted at espe- 
cially low levels. 

These results indicate that baileyi and 
attwateri are generally distinguishable at 
the level of the individual, but that a 
few individuals of one taxon may closely 
resemble members of the other morphol- 
ogically. As previously discussed, most 
skulls of baileyi can be identified by the 
three scored cranial characters included 
in the discriminant function analysis. Of 
these, only one (sphenopalatine vacui- 



ties) was weighted relatively high. Re- 
flectance values were computed by anal- 
ysis of variance and SS-STP to be signifi- 
cantly different between baileyi and at- 
twateri, but for some reason, probably 
because of the high within-group vari- 
ance, these scores are not weighted no- 
ticeably higher than cranial dimensions. 

A frequency histogram showing sepa- 
ration of the reference samples of N. f. 
campestris and N. f. attwateri together 
with the projection of four specimens 
from locality 5 (all from Ellsworth 
County, Kansas) is shown in figure 35. 
No overlap between the two samples is 
observed and all specimens are "best" 
considered in the sample with which they 
were originally placed. The mean and 
extreme (in parentheses) discriminant 
scores for the 36 specimens of attwateri 
(localities 6-10) and 27 specimens of 
campestris (localities 2-4), respectively, 
are 13.64 (11.05-15.32) and 18.66 (16.35- 
20.66 ) . The discriminant multipliers cal- 
culated for the comparisons are shown 
in table 14. That for rostral breadth is 
especially high and those for reflectance 
of blue and green are relatively high. 
Color reflectance was expected to be 
heavily weighted, considering the differ- 
ences in color between members of the 
two subspecies. Several characters are 
weighted relatively low, especially con- 
dylobasilar length. 

Within the attwateri reference sam- 
ple, there is a slight but noticeable ten- 
dency for the discriminant scores of spec- 
imens from localities farthest from the 
range of campestris to be least like those 
of campestris. Furthermore, within the 
campestris reference sample there exists 
an obvious tendency for specimens from 
locality 4 (adjacent to the range of 
attwateri ) to cluster toward the attwateri 
reference sample. The specimen of 
campestris (KU 119700) with the second 
lowest discriminant score ( 17.11) is from 
a locality in Russell County, Kansas, only 
one mile west of the Russell-Ellsworth 
County boundary, which I have con- 
sidered the general line of demarcation 
between the two races. Discriminant 



122 



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WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



123 



2 - 









































10 
10 
8 

7 
7 
7 
6 


9 

9 
8 

8 
7 
7 
7 


10 

9 

9 

8 
7 

7 
6 






7 
7 

7 
7 
7 
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7 
7 
6 


1 

1 
1 
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12.5 13.5 14.5 15.5 16.5 17.5 18.5 

Discriminant Score 



19.5 



20.5 



21.5 



Fig. 34. Frequency histogram of discriminant scores computed by discriminant function analysis 
comparing individuals of Neotoma floridana attwateri (6-10) and N. f. baileyi (1). See figure 8 for 
geographic area of origin, indicated by numerals on the histogram, of each specimen. 



scores of two of four specimens from just 
east of this line are intermediate between 
the extremes of the two reference sam- 
ples. Although the scores of the other 
two are within the extremes for attwateri, 
they are near the campestris side of the 
histogram. 

As determined by these analyses, N. 
f. campestris and N. f. attwateri are con- 



sistently distinct at the level of the indi- 
vidual. The area of presumed secondary 
intergradation apparently includes both 
Russell and Ellsworth counties, Kansas, 
because specimens from this area tend 
to have convergent, albeit distinct, dis- 
criminant scores. Additional specimens 
from the relatively narrow zone of con- 
tact between the two taxa might reveal 





















5 






























9 

8 
8 

7 
7 
7 
6 
6 


9 

8 
8 

7 
7 
7 
7 
6 






10 
9 

7 
7 
7 
7 
6 






10 
7 
7 

7 
6 




4 
4 

4 
4 
3 


4 
3 
3 
3 
3 


4 
4 
3 
3 


7 
7 
6 






4 
4 
4 


3 
3 

2 


4 
3 
3 










9 
6 


5 


5 






4 
3 








10 




10 


7 


5 


4 




3 





10.6 



11.6 



12.6 



13.6 



14.6 



15.6 



16.6 



17.6 



18.6 



19.5 



Discriminant Score 



20.6 



21.6 



Fig. 35. Frequency histogram of discriminant scores computed by discriminant function analysis 
comparing Neotoma floridana attwateri (5-10) and N. f. campestris (2-4). Solid lines enclose in- 
dividuals that were included in the two reference samples, whereas dashed lines enclose individuals 
of attwateri (5) from a geographically intermediate area whose scores were computed on the basis 
of discriminant multipliers computed during comparison of the reference samples. See figure 8 for 
geographic area of origin, indicated by numerals on the histogram for each specimen. 



124 



MISCELLANEOUS PUBLICATION" MUSEUM OF NATURAL HISTORY 



overlap of discriminant scores on the 
histogram between the two reference 
samples. 

The histogram showing frequency of 
discriminant scores for 41 Neotoma mi- 
cropus canescens, 27 Neotoma floridana 
campestris, and 11 laboratory-bred hy- 
brids is shown in figure 36. Mean and 
extreme (in parentheses) scores for 
canescens and campestris are, respec- 
tively, -12.33 (-14.20- -9.31) and -5.53 
(-7.82- -3.80). In each reference sam- 
ple, one individual has a discriminant 
score that approaches the scores of the 
other species, but in both instances the 
specimens are "best" included with the 
conspecific reference sample. With these 
two individuals included, the reference 
samples are separated by 1.49 units, 
whereas without them the separation 
would have been 3.71 units. As noted 
above, specimens of campestris from lo- 
cality 4 tend to have scores that are more 
like those of attwateri than are the scores 
of specimens from localities 2 and 3. A 
similar relationship is not observed when 
campestris is computed against canes- 



cens. Discriminant multipliers computed 
for the 17 characters are given in table 
14. One cranial dimension, interorbital 
constriction, is weighted especially heav- 
ily. This undoubtedly results from the 
previously discussed ( see account of qua- 
litative cranial characters) differences in 
the morphology of the interorbital region. 
All three scored cranial characters are 
weighted relatively heavily, but only 
morphology of the sphenopalatine vacui- 
ties is given an absolute multiplier value 
greater than unity, indicating that differ- 
ences in the vacuities between the two 
races are more consistent ( less variance ) 
than differences in the anterior spine and 
posterior margin of the palate. Reflec- 
tance of red and green and the summa- 
tion of all reflectance readings are 
weighted low, but the reflectance value 
for blue is computed an above average 
discriminant multiplier. 

Discriminant scores were computed 
for 11 laboratory-bred hybrids and pro- 
jected onto the histogram. Of five indi- 
viduals of the first filial generation (Fl), 
two have scores in the same frequency 



6- 



-14.3 











F2 




Fl 


Fl 


F2 
Fl 










Fl 

Fl 


F3 ; 
F2 i 
















• 


D 
D 

C 

C 
C 

B 
B 
B 
B 








D 
C 

C 
C 

B 
B 

B 
B 














D 

D 

C 
C 
B 
B 






D 

C 
B 

B 
B 


3 




4 
4 
3 
3 
3 




D 
D 
C 
B 


D 
C 
C 
C 


4 
4 
3 
3 


3 4 


3 3 


4 






C 
B 


D 
B 








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4 
3 




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C 


F2 : 


4 


2 




4 



■13.3 



■12.3 



-11.3 



-10.3 



-9.3 



-8.3 



-7.3 



-6.3 



-5.3 



Discriminant Score 



-4.3 



-3.3 



Fig. 36. Frequency histogram of discriminant scores computed by discriminant function analysis 
comparing Neotoma floridana campestris; (2-4) and N. microtias canescens (B-D). See figure 35 for 
significance of solid and dashed lines. Fl and F2 indicate lahoratorydared hybrids between the 
two taxa of the first and second filial generations, respectively. F3 denotes a back-cross individual 
whose non-hybrid parent was an A 7 . /. campestris. See figure 8 for geographic area of origin, indi- 
cated by numerals and letters on the histogram, for other specimens. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



125 



class as the "aberrant" individual of 
campestris discussed above. The other 
three have scores between the extremes 
of the canescens reference sample. These 
results are somewhat surprising, because 
I had expected Fl hybrids would fall in 
the 3.7 unit zone between the two refer- 
ence samples. Considering the results of 
discriminant analysis of Fl hybrids, the 
scores of specimens from the second filial 
generation ( F2 ) are about as expected. 
Again there is a tendency for the scores 
to be more like those of canescens than 
those of campestris. The range of varia- 
tion is slightly greater than that of Fl's, 
and the range of variation is less than 
that seen for the two reference samples. 
Only one adult (of 30 weeks of age or 
more) back-cross individual was avail- 
able. This woodrat (F3), the progeny 
of an Fl hybrid mated to a campestris, 
has a discriminant score of -7.52, which 
placed it within the campestris range on 
the histogram. 

The separation between N. f. cam- 
pestris and N. m. canescens is adequate 
to demonstrate that the two can be dis- 
tinguished by discriminant analysis. In 
the absence of the two extreme indi- 
viduals, the separation would have been 
relatively great considering the small 
number of characters used and the close 
relationship of the two species. How- 
ever, larger samples probably would 
show that the two specimens discussed 
are not "aberrant," but rather near the 
extremes of discriminant scores of the 
two taxa compared. 

Reference samples of 36 N. f. attwa- 
teri from localities 6-10 and 41 N. m. 
canescens from localities B-D were used 
to compute discriminant multipliers in 
comparisons of these two taxa. Mean 
and extreme (in parentheses) dicrim- 
inant scores for individuals of the refer- 
ence samples were 12.77 (10.29-14.98) 
for attwateri and 19.54 (17.34-21.56) for 
canescens. All individuals of both sam- 
ples were computed to be in the "cor- 
rect" sample; when discriminant scores 
were plotted on a frequency histogram 
( Fig. 37 ) , none of the members of either 



reference sample had deviate scores re- 
sulting in placement in a class disjunct 
from other classes of the species. 

As shown in table 14, rostral breadth 
again is weighted relatively heavily. 
Other characters that appear to differ 
consistently between the two taxa are 
interorbital constriction, sphenopalatine 
vacuities, and color reflectance of blue. 
The summated reflectance score (total) 
was given a multiplier value of 0.0, and 
thus was of no use in distinguishing in- 
dividuals of N. f. attwateri and N. m. 
canescens. Mastoid breadth also was 
shown to be of little value in distinguish- 
ing members of the two taxa. Discrim- 
inant scores of 40 woodrats from a variety 
of sources were computed and projected 
onto the frequency histogram (Fig. 37) 
with scores of specimens in the two ref- 
erence samples. This test group is com- 
posed of the following specimens : 1 ) 12 
laboratory hybrids of the first filial ( Fl ) 
generation; 2) six hybrids of the second 
filial (F2) generation; 3) two back-cross 
hybrids resulting from the mating of Fl 
hybrids with mlcropus (M3); 4) eight 
specimens that I had previously identified 
as micropus (SI) from the locality of 
sympatry of the two reference taxa (3 
mi S Chester, Major Co., Oklahoma); 
5) four specimens that I had previously 
identified as floridana (S2) from the lo- 
cality of sympatry; 6) five specimens 
previously identified as natural hybrids 
from that locality (S3); 7) and three 
specimens from 8.9 mi S Aledo (14 mi 
SW Fort Worth), Parker Co., Texas (T), 
that did not appear to be typical repre- 
sentatives of floridana. 

Six of the Fl hybrids have discrim- 
inant scores between the extremes of the 
scores of the parental species, as was 
expected for all. Five of the other six 
have scores that were near the lower end 
of the range of N. m. canescens, but the 
score of the sixth is like that of typical 
canescens. Most Fl hybrids apparently 
tend to be intermediate in the 17 char- 
acters employed, but somewhat more 
like micropus than floridana. Second 
generation hybrids ( F2 ) are, on the aver- 



126 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



■ 
























SI 








• 
























SI 








D 


























D 




























SI 




C 












S2 














SI 


D 




C 








. 




10 
9 
9 
7 




: t 

: s2 

:S2 








F2 


SI 
SI 
SI 
F2 


D 
D 
C 

c 


Fl 


B 

B 
B 
B 








8 
8 
7 


D 
D 
C 


: S3 
: S3 


SI 
M3 


7 8 






T 


9 

7 
7 
7 


7 

7 

7 
6 


7 7 
7 7 
7 6 
7 6 






S3 F2 

S3 Fl 
Fl Fl 
Fl Fl 


F2 
Fl 
Fl 


Fl 
Fl 


Fl 


c 

B 
B 
B 


C 
C 
B 
B 


B 
B 
B 
B 


F2 


M3 






S2 




10 
9 


T 




S3 
F2 
Fl 


D 
C 
B 


C 

c 

B 








7 




10 
7 


6 






D 

B 


D 
C 


C 

c 




6 


10 


6 


6 


8 




C 



10.2 11.2 12.2 13.2 14.2 15.2 16.2 172 

Discriminant Score 



182 



19.2 



20.2 



21.2 



22.2 



Fig. 37. Frequency histogram of discriminant scores computed by discriminant function analysis 
comparing Neotoma floridana attwateri (6-10) and N. micropus canescens (B-D). See figure 35 for 
significance of solid and dashed lines and see figure 8 for geographic area of origin, indicated by 
symbols on the histogram, for most specimens. Those not included in figure 8 and their identifying 
symbols (in parentheses) are as follows: laboratory-bred hybrids between the two taxa of the first 
and second filial generations (Fl and F2, respectively); laboratory-bred back-cross hybrids whose 
non-hybrid parent was N. m. canescens (M3); specimens from 3 mi S Chester, Major Co., Okla- 
homa, that had been identified previously as N. micropus, N. floridana, or hybrids (SI, S2, and S3, 
respectively); and specimens from 8.9 mi S Aledo, Parker Co., Texas, that were suspiciously atypical 
in color ( T ) . 



age, slightly more ?7iicropus-\ike than are 
Fl hybrids, and also are more variable. 
The score of one approaches the upper 
extreme of micropus scores; that of an- 
other approaches the most micropus-\ike 
floridana scores. None overlapped the 
scores of floridana. One of the two back- 
cross specimens ( M3 ) demonstrates no 
perceptible affinities for floridana, but 
the score of the other is similar to those 
of Fl hybrids. 

Considering animals from natural pop- 
ulations, the three suspiciously-colored 
specimens from Parker County, Texas, 
all have discriminant scores typical of 
floridana. The scores of two are above 
the mode for the floridana reference sam- 
ple and one is near the upper extreme; 
none could be identified as "hybrid" or 



"intergrade" on the basis of discriminant 
scores. The scores of seven of the spec- 
imens from the area of sympatry that 
had been identified as micropus (SI) are 
typical of the scores of reference mi- 
cropus. The score of the eighth (17.68), 
however, is larger than that of only one 
individual in the micropus reference sam- 
ple, and thus similar to scores of labora- 
tory-bred Fl hybrids. All four of the 
specimens identified as IV. floridana (S2) 
have scores within the extremes of ref- 
erence floridana. One, in fact, is near the 
lower limit for floridana, but two others 
have scores slightly above the mode. 
Of greatest interest is the placement on 
the histogram of scores of the five speci- 
mens identified as natural hybrids; all 
have scores between the extremes of the 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



127 



two reference samples and are in fre- 
quency classes with known Fl and F2 
hybrids. 

These results show that laboratory 
reared hybrids between N. floridana and 
N. micropus tend to have discriminant 
scores intermediate between those of 
non-hybrids, but when not intermediate 
they are more like micropus than flori- 
dana. Second generation hybrids again 
appear to be more variable and also 
more micropusAike than Fl hybrids. 
Backcross hybrids, as expected, tend to 
be either intermediate or more like their 
non-hybrid parent. Woodrats from the 
known area of sympatry in northern 
Oklahoma may be similar to members 
of either species, or they may be inter- 
mediate. Results of discriminant func- 
tion analysis further substantiate conclu- 
sions by Spencer (1968) and by me that 
the two species interbreed at the locality 
of sympatry. In addition, it can be seen 
that identifications based on visual anal- 
ysis of pelage and cranial characteristics 
are highly reliable, as indicated by re- 



sults of discriminant function analysis. 
Although the series of specimens from 
Parker County, Texas, near the western 
edge of the range of the species in north- 
ern Texas, are suspiciously grayish, spec- 
imens from that locality are either typical 
floridana or at least much more like flori- 
dana than micropus. 

It appears that discriminant function 
analysis is a sophisticated statistical tool 
that has tremendous potential in studies 
of geographic variation, especially in lo- 
cating zones of marked morphological 
change (see Rees, 1970, for comparable 
results in studies of white-tailed deer), 
and for distinguishing natural hybrids. 
However, the observed tendency for 
floridana-micropus Fl and F2 hybrids to 
be more like micropus than floridana in- 
dicates that hybrids of known ancestry 
(laboratory-bred) should be used as 
"controls" whenever possible in discrim- 
inant analyses to determine where na- 
tural hybrids likely will score relative to 
the scores of the parental species. 



NON-MORPHOLOGICAL CHARACTERS 



COMPARATIVE REPRODUCTION 

In view of the emphasis placed on 
"reproductive isolation" in the biological 
species concept (Mayr, 1965:19), studies 
of reproductive patterns and habits con- 
stitute a major aspect of investigations of 
closely related taxa. It has been sug- 
gested (erroneously I think) that evi- 
dence of hybridization among animals 
having internal fertilization implies con- 
specificity. As presently understood, 
laboratory experiments in hybridization 
merely provide an indication of the pres- 
ence, absence, or efficiency of isolating 
mechanisms, especially postmating mech- 
anisms (see Mayr, 1963:92). Brand and 
Ryckman ( 1969 ) demonstrated a clear 
understanding of this concept in their 
interpretations of studies on Peromyscus. 
Hybridization in natural habitats is more 
often indicative of conspecificity, but as 
stated by Mayr (1969:195) "allopatric 



forms that hybridize only occasionally in 
the zone of contact are full species." In 
fact, populations that have diverged mor- 
phologically during isolation often hy- 
bridize when geographic contact is re- 
established until such time as selection 
has established isolating mechanisms or 
reinforced incipient mechanisms (Key, 
1968). Premating isolating mechanisms, 
such as habitat isolation, clearly are 
tenuous forms of isolation, but they may 
be sufficiently effective to prevent loss of 
species integrity as a result of hybridiza- 
tion. The emphasis on reproductive iso- 
lation would seem better placed on the 
abilities of taxa to maintain their respec- 
tive specific integrities rather than on the 
production of hybrids. Nevertheless, 
studies of hybridization both in the labo- 
ratory and the field often serve as im- 
mensely useful indicators of animal rela- 
tionships. 

Breeding Cages. — Two cages were 



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MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



constructed especially for breeding 
woodrats in the laboratory. Each was 60 
by 60 by IS inches with a M-inch plywood 
floor and hinged top. The sides and top 
were of /2-inch hardware cloth secured 
on the inside of a wooden frame. Two 
other cages constructed for other pur- 
poses were found to be excellent breed- 
ing cages. These were 60 by 18 by 18 
inches with M-inch plywood floors and 
sides, and with hinged tops of hardware 
cloth on wood frames. Internally, these 
cages were constructed so that remov- 
able hardware cloth partitions on wood 
frames could be inserted at one-foot in- 
tervals. The partitions had sliding metal 
doors allowing woodrats to be separated 
or penned together easily and without 
handling. When these four cages were 
in use, an upright rack of four metal 
cages, 48 by 24 by 18 inches, frequently 
was converted into two "two story" 
breeding cages by replacing the metal 
trays that served as the floor of the upper 
and third (from the top) cages with 
trays 24 by 24 inches. Attempts to breed 
woodrats in unconverted cages, 48 by 24 
by 18 inches, and the smaller 24 by 24 
by 18 inch cages never were successful 
and often resulted in death of one of 
the rats. 

Recognition of Breeding Readiness. 
— External indications of breeding con- 
dition for both sexes were described by 
Rainey (1956:605-609) for Neotoma 
floridana, and by Raun (1966:14-17) for 
N. micropus. In breeding males the 
testes become noticeably enlarged and 
scrotal; the swollen convoluted cauda 
epididymis forms a conspicuous bulge 
(Linsdale and Tevis, 1951:354), and the 
skin of the scrotum appears thinner, 
more darkly pigmented, and less haired 
than in nonbreeding males. In both the 
field and the laboratory it was noted that 
these characteristics are somewhat more 
easily discernible in breeding floridana 
males than in breeding micropus males. 
Also in floridana, the testes often descend 
farther into the scrotal sac than do the 
testes of micropus males. Healthy adult 
laboratory males of both species had ap- 



parently viable sperm in the epididy- 
mides and testes throughout the year, 
even when the testes were abdominal 
and reduced in size. In sexually inactive 
females, the vulva is imperforate and 
cornified, the clitoris is small and white 
or pinkish, and the teats are small. 
Breeding females are easily distinguished 
by a turgid, perforate vagina and an en- 
larged, vascularized clitoris. 

Age at Sexual Maturity. — Both male 
and female woodrats born early in spring 
usually appear to be in breeding condi- 
tion by late summer. The testes of young 
males are smaller than those of adults 
and the cauda epididymis protrudes less; 
both the epididymides and testes contain 
sperm. Several attempts were made to 
place first-year males of micropus with 
adult breeding females, but each attempt 
was necessarily terminated to prevent 
the male from being killed. A first-year 
floridana male was placed with an adult 
female floridana from 8 August until 4 
September 1967; although the two were 
compatible, they were never observed to 
display sexual interest nor to copulate; 
no litter resulted. The same male sired 
several litters during the 1968 and 1969 
breeding seasons. 

In late summer of 1968, two first-year 
females of each species were placed with 
adult males of their own species for more 
than two weeks each, but no young was 
born to either. One of three subadult 
female N. f. baileyi (Table 15), obtained 
in late August of 1968, was nursing three 
young judged to be less than two weeks 
of age; the other two females were 
neither pregnant nor lactating. At least 
occasional females bear young in the 
natural environment late in the season 
of the year in which they are born. 
Brown (1969:538) found that female 
Neotoma mexicana born in the first lit- 
ters of spring (April and May) normally 
produce litters in June and July, often 
while still at least partially in juvenile 
pelage. This clearly is not the case in 
either N. floridana or A 7 , micropus. Young 
of both sexes born as late as August were 
consistently successful breeders in the 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



129 



laboratory by March of the following 
year. 

Breeding Seasons. — As indicated by 

age composition of samples of N. micro- 
pus and as reported by Rami (1966:14), 
breeding takes place throughout the year 
in southern populations of the species, 
with only a slight tendency for season- 
ality. Females in northern populations 
of micropus (Spencer, 1968:45, and Fin- 
ley, 1958:486; Tables 15 and 16) appar- 
ently begin breeding in December and 
January, produce at least two and prob- 
ably three litters before July, and some 
females have an additional litter and 
possibly two between early August and 
the end of October. Neotoma floridana 
in Kansas (Tables 15 and 16; Rainey 
1956:609-613) begin breeding in Febru- 
ary and females bear their first litters in 



March or April and their second in May 
or June. Most females are appreciatively- 
less active reproductively in July, then 
have an additional litter in August or 
September with occasional litters being 
born as late as October. As indicated in 
tables 15 and 16, the first litter of female 
A7. /. baileyi is born in April, a second in 
June, and a third in July or August. I 
doubt that baileyi produces litters after 
mid-September, but available data do 
not preclude the possibility. Late sum- 
mer and autumn breeding in both species 
may involve mostly young females born 
earlier that year. 

Estrous Cycle. — Techniques described 
by Chapman (1951:269) and Zarrow et 
al. (1964:36-37) for determination of 
estrus by examination of cells lining the 
vagina were attempted early in my 



TARLE 15. Reproductive status of adult and subadult Neotoma floridana and N. micropus females 
captured in Nebraska, Colorado, Kansas, and Oklahoma from September, 1966 to April, 1969. 



Locality 
( county ) 



Date 
captured 



Age 



Date 
litter 
born 



Number 
progeny born 



Number 

progeny 

collected 

with female 



oV 



9? 



cfcf 



?9 



Remarks 



Cherry 

Cherry 
Cherry 
Cherry 
Cherry 
Cherry 

Cherry 
Cherry 
Cherry 

Cherry 

Rock 

Rock 



Logan 
Logan 

Ness 



31 Mar. 

31 Mar. 

31 Mar. 

31 Mar. 

31 Mar. 

31 Mar. 

31 Mar. 
24 Aug. 
24 Aug. 

24 Aug. 

21 Aug. 

22 Aug. 



29 Aug. 
29 Aug. 



Adult 
Adult 
Adult 
Adult 
Adult 
Adult 

Adult 

Subadult 

Adult 

Subadult 
Subadult 
Subadult 



Neotoma floridana baileyi 
13 Apr. 2 2 

9 Apr. 2 2 



26 Apr. 
6 Apr. 



16 Apr. 



Neotoma floridana campestris 



Adults (2) 
Subadult 



4 Sept. Subadult 



No litter born 



Died 17 Apr.; 
had 3 resorbing 
embryos 

No litter bom 
Killed 29 Aug.; 
had 4 embryos 
X 45 mm. 
Killed 29 Aug.; 
not pregnant 
Killed 29 Aug.; 
not pregnant 
Killed 29 Aug.; 
not pregnant 

No litters born 
Died 8 Sept.; 
not pregnant 
Killed 4 Sept.; 
not pregnant 



130 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 15.— Continued. 



Number 



Number 
progeny 
collected 



Locality 
( county ) 



Date 
captured 



Age 



Date 
litter 
born 



progeny bom with female 



9? 



dtf 99 



Remarks 



Ness 

Finney 

Finney 

Finney 

Finney 

Hodgeman 

Ellis 
Ellis 

Ellis 

Russell 

Russell 

Russell 



Major 

Major 

Douglas 

Douglas 

Douglas 

Douglas 



Major 



4 Sept. 

5 Sept. 
5 Sept. 
5 Sept. 
5 Sept. 
8 Sept. 

18 Dec. 

18 Dec. 

19 Dec. 

21 Dec. 
21 Dec. 
21 Dec. 

31 Jan. 
31 Jan. 
3 Mar. 
10 Mar. 
10 Mar. 
10 Apr. 



Ellsworth 24 Sept. 

Ellsworth 14 Oct. 

Ellsworth 14 Oct. 

Ellsworth 14 Oct. 

Douglas 18 Oct. 

Douglas 7 Nov. 

Ellsworth 21 Dec. 



Major 31 Jan. 

Haskell 24 Feb. 

Haskell 24 Feb. 



Subadult 

Subadult 

Adults (2) 

Subadults ( 5 ) 

Adults (4) 

Adult 

Adults (9) 
Adults (2) 

Adults (2) 

Adult 

Adults (4) 

Adult 



Adult 

Adult 

Adult 

Adult 

Subadult 

Adult 



Neotoma floridana attwateri 
10 Feb. 2 

10 Mar. 2 1 

6 Apr. 1 3 



7 June Adult 



Subadults (2) 

Adult 

Subadult 

Subadults (2) 

Adults (2) 
Subadults (2) 
Adults (2) 



Neotoma micropus canescens 



Adults (3) 

Adult 

Adult 



Killed 13 Sept.; 
not pregnant 
Killed 5 Sept.; 
not pregnant 
Killed 5 Sept.; 
neither pregnant 

Killed 13 Sept.; 
none pregnant 
Killed 13 Sept.; 
none pregnant 
Killed 13 Sept.; 
not pregnant 
No litters born 
Killed 18 Dec; 
neither pregnant 
Killed 21 Dec; 
neither pregnant 
Killed 21 Dec; 
not pregnant 
Killed 13 Jan.; 
none pregnant 
No litter born 



-- 


-- 


No litter bom 


-- 


- 


No litter born 





2 


Killed 11 Apr.; 
not pregnant 
Killed 7 June; 
had 4 embryos 
X 25 mm 
Killed 24 Sept.; 
neither pregnant 


- 


- 


Killed 14 Oct.; 
not pregnant 
Killed 14 Oct.; 
not pregnant 


-- 


~ 


Killed 7 Nov.; 
neither pregnant 
No litters born 


- 


- 


No litters born 
Killed 2 Jan.; 
neither pregnant 

No litters born 





2 


No litter born 





2 


No litter born 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



131 



TABLE 15.— Concluded. 

















Number 




Locality 
( county ) 


Date 
captured 


Age 


Date 
litter 
born 


Number 
progeny born 


progeny 

collected 

with female 




dV 


$2 


dd 


99 


Remarks 


Haskell 


24 Feb. 


Adult 












Aborted 3 embryos 




















on 3 Mar. 


Haskell 


24 


Feb. 


Adult 


3 Mar. 


2 


1 


__ 


.. 


.. 


Haskell 


24 


Feb. 


Adult 


29 Feb. 


2 


2 


.. 


.. 


.. 


Haskell 


24 


Feb. 


Adult 




._ 




_ 


_ 


No litter born 


Barber 


9 


Mar. 


Adult 


11 Mar. 


3 





„ 


._ 


.. 


Barber 


10 


Mar. 


Adult 


13 Mar. 


3 





.. 


.. 


__ 


Barber 


10 


Mar. 


Subadult 


_ 


__ 


.. 


__ 


.. 


No litter born 


Haskell 


6 


Apr. 


Adult 


-- 


- 


- 





2 


Killed 11 Apr.; 
not pregnant 


Haskell 


6 


Apr. 


Adult 


-- 


-- 


-- 


1 


1 


Killed 11 Apr.; 
not pregnant 


Haskell 


6 


Apr. 


Adult 


-- 


-- 


-- 


1 


2 


Killed 11 Apr.; 
not pregnant 


Baca 


8 


Apr. 


Adult 


__ 


_. 


.. 


1 


1 


No litter born 


Baca 


8 


Apr. 


Adult 


__ 


__ 


.. 


_. 


__ 


No litter bom 


Baca 


18 


May- 


Adult 


.. 


__ 


_. 


2 


1 


No litter born 


Baca 


18 


May 


Adult 


__ 


__ 


__ 


2 


2 


No litter born 


Baca 


18 


May 


Adult 


.. 


_. 


— 


1 


3 


No litter born 


Baca 


18 


May 


Adult 


4 June 


2 


2 


2 


2 


._ 


Baca 


18 


May 


Adult 


24 May 


3 








1 


__ 


Baca 


18 


May 


Adult 


31 May 


4 





— 


-_ 


__ 


Baca 


18 


May 


Adult 


.. 


— 


.. 


.. 


.. 


No litter born 


Meade 


5 


June 


Adult 


.. 


.. 


__ 


2 


1 


No litter born 


Haskell 


6 


June 


Adult 


__ 


.. 


.. 


2 





No litter born 


Haskell 


6 


June 


Adult 


_ 


_ 


.. 


2 


1 


No litter born 


Haskell 


6 


June 


Adult 


17 June 


1 


1 


1 


1 


.. 


Haskell 


6 


June 


Adult 


13 June 


1 


2 


.. 


.. 


__ 


Haskell 


6 


June 


Adult 


24 June 


3 


1 


_ 


_ 


._ 


Haskell 


6 


June 


Adult 


29 June 


2 


1 


.. 


.. 


._ 


Major 


6 


June 


Adults (2) 


_. 


__ 


.. 


.. 


.. 


No litters born 


Barber 


4 


July 


Subadults ( 3 ) 


— 


- 


— 


— 


— 


Killed 19 June; 



4 July 



Adult 



11 Aug. 


Subadults (2) 


11 Aug. 


Adult 


11 Aug. 


Adult 


7 Sept. 


Adults (2) 


7 Sept. 


Subadult 


24 Sept. 


?? (6) 


22 Oct. 


?? (7) 


13 Nov. 


?? (2) 


25 Nov. 


Adults (3) 



none pregnant 
Killed 19 July; 
not pregnant 
Killed 16 Aug.; 
neither pregnant 
Killed 16 Aug.; 
not pregnant 
Killed 19 Aug.; 
not pregnant 
Killed 13 Sept.; 
neither pregnant 
Killed 13 Sept.; 
not pregnant 
No litters born 
No litters born 
No litters born 
No litters born 



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MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



study. Some rats did not seem to be af- 
fected by the daily handling and con- 
tinued to cycle as described by Chapman 
(1951:271); other individuals became 
hyperactive, lost weight, were difficult to 
handle, and the vagina became cornified 
and inactive. My limited observations 
on females that continued to cycle agree 
in general with the four- to six-day 
estrous cycle described by Chapman (loc. 
cit.) for N. floridana, and no meaningful 
differences were observed in the cycles 
of females of the two species or of an 
Fl hybrid female. 

Zarrow et al (1964:39) described a 
technique for monitoring the estrous cy- 
cle of female white rats (genus Rattus) 
by measuring daily activity of cycling 
females in activity cages. This technique 
also was tested, but variation in the ac- 
tivity between females far exceeded that 
of daily activity of any individual female. 
Some females averaged in excess of 8000 
revolutions per day whereas others never 
recorded more than 500 revolutions and 
averaged less than 200 revolutions. Ac- 
tivity of two first-year adult virgin fe- 
males (one floridana, the other micropus) 
for the 20-day period from 12 to 31 
March 1968 is shown in figure 38. This 



particular example is slightly atypical be- 
cause the floridana was more active than 
the micropus. Normally floridana fe- 
males turned fewer revolutions of the 
wheel than did micropus females. Both 
rats were removed from the activity cage 
the morning of 31 March and were caged 
with an adult male of their species until 
12 April. The female floridana gave birth 
to a litter of five young on 6 May but no 
litter was born to the micropus as a re- 
sult of that attempted mating. Females 
removed from an activity cage and 
placed with males at the peak of activity, 
which would be expected to correspond 
with estrus, did not demonstrate greater 
mating success than other females. The 
peaks in activity generally followed 
three- to six-day cycles for both species 
and probably were associated, at least in 
part, with the estrous cycle. However, 
the technique did not give reliable and 
precise data on the estrous cycles of the 
two species, and therefore was discon- 
tinued early in the 1968 breeding season. 
Behavioral Aspects of Breeding. — 
Several behavioral differences were 
noted that probably affected breeding 
success in the laboratory. Certain rats 
did not seem to adapt to captivity and 



TABLE 16. Reproductive data recorded on specimen labels of adult and subadult Neotoma 
floridana, N. micropus, and N. angustipalata females. 



Number 



Date 



Pregnant 
No ( Number Number 

Embryos Embryos) Young 



Lactating 



78376 

4311/ 

5034 USNM 
73386 



50185 
51612 
72600 



37098 
37100 

34747 



4986 



N. floridana baileyi from Nebraska 

15 May X 

16 June 

15 July __ 4 

N. floridana campestris from Nebraska 
15 August X 

1 November X 

24 November X 

N. floridana campestris from Colorado 

21 May X 

22 May _ 4 

23 November X 



N. floridaim campestris from Kansas 



25 August 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



133 



TABLE 16.— Concluded. 











Pregnant 












No 


( Number 


Number 




Number 


Date 


Embryos 


Embryos ) 


Young 


Lactating 






N. 


floridana attivateri from Kansas 






654 


9 


March 










X 


53846 


10 


March 





3 








78998 


12 


October 


X 








— 


16111 


1 


November 


X 











68578-80 


13 


November 


X 








— 


22628 


29 


November 

N.fl 


X 

oridana attwateri f 


rom Oklahoma 


— 




4191 


19 


October 


... . 


— 


4 


X 






N 


, floridana attwateri from Texas 






1037 FWCM 




February 


X 


_ 


.... 





23391 TCWC 


27 


September 











X 


51718 


22 


October 


X 











3848 TCWC 


27 


October 


X 











971 FWCM 


24 


November 


X 


— - 


-- 


— 






N. 


micropus canescens from Kansas 






69605 


15 


June 


__.. 








X 


13994 


7 


July 


.___ 








X 


38919 


21 


July 


X 








— 


38914 


22 


July 


X 











98190 


30 


November 


X 












79088 



N. micropus canescens from New Mexico 
14 June 3 

N. micropus canescens from Oklahoma 



74550-51 


1 


December 




X 


.... 






N. 


micropus canescens from Texas 


56834 


22 


August 







2 


56835 


22 


August 










51719 


30 


October 




X 


— 






N. micropi 


us canescens from Coahuila 


36324 


31 


March 




.... 





36329 


31 


March 




X 





56710 


5 


December 




X 





56712 


9 


December 






2 






N. micropus microp 


us from Tamaulipa: 


56910 


17 


May 










56912 


19 May 




X 




56914 


19 


May 







2 


56915 


21 


May 







2 


56918 


22 


May 




X 





56960-63 


7 


June 




X 





56954 


10 


June 







2 


56955-56 


10 


June 




X 





89135 


13 


November 




X 





89137-39 


13 


November 




X 





89141-42 


13 


November 




X 





89144 


13 


November 




X 








N. 


angu: 


itipalata 


from Tamaulipas 


58865 


21 


May 




X 





8138 UNAM 


11 


July 




__ 


1 



X 



134 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 




Fig. 38. Daily activity of non-pregnant first-year female woodrats from March 12-31: 
A — Neotoma floridana attwateri; B — N. micropus canescens. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



135 



conditions of the laboratory; these indi- 
viduals never became accustomed to 
handling and either would dash about 
the cage or cower defensively in a corner 
when the cage door was opened. When 
placed in a breeding cage these rats be- 
haved in the same manner, initially and 
whenever an investigator was in the ani- 
mal rooms. Although most were not 
especially good breeders, some did breed 
and successfully rear litters. Wood (1935: 
106) observed similar behavioral patterns 
and resultant lowered reproductive suc- 
cess in certain individuals of Neotoma 
fuscipes. This type of behavior was 
never observed in a N. floridana that had 
been in the laboratory for as long as one 
week. It was prevalent in N. m. 
canescens that were collected in Haskell 
County, Kansas, and Baca County, Colo- 
rado. The habitat from which these ani- 
mals were obtained is open grassland 
with practically no cover additional to 
structures built by the rats. Possibly such 
behavior is genetically based and has 
selective advantage for woodrats living 
in open areas. 

When a male and female were placed 
together they generally spent some time 
sniffing each other, especially the ventral 
dermal gland (Howell, 1926:16) and 
genitalia. This was often followed by 
sparring or fighting. If the female estab- 
lished dominancy she generally pursued 
the male relentlessly, biting the tail and 
lumbar region of his back; if the two 
were left together, the male eventually 
was killed. If the male established dom- 
inancy, the fighting usually did not last 
long and such matchings frequently re- 
sulted in the birth of a litter. A few 
males were able to establish dominancy 
with little or no fighting; these generally 
were the most successful breeders. Oc- 
casional males behaved as described 
for dominant females and if not removed 
would kill the female in a relatively short 
time. Usually these were young and in- 
experienced males, and in at least one 
instance, a male micropus that behaved 
in this fashion during his first breeding 
season was a successful breeder the fol- 



lowing year. It usually could be deter- 
mined within an hour whether or not 
two rats were compatible; if either was 
clearly endangered, they were separated. 
However, most deaths resulted when a 
pair would appear to be compatible for 
a period of several hours or even days, 
after which one, usually the female, 
would kill the other. In initial attempts 
to breed woodrats in the laboratory, each 
breeding cage was supplied with two 
nest-boxes, an abundance of shredded 
paper, and occasionally with sticks of 
wood and pieces of corrugated card- 
board. Almost invariably one rat would 
attempt to hoard all the materials and 
constant fighting resulted. Later it was 
discovered that less strife resulted when 
the rats were not given nest-boxes and 
when only enough shredded paper was 
provided for each rat to construct a small 
cup-shaped nest. 

Several investigators (Egoscue, 1957, 
1962; Feldman, 1935) left compatible 
pairs together for the entire breeding 
season, including that time when young 
were born and reared. I attempted this 
only once; on 2 March 1967 a pair of 
N. f. campestris was placed in a "two 
story" breeding cage (described above). 
They nested together on the bottom level 
for several days before the male moved 
to the upper tray; at that time both 
seemed normal and no other indication 
of strife was observed. On 5 April a 
litter of three newborn young was ob- 
served and the male continued to nest 
unmolested on the upper level. On the 
morning of 15 April one young was ab- 
sent and the male was being chased by 
the female. The male was alive on the fol- 
lowing morning, but severely wounded. 
He was removed from the cage, treated 
for the wounds, and placed in a separate 
cage where he recuperated. 

The recuperative powers of both spe- 
cies are remarkable. On separate occa- 
sions a male of each species was so 
severely wounded by a female that the 
skin of the lower back was completely 
missing, exposing large areas of muscle 
from the middle of the back to the base 



136 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



of the tail. Both males were treated 
regularly with disinfectant and both sur- 
vived. The new skin was largely scar 
tissue, and hair was sparse on the back 
of the micropus but dense and normal 
on the floridana, albeit a "line" of de- 
marcation always was visible surround- 
ing the scar. 

Breeding Performance in the Labora- 
tory. — Tables 17 and 18 summarize 
laboratory breeding performances of fe- 
males and males, respectively. The 
tabulated results are qualified, as fol- 
lows : 1 ) An attempted mating was "suc- 
cessful" if at least one live progeny re- 
sulted; 2) Matings were attempted only 
between adult woodrats that appeared 
externally to be in breeding condition; 
3) No attempts prior to 1 February or 
after 1 September are included; 4) At- 
tempts to breed woodrats born earlier 
the same summer are excluded; 5) Mat- 
ings attempted in cages other than the 
three types of breeding cages described 
above are excluded; and 6) A mating 
attempt was considered only if the two 
rats were together for at least 24 hours. 
If two rats remained compatible they 
were left together for a minimum of six 
days, which is approximately the length 
of the estrous cycle, and a maximum of 
12 days. 

As considered herein, all of the pop- 
ulations of Neotoma micropus from 
which live woodrats were collected for 
study in the laboratory are of the sub- 
species N. m. canescens. However, the 
reproductive performance of woodrats 
from the more open habitats of westerly 
localities (Baca County, Colorado, and 
Haskell County, Kansas) was so dis- 
tinctly different from that of woodrats 
from the two more easterly localities 
( Barber and Meade counties, Kansas) 
that I have considered them separately 
as "N. m. canescens (1)" and "N. m. 
canescens (2)," respectively. Both sexes 
of N. m. canescens ( 1 ) were considerably 
less successful reproductively in the lab- 
oratory than any of the other woodrats 
studied. This probably resulted from the 
inability of individuals from these two lo- 



calities to adjust to laboratory conditions. 

Females of N. f. campestris were also 
relatively unsuccessful breeders, but 
males of the race were more successful 
than males of any other taxon. As dis- 
cussed above, successful mating attempts 
generally were those in which the males 
were dominant. Neotoma floridana 
campestris is the largest of the woodrats 
studied and members of both sexes gen- 
erally were able to physically dominate 
another kind of rat when placed in 
breeding cages. When two campestris 
were placed together, the female dom- 
inated more frequently than did the 
male. 

Members of each of the four races, 
N. f. baileyi, N. f. campestris, N. f. attwa- 
teri, and N. m. canescens, of the two 
species studied, were successfully crossed 
with members of each of the other races 
at least twice. Beciprocal crosses were 
successful for five of the six possible 
mating combinations. No offspring re- 
sulted from the four occasions when 
baileyi males were placed with campes- 
tris females, constituting the only unsuc- 
cessful reciprocal cross. Of the four at- 
tempts, a male baileyi was killed in one 
and the male was wounded in two of 
the other three. 

Both sexes of the three types of sub- 
specific "hybrids" demonstrated fertility 
with the exception of female campestris 
X attwateri. Only one of five females 
produced from this cross ever was placed 
with a male and no progeny were pro- 
duced; it seems unlikely, however, that 
females of the cross were infertile. The 
only female of the cross saved for breed- 
ing studies was accidentally killed before 
a second attempt to mate her could be 
made. 

Of the possible kinds of hybrids in- 
volving micropus and one of the three 
subspecies of floridana, the fertility of 
N. f. baileyi X N. m. canescens females 
was not tested, but a male of that cross 
produced a litter of four when mated 
with a baileyi female. The other two 
kinds of N. floridana (attwateri and 
campestris) X N. m. canescens hybrid 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



137 



TARLE 17. Reproductive performance of Neotoma floridana, N. micropus, and hybrid females 

in the laboratory. 



Mali's 



Number Number Number Mean Mode 

matings successful Percent progeny litter litter 

attempted matings success ? ? size size 



Progeny 

per 
attempted 

mating 



Neotoma floridana baileyi females 



N. f. baileyi 

N. f. campestris 

N. f. attwateri 

N. m. canescens ( 1 ) 

N. m. canescens (2) 

N. f. baileyi X 

N. f. attwateri 
N. f. baileyi X 

N. m. canescens 
TOTAL 



N. f. baileyi 

N. f. campestris 

N. f. attwateri 

N. m. canescens ( 1 ) 

N. m. canescens ( 2 ) 

N. f. campestris X 

N. f. attwateri 
N. f. attwateri X 

N. m. canescens 
TOTAL 



N. f. baileyi 
N. f. campestris 
N. f. attwateri 
N. m. canescens ( 1 ) 
N. m. canescens (2) 
N. f. attwateri X 
N. m. canescens F 2 
TOTAL 



N. f. baileyi 
N. f. campestris 
N. f. attwateri 
N. m. canescens ( 1 ) 
N. m. canescens (2) 
N. f. baileyi X 
N. f. attwateri 
TOTAL 



N. f. baileyi 

N. f. campestris 

N. f. attwateri 

N. m. canescens ( 1 ) 

N. m. canescens (2) 

N. f. baileyi X 

N. m. canescens 
N. f. attwateri X 

N. m. canescens 
TOTAL 



11 4 


36.4 


6 


8 


3.5 


3-4 


1.27 


5 5 


100.0 


10 


9 


3.8 


4 


3.80 


1 1 


100.0 


2 


1 


3.0 


3 


3.00 


4 


0.0 










0.00 


3 1 


33.3 





1 


1.0 


1 


0.33 


1 1 


100.0 


2 


2 


4.0 


4 


4.00 


1 1 


100.0 


2 


2 


4.0 


4 


4.00 


26 13 


50.0 


22 


23 


3.5 


4 


1.73 


Neotoma floridana campestris females 








4 


0.0 










0.00 


18 5 


27.8 


4 


10 


2.8 


3 


0.78 


5 2 


40.0 


3 


3 


3.0 


2-4 


1.20 


9 


0.0 










0.00 


6 2 


33.3 


2 


5 


3.5 


3-4 


1.17 


2 1 


50.0 


2 


1 


3.0 


3 


1.50 


1 


0.0 










0.00 


45 10 


22.2 


11 


19 


3.0 


3 


0.67 


Neotomii 


! floridana attwateri females 








1 1 


100.0 


2 


1 


3.0 


3 


3.00 


2 2 


100.0 


3 


2 


2.5 


2-3 


2.50 


9 6 


66.7 


12 


10 


3.7 


3 


2.44 


3 2 


66.7 


2 


2 


2.0 


2 


1.33 


6 2 


33.3 


6 


1 


3.5 


3-4 


1.17 


1 1 


100.0 


1 


2 


3.0 




3.00 


22 14 


63.6 


26 


18 


3.1 


O 


2.00 


Neotoma micropus canescens ( 1 ) females 








1 


0.0 










0.00 


2 1 


50.0 


3 


1 


4.0 


4 


2.00 


2 


0.0 










0.00 


15 


0.0 










0.00 


5 4 


80.0 


6 


4 


2~5 


2-3 


2.00 


1 


0.0 










0.00 


26 5 


19.2 


9 


5 


2.8 


2-3 


0.54 


Neotoma m 


icropus canescens ( 2 ) females 








4 2 


50.0 


6 


2 


4.0 


4 


2.00 


6 5 


83.3 


6 


10 


3.2 


3-4 


2.67 


6 2 


33.3 


2 


4 


3.0 


3 


1.00 


10 1 


10.0 


2 


1 


3.0 


3 


0.30 


8 4 


50.0 


6 


5 


2.8 


3 


1.38 



0.0 



0.00 



4 


2 


50.0 


2 


1 


1.5 


1-2 


0.75 


39 


16 


41.0 


24 


23 


2.9 


3 


1.21 



138 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 17.— Continued. 



Males 













Progeny 


Number Number 




Number 


Mean 


Mode 


per 


matings successful 


Percent 


progeny 


litter 


litter 


attempted 


attempted matings 


success 


dd 9 9 


size 


size 


mating 



N. f. baileiji X 
N. f. campestris 



N. f. baileiji X 
N. f. attwateri 



N. f. campestris X 
N. f. attwateri 



N. f. baileyi X N. f. campestris female 

2 2 100.0 2 2 

N. f. baileyi X N. f. attwateri female 

1 1 100.0 1 2 

A 7 . /. campestris X N. f. attivateri female 



2.0 



3.0 







0.0 



N. f. campestris X N. m. canescens females 



N 
N. m. canescens ( 1 ) 



/. baileyi X (N. f. baileyi X N. m. canescens) female 
1 0.0 

All Neotoma floridana females 



2.00 



3.00 



0.00 



N. f. campestris 


1 


1 


100.0 


1 


1 


2.0 


2 


2.00 


N. m. canescens (2) 


1 


1 


100.0 


2 


1 


3.0 


3 


3.00 


N. f. campestris X 


















N. m. canescens 


6 


2 


33.3 


2 


2 


2.0 


2 


0.67 


N. f. attwateri X 


















N. m. canescens 


3 


2 


66.7 


2 


3 


2.5 


2-3 


1.67 


N. m. canescens X 


















(N. f. attwateri X 


















N. m. canescens) 


1 





0.0 










0.00 


TOTAL 


12 


6 


50.0 


7 


7 


2.3 


2 


1.17 




N.f. 


attwateri 


X N. m. 


canescens ¥^ 


females 








N. f. attwateri 


1 





0.0 










0.00 


N. f. campestris X 


















N. m. canescens 


1 


1 


100.0 





2 


2.0 


2 


2.00 


N. f. attwateri X 


















N. m. canescens 


6 


2 


33.3 


3 


2 


2.4 


2-3 


0.83 


TOTAL 


8 


3 


37.5 


3 


4 


2.3 


2 


0.88 




N.f. 


attwateri X N. m. 


canescens F. 


females 








N. f. baileyi 


1 


1 


100.0 


1 


2 


3.0 


3 


3.00 


N. f. attwateri X 


















N. m. canescens F- 


1 





0.0 










0.00 


TOTAL 


2 


1 


50.0 


1 


2 


3.0 


3 


1.50 



N. floridana 


63 


31 




49.2 


49 


51 


3.2 


3 


1.59 


N. micropus 


31 


7 




22.6 


10 


9 


2.7 


2-3-1 


0.61 


Species-hybrids 


3 


2 




66.7 


3 


4 


3.5 


3-4 


2.33 


TOTAL 


97 


40 




41.2 


62 


64 


3.2 


3 


1.30 






All Neotoma micropus femal 


es 








N. micropus 


38 


9 




23.7 


14 


10 


2.7 


3 


0.63 


N. floridana 


22 


10 




45.5 


17 


17 


3.4 


4 


1.55 


Species-hybrids 


5 


2 




40.0 


2 


1 


1.5 


1-2 


0.60 


TOTAL 


66 


21 
All 


spec 


31.8 
ies-hybi 


33 

id females 


28 


2.9 


3 


0.92 


N. floridana 


3 


2 




66.7 


2 


3 


2.5 


2-3 


1.67 


N. micropus 


2 


1 




50.0 


2 


1 


3.0 


3 


1.50 


Species-hybrids 


18 


7 




38.9 


7 


9 


2.3 


2 


0.89 


TOTAL 


23 


10 




43.5 


11 


13 


2.4 


2 


1.04 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



139 



TABLE 17.— Concluded. 















Progeny 




Number Number 




Number 


Mean 


Mode 


per 




matings successful 


Percent 


progeny 


litter 


litter 


attempted 


Males 


attempted matings 


success 


dV ?? 


size 


size 


mating 







All 


non-hybrid females 










Same species 
Other species 
Species-hybrids 
TOTAL 


101 

53 

8 

162 


40 

17 

4 

61 


39.6 
32.1 
50.0 

37.7 


63 

27 

5 

95 


61 

26 

5 

92 


3.1 
3.1 
2.5 
3.1 


3 

4 

1-2-3-4 

3 


1.23 
1.00 
1.25 
1.15 








All females 










All males 


185 


71 


38.4 


106 


105 


3.0 


3 


1.14 



females demonstrated fertility as did 
males of all three crosses. One male and 
one female floridana X micropus of the 
second generation were successful when 
mated to a female and a male floridana, 
respectively, but they did not produce a 
litter when placed together. Only two 
attempts were made to mate woodrats 
that resulted from backcrosses. Neither 
was successful and the fertility of these 
woodrats was not established. However, 
in view of the success of other hybrids, 
I suspect that backcross progeny were 
fertile and might have produced young 
if more attempts to mate them had been 
conducted. 

Gestation. — Published information on 
the gestation periods of Neotoma flori- 
dana and N. micropus is meager and in- 
consistent. Knoch (1969:363) observed 
a range of 33 to 36 days for gestation of 
three litters of N. f. attwateri. The gesta- 
tion period for N. f. floridana, as deter- 
mined in independent studies, was esti- 
mated at 33 to 39 days (Pearson, 1952: 
461) and six weeks (Hamilton, 1953: 
182). Poole (1940:266) suggested gesta- 
tional limits of 30 to 36 days for N. f. 
magister. The gestation period of N. 
micropus was calculated to be less than 
33 days by Feldman (1935:301). Spen- 
cer (1968:25) calculated gestation of 
two litters of each species (probablv N. 
f. attwateri and N. m. canescens) . Both 
litters of floridana young were born 35 
days following copulation; parturition 
followed copulation by 33 days in one 
instance and 38 in another for micropus. 
Several hybrid females studied by Spen- 



cer (loc. cit.) had gestation periods of 34 
to 36 days. Additionally, he observed 
one female each of floridana and micro- 
pus that copulated during post-partum 
estrus and did not parturiate until 51 
and 55 days, respectively, had elapsed. 
A female N. m. canescens collected by 
Spencer (1968:42) with a litter judged 
to be less than 10 days of age was not 
placed with a male until after she pro- 
duced a litter in captivity 46 days later. 
In this study only a single female 
(N. f. campestris) was caged with a male 
at the time of parturition and a second 
litter was not observed. Although sev- 
eral females nursing litters at the time 
of capture (Table 15) later produced 
second litters without having been placed 
with males, no litter was produced late 
enough to indicate an extended period 
of gestation. The technique of leaving 
males and females together for several 
days was not conducive to determination 
of the gestation period. However, in 
several instances pairs were separated 
after a few days because of fighting. 
Litters born as a result of these matings 
had relatively narrow gestational limits. 
The two shortest terms of gestation had 
maximum durations of 32 days. In one 
case the female was an N. f. baileyi that 
had been bred to an N. f. campestris 
male, whereas the other was a floridana 
X micropus hybrid female mated to a 
hybrid male of the same cross. The 
longest gestation calculated had minimal 
and maximal limits of 37 and 41 days, 
respectively, and was for an N. m. 
canescens female that had been mated to 



140 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 18. Reproductive performance of Neotoma floridana, N. micropus, and hybrid males 

in the laboratory. 



Females 



Number Number Number Mean Mode 

matings successful Percent progeny litter litter 

attempted matings success ? $ size size 



Progeny 

per 

attempted 

mating 



Neotoma floridana baileyi males 



N. f. baileyi 




11 


4 


36.4 


6 


8 


3.5 


3-4 


1.27 


N. f. campestris 




4 





0.0 












0.00 


N. f. attwateri 




1 


1 


100.0 


2 


1 


3.0 


3 


3.00 


N. m. canescens 


(1) 


1 





0.0 










0.00 


N. m. canescens 


(2) 


4 


2 


50.0 


6 


2 


4.0 


4 


2.00 


N. f. attwateri X 




















A 7 , m. canescens F_ 


1 


1 


100.0 


1 


2 


3.0 


3 


3.00 


TOTAL 




22 


8 


36.4 


15 


13 


3.5 


3-4 


1.27 








Neotoma floridana 


•ampestris males 








N. f. baileyi 




5 


5 


100.0 


10 


9 


3.8 


4 


3.80 


N. f. campestris 




18 


5 


27.8 


4 


10 


2.8 


o 
O 


0.78 


N. f. attwateri 




2 


2 


100.0 


3 


2 


2.5 


2-3 


2.50 


X. m. canescens 


(1) 


2 


1 


50.0 


3 


1 


4.0 


4 


2.00 


N. m. canescens 


(2) 


6 


5 


83.3 


6 


10 


3.2 


3-4 


2.67 


N. f. campestris 


X 


















N. m. canescens 


1 


1 


100.0 


1 


1 


2.0 


2 


2.00 


TOTAL 




33 


19 


57.6 


27 


33 


3.2 


3 


1.82 








Neotoma fl 


oridana 


attwateri males 








N. f. baileyi 




1 


1 


100.0 


2 


1 


3.0 


3 


3.00 


N. f. campestris 




5 


2 


40.0 


3 


3 


3.0 


2-4 


1.20 


N. f. attwateri 




9 


6 


66.7 


12 


10 


3.7 


3 


2.44 


N. m. canescens 


(1) 


2 





0.0 










0.00 


N. to. canescens 


(2) 


6 


2 


33.3 


2 


4 


3.0 


3 


1.00 


N. f. attwateri X 




















N. m. canescens Fi 


1 





0.0 










0.00 


TOTAL 




24 


11 


45.8 


19 


18 


3.4 


3 


1.54 






Neotoma mici 


opus canescens ( 1 ) 


males 








N. f. baileyi 




4 





0.0 










0.00 


N. f. campestris 




9 





0.0 










0.00 


N. f. attwateri 




3 


2 


66.7 


2 


2 


2.0 


2 


1.33 


N. m. canescens 


(1) 


15 





0.0 










0.00 


N. m. canescens 


(2) 


10 


1 


10.0 


2 


1 


3.0 


3 


0.30 


N. f. baileyi X 




















(N. f. baileyi X 


















N. to. canescens) 


1 





0.0 










0.00 


TOTAL 




42 


3 


7.1 


4 


3 


2.3 


2 


0.17 






Neotoma micropus canescens (2) 


males 








IV. /. baileyi 




3 


1 


33.3 





1 


1.0 


1 


0.33 


-V. /. campestris 




6 


2 


33.3 


2 


5 


3.5 


3-4 


1.17 


X. j. attwateri 




6 


2 


33.3 


6 


1 


3.5 


3-4 


1.17 


X. m. canescens 


(1) 


5 


4 


80.0 


6 


4 


2.5 


2-3 


2.00 


X. m. canescens 


(2) 


8 


4 


50.0 


6 


5 


2.8 


3 


1.38 


N. f. campestris 


X 


















N. to. canescens 


1 


1 


100.0 


2 


1 


3.0 


3 


3.00 


TOTAL 




29 


14 


48.3 


22 


17 


2.8 


3 


1.34 



N. f. baileyi X 
N. f. campestris 



N. f. baileyi 
N. to. canescens 



2 



.V. /. baileyi X N. f. campestris male 



100.0 



N. f. baileyi X .V. /. attwateri males 
1 1 100.0 2 2 

1 0.0 



2.0 



4.0 



2.00 



4.00 
0.00 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



141 







TABLE 18.— Continued. 










Females 


Number 

matings 

attempted 


Number 
successful 

matings 


Percent 
success 


Number 
progeny 


Mean 
litter 
size 


Mode 
litter 
size 


Progeny 

per 

attempted 

mating 


N. f. baileyi X 
N. f. attwateri 


1 


1 


100.0 


1 


2 


3.0 


3 


3.00 


TOTAL 


3 


2 


66.7 


3 


4 


3.5 


3-4 


2.33 




N.f 


. campesi 


ris XN.f. 


attwateri 


males 








N. f. campestris 


o 


1 


50.0 


2 


1 


3.0 


3 


1.50 


X. f. campestris X 
N. f. attwateri 


1 





0.0 










0.00 


TOTAL 


3 


1 


33.3 


2 


1 


3.0 


3 


1.00 




N. 


/. baileyi 


X N. m. canescens males 








X. /. baileyi 


1 


1 


100.0 


2 


2 


4.0 


4 


4.00 


N. m. canescens (2) 


1 





0.0 










0.00 


TOTAL 


2 


1 


50.0 


2 


2 


4.0 


4 


2.00 




N.f. 


campest; 


ris X N. m. 


canescent 


( males 








N. f. campestris X 
N. m. canescens 


6 


2 


33.3 


2 


2 


2.0 


2 


0.67 


N. f. attwateri X 


















N. m. canescens 


1 


1 


100.0 





2 


2.0 


2 


2.00 


TOTAL 


7 


3 


42.9 


2 


4 


2.0 


2 


0.86 



N. f. attwateri X N. m. canescens Fi males 



N. f. campestris 

N. m. canescens (2) 

N. f. campestris X 

N. m. canescens 
N. f. attwateri X 

N. m. canescens Fi 
TOTAL 



N. f. attwateri 
N. f. attwateri X 
N. m. canescens F? 
TOTAL 



6 
14 



0.0 
50.0 

66.7 

33.3 
42.9 



1.5 

2.5 

2.5 
2.2 



1-2 
2-3 

2-3 

2 



N. f. attwateri X N. m. canescens F^ males 

1 1 100.0 1 2 3.0 



0.0 
50.0 



I 



3.0 



N. m. canescens X (N. f. attwateri X N. m. canescens) male 
N. f. campestris X 

N. m. canescens 1 0.0 

All Neotoma floridana males 



0.00 
0.75 

1.67 

0.83 
0.93 



3.00 

0.00 
1.50 



0.00 



N. floridana 


63 


31 


49.2 


49 


51 


3.2 


3 


1.59 


N. micropus 


22 


10 


45.5 


17 


17 


3.4 


4 


1.55 


Species-hybrids 


3 


2 


66.7 


2 


3 


2.5 


2-3 


1.67 


TOTAL 


88 


43 


48.9 


68 


71 


3.2 


3 


1.58 






All Neotoma micr 


opus male; 










N. floridana 


31 


7 


22.6 


10 


9 


2.7 


2-3-4 


0.61 


N. micropus 


38 


9 


23.7 


14 


10 


2.7 


3 


0.63 


Species-hybrids 


2 


1 


50.0 


2 


1 


3.0 


3 


1.50 


TOTAL 


71 


17 

All 


23.9 
species-hyb] 


26 
id males 


20 


2.7 


3 


0.65 


N. floridana 


3 


2 


66.7 


3 


4 


3.5 


3-4 


2.33 


N. micropus 


5 


2 


40.0 


2 


1 


1.5 


1-2 


0.60 


Species-hybrids 


18 


7 


38.9 


7 


9 


2.3 


2 


0.89 


TOTAL 


26 


11 


42.3 


12 


14 


2.4 


2 


LOO 



142 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 18.— Concluded. 



Females 


Number 

matings 

attempted 


Number 
successful 
matings 


Percent 

success 


Number 
progenv 

tftf $? 


Mean 
litter 
size 


Mode 
litter 
size 


Progeny 

per 

attempted 

mating 






All 


ion-hvbrid 


males 










Same species 
Other species 
Species-hybrids 
TOTAL 


101 

53 

5 

159 


40 

17 

3 

60 


39.6 
32.1 
60.0 

37.7 

All males 


63 

27 

4 

94 


61 

26 

4 

91 


3.1 
3.1 

2.7 
3.1 


3 
4 
3 
3 


1.23 
1.00 
1.60 
1.16 


All females 


185 


71 


38.4 


106 


105 


3.0 


3 


1.14 



a male of the same race. Minima and 
maxima frequently were 33 to 36 days. 

No clearcut differences were observed 
in gestation periods of the two species 
either by me or by Spencer ( 1968 ) . Ap- 
parently the gestation period normally 
fluctuates from 32 to 38 days with a 
modal duration of 35 days. Post-partum 
estrus and prolonged gestation appar- 
ently occur in both species, but the fre- 
quency of this phenomenon is not well 
known and the physiology associated 
therewith has not been investigated. 

Size of Litters. — Literature pertaining 
to litter size of Ncotoma floridana has 
been summarized by Rainey ( 1956:613). 
In most populations that have been 
studied, females regularly produced lit- 
ters of one to four; occasional litters of 
five have been reported. Modal litter 
size for the species is three and the mean 
usually is near three. Litter size of N. 
micropus (Asdell, 1964:279) is appar- 
ently slightly smaller. Feldman (1935: 
301, 302) studied members of this species 
from Carlsbad, New Mexico; each of 11 
litters consisted of two young and in 
each litter both progeny were of the 
same sex. 

Size of litters born to females of the 
northern N. f. baileyi in the laboratory 
was slightly greater than those of any of 
the other woodrats, as evinced both by 
the mean (3.5) and the mode (four). 
Litter size of the other two subspecies 
of N. floridana and that of N. m. canes- 
cens are comparable, having means near 
3.0 and modes of three. Two litters born 



to N. f. baileyi X N. f. campestris "hy- 
brid" females had only two progeny each. 
This may indicate some type of partial 
sterility, but more observations would be 
necessary to draw meaningful conclu- 
sions. The single litter born to an N. f. 
baileyi X N. f. attwateri "hybrid" female 
was the same as the modal litter size 
(three) of floridana females; a male of 
this cross sired a litter of four when 
mated to a baileyi female. 

Litter size of species-hybrids was no- 
ticeably lower than that of either of the 
parental species. Considering all mat- 
ings involving at least one species-hy- 
brid, modal litter size both of males and 
of females was only two and the mean 
for both was 2.4. Because hybrid males 
sired only four litters with non-hybrid fe- 
males and hybrid females produced only 
five litters from matings with non-hybrid 
males, it was not possible to determine 
unequivocally from the data whether lit- 
ters of hybrids are smaller because of 
partial sterility in both sexes or only in 
one. However, it can be seen in tables 
17 and 18 that no hybrid female pro- 
duced a litter of more than three young, 
whereas one hybrid male sired a litter of 
four when mated to a floridana female. 
Of the 71 litters born as a result of labo- 
ratory matings, only two consisted of a 
single progeny; one of these matings was 
between a hybrid male and a micropus 
female. Mean litter size of non-hybrid 
females bred to hybrid males was 2.5 
whereas that of the reciprocal was 2.7. 
Matings involving two hvbrid individuals 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



143 



averaged only 2.3 progeny per litter, pos- 
sibly indicating that hybrids of both sexes 
are less fertile than non-hybrids. 

Table 15 provides additional informa- 
tion on litter size and seasonal patterns 
of reproduction. Data presented in table 
16 give further information on litter sizes 
and the reproductive season over a wide 
geographic area. Litter sizes of fioridana 
and micropus may vary geographically, 
with more northerly populations having 
larger litters. In N. f. bailey i the mean 
was more than 3.5 and the mode was 
four progeny per litter; these data are 
based on successful matings in the labo- 
ratory, parturiation of previously con- 
ceived litters in the laboratory, and em- 
bryo counts recorded on specimen labels. 
All parameters studied indicate that N. 
f. campestris, N. f. attwateri, and north- 
ern populations of N. m. canescens most 
frequently have litters of three young 
each and that the mean usually is near or 
only slightly greater than three. South- 
ern populations of canescens most fre- 
quently have litters of two progeny as 
seen in table 16 and reported by Rami 
(1966:17) and Baker (1956:286). 

The correlation between latitude and 
litter size of mammals has been observed 
previously (Lord, 1960, and others) and 
probably has been best explained by 
Spencer and Steinhoff ( 1968 ) , who ex- 
panded the theorv originally put forth 
by Lack (1948, i954). Individuals of 
northern populations have shorter breed- 
ing seasons and can place more progeny 
in subsequent generations by exerting 
more "energy" per litter on large litters, 
whereas those in southern populations 
are most successful by conserving 
"energy" expended per litter and produc- 
ing more litters with each containing 
fewer individuals. In the woodrats 
studied, at least, information discussed 
previously regarding breeding seasons 
further substantiates the hypothesis. 

Sex Ratios at Birth. — Sex ratios of 
progeny of all rats studied appear to be 
the typical one to one relationship. The 
only sample that deviates significantly 
(P<0.05, tested by Chi-square) is the 



26 males to 12 females born to N. micro- 
pus females that were pregnant when 
captured; four of 11 litters consisted only 
of male offspring. However, among 
young micropus collected with adult fe- 
males there were more females than 
males and when the two samples are 
considered together the number of males 
only slightly exceeds the number of fe- 
males. 

Reproduction in Neotoma angusti- 
palata. — Information on the reproductive 
habits of N. angustipalata is limited. 
Hooper (1953:9) reported two nursing 
young collected with a female on 19 
May, and an adult female (Table 16) 
contained a single embryo when ob- 
tained in July. Two juveniles (UNAM 
2166 and 2167) were collected on 6 
October. 

Discussion and Conclusions. — Repro- 
ductive habits of N. fioridana and N. 
micropus vary both intra- and inter- 
specifically. In the primary study area, 
the first litters of micropus are born two 
or three weeks prior to the first litters of 
fioridana, but the breeding seasons of the 
two species are otherwise approximately 
the same. Laboratory and field observa- 
tions conducted by me, and Spencer 
(1968) show that the two species do 
hybridize, and that hybrid progeny are 
somatically and reproductively viable. 
However, hybridization results in partial 
hybrid sterility, as evinced by reduced 
litter size. Reproductive isolation is at 
best incomplete between the two species 
and they probably will hybridize at all 
localities of sympatry, at least until selec- 
tion has had sufficient time to establish 
and reinforce a mechanism of reproduc- 
tive isolation. Only a single area of sym- 
patry is presently known and the re- 
sultant hybrid zone (see account of N. 
m. canescens above) has not increased 
in size during the five years that it has 
been under observation. Furthermore, 
no conslusive evidence exists to indicate 
that the hybridization in north-central 
Oklahoma is introgressive or that intro- 
gression has occurred elsewhere along 
the potential zone of contact between 



144 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



the two species. Reproductive and distri- 
butional evidence indicate that the two 
species may be in an allopatric phase of 
speciation as described by Key (1968), 
wherein dynamic tension zones, such as 
the mixed population in north-central 
Oklahoma, are formed prior to establish- 
ment of full reproductive isolation. 

COMPARATIVE SEROLOGY 

The dependency of protein synthesis 
on genetic control indicates that physico- 
chemical and immunological characteris- 
tics of protein macromolecules are phe- 
notypic expressions of the genotype. 
Comparative study of proteins, therefore, 
serves as an important means of studying 
the relationships of animals (Florkin, 
1964; Boyden, 1964 ) . Evolutionary rates 
of serological characters undoubtedly are 
stochastic (Kirsch, 1969), as are those 
of most characters. 

Starch Gel Electrophoresis of 
Hemoglobins 

Electrophoretically demonstrable var- 
iation in mammalian hemoglobins has 
been the subject of much study recently. 
In the Carnivora, hemoglobins appear to 
be relatively stable even at the ordinal 
level (Seal, 1969), whereas in the Chir- 
optera variation has been reported at 
the familial and generic levels ( Mitchell, 
1966; Valdivieso et al, 1969). Hemo- 
globin ionographs of primates (Neel, 
1961; Ingram, 1963; Hill and Buettner- 
Janusch, 1964; Sullivan and Nute, 1968) 
and rodents (Johnson, 1968; Foreman, 
1960; and others) have been shown to 
vary intraspecifically in many taxa. Ad- 
ditionally, Foreman (1964) discovered 
by tryptic hydrolysis that in the genus 
Peromyscus some electrophoretically 
identical hemoglobins are chemically 
distinct. 

Birney and Perez (1971) reported 
multiple hemoglobins in Neotorna flori- 
dana, N. micropus, and laboratory-bred 
hybrids of the two species. They ob- 
served major bands of four migration 
rates, designated (from slowest to 



fastest) 1', 1, 2, and 3, and several minor 
bands that were not studied. Based on 
the number and position of major elec- 
trophoretic bands, seven distinctive he- 
moglobin patterns or phenotypes were 
described and labeled A through G as 
follows (Fig. 39): "A" occurred only in 
micropus and consisted of band 1 with 
a leading diffuse zone that terminated in 
a minor band at position 3; "B" was ob- 
served in both species and in hybrids and 
consisted of bands 1 and 2 and a leading 
diffuse zone; "C", observed only in flori- 
dana and hybrids, was composed of 
bands 1, 2, and 3; "D" consisted of bands 
2 and 3 with a trailing diffuse zone and 
also was limited to floridana and hybrids; 
"E" was seen only in micropus and hy- 
brids and was composed of bands 1' and 
2 with a long leading diffuse zone and a 
terminal minor band; "F" was observed 
only in floridana and consisted of a heavy 
band, considered to be band 1, preceded 
by a short diffuse zone; "G" was observed 
only in laboratory-bred hybrids and con- 
sisted either of bands 1', 2, and 3 or of 
all four major bands. 

Results of electrophoresing precipi- 
tated globins by the urea — veronal 
method of Chernoff and Pettit (1964) in- 
dicated to Birney and Perez ( 1970 ) that 
the electrophoretically demonstrable var- 
iation resided in the beta (/?) chains of 



— 








ORIGIN 








r 
1 


_ 


M 


_ 




- 


_ 


- 


2 




■■ 


M 


M 


wm 





« 


3 

4 

+ 








™ 


"" 






■" 


A 


B 


C 


D 


E 


F 


G 



Phenotypes 

Fig. 39. Diagrammatic representation of 
electrophoretic patterns ( phenotypes ) of hemo- 
globins of Neotoma floridana and N. micropus. 
Major bands are represented by solid rectangles 
and minor bands by horizontal lines. The cath- 
ode is indicated by a minus sign and the anode 
by a plus sign. See Birney and Perez (1971) 
for photographs of starch gels showing electro- 
phoresed woodrat hemoglobins. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



145 



the hemoglobin molecules. They further 
proposed tentative models that explained 
the inheritance patterns observed and 
demonstrated a possible sequence for the 
evolution of multiple beta loci in the spe- 
cies studied. According to the model, 
multiple beta loci have arisen by gene 
duplication so that at least three such 
loci (probably closely linked) now are 
present in floridana and at least two exist 
in micropus. Neotoma micropus may 
have either a third locus for production 
of the beta peptides of molecules forming 
band 1', or genes producing these pep- 
tides may be allelic with those producing 
the beta peptides seen in band 1. "Alleles" 
that produce no peptide (termed ft° al- 
leles) apparently are present at all beta 
loci. These non-functional alleles may be 
either deleted areas on the chromosomes 
or they may be areas that are physically 
present but under control of modifier 
genes, or for other reasons do not con- 
tribute a peptide chain. If modifier 
genes are involved, it is likely that the 
minor bands result from limited produc- 
tion of the same peptides that form major 
bands when the ft locus involved is fully 
active. 

Materials and Methods. — Studies of 
hemoglobin samples discussed here were 
conducted simultaneously with those re- 
ported by Birney and Perez ( 1971 ) . De- 
tailed methods were outlined in that re- 
port and are only summarized here. 
Samples of whole blood were suspended 
in a trisodium citrate anticoagulate, 
washed three times in phosphate buf- 
fered saline, and lysed in distilled water. 
Hemoglobin phenotypes were deter- 
mined by horizontal starch-gel electro- 
phoresis in sodium borate buffer. Gels 
were sliced and stained in a solution of 
amido black in water-methanol-glacial 
acetic acid. The iodoacetimide method 
described by Riggs ( 1965 ) was em- 
ployed to determine that none of the 
observed bands resulted from polymer- 
ization. Laboratory-bred woodrats are 
not included in the discussion of hemo- 
globin variation presented here because 
they would tend to bias the frequency 



of various phenotypes in favor of the 
phenotype(s) of their parents. 

Results and Discussion. — Frequencies 
of the seven hemoglobin phenotypes ob- 
served in natural populations of Neotoma 
floridana and N. micropus are shown in 
table 19. At the time ancestral popula- 
tions of floridana and micropus consti- 
tuted a single species, it would appear 
that only hemoglobin bands 1 and 2 were 
present. These two bands are common 
to both species and when they occur to- 
gether to form phenotype B, the patterns 
of the two species are essentially indis- 
tinguishable. When band 1 occurs with- 
out band 2 (phenotypes A and F), it is 
heavier; the band migrates slightly 
slower in floridana, and has a longer 
leading diffuse zone in micropus. The 
major band probably is formed by the 
same, or only slightly modified, peptides. 
The single banded situation may be the 
primitive hemoglobin phenotype for the 
two species, or phenotypes A and F both 
may have been secondarily derived after 
the two species were isolated. In any 
event, it appears that ft 1 and ft 2 both 
were present at the time of isolation be- 
cause both were expressed by some indi- 
viduals of the two species from every 
locality from which I have a sample of 
three or more individuals. 

The ft 1 ' and ft s alleles apparently 
originated in populations of micropus 
and floridana, respectively, after the two 
incipient species were geographically iso- 
lated. Although both alleles are present 
in the sample of woodrats from 3 mi S 
Chester, Major Co., Oklahoma, they have 
not been observed together elsewhere; 
ft 1 ' is not known for floridana nor is ft 3 
known for micropus. If the ft 1 ' allele 
ever was present in floridana, or if ft 3 
ever was present in micropus, they have 
been lost secondarily or exist in those 
species in extremely low frequency. 

It is not known whether the genes 
controlling production of the beta chains 
of molecules forming bands 1 and 1' are 
alleles of a single locus or if they occur 
at separate loci. Similarly, it is not known 
with certainty what phenotype results 



146 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



TABLE 19. Frequency, expressed in percent, of seven hemoglobin phenotypes at selected 
localities of Neotoma floridana and N. micropus. 



Hemoglobin Phenotype 



Origin of samples 



N 



I) 



Cherry Co., Nebraska 
Rock Co., Nebraska 
All localities 

Logan Co., Kansas 
Finney Co., Kansas 
Ness Co., Kansas 
Hodgeman Co., Kansas 
Ellis Co., Kansas 
Russell Co., Kansas 
All localities 

Ellsworth Co., Kansas 
Douglas Co., Kansas 
All localities 



All localities 





Neotoma floridana baileyi 




17 


5.9 


52.9 


41.2 


2 




50.0 


50.0 


19 


5.3 


52.6 


42.1 




Neotoma floridana < 


:ampestris 




3 


66.7 




33.3 


6 


66.7 






3 


100.0 






2 




100.0 




4 


100.0 






17 


5.9 


35.3 


58.8 


35 


40.0 


22.9 


31.4 




Neotoma floridana 


att water i 




4 


75.0 




25.0 


13 


76.9 


23.1 




17 


76.5 


17.6 


5.9 



Neotoma floridana 
71 39.4 29.6 

Neotoma micropus canescens 



28.2 



33.3 



5.7 



2.8 



Baca Co., Colorado 


29 


10.3 


20.7 




69.0 




Hamilton Co., Kansas 


2 


50.0 






50.0 




Haskell and Stevens 














cos., Kansas 


22 


18.2 


40.9 




40.9 




Meade Co., Kansas 


6 




50.0 




50.0 




Barber Co., Kansas 


13 




46.2 




53.8 




All localities 


72 


11.1 


33.3 





55.6 





Neotoma from 3 mi S Chester, 


Major Co. 


Oklahoma 




Specimens morphologically 














like N. micropus 


5 





40.0 




40.0 


20.0 


Specimens morphologically 














like hybrids 


8 





12.5 


25.0 


12.5 


50.0 


All specimens 


13 


-- 


23.1 


15.4 


23.1 


38.4 



when both genes are present (Birney 
and Perez, 1971). Therefore, it is not 
possible to calculate their frequency ac- 
curately. Moreover, no 7nicropus has 
been observed that lacked both bands 
1 and I', but breeding data presented by 
Birney and Perez indicate that the /3° 
allele also occurs in low frequency at 
the /3 1 -/? 1 ' locus(i) in that species, as it 
does in floridana. A crude estimate of the 
frequency of fi 1 and /3 1 ' can be calculated 
by the Hardy-Weinberg formula, if it is 
assumed that (3 1 and /2 1 ' are allelic, that 
when both are present fi x ' acts as a dom- 
inant, and that the frequency of the 
f3° allele associated with that locus is 
sufficiently low to be ignored. By 



using this formula and following the 
genetic scheme proposed by Birney and 
Perez ( 1971 ) , estimates of the frequency 
of all other alleles for both species can 
be calculated as accurately as size of 
available samples permits (Table 20). 

Changes in hemoglobin allele fre- 
quency of Mus musculus on the Jutland 
Peninsula appeared to Selander, Hunt, 
and Yang (1969:384) to be directional 
from west to east, but in the United 
States variation apparently is north to 
south (Selander, Yang, and Hunt, 1969: 
285). The frequency of the /3 1 ' allele in 
N. micropus fluctuates geographically, 
but no clear picture of the nature of this 
variation emerges from examination of 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



147 



the three populations (Table 20) which 
have sufficiently large samples to warrant 
calculation of gene frequencies. Some 
individuals at all localities sampled pos- 
sess the allele and it probably is wide- 
spread in the population. However, it 
was not found to be fixed at any locality. 
The ft 2 locus is polymorphic at the four 
western localities sampled, but the /?- 
allele may be fixed in eastern populations 
of the species as indicated by the absence 
of phenotype A in samples from Meade 
and Barber counties and in the "hybrid" 
sample from Oklahoma. The ft- locus 
was polymorphic in N. floridana at only 
one locality (Finney County, Kansas), 
but additional sampling might have 
yielded animals of phenotype F from 
other localities. 

Two populations of IV. floridana 
(campestris from Russell County and 
bailey i) appear to have slightly higher 
frequencies of the /3 1 allele and consider- 
ably higher frequencies of the (3 s allele 
than do other populations of the species 
(Table 20). Of the 17 woodrats from 
Russell County, 16 were from a single 
juniper windbreak and all of these had 



the /8 3 allele; hemoglobin of the only 
animal obtained from another windbreak 
several miles distant lacked band 3. 

None of the 13 individuals of N. f. 
attwateri from Douglas County lacked 
band 1, but hemoglobin of one of four 
animals from Ellsworth County (near 
the attwateri-campestris subspecies boun- 
dary ) did not form the band ( Table 19 ) . 
Frequency of /? 8 appears to be low in the 
sampled populations of N. f. attwateri, 
but the relatively high frequency of this 
allele in the "hybrid" population from 
Major County, Oklahoma, indicates that 
in adjacent populations of N. f. attwateri 
the frequency of this allele is either rela- 
tively high or that phenotype G conveys 
a strong selective advantage. 

Presence of hemoglobin phenotype G 
in several individuals from 3 mi S Ches- 
ter, Major Co., Oklahoma, clearly indi- 
cates that the two species have hybrid- 
ized at this locality. The phenotype has 
been observed previously in known hy- 
brids (Birney and Perez, 1971), but not 
in woodrats of either species from local- 
ities of allopatry. 

Functional relationships of the dif- 



TABLE 20. Frequency of hemoglobin alleles at selected localities of Neotoma floridana and 
N. micropus. Localities with samples of less than 10 individuals are not shown separately but 

are included in totals. 



Sample 



N 



j3l' 131 /3o a 



/33 /3o" 



Neotoma floridana baileyi 

Cherry County, Nebraska 

All localities 
Neotoma floridana campestris 

Russell County, Kansas 

All localities 
Neotoma floridana attwateri 

Douglas County, Kansas 

All localities 
Neotoma floridana 

All localities 
Neotoma micropus canescens 

Baca County, Colorado 

Haskell and Stevens counties, Kansas 

Barber County, Kansas 

All localities 
Neotoma sp. 

Major County, Oklahoma 



17 


0.00 


0.36 


0.64 


1.00 


0.00 


0.76 


0.24 


19 


0.00 


0.35 


0.65 


1.00 


0.00 


0.77 


0.23 


17 


0.00 


0.23 


0.77 


1.00 


0.00 


0.76 


0.24 


35 


0.00 


0.44 


0.56 


0.76 


0.24 


0.37 


0.63 


13 


0.00 


1.00 


0.00 


1.00 


0.00 


0.12 


0.88 


17 


0.00 


0.76 


0.24 


1.00 


0.00 


0.13 


0.87 


71 


0.00 


0.47 


0.53 


0.83 


0.17 


0.35 


0.65 


29 


0.44 


0.56 


0.00 


0.68 


0.32 






22 


0.23 


0.77 


0.00 


0.57 


0.43 






13 


0.32 


0.68 


0.00 


1.00 


0.00 






72 


0.33 


0.67 


0.00 


0.67 


0.33 


— 


— 


13 






___. c 


1.00 


0.00 


0.32 


0.68 



See text for assumptions made to calculate frequencies of these alleles for N. micropus. 
There presently is no evidence that this locus occurs in N. micropus. 
Frequency of these alleles in this population cannot be calculated. 



148 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



ferent hemoglobin phenotypes are un- 
known. The data appear to indicate a 
poorly defined tendency for animals from 
arid habitats to have fewer electropho- 
retic bands (thus fewer kinds of beta 
polypeptides) than animals from more 
mesic habitats. Man well et ah (1963) 
found that hemoglobins of hybrids may 
have selective advantages over those of 
either parental species in some birds, 
but no data are available on this subject 
for woodrats. 

Immunoelectrophoresis of Esterases 

It has been shown that injections of 
whole serum alone stimulate production 
of a relatively specific antiserum of low 
antibody titer (Durand and Schneider, 
1963), but that whole serum emulsified 
with complete Freund's adjuvant results 
in an antiserum of relatively high anti- 
body titer and low specificity (Anthony, 
1965). Because adjuvant was used in 
this study, antisera were of the latter 
type. A pilot study of precipitin tests 
( Boyden, 1964, and elsewhere ) indicated 
that either the antisera were not suf- 
ficiently specific to distinguish minor dif- 
ferences in woodrat proteins, or that pro- 
teins of the closely related woodrats un- 
der study had not diverged perceptibly 
at the sites of antigen-antibody reaction. 
Anthony ( 1965 ) found that precipitin 
tests were inefficient for comparing 
closely related races and species of the 
genus Canis. 

Micro-immunoelectrophoresis(Schnei- 
degger, 1955) has a distinct advantage 
over precipitin testing because individual 
arcs of precipitate are formed. However, 
Gerber ( 1968 ) observed that neither to- 
tal counts nor weighted scores based on 
intensity of general protein arcs were 
reliably indicative of systematic relation- 
ships of bats. To reduce the number of 
arcs to be considered, Anthony ( 1965 ) 
conducted immunoelectrophoresis and 
differentially stained only for esterases. 

Because intra- and interspecific varia- 
tion in esterases is well known (see Au- 
gustinsson, 1961) and because it was 
desirable to determine if the immune 



reaction might further elucidate informa- 
tion on the relationships of woodrats, this 
technique was employed. 

Materials and Methods. — Rats were 
bled by cardiac puncture. Sera were sep- 
arated by centrifugation and preserved 
by freezing at -15°C. Antisera against 
pooled samples of whole sera were pre- 
pared in rabbits following the procedure 
outlined by Gerber and Birney (1968: 
413). Antisera obtained following the 
second series of immunizing injections 
were used in all reactions. Woodrats 
from which sera were used for produc- 
tion of antiserum are as follows: Neo- 
tonia floridana baileyi — 15, from Cherry 
County, Nebraska (A); N. f. campestris 
— 8, from Logan and Finney counties, 
Kansas (B); N. f. attwateri — 14, from 
Douglas County, Kansas (F); N. f. 
magister — 4, from Giles County, Virginia 
(G); N. m. canescens — 16, from Haskell 
County, Kansas (I); N. m. canescens — 
13, from Barber County, Kansas (K). 
Serum of each of the above-listed wood- 
rats also was used in reactions with anti- 
sera and, in addition, sera of woodrats 
listed below were reacted against anti- 
sera but not used in production of the 
latter: N. f. campestris — 14, from Ellis 
County, Kansas (C); N. f. campestris — 
4, from Russell County, Kansas (D); N. 
f. attwateri — 1, from Ellsworth County, 
Kansas (E); N. m. canescens — 11, from 
Baca County, Colorado (H); IV. m. 
canescens — 7, from Meade County, Kan- 
sas (J); Neotoma sp. — 3, from area of 
sympatry in Major County, Oklahoma 
( L) . Letters following localities indicate 
geographic origin of specimens in figure 
42 and table 21. All animals used were 
adults and had been in captivity at least 
two weeks. An attempt was made to in- 
clude an equal number of animals of 
both sexes in each sample, but smaller 
samples did not always have equal sex 
ratios. 

The sample of Neotoma floridana 
magister was included to serve as a 
standard for other comparisons and be- 
cause the taxonomic status of this taxon 
is unclear; ?nagister may be a species dis- 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



149 



tinct from other populations of floridana. 

Concentration of protein-nitrogen for 
Immunoelectrophoresis and for injecting 
rabbits was determined with an Aloe- 
Ilitachi hand protein-refractometer. Se- 
rum was diluted to contain one gram per 
cent protein. Slides for immunoelectro- 
phoresis were prepared by layering three 
ml of a two percent Ionager solution on 
each microscope slide. The arrangement 
of antigen wells and antibody troughs 
used is shown in figure 40. Electropho- 
resis was conducted in Michalis' buffer, 
ionic strength 0.05, pH 8.7, for 35 min- 
utes at 40 volts. Ten lambda of unpooled 
serum from individual woodrats were 
placed in each antigen well immediately 
prior to electrophoresis. Each slide was 
prepared in duplicate. Following elec- 
trophoresis, gel in the precut trough was 
removed and the trough filled with anti- 
serum. Reactants were allowed to inter- 
act in a humidity chamber for 24 hours. 
Unbound protein was removed by wash- 
ing the agar slides for two days in three 
washes of borate-buffered saline, pH 8.6. 
Salts were removed similarly in three 
rinses of distilled water. The agar then 
was dried to a thin film and stained for 
esterase activity. The staining solution 
consisted of 40 ml of 0.2 M Tris-maleate 
and 0.2 M sodium hydroxide adjusted to 
a pH of 7.0, 1 ml of one per cent oc - 
naphthyl acetate (in acetone), and 20 
mg of Fast Blue RR diazonium salt. 
Reagents were mixed immediately be- 
fore use and gels incubated in the solu- 
tion for 20 minutes at room temperature. 
Stained slides were soaked for 15 min- 
utes in a two per cent glycerol solution 
to prevent cracking and peeling of the 
agar. 

The size and intensity of the major 
esterase band (Fig. 41) formed by the 
antigen of each woodrat against each 
antiserum was assigned a value on a 
scale of zero to eight. The minor band 
was scored similarly on a zero to two 
scale. Exemplary slides were selected 
with bands of each value to standardize 
scoring. The two values for each indi- 
vidual were added together and sub- 



01 

■a 
o 

■S 
(0 

O 


Antigen well 

& 

Antibody trough 


"O 

o 
c 

< 


1 1 


O 



Fig. 40. Diagrammatic representation of 
microscope slide with Ionagar gel as used for 
Immunoelectrophoresis. 

jected to a Y + 1 conversion to eliminate 
zero scores. These values then were 
averaged for the woodrats from each lo- 
cality. Because six antisera were used 
and two bands were considered for each 
antiserum, a total of 12 values was calcu- 
lated for specimens from each locality. 
These values were used as characters and 
the sample from each locality was treated 
as an OT U in the CLSNT subroutine dis- 
cussed previously. 

Results and Discussion. — Mean values 
of scores for size and intensity of esterase 
bands are shown in table 21. It is im- 
mediately apparent that band scores for 
the population of N. f. campestris from 
Ellis County are highest in every case. 
Normally, in immunological tests, the 
homologous reaction is expected to ex- 
ceed all cross reactions, and cross reac- 
tions are considered in terms of percent 
immunological correspondence to the 
homologous reaction, which is set at 100. 
This technique is clearly not applicable 
in evaluation of the data at hand; even 
when the population from Ellis County 
is disregarded, the homologous reaction 
invariably is exceeded by at least one 
other cross reaction. 

Anthony (1965) found that the im- 
munological response to esterase antigens 
in cross reactions often surpassed that in 
reference reactions in studies of dogs. 
Several variables apparently interact to 
result in this phenomenon. The number 
of evolutionarily based changes in ester- 
ase molecules at antibody-antigen reac- 
tion sites between closely related popula- 
tions undoubtedly is low, antiserum pro- 
duced against an emulsion of whole 
serum and adjuvant is not highly specific, 
individual subjects have varying concen- 



150 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



Fig. 41. Examples of esterase bands formed 
by differentially staining antigen-antibody pre- 
cipitate in dried Ionagar on microscope slides. 
The antiserum used was prepared against the 
serum of Neotoina floridana campestris. Sepa- 
rate samples of serum from two woodrats were 
placed in the wells (left and right) of each 
slide as follows: A — N. f. campestris from lo- 
cality C; B — N. f. baileyi from locality A; C — 
N. f. attwateri from locality F; D — N. f. magis- 
ter from locality G; E — N. micropus canescens 
from locality I; F — N. m. canescens from lo- 
cality K. See accompanying text for explanation 
of locality codes. 



trations of an enzyme in the serum de- 
pending on a variety of both intrinsic 
and extrinsic factors (see, for example, 
Jones and Bunde, 1970), and the cataly- 
tic action of enzymes is often reduced by 
reaction with corresponding antibodies, 
especially in antibody excess (Cinader, 
1957:373). If the antigen of a given sam- 
ple contained a sufficient quantity of 
esterase molecules to stimulate produc- 
tion of a high titer of anti-esterase anti- 
bodies of relatively low specificity, and 
if a related sample contained the same 
or a similar esterase in greater quantity, 
the cross reaction would be expected to 
exceed the reference reaction when the 
two samples were tested. Therefore, the 
immune reaction involving single en- 
zymes has severe limitations when com- 
paring closely related taxa. 



Nevertheless, Anthony (1965) found 
that correlations of these kinds of data 
frequently corresponded well with gen- 
erally accepted theories of relationships 
of various breeds of dogs. The correla- 
tion and distance phenograms as calcu- 
lated by CLSNT for the woodrats studied 
are shown in figure 42. Values for IV. /. 
campestris (C) from Ellis County are 
sufficiently greater than values for other 
samples that the distance phenogram 
separates that sample from all others at 
a distance (2.36) nearly double that 
(1.24) of the next major separation. 
Elsewhere in the distance phenogram, 
the two samples of N. f. attwateri appear 
as a subgroup closely allied to the hybrid 
sample from Oklahoma, the three sam- 
ples of N. m. canescens from adjacent lo- 
calities in Kansas form a single subgroup, 
but samples from the remaining localities 
do not correspond well with other data 
concerning relationships. 

In the correlation phenogram, which 
should reflect the relative degree of re- 
activity ( enzyme similarity? ) rather than 
the magnitude of reactions, the Ellis 
County population is closely coupled 
with the sample of N. f. attwateri from 
nearby Ellsworth County. The sample 
of N. f. attwateri from Douglas County 
is next to join that subgroup, followed 
by the sample from the locality of sym- 
patry. It was expected that the popula- 
tion of N. f. campestris (D) from Russell 
County, which is geographically and 
morphologically intermediate between 
those from Ellis and Ellsworth counties, 
would also be in that subgroup. How- 
ever, that sample formed a relatively 
distinct subgroup with the sample of N. 
f. magister, to which it certainly is not 
closely allied either geographically or 
morphologically. 

The sample of N. f. baileyi, and to 
a lesser extent, the sample of N. f. cam- 
pestris (B) from Logan and Finney 
counties, Kansas, appear in both pheno- 
grams to have esterases more like those 
of N. micropus than like those of other 
populations of N. floridana. This rela- 
tionship may somehow correspond more 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



151 



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152 



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|— N.f. baileyi A 

- N. m. canescens H 

- N. m. canescens I 

- N. f. campestris B 

- N. m. canescens K 

- N. m. canescens J 

- N. f. campestris D 

- N. f. magister G 

- N. f . campestris C 

- N. f. attwateri E 

- N.f. attwateri F 

- Neotoma sp. L 



0.26 -0.06 



0.16 



0.36 0.56 



0.76 



B 



2.36 



1.96 1.56 



1.16 



N.f. baileyi 



N.f. campestri s B 

' N. m. canescens H 

N. m. canescens K 

N. m. canescens | 

N. m . canescens j 

N. f. campestris D 

N. f. magister G 

N. f. attwateri E 

N. f. attwateri F 

Neotoma sp. L 

N. f. campestris C 



0.76 0.36 



Fie. 42. Correlation (A) and distance (B) phenograms generated from 
mean scores of size and intensity of precipitated esterase-antibody bands. The 
coefficient of cophentic correlation of A is 0.792, whereas that of B is 0.895. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



153 



to adaptation to arid, relatively harsh en- 
vironments than to phytogeny. For 
whatever reason, both phenograms also 
indicate that, with respect to esterases, 
the sample of suspected hybrids from 
Major County, Oklahoma, more closely 
resembles floridana. from eastern Kansas 
than it does western populations of mi- 
cropus. This result is not consistent with 
characteristics of pelage and skulls of the 
specimens involved. 

The fact that rather well marked dif- 
ferences in the antibody-antigen esterase 
bands were observed between woodrats 
of the two species from different locali- 
ties clearly shows that esterases in wood- 
rats differ qualitatively, quantitatively, 
or both. However, these data must be 
interpreted with respect to all other data 
relating to the supposed relationships of 
the various populations studied. Addi- 
tional studies on individual variation of 
esterases, quantitative variation of the 
esterases of an individual under various 
environmental conditions, and antibody 
specificity to enzymes will be necessary 
before data such as these can be fully 
and reliably interpreted with respect to 
the relationships of mammals. 

COMPARATIVE KARYOLOGY 

The karyotype of Neotoma floridana 
first was described by Cross ( 1931 ), who 
reported the diploid number as 52. Mat- 
they ( 1953 ) verified the diploid number 
and described two large submetacentric 
and two large subtelocentric chromo- 
somes in the complement. Mitotic chro- 
mosomes of Neotoma micropus were 
described by Hsu and Benirschke 
(1968); the diploid number was shown 
to be 52 and the karotype illustrated re- 
sembled that reported for floridana. 

Baker and Mascarello (1960) de- 
scribed the chromosomes of several spe- 
cies of Neotoma, and redescribed the 
karyotypes of both floridana and micro- 
pus. They reported that the number of 
large biarmed elements varies from one 
to four in micropus, but that females of 
floridana have four biarms and males 



have three. They concluded that the Y 
is a medium-sized subtelocentric chro- 
mosome in both species. The chromo- 
somal polymorphism in micropus was 
discussed by Baker et ah ( 1970 ) and 
shown to be a widespread phenomenon 
geographically, involving the X chromo- 
somes and one pair of large autosomes. 

Materials and Methods. — Prepara- 
tions of chromosomes were made from 
cells in bone marrow using a modifica- 
tion of the blaze-dry techniques de- 
scribed by Patton (1967) and Lee 
(1969). Chromosomes were stained in 
a saturated solution of crystal violet. 
Only specimens collected from natural 
populations are reported. Results dis- 
cussed below are based on study of at 
least 10 chromosome spreads from each 
of 58 woodrats, including specimens of 
Neotoma floridana baileyi, N. f. campes- 
tris, N. f. attwateri, and Neotoma micro- 
pus canescens. Included also are six 
specimens collected from the area of 
sympatry between floridana and micro- 
pus — 3 mi S Chester, Major Co., Okla- 
homa. 

The maximum number of chromo- 
somes counted in any cell was 52. Some 
cells had less than 52 chromosomes, but 
the difference undoubtedly resulted from 
a loss of chromosomes during prepara- 
tion. Those having less than 52 chromo- 
somes were not studied or included in 
the 10 counts. In complete cells, no in- 
traindividual variation beyond that at- 
tributable to differential contraction of 
chromosomes was observed. 

Results and Discussion. — A consistent 
but relatively subtle ( and heretofore un- 
noted) difference exists between the 
karyotypes of Neotoma floridana and 
Neotoma micropus, irrespective of the 
number of large biarmed elements. In 
the karyotype of both there is a graded 
series of 22 pairs of so-called acrocentrics. 
However, only rarely can chromatin be 
seen beyond the centromere opposite the 
arm in metaphase preparations of the 
acrocentric chromosomes of micropus, 
whereas in floridana there is invariably a 
visable amount of chromatin beyond the 



154 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



centromeres of at least the larger acro- 
centrics. These tiny "arms" are evident 
in the karyotype of an N. f. attwateri 
illustrated by Baker and Mascarello 
(1969:189) and also were present in the 
karyotypes of floridana studied by me. 

If considered to be chromosome arms, 
these bits of chromatin would increase 
the Fundamental Number (FN) of the 
karyotype of N. floridana. Only in re- 
laxed spreads of N. f. campestris, how- 
ever, are these "arms" sufficiently large 
to cause difficulty in determining the 
number of biarmed chromosomes. Until 
more information concerning these 
"arms" is available, I consider it best not 
to include them in calculations of the 
FN and have attempted to distinguish 
such chromosomes from the subtelocen- 
trics that are involved in the polymorphic 
system. Although it may be misleading 
to refer to these chromosomes as acro- 
centrics, I will do so in an attempt to 
preserve the terminology used by Baker 
and Mascarello (1969). ' 

In the chromosomal complement of 
each of the nine female N. f. baileyi ex- 
amined, only two large and distinctly 
biarmed elements were seen (Fig. 43); 
in each instance the two biarms were of 
nearly equal size. Two distinctly bi- 
armed elements (one noticeably larger 
than the other) also were seen among the 
chromosomes of each of the four male 
baileyi karyotyped (Fig. 43). There is 
no chromosome in baileyi males that 
closely resembles the chromosome Baker 
and Mascarello ( 1969:189) designated as 
the Y of N. f. attwateri. Therefore, I 
consider the smaller of these two sub- 
metacentric elements as the Y chromo- 
some and the larger as the X. In three 
male N. f. attwateri from Douglas 
County, Kansas, four biarmed elements 
were observed (Fig. 44). Three had 
arms of unequal length and were dis- 
tinctly larger than the fourth in each in- 
stance. The fourth was indistinguishable 
from the chromosome thought to be the 
Y in baileyi. Each of six N. f. attwateri 
females ( two from Ellsworth County and 
four from Douglas County, Kansas) had 



four, large, biarmed chromosomes that 
were indistinguishable from the three 
larger biarms described for males. The 
karyotype of these females was like that 
described by Baker and Mascarello (loc. 
cit.) for five females from Payne Count}', 
Oklahoma. Apparently the Y chromo- 
some varies in attwateri, but because I 
examined only three males from a single 
locality, and Baker and Mascarello 
studied only two from another locality, 
it is not possible to determine if the vari- 
ation is geographic or if it is polymorphic 
at some localities. Available evidence in- 
dicates that the number of large biarmed 
chromosomes exclusive of the Y is con- 
stant in attwateri at four in females and 
three in males. 

A small submetacentric chromosome 
that is indistinguishable from the Y in 
baileyi and in attwateri from Douglas 
County was seen in the karyotypes of 
three of four N. f. campestris males. These 
animals were from Logan, Finney, and 
Russell counties, Kansas. The fourth male, 
from Ness County, Kansas (Fig. 44), 
lacked such a chromosome, but several 
"acrocentrics" in the preparation had suf- 
ficiently large "arms" beyond the centro- 
mere as to be considered subtelocentrics; 
one of these probably is the Y. Addition- 
ally in the Ness County male, there is 
one large submetacentric, one large sub- 
telocentric, and another large chromo- 
some that may be a subtelocentric. In 
the karyotype of each of the other three 
animals there is one large submetacen- 
tric chromosome, one distinctly subtelo- 
centric element, and a third large chro- 
mosome that probably is a subtelocentric 
but may be an "acrocentric." The karyo- 
types of nine female campestris all were 
characterized by two large submetacen- 
trics and either one or two large subtelo- 
centrics. One female from Finney 
County had two subtelocentrics in all 
except one of the cells examined; chro- 
mosomes in this cell were severely con- 
tracted and the two subtelocentrics were 
indistinguishable from acrocentrics of 
similar size. The presence of two large 
submetacentrics in females and one in 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 155 



i* il 01 ia ** 

A* *•* A« *** ** 



H « ~ Q 



II II II II I* M II II 



I* ■■ 



*•> «< 



tf* 



A* *\A Afl /** -"*a /&*• ^*A *^ 



>«■ «"»«* <*<» *# ^*» 



«•«> nm> ««% 



Fig. 43. Karyotypes of a female (A) and a 
male (B) Neotoma floridana baileyi from Rock 
and Cherry counties, Nebraska, respectively. 
The scale applies to both karyotypes. 

males indicates that these are the X 
chromosomes. The presence of one sub- 
telocentric in some females and two in 
others may represent a polymorphic sys- 
tem the same as, or similar to, that dis- 
cussed by Baker et al. (1970) for N. 
micropus. On the other hand, these 
observations may be a result of the dif- 
ficulty in distinguishing large subtelo- 
centrics from the so-called acrocentrics. 

A medium-sized subtelocentric chro- 
mosome was present in each of the 
karyotypes of five N. m. canescens males 
( three from Barber Count) 7 and two from 
Haskell County, Kansas). This element 
was not seen in any of the karyotypes of 
11 females and undoubtedly is the Y 
chromosome as shown by Baker and 
Mascarello (1969) and by Baker et al. 
( 1970) . Both males from Haskell County 
had one large submetacentric and one 
large subtelocentric in addition to the 
Y chromosome. The three males from 
Barber County each had one large sub- 
metacentric and two large subtelocen- 
trics. 

Three of four female N. m. canescens 
from Baca County, Colorado, one of two 
from Haskell Countv, Kansas, and four 



if 



1. 



XY 



It M It H II » »• " 



#• 



• • 



•• 



tfc 



• • 



Fig. 44. Karyotypes of a male Neotoma 
floridana attwateri (A) from Douglas County, 
Kansas, and a male N. f. campestris (B) from 
Ness County, Kansas. The scale applies to both 
karyotypes. 

of five from Barber County, Kansas, each 
had two large submetacentrics and two 
large subtelocentrics. The karyotypes of 
these animals were indistinguishable 
from that illustrated by Hsu and 
Benirschke (1968) for a micropus fe- 
male. The other three females each had 
two large submetacentrics, but only a 
single subtelocentric. 

Two males, both identified as hy- 
brids, from the area of sympatry between 
floridana and micropus (3 mi S Chester, 
Major Co., Oklahoma) had karyotypes 
indistinguishable from those of the three 
male N. micropus from Barber County, 
Kansas. Four females identified as mi- 
cropus from that locality each had four 
large biarmed elements. The karyotypes 
of three of these were indistinguishable 
from that of micropus females having 
four biarms, but the fourth had two acro- 
centrics with tiny "arms" as described 
for floridana. The presence of floridana- 



156 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



like acrocentrics in the karyotype of this 
animal undoubtedly resulted from hy- 
bridization of the two species. A female 
identified as a hybrid had three distinctly 
biarmed elements, but spreads were not 
sufficient to determine the presence or 
absence of "arms" beyond the centro- 
mere of large acrocentrics. 

The polymorphic system involving 
the number of large biarmed chromo- 
somes in N. micropus reported by Baker 
and Mascarello ( 1968 ) and discussed by 
Baker et al. (1970) probably will be 
found to exist throughout the range of 
the species. Baker et al. discussed vari- 
ation in number of biarms in animals 
from three widely separated localities in 
Texas and one locality in Oklahoma. The 
karyotype is now known to be variable 
at one locality in Colorado and two in 
Kansas. The only locality from which 
specimens of micropus have been karyo- 
typed and not reported to be polymor- 
phic is 16 km N Ciudad Victoria, Tamau- 
lipas (Hsu and Benirschke, 1968). These 
animals were of the subspecies N. m. mi- 
cropus, whereas the polymorphic popula- 
tions all are N. m. canescens. However, 
Hsu and Benirschke ( 1968) did not indi- 
cate if chromosomes of more than two 
rats (the karyotypes illustrated) from 
Tamaulipas were examined. Baker et al. 
(1970) discussed the possible origin of 
polymorphism in micropus; apparently it 
is the result of neither a Robertsonian 
change (as frequently is seen in mam- 
mals) nor of a single pericentric inver- 
sion. These authors suggested that both 
inversions and translocations may be in- 
volved in the origin of this system. 

The discovery of a submetacentric Y 
chromosome in some populations of N. 
floridana is of interest. No other species 
of the genus has been reported to have 
a submetacentric Y chromosome and, 
although the karyotype of N. f. baileyi 
was not found to vary, these findings in- 
dicate that a previously undescribed 
polymorphism exists in the Y chromo- 
some of N. f. attwateri and N. f. campes- 
tris. The number of large biarmed chro- 
mosomes (exclusive of the Y) has not 



been found to vary from three in males 
and four in females for N. f. attwateri, 
but only two biarms were seen in the 
karyotype of the nine baileyi females and 
only one ( exclusive of the Y ) in the four 
baileyi males examined. In N. f. campes- 
tris, the number of large submetacentric 
chromosomes seems to be constant at two 
in females and one in males. Although 
it is difficult to distinguish large subtelo- 
centrics from some "acrocentrics" in rats 
of this subspecies, apparently the num- 
ber fluctuates from zero to two. The 
large biarms in baileyi and the large sub- 
metacentrics in campestris probably are 
the X chromosomes, but in attwateri the 
X chromosomes cannot be certainly 
identified. 

As shown by Baker et al. ( 1970), the 
X chromosomes in micropus cannot be 
distinguished with certainty, because 
polymorphism is involved and also be- 
cause the relative lengths of the arms in 
the large, biarmed chromosomes is vari- 
able. In the micropus examined by me, 
at least one large submetacentric always 
was found in males and two such ele- 
ments were present in females; in the 
absence of other information these would 
appear to be the X chromosomes. How- 
ever, Baker et al. ( 1970 ) reported two 
females that had only one large, biarmed 
chromosome. All males examined by 
them had at least one biarmed chromo- 
some in addition to the smaller subtelo- 
centric Y. This chromosome probably is 
the X, but as seen in the two females 
having only a single biarmed element, 
at least one X can be an acrocentric in 
females. 

Because of the limited number of 
animals examined and the chromo- 
somal complexity of this group, a discus- 
sion of the evolution of chromosomes in 
N. floridana and N. micropus is some- 
what premature. However, in N. flori- 
dana previously reported bv Cross 
(1931), Matthey (1953), and Baker and 
Mascarello ( 1969 ) , and in N. f. attwateri 
from northeastern Kansas, the number 
of biarmed chromosomes was always 
four in females and three plus the Y in 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



157 



males. This is also the number of biarms 
reported for N. in. micropus from 
Tamaulipas and the most common karyo- 
type seen in N. m. canescens. It is likely, 
then, that this is the karyotype from 
which others have evolved. The number 
of large biarms is unstable in micropus 
and possibly fluctuates in N. f. campes- 
tris, but in N. f. baileyi the two biarmed 
autosomes have been replaced by two 
acrocentrics. 

Because the Y chromosome is a me- 
dium-sized subtelocentric in all popula- 
tions of A 7 , micropus examined and in all 
floridana that have been examined ex- 
cepting baileyi, some compestris, and the 
attwateh from northeastern Kansas, the 
subtelocentric undoubtedly is the primi- 
tive Y chromosome and the submetacen- 
tric is derived. If it is eventually found 



that the lengthened arm of the submeta- 
centric Y was acquired by a transloca- 
tion of an arm of one of the original 
biarmed autosomes, then the two poly- 
morphic systems may have a common 
origin. In any event, the submetacentric 
Y chromosome evidently was present in 
at least some floridana males prior to the 
time baileyi and campestris dispersed to 
the geographic areas they now occupy. 
The apparent fixation of this element in 
baileyi is not surprising considering that 
the subspecies is isolated in a relatively 
small geographic area. The submetacen- 
tric Y probably is commoner than the 
subtelocentric in campestris. Both forms 
of the Y chromosome are known in at- 
twateri; but the relative status of the 
two is not known. 



SUMMARY AND ZOOGEOGRAPHIC CONSIDERATIONS 



Neotoma angustipalata, N. floridana, 
and N. micropus form a closely related 
complex of almost entirely allopatric 
taxa. The distributions of floridana and 
micropus are most appropriately termed 
stasipatric. Key (1968:22) discussed 
stasipatry as follows : "We could perhaps 
distinguish a condition of 'stasipatry' as 
a special case of parapatry in which the 
zone of overlap is limited by an impair- 
ment of the fecundity of freely produced 
hybrids rather than by ecological fac- 
tors." The only known locality where 
the two species occur together (3 mi S 
Chester, Major Co., Oklahoma) is char- 
acterized by the presence of hybrids, 
identification of which was based on a 
variety of comparisons with hybrids 
reared in the laboratory. For example, 
the electrophoretic pattern of hemoglo- 
bins of some animals from the locality 
of sympatry was otherwise observed only 
in known hybrids; discriminant function 
analysis based on 17 characters of speci- 
mens of the two groups indicated they 
were generally intermediate between 
non-hybrid specimens of the two species; 
and the karyotype of one animal from the 
locality in question almost certainly con- 



tained chromosomes derived from both 
species. 

There is no reason to believe that 
floridana and micropus ever have oc- 
curred together without producing na- 
tural hybrids or that they will do so in 
the near future. Although floridana gen- 
erally is an inhabitant of relatively mesic 
woodland habitats (N. f. campestris be- 
ing a notable exception) and micropus 
generally is associated with arid grass- 
lands, either species probably could ex- 
pand its range (at least slightly) in the 
absence of the other (although the exis- 
tence of a relatively broad hiatus be- 
tween the distributions of the two species 
throughout much of the region of poten- 
tial contact might argue against the latter 
point ) . In any event, the two apparently 
hybridize when in contact and results of 
laboratory breeding studies strongly sug- 
gest some hybrid inviability. By defini- 
tion, then, "stasipatry" best explains the 
distributional relationship of these two 
woodrats. 

The distribution of IV. floridana is 
not contiguous with that of N. angusti- 
palata. Neotoma micropus and N. an- 
gustipalata occupy adjacent geographic 



158 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



areas, but sympatry is unknown and no 
evidence of natural hybridization has 
been uncovered (but, see Alvarez, 1963: 
452). To predict how micropus and 
angustipalata would act if they were 
sympatric clearly is speculative; repre- 
sentatives of angustipalata are larger 
than are those of micropus from adjacent 
localities in Mexico and I doubt that the 
two would hybridize. However, size 
alone apparently is a relatively inefficient 
isolating mechanism among woodrats. 
Morphologically, angustipalata is approx- 
imately as distinct from both floridana 
and micropus as these two species are 
from each other. 

Considering the fact that floridana 
and micropus hybridize in the laboratory 
and also in nature, some systematists 
might argue that the two are conspecific. 
However, micropus and floridana have 
maintained a high level of specific in- 
tegrity in the past, apparently are doing 
so at present, and I predict, after exten- 
sive field and laboratory study, that they 
will continue to do so. Although there 
obviously is at least some genetic com- 
patibility between floridana and micro- 
pus, the process of speciation between 
the two is essentially complete, and I 
regard it as having reached an irrever- 
sible point in time. Furthermore, I do 
not believe that our understanding of 
the evolutionary history and systematic 
relationship of these rats would be en- 
hanced by formally placing micropus in 
the specific synonymy of floridana. In 
fact, such an arrangement would suggest 
that the two intergrade broadly and are 
more closely related than is the case. If 
considered as a single species, individuals 
or populations that should be studied 
separately might eventually be treated 
together in research by non-taxonom- 
ically oriented biologists, whose research 
design is partially dependent on deci- 
sions by taxonomists. 

Despite my convictions that floridana 
and micropus should be considered sepa- 
rate species, certain data indicate that 
hybridization is, or recently has been, 
introgressive. Analyses of frequency and 



size of the fork on the anterior palatal 
spine and of the morphology of the pos- 
terior margin of the bony palate indicate 
that in some instances one or more pop- 
ulations of one species from localities 
geographically contiguous with popula- 
tions of the other may have acquired 
selected genetic material introgressively. 
This was suggested most strongly by pop- 
ulations of floridana in Oklahoma and 
Texas. Also, specimens of micropus from 
localities adjacent to the range of flori- 
dana in south-central Kansas and coastal 
Texas are larger (thus somewhat like 
floridana) than specimens of micropus 
from localities not geographically contig- 
uous with populations of floridana. It is 
possible that each species is selectively 
acquiring a limited amount of genetic 
material from the other (Key, 1968; 
Lewontin and Birch, 1966). However, 
certain other characters, such as electro- 
phoretic patterns of hemoglobins and 
analyses of karyotypes, do not indicate 
introgression. Introgression is extremely 
difficult to "prove" or "disprove," and in 
the case of floridana and micropus 
elucidation of this phenomenon must 
await additional data. 

The micropus species-group estab- 
lished by Burt and Barkalow (1942) is 
meaningless. The three species studied 
(angustipalata, floridana, and micropus) 
share a common ancestor in the not too 
distant past and represent a single spe- 
cies-group, the florid ana-group. Ander- 
son (1969) and Finley (1958) have 
shown that N. albigula is closely allied 
to N. micropus (Burt, 1960; Hooper, 
1960), and Anderson (1969) indicated 
the possibility that floridana, micropus, 
and albigula eventually may best be con- 
sidered a single species. Thus, it would 
seem that albigula and related species 
(palatina, nelsoni, and varia — see Hall 
and Genoways, 1970) also should be in- 
eluded in the florid ana-group. 

When the nomenclatorial arrange- 
ments of floridana and micropus are con- 
sidered below the level of the species, 
some conclusions are relatively clearcut, 
whereas others are somewhat arbitrary. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



159 



Among populations of floridana studied, 
total geographic variation was less than 
that found in micropus. Neotoma flori- 
dana baileyi has certain unique features 
of the skull, and is relatively less variable 
than other samples as evinced by the 
absence of intraspecific variation in chro- 
mosomal complement and by lower co- 
efficients of variation in most mensural 
characters; baileyi also has evolved a 
relatively distinctive pattern of repro- 
duction. In certain aspects, some cranial 
dimensions and color for example, baileyi 
appears to have its affinities as much 
with campestris as with att water i, but in 
final multivariate analysis, baileyi ap- 
peared more like attivateri than like 
campestris. As discussed beyond, the 
probable evolutionary history of these 
woodrats also suggests that the affinities 
of baileyi are with attivateri. 

Neotoma floridana campestris is the 
most distinctive of the western subspe- 
cies of floridana with respect to color. 
Statistical analysis of mensural data indi- 
cated that in a few instances attwateri 
is larger than campestris. Specimens in 
a sample of campestris from Colorado 
and Nebraska were especially small rela- 
tive to those in two samples of attwateri 
from localities in Kansas. A tendency 
was observed for woodrats from the zone 
of intergradation between campestris 
and attwateri to be larger than indi- 
viduals in adjacent populations of either 
subspecies and for rats from localities 
west of this zone to become clinally 
smaller. Apparently, campestris exists in 
relatively small and semi-isolated popu- 
lations that occupy discontinuous areas 
of suitable habitat. One acquires this 
impression in field study of campestris 
and additional evidence of localized 
stocks includes: 1) high variability of 
mensural characters in samples of this 
subspecies; 2) two of six animals from a 
semi-isolated population in Finney 
County, Kansas, had unique hemoglobin; 
and 3) three males each from different 
populations had a submetacentric Y chro- 
mosome, but a male from a fourth pop- 



ulation had a subtelocentric Y chromo- 
some. 

Neotoma floridana attwateri, as here 
recognized, includes those animals pre- 
viously assigned to attivateri and to the 
subspecies osagensis. As indicated above, 
specimens assignable to attivateri from 
near the range of campestris are espe- 
cially large. Those from southeastern 
Kansas and southern Texas were next 
largest among the samples studied, and 
those from eastern Oklahoma and north- 
eastern Kansas were smallest. The sub- 
species has not been found to be poly- 
morphic for the number of large biarmed 
chromosomes, but it is polymorphic in 
the morphology of the Y chromosome. 
Three males from northeastern Kansas 
had a distinct submetacentric Y element, 
whereas two from near Stillwater, Okla- 
homa (Baker and Mascarello, 1969), had 
the more common subtelocentric Y. 

Variation in Neotoma micropus is 
more easily definable geographically 
than that in A7. floridana, but more dif- 
ficult to resolve nomenclatorially at the 
subspecific level. N. m. planiceps is 
known only by the holotype; thus varia- 
tion within the subspecies is unknown. 
The holotype is a small woodrat similar 
in size to other Mexican representatives 
of the species. Multivariate analyses 
indicated that planiceps is relatively dis- 
tinct morphologically from both canes- 
cens and micropus. Possibly N. m. plani- 
ceps and N. angustipalata represent a 
single taxon. The holotype of the former 
is a young adult and conclusions regard- 
ing the affinities of planiceps must be 
regarded as tentative. 

The name N. m. micropus has been 
restricted to the brownish, long-tailed 
woodrats that occur on the coastal plain 
and Sierra de Tamaulipas in the state of 
Tamaulipas. An appreciable amount of 
geographic variation exists even within 
this restricted area. Woodrats become 
progressively less brownish and more 
grayish from south to north in Tamauli- 
pas. Variation in size especially and that 
in color to a lesser extent forms a sharp 
stcp-cline across the lower Rio Grande. 



160 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



However, the zone of contact between 
micropus and canescens in western 
Tamaulipas and eastern Nnevo Leon is 
relatively broad; the type locality of N. 
m. micropus ( Charco Escondido, Tamau- 
lipas) is in this zone of intergradation, 
but woodrats from that locality resemble 
more closely those from coastal Tamauli- 
pas than rats from most of the range of 
N. m. canescens. 

Neotoma micropus canescens is the 
most variable subspecies studied. Speci- 
mens from northern and eastern parts of 
the range are larger than those from 
southern and western localities, with the 
exception that specimens from coastal 
southern Texas are among the largest of 
the species. The darkest individuals oc- 
cur in the northeastern parts of the range, 
but members of the subspecies become 
progressively paler from east to west. 
Distributional records of available spec- 
imens indicate that a large area in cen- 
tral Texas is not inhabited by N. micro- 
pus. If true, populations of large wood- 
rats from coastal southern Texas are only 
circuitously connected geographically 
with populations of large woodrats to 
the north. Routes of gene flow between 
northern and southern populations of 
large woodrats thus would include pop- 
ulations of smaller western rats. The sub- 
species canescens could be subdivided 
into five subspecies with some merit as 
discussed previously. Another logical ar- 
rangement might recognize the small 
pallid woodrats of New Mexico, south- 
western Texas, and adjacent Mexico ( ex- 
clusive of coastal Tamaulipas) as one 
subspecies (leucophea) and restrict the 
name canescens to the large woodrats 
from the northern and eastern parts of 
the range of the subspecies as here recog- 
nized. However, such an arrangement 
would not account for intermediacy in 
size and color of woodrats from south- 
eastern Colorado, the panhandle of 
Texas, and non-coastal southern Texas. 
It might also result in an arrangement 
whereby populations of one subspecies 
are separated by populations of another. 

Neotoma angustipalata is known by 



too few specimens to permit a meaning- 
ful analysis of intraspecific variation. 
Hooper ( 1953 ) commented on the ex- 
treme variability in this species and I 
observed the same phenomenon. More 
specimens of this enigmatic species are 
needed. 

SUGGESTIONS FOR ADDITIONAL 
RESEARCH 

Many aspects of the biology, and in 
particular the systematica, of woodrats 
of the floridana species-group (as here 
defined) need additional study. I have 
attempted throughout the preceding dis- 
cussions to indicate these needs, and 
summarize them here. My study and 
others (Anderson, 1969; Finley, 1958) 
demonstrated the importance of con- 
tinued field and laboratory work on the 
distributional and systematic relation- 
ships of N. albiguJa with both N. flori- 
dana and N. micropus. Especially criti- 
cal geographic areas include southeastern 
Colorado, New Mexico, western Texas, 
the Edwards Plateau, southern Chihua- 
hua, and montane areas of Coahuila. 

Additional field work to study the 
exact distributional relationships of flori- 
dana and micropus is needed in south- 
eastern Colorado, and throughout the 
area of general contact in Oklahoma and 
Texas. Sustained search for areas of 
sympatry and continued study of the one 
such area now known should result in 
elucidation of the distinctiveness of the 
two species and the presence or absence 
of introgression. Collecting efforts in that 
area of central Texas not now known to 
be inhabited by either Neotoma floridana 
or Neotoma micropus will elucidate the 
distributional status of woodrats and po- 
tential routes of gene flow in that state. 
The acquisition of additional specimens 
of N. m. micropus and N. m. canescens 
from Tamaulipas will help to clarify the 
relationships of these two taxa. Speci- 
mens from southern Tamaulipas and San 
Luis Potosi are needed to assess the sys- 
tematic status of N. angustipalata and 
N. m. planiceps and to better understand 
the distributional relationship of these 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



161 



woodrats with adjacent populations of 
N. m. micropus and N. m. canescens. 

Certain problems requiring a com- 
bination of field and laboratory research 
have been studied, but most still lack 
definitive solutions. Birney and Perez 
( 1971 ) presented hypotheses concerning 
the nature of variation and the mode of 
inheritance of woodrat hemoglobin, but 
these hypotheses need to be tested and 
refined. The chromosomal polymorphism 
in the number of large biarmed chromo- 
somes first reported for N. micropus by 
Baker and Mascarello (1969), discussed 
by Baker et ah (1970), and observed in 
N. floridana by me needs to be analyzed 
more intensively from the standpoint of 
evolution, geographic distribution, and 
function. Baker and Mascarello (1969: 
195) stated that "our results demand . . . 
introduction of individuals to wild pop- 
ulations different in chromosomal consti- 
tutions." I do not believe that such a 
means of study is necessary or advisable 
and am strongly opposed to research 
that might alter natural patterns of evolu- 
tionary phenomena in animals. How- 
ever, studies wherein mating of captive 
individuals of "different chromosomal 
constitution" could be followed with 
analysis of meiosis in progeny would be 
enlightening. The polymorphism involv- 
ing the Y chromosome in N. floridana 
should be studied to discern its distribu- 
tion and origin. 

Boice ( 1969 ) observed behavioral 
differences between N. albigula and N. 
micropus and Birney and Twomey 
( 1970 ) reported evidence for physiolog- 
ical divergence of N. floridana and N. 
micropus. These areas of research hold 
promise in their own right and in terms 
of clarifying the overall systematics of 
the woodrats of the floridana species- 
group. 

ZOOGEOGRAPHIC COMMENTS 

Hibbard (1967:128) suggested that 
"the stock that gave rise to Neotoma 
must have separated off from a general- 
ized cricetine in the Upper Miocene." 
He considered the extinct genus Plio- 



tomodon, named by Hoffmeister (1945) 
from Pliocene deposits in California, as 
a specialized side branch related to Neo- 
toma, but not in the direct lineage of 
Recent woodrats. The specimen from 
the Cumberland Cave Fauna (Pleisto- 
cene) named as a distinct genus, Para- 
hodomys, by Gidley and Gazin (1933: 
356) may represent another such off- 
shoot, but also best may be considered 
as a member of the genus Neotoma. 

The three species of Neotoma re- 
ferred to the subgenus Paraneotoma by 
Hibbard (1967) from the Upper Plio- 
cene and Middle Pleistocene of Kansas 
are more like N. (Hodomys) alleni than 
Recent members of the subgenus Neo- 
toma. It is not possible to determine 
whether Paraneotoma is ancestral to Re- 
cent Neotoma or if the subgenus repre- 
sents a once widely distributed group 
of species related to N. alleni. Alvarez 
(1966:9) named N. magnodonta from 
the Middle or Upper Pleistocene of Mex- 
ico ( state of Mexico ) as a member of the 
subgenus Hodomys; thus it clearly is not 
in the lineage of the floridana species- 
group. The only other fossil named as 
a distinct species that might relate sig- 
nificantly to the evolutionary history of 
the floridana species-group is N. ozark- 
ensis, which was described by Brown 
(1909:196) from Middle to Late Pleisto- 
cene (Conard Fissure) deposits of 
northern Arkansas. This woodrat may 
prove to be no more than a subspecies 
of floridana; however, if the specimens 
are from pre-Wisconsin deposits it is 
likely that they predate all but the ear- 
liest processes of divergence of floridana 
and micropus. 

These fossil records indicate that the 
genus Neotoma originated in the late 
Miocene or early Pliocene and evolved 
during the Pliocene to the extent that 
presently recognized subgenera were dis- 
tinct by the beginning of the Pleistocene. 
There is no evidence that woodrats of 
the floridana-group inhabited the Central 
Plains during the Yarmouth. Neotoma 
(Paraneotoma) taylori occurred in at least 
parts of the Great Plains at that time 



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MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



(Hibbard, 1967; 1970). Hibbard (1963: 
209) reported a specimen that he con- 
sidered more like floridana than micropus 
from a late Illinoian fauna in Kansas, 
and Hibbard and Taylor (1960:175) re- 
ported N. micropus from the Sangamon 
of Kansas. These specimens were tenta- 
tively identified on the basis of the shape 
of the posterior triangle of the anterior 
loop of Ml. Semken (1966:151) and 
Dalquest et al. (1969:249) have indi- 
cated, and I concur, that this is not a 
diagnostic character to distinguish the 
two species. Semken (loc. cit.) reported 
additional material from the late Illi- 
noian that compared favorably with mi- 
cropus, but he elected not to assign the 
material to either species. 

Dalquest et al. (1969) reported N. 
floridana, N. micropus, and N. albigula 
from deposits considered to be 11,000 to 
8000 years BP. Although I have not 
examined this material, neither the mea- 
surement they used for specific identifica- 
tion (breadth of molar rows) nor any 
other single measurement taken by me 
will serve to distinguish Recent speci- 
mens of the three species. Furthermore, 
identification of Recent specimens of the 
three based on fragmentary skulls and 
lower jaws would be difficult, especially 
distinguishing between floridana and mi- 
cropus. Possibly albigula occurred sym- 
patrically with either floridana or micro- 
pus on the Edwards Plateau in the late 
Pleistocene, but I question whether mi- 
cropus and floridana were in sympatry 
that early and I cannot conceive of all 
three species having occurred there 
simultaneously. 

As I interpret these findings they indi- 
cate that woodrats of the floridana-grou-p 
occurred on the Great Plains by late 
Illinoian. They may have diverged from 
related groups as late as the Illinoian. 
Neotoma albigula and related species also 
could have diverged from a floridana- 
like stock during the Illinoian, because 
results of most studies (e.g. Sprague, 
1941; Burt and Barkalow, 1942; Burt, 
I960; Hooper, 1960) indicate that micro- 
pus and floridana are more alike mor- 



phologically than either resembles al- 
bigula. 

With the advance of Wisconsin ice, 
the basal stock of floridana probably re- 
treated southward. Neotoma albigula 
might have been restricted to the Mexi- 
can Plateau or to the region of southern 
California, Arizona, and New Mexico (or 
both), micropus to the lowlands of 
coastal southern Texas and Tamaulipas, 
and floridana to the southeastern United 
States, possibly to peninsular Florida 
(see Sherman, 1952; Blair, 1958). Guil- 
day et al. (1964:158) suggested that N. 
f. magister survived Wisconsin glaciation 
in the southern Appalachian Mountains. 
In view of the striking morphological 
and ecological distinctness of magister 
as compared with all other subspecies of 
floridana, I agree with Guilday et al. and 
further suggest that magister and flori- 
dana eventually will be found to repre- 
sent biological species at least as distinct 
as floridana and micropus. However, the 
status of magister is beyond the scope of 
the present paper and the relationship 
of this taxon must await detailed field 
and laboratory study. 

Speculation on the distribution in 
Wisconsin time of Neotoma angustipa- 
lata and Neotoma palatina also is of in- 
terest. The affinities of angustipalata as 
shown herein are clearly with micropus 
and floridana, but proclivities toward 
one, more than the other, are lacking. 
Neotoma palatina is thought to be most 
closely related to N. albigula. Neotoma 
angustipalata has a relatively restricted 
range in southern Tamaulipas and San 
Luis Potosi, whereas palatina is restricted 
to the barranca of Rio Balanos, associated 
tributaries, and adjacent uplands. Be- 
sides micropus and floridana, only angus- 
tipalata and palatina are characterized 
by the absence of a maxillovomerine 
notch. Possibly this characteristic has 
evolved twice, but the solid vomerine 
septum of these four species may be in- 
dicative of a pre-Wisconsin common an- 
cestor. Neotoma palatina apparently was 
sufficiently isolated from adjacent popu- 
lations of albigula to effect speciation. 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



163 



Neotoma angustipalata probably was iso- 
lated in montane habitats of the Sierra 
Madre Oriental during the Wisconsin, 
whereas micropus occurred on the coastal 
lowlands. Both angustipalata and pala- 
tum represent peripherally-distributed 
species that have managed to avoid ex- 
tinction, but for some reason (possibly 
the presence of adjacent populations of 
micropus and albigula, respectively) have 
been unable to significantly expand their 
ranges since the recession of Wisconsin 
ice. 

Recent advances in paleobiology, ge- 
ology, and meteorology have improved 
understanding of late Pleistocene and 
Holocene climatic and vegetational pat- 
terns on the Great Plains. These data 
were summarized by Hoffmann and 
Jones (1970) according to post-Pleisto- 
cene chronology and terminology pro- 
posed by Bryson et al. (1970). During 
Full-glacial (to approximately 13,000 
BP), floridana and micropus probably 
were completely isolated in their respec- 
tive refugia. Following initial isolation, 
the two incipient species evolved dis- 
tinctive hemoglobins from the original 
double-banded phenotype. Differences 
in chromosomal complements, morphol- 
ogy, and color also have evolved under 
differential selective pressures since that 
time. Blair (1958) included floridana 
and micropus in a list of mammals and 
reptiles that previously were isolated into 
eastern and western populations, but that 
since have reestablished contact in the 
forest-grassland ecotone. The barrier 
that isolated micropus and floridana 
along the Gulf Coast of the southeastern 
United States may have been the Missis- 
sippi Embayment, but as discussed by 
Blair (1958) most species separated by 
this barrier remain disjunct. During the 
more equable climate of Late-glacial 
(13,000 to 10,500 BP), and with north- 
eastward retreat of continental ice (de- 
spite minor phases of retreat and read- 
vance), both isolated populations began 
a northward dispersal. During the more 
continental climates of the Pre-boreal 
(10,500 to 9140 BP), Boreal (9140 to 



8450 BP), and Atlantic (8450 to 4680 
BP), micropus and floridana reached 
their present limits of distribution and 
floridana at least occurred somewhat 
farther north and west of the present 
range (see Jones, 1964). It probably 
was during this time that woodrats ad- 
vanced northward along the Missouri 
and westward along the Niobrara rivers. 
The Smoky Hill, Saline, Republican, Ar- 
kansas, and possibly other rivers and 
tributaries served as corridors for flori- 
dana to disperse across western Kansas 
into eastern Colorado and southwestern 
Nebraska. Several late Pleistocene-early 
Recent records of floridana from locali- 
ties north of the present range are avail- 
able ( e.g., Parmalee and Jacobson, 1959; 
Bader and Hall, 1960; Parmalee et al. 
1961). Morphologically, N. f. baileyi 
somewhat resembles N. f. campestris, 
especially those specimens from popula- 
tions in Colorado and southwestern Ne- 
braska. Possibly there was appreciable 
north-south gene flow through eastern 
and central Nebraska during this period. 
However, I doubt that the Sand Hills 
region of Nebraska ever was inhabited 
by floridana and the similarities between 
baileyi and campestris more likely repre- 
sent convergence. When all characters 
are considered, baileyi clearly is more 
closely related to attwateri from north- 
eastern Kansas than to campestris. 

During and following Full-glacial, the 
Sierra de Tamaulipas may have served 
as a barrier for the small, brownish, long- 
tailed woodrats that presently occur 
there. When populations of micropus 
subsequently dispersed northward, these 
rats reestablished contact and inter- 
graded with other populations. The re- 
sult of this intergradation and subse- 
quent selection is the coastal subspecies 
to which the name N. m. micropus is re- 
stricted. The evolutionary history of N. 
m. planiceps cannot be understood until 
the relationships and status of this 
nominal subspecies are better known. 
However, planiceps apparently is iso- 
lated from other populations of micropus 
on the Mexican Plateau at present, but 



164 



MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



probably has not been isolated since the 
Full-glacial. 

The Sub-boreal (4680 to 2690 BP) 
probably was the coolest post-glacial pe- 
riod on the Northern Great Plains. This 
period was characterized by a southward 
shift in both the northern and southern 
limits of the boreal forest. It probably 
was during this cooler period that flori- 
clana retreated slightly southward and 
eastward, leaving the isolated N. f. 
baileyi in the sheltered canyons of the 
Niobrara River and associated tribu- 
taries. Jones (1964) and Hoffman and 
Jones (1970) suggested that baileyi be- 
came isolated during a hot, dry post- 
glacial period. Although that hypothesis 
remains plausible, it is now thought that 
the earliest period characterized by hot, 
dry climate was the Scandic ( 1690 to 
1100 BP); the degree of distinctness ex- 
hibited by baileyi suggests a longer pe- 
riod of isolation. Rainey ( 1956 ) and 
Jones ( 1964 ) discussed the apparent in- 
ability of N. f. attwateri to extend its 
range into superficially suitable habitat 
in southeastern Nebraska; attwateri pos- 
sibly is unable to move farther north be- 
cause of the severity of the climate, espe- 
cially in winter. Riparian habitats that 
appear suitable for habitation by baileyi 
are present in southern South Dakota, 
but for some reason (possibly the ab- 
sence of enough shelter during winter) 
woodrats have not been found there. 
Perhaps baileyi has been able to persist 
in north-central Nebraska only in spe- 
cially sheltered areas, the most important 
element furnished by the canyons of the 
Niobrara being protection from severe 
winters rather than a relatively cool en- 
vironment during hot, dry summers. 

The Sub-boreal also may have iso- 
lated N. f. campestris from N. f. attwa- 
teri, and the two probably were disjunct 
for an extensive period. Contact may 
have been reestablished in the relatively 
warm moist Sub-Atlantic, broken again 
during the dryer Scandic, and not rees- 
tablished until European man fostered 
the spread of riparian and other wood- 
land habitats in north-central Kansas. Al- 



though the two subspecies appear to 
have been separated for a lengthy pe- 
riod, they are presently in contact. Dur- 
ing the dry Scandic and possibly during 
other periods as well, it appears that 
campestris was distributed in an un- 
known number of small isolated popula- 
tions in disjunct and probably marginal 
habitats. 

Since the time of initial isolation, the 
submetacentric Y chromosome appar- 
ently became fixed in baileyi, but the 
translocation obviously had occurred 
prior to isolation as it is seen also in 
campestris and in attivateri from north- 
eastern Kansas. Origin of the /3 s hemo- 
globin locus also occurred prior to the 
time of isolation, because the /? 3 allele 
is seen in all three of the western sub- 
species of foridana. During the warm, 
wet Neo-Atlantic and since that time, 
campestris probably has dispersed some- 
what from the isolated, relict populations 
of the Scandic, but continues to occur 
in relatively disjunct, semi-isolated pop- 
ulations. 

With the possible exception of N. m. 
micropus and N. m. planiceps, I doubt 
that any of the populations of micropus 
have evolved long in isolation from other 
members of the species. Variation in 
size and color both are clinal, the chro- 
mosomal polymorphism involving num- 
ber of large biarmed elements has been 
observed at localities from which signifi- 
cant numbers of woodrats have been 
karyotyped (the only exception is N. m. 
micropus from north of Ciudad Victoria, 
Tamaulipas), and no marked changes 
in hemoglobin phenotypes were observed 
in northern populations of the species. 

Neotoma micropus and N. floridana 
apparently evolved in the classical man- 
ner during the Pleistocene as a result of 
isolation during glacial advance. Al- 
though two species in my estimation, 
they are closely related, recently evolved, 
and retain limited genetic compatibility. 
It is impossible to define precisely at 
what stage two evolving phena should 
be called species, but as I understand 
floridana and micropus the process of 



WOODRATS (GENUS NEOTOMA) IN CENTRAL NORTH AMERICA 



165 



evolution almost certainly has reached a 
point in time whereby irreversible dif- 
ferentiation has taken place. Although 
micropus and floridana apparently did 
not evolve exactly according to the stasi- 
patric model (White et «/., 1967; Key, 
1968), they are stasipatrically distributed 
today and apparently are continuing the 
process of speciation in a manner similar 
to that seen in morabine grasshoppers, 
for which this model was proposed. That 
is, the two species are in contact and 



form a tension zone wherein hybrids 
with reduced viability are produced. 
This tension zone undoubtedly shifts 
slightly within the deciduous forest- 
grassland ecotone in response to environ- 
mental changes. Introgression of a few 
advantageous genes may be occurring in 
one or both species as a result of hy- 
bridization within the tension zone, but 
clearly introgression (if it has occurred 
at all) has been limited and mostly pre- 
vented by rigid selection. 



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MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



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Key, K. H. L. 

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1968. Biology of Peromyscus (Rodentia). 
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Kirsch, J. A. W. 

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Knoch, H. W. 

1969. The eastern wood rat, Neotoma flori- 
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KOOPMAN, K. F., AND P. S. MARTIN 

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Lack, D. 

1948. The significance of litter-size. Tour. 
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Lawlor, T. E. 

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Lawrence, B., and W. H. Bossert 

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Lay, D. W., and R. H. Baker 

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Lee, M. R. 

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LlNSDALE, J. M., AND L. P. TeVIS 

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Mayr, E. 

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McCarley, W. H. 

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Mearns, E. A. 

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Murphy, M. F. 

1952. Ecology and helminths of the Osage 
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Patton, J. L. 

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MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY 



mice, genus Perognathus (Rodentia: 
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Pearson, P. G. 

1952. Observations concerning the life his- 
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Academic Press, New York, xvi + 

519 pp. 



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variation, pathology, and evolution. By Carlton J. Phillips. Pp. 1-138, 49 figs. 
September 24, 1971. Paper bound $5.00 postpaid. 

56. Systematics of the chiropteran family Mormoopidae. By James Dale Smith. Pp. 
1-132, 40 figs. March 10, 1972. Paper bound $5.00 postpaid. 

58. Systematics of three species of woodrats (genus Neotoma) in central North 
America. By Elmer C. Birney. Pp. 1-173, 44 figs. April 13, 1973. Paper bound 
$7.50 postpaid. 

MONOGRAPHS IN MAMMALOGY 

2. Readings in mammalogy. By J. Knox Jones, Jr. and Sydney Anderson. Pp. ix + 
586. 1970. Paper bound $8.00 postpaid. 

3. The distribution of mammals in Colorado. By David M. Armstrong. Pp. x + 415, 
8 pis. Cloth bound $16.00 postpaid. 










flookbind : 'K. Cc.; \nc: 
Boston '0, Mass." 




2044 093 361 624 



Date Due