(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Demography and life history of Arabis fecunda in Ravalli and Beaverhead Counties, Montana"

:fW^~ 



>83. 123 
411dLha 
1994 



Lesica* Peter 

Demography and 
life history of 
Arabis fecunda in 
Ravalli and 
Beaverhead 
Counties* Montana 



^Krk,^4^ 






563.123 
N lldLha 

IS94 



MONTANA STATE LIBRARY 



3 0864 0010 3928 1 



DEMOGRAPHY AND LIFE fflSTORY OF ARABIS FECUNDA 
IN RAVALLI AND BEAVERHEAD COUNTIES, MONTANA 



Prepared by: 

Peter Lesica 

929 Locust 

Missoula, MT 59802 

and 



J. Stephen Shelly 

Montana Natural Heritage Program 

1515 E. 6th Ave. 

Helena, MT 59620 



Prepared for: 

USDA Forest Service 

Beaverhead National Forest 

610 N. Montana 

Dillon, MT 59725 






TON 



January 1994 



P 



s;^k^i 



i {■ 



I ir\ 



i Vl\ 



© 1994 Montana Natural Heritage Program 

This report should be cited as follows: 

Lesica, P. and J. S. Shelly. 19941 Demography and life history of Arabis fecunda in Ravalli and Beaverhead counties, Montana. 
Unpublished report to the Beaverhead National Forest Montana Natural Heritage Program, Helena. 29 pp. 



Summary 
We monitored individuals of Arabis fecunda over four consecutive years 
at three sites in order to gain knowledge of this rare plant's life history. 
Arabis fecunda is a short-lived perennial with high fecundity. Recruitment is 
high as is mortality of juveniles. Plants flower by bolting or producing 
axillary inflorescences. Bolting plants produced 2.5 times as many seeds, 
matured earlier but had much higher mortality compared to axillary-flowering 
plants. Seeds germinate readily without stratification. Seed dormancy is 
induced by cold/dark conditions at some sites but not others. 

Recruitment rate, survivorship, age at maturity and fecundity varied 
significantly among sites. Much of this difference in life history traits was 
due to differential bolting frequencies among the three sites. These results 
suggest that life history traits are locally adapted and that adaptive genetic 
differences may exist between populations. 

Populations in the southern portion of A_^ fecunda' s range appear to be 
stable and will be most sensitive to changes that cause a reduction in 
recruitment. On the other hand, populations in the north may be declining and 
should be most sensitive to declines in adult survivorship. 

Introduction 
Passage of the Federal Endangered Species Act of 1973 and subsequent 
recognition of the value of conserving biotic diversity (Wilson 1988) have 
resulted in many government agencies becoming active in species conservation. 
Surveys to determine the location and size of populations of rare species are 
being conducted on public lands throughout the west. These surveys are 
necessary in any species conservation program; however, knowing the location 
and size of populations at any one point in time is only the first step in a 
long-term protection strategy. (Sutter 1986). Extinction is a process 
requiring an understanding of population dynamics (Menges 1986). Periodic 



i 



inventories can detect trends but will do little to determine causality or 
help generate predictive hypotheses (Palmer 1987). Long-term conservation 
requires a knowledge of many life history parameters including fecundity, 
recruitment, survivorship, age structure, and population flux. Demographic 
monitoring techniques can provide information on factors regulating population 
density and persistence (Palmer 1987). This information, in turn, provides an 
essential basis for management decisions. 

Arabis fecunda is a candidate for listing as a threatened or endangered 
species by the U.S. Fish and Wildlife Service (USDI-FWS 1993), is considered 
sensitive in Region One of the U.S. Forest Service, and is considered 
threatened in Montana (Lesica and Shelly 1991). Little is known about the 
life history and demography of Arabis fecunda populations. The purpose of 
this study is to determine demographic patterns and variability for this rare 
species and to use this knowledge to recommend appropriate management 
strategies for conservation. 

METHODS 
The Species 

Arabis fecunda Rollins is a rosette-forming, perennial in the Mustard 
Family (Brassicaceae) . This recently described species (Rollins 1984) is 
endemic to highly calcareous soils in the foothills of the Sapphire Range in 
Ravalli County and in the Pioneer Range in Beaverhead and Silver Bow counties 
in southwest Montana. Arabis fecunda plants flower in April and May, and 
fruits mature in June and July. Flowering occurs in one of two ways: (1) 
axillary flowering - 1 to many decumbent inflorescence stems develop from 
axillary buds among the tightly clustered leaves of the rosette or (2) bolting 
- a single inflorescence stem is produced from the terminal bud in the center 
of the rosette. Bolting inflorescences are generally larger and leafier than 
axillary inflorescences. An individual rosette may produce axillary 
inflorescences for numerous years, while bolting rosettes always die. Some 



• 



rosettes are iteroparous, producing axillary inflorescences for 1-many years 
before either dying or bolting and then dying. Others bolt once and are 
essentially semelparous. Individuals may branch at the root crown to form 
multi-rosette plants at any time during the life cycle. This is not 
vegetative reproduction as individual rosettes from multi-rosette plants never 
become independent plants. If only a portion of the rosettes in a multiple- 
rosette plant bolt, the whole plant may or may not die. 

Study Sites 

We conducted our study at Charleys Gulch in Ravalli County and Lime 
Gulch and Vipond Park in Beaverhead County, Montana. The Charleys Gulch site 
is on a moderate southwest-facing slope, at 1525 m. At Hamilton, ca. 8 km 
southwest and 300 m lower, mean temperatures for July and January are 19.4° 
and -3.8° C respectively, and mean annual precipitation is 32 cm. Vegetation 
surrounding the sites is foothills Aqropyron - Festuca grasslands with scattered 
Pinus ponderosa Dougl. and Pseudotsuqa menziesii (Mirb. ) Franco. The Lime 
Gulch site occurs on moderate east- and west-facing slopes above a small 
drainage on the east side of the Pioneer Range at ca 1890 m. The Vipond Park 
site is on a moderate south-facing slope at 2195 m at the north end of the 
Pioneer Range. The two sites are separated from each other by ca. 32 km and 
from the Ravalli County site by ca. 130 km. For Divide, at 1675 m and north 
and east of the two sites, mean temperatures for July and January are 17.2° 
and -7.2° C respectively, and mean annual precipitation is 31 cm. Vipond Park 
is appreciably higher than the recording station, and thus likely experiences 
colder temperatures and greater precipitation. Vegetation around Lime Gulch 
is Juniperus / Cercocarpus woodland, while it is Artemisia - Festuca - Aqropyron 
steppe at Vipond Park. 

Soils at all sites are highly calcareous sandy loams derived from 
outcrops of metamorphosed calc-silicates or limestone. These soils have a 
tendency to slump on moderate to steep slopes. Vegetation at these sites is 



sparse compared to surrounding grasslands and woodlands. Cryptogamic soil 
crusts are coiranon at Charleys Gulch and Lime Gulch (Lesica and Shelly 1992a) . 
Soils at Charleys Gulch have a lighter albedo than those at the Beaverhead 
County sites. 

Field methods 

In 1987 we established two permanent transects, one of 5 and one of 12 
contiguous 1-m- plots at Charleys Gulch. In 1989 we established two permanent 
transects of 12 contiguous 1-m^ plots each at both Lime Gulch and Vipond Park. 
Transects were located to be representative of the populations a whole. We 
censused Arabis fecunda in 1988-93 at all three sites. Sampling was conducted 
in late May at Charleys Gulch, mid-June at Lime Gulch and late June or early 
July at Vipond Park. We chose these times because A_^ fecunda fruits were 
mature or nearly so, but dispersal had not yet occurred. Plants smaller than 
0.5 cm in diameter were not recorded because they could not be reliably 
distinguished from other species. 

Individual A^ fecunda plants were mapped and recorded following methods 
outlined in Lesica (1987) and using the following life history stage 
classification system: 

Small (S) = single vegetative rosette < 2 cm in diameter 
Juvenile (J) = single vegetative rosette > 2 cm in diameter 
Multiple-rosette (M) = multiple vegetative rosettes 
Reproductive (R) = plants producing 1-many inflorescences 

In addition, for each reproductive plant we recorded the number of 
inflorescences and the number of fruits matured. We recorded which plants 
bolted in 1990-93. 



A plants 's demographic properties are often more closely correlated with 
size and life-history stage rather than age (Werner and Caswell 1977, Caswell 
1989), although both may be important in predicting an individual's fate 
(Young 1985). We chose these classes because they are correlated with age as 
well as size and because they also represent a reasonable compromise between 
having many categories with too few observations each and few categories with 
many observations (Vandermeer 1978). 

In each year we collected one fruit from the middle of the inflorescence 
of each of 25 randomly chosen plants growing near the transects at each site. 
We counted the number of mature or nearly mature seeds in each fruit to obtain 
an estimate of seeds per fruit for each site. 

In 1993 we collected one fruit each from 25 randomly selected axillary 
flowering plants and 25 bolting plants from each site. After counting the 
number of mature or developing seeds, those from Charleys Gulch and Vipond 
ParJc were used in germination tests. Seeds from Lime Gulch were not mature 
enough to be used. Seeds were stored dry at room temperature for 4 months 
prior to the tests. Two treatments were tested: (1) warm/light - constant 
20°C with 14 hours of constant light per day and (2) cold/dark - constant 5°C 
in the dark. Seeds were placed on moist filter paper in petri dishes, 20 
seeds from a single parent per dish with 6 bolting and 6 axillary flowering 
replicates from each site for each treatment. The warm/light and cold/dark 
treatments were given for 8 and 20 days respectively. Germinated seeds were 
recognized by the radicle emerging at least 1 mm from the seed coat. 

We estimated canopy cover to the nearest 5% of all vascular plants as 
well as cover of rock, bare soil and basal vegetation in each plot (Daubenmire 
1959) . 



>? 



Data analysis 

Stage-structured transition matrix projection models summarize the way 
in which survival, growth and reproduction at various life-history stages 
interact to determine population growth (Caswell 1989, van Groenendael et al. 
1988). Matrix projections assume fixed transition probabilities between 
stages in a population through time (Lefkovitch 1965, Menges 1990). They 
assume density-independent population growth and thus do not give an accurate 
projection of long-term population future. Nonetheless, they can be used to 
summarize short-term population dynamics or compare the dynamics of two 
populations (Caswell 1989). One-year transition probabilities were estimated 
as the number of plants in life-stage class i moving into class j. over the 
course of one year divided by the number of plants in stage i at the beginning 
of the year. This method assumes that an individual's transition depends only 
on its life-stage class at the beginning of the period and is independent of 
its transition the previous year. The equilibrium growth rate {k) is the 
dominant eigenvalue of the transition matrix (Caswell 1989, Lefkovitch 1965). 
X > 1.0 indicates population increase, while X < 1.0 indicates decrease. X 
integrates the effects of survival, growth and fecundity of the different 
life-history stages into a single parameter. Details on the construction and 
use of matrix population models can be found in Caswell (1989) and Menges 
(1990) . 

Elasticity measures the relative change in the value of X in response to 
changes in the value of a transition matrix element. Elasticity matrices 
allow comparison of relative importance to population growth and fitness among 
the various life history transitions (de Kroon et al. 1986). Elasticities sum 
to unity and regions of the matrix may be summed to compare the importance of 
growth and survival to recruitment (Caswell 1986) . 

When the majority of seeds pass directly from production to germination 
in less than one year, seeds should not appear as a separate stage in matrix 



models (Caswell 1989, Silvertown et al. 1993). In most cases, the majority of 
seeds probably germinate without a dormant period (see Results), and we have 
used matrices with reproductive transition and recruitment columns combined to 
calculate X. We calculated separate elasticities for reproductive transitions 
and recruitment by dividing the reproductive+recruitment elasticities 
proportionately between their two components. 

We used the ratio of new recruits to survivors to compare annual 
recruitment rates among populations. Growth was measured as the ratio of 
plants in each population that grew into a larger size class to those that 
remained in the same class or became smaller. We examined differences in age 
at maturity by comparing ratios of plants that flowered during the first two 
years to those that flowered later. Differences in recruitment, growth, new 
recruit survival, survival of bolting plants, age at maturity and proportion 
of bolting plants were assessed with an overall chi-square goodness of fit 
test. If a 3 X 3 test showed a significant result, I used 2X2 tests to 
determine which pairs of sites were different. Probability values were not 
corrected for multiple tests. 

We compared survivorship of the uneven-age sample population present in 
1989 and the 1990 cohort among the sites using the nonparametric logrank test 
(Pyke and Thompson 1986, Hutchings et al. 1991). Survivorship curves were 
constructed following methods outlined in Hutchings et al. (1991). 
Probability values were not adjusted for multiple tests. 

The effects of site (population), year and bolting on number of fruits 
per plant and number of seeds per fruit were analyzed using analysis of 
variance (ANOVA) followed by contrast tests. Dependent variables were log- 
transformed prior to analysis. The effects of treatment, site and bolting on 
the arcsine-transformed proportion of germinating seed were also analyzed by 
ANOVA. 



Results 

Vegetation 

Mean canopy cover estimates for common vascular plant species are 
presented in Table 1, Total basal vegetation cover was lower at Charley's 
Gulch compared to Lime Gulch or Vipond Park (Table 1). Graminoids were common 
at Lime Gulch, but forbs were more common at the other two sites. Amounts of 
bare soil were highest at Charleys Gulch, intermediate at Lime Gulch, and 
lowest at Vipond Park, while rock was more abundant at Vipond Park (Table 1). 

Population Growth 

Density of Arabis fecunda varied among sites and years (Fig. 1). 
Population size was more variable at Lime Gulch and Vipond Park than at 
Charleys Gulch. The coefficient of variation for density for 1989-93 was 22% 
at Lime Gulch and Vipond Park but was 18% at Charleys Gulch. 

Equilibrium population growth rate (X) also varied among sites and years 
(Table 2). X was lowest and least variable at Charleys Gulch. In 1989 there 
were no reproductive plants at Lime Gulch, but there were many in 1990. Thus, 
1989-90 was a year of exceptional growth at Lime Gulch, but X was nearly 
constant in the three ensuing year. X showed the most consistent high 
variation at Vipond Park. 

Recruitment 

The ratio of new Arabis fecunda recruits to number of survivors was 
significantly greater at Vipond Park compared to Charleys Gulch for all four 
transition years (Fig. 2). In most years Vipond Park had higher recruitment 
than Lime Gulch, and Lime Gulch had higher recruitment than Charleys Gulch 
(Fig. 2). When all four years are pooled, the ratio of new recruits to number 
of survivors is 0.31 for Charleys Gulch, 0.55 for Lime Gulch, and 0.95 for 
Vipond Park, and these differences are significantly different between all 
possible pairs of sites (P<0.001). 



" Survivorship 

Survivorship of the 1990 Arabis fecunda cohort over 1990-93 was 
significantly lower at Vipond Park than at either Lime Gulch (LR=9.22, P<0.01) 
or Charleys Gulch (LR=3.96, P=0.05; Fig. 3). Survivorship at Lime Gulch and 
Charley's Gulch was not different (LR=0.01, P=0.91; Fig. 3). Analysis of the 
depletion curve for the 1989 uneven-age populations gave similar results. 
Arabis fecunda populations at Charleys Gulch and Lime Gulch have type II 
survivorship curves where number of deaths is a constant with time, while the 
Vipond Park population's survivorship fits more closely a type III curve, 
where probability of death is a constant (Deevey 1947). 

From 1991 through 1993, the proportion of new recruits that survived was 
67% at Charleys Gulch, 74% at Lime Gulch and 57% at Vipond Park. The ratio of 
survivors to deaths of new recruits at Vipond Park was significantly lower 
than either Lime Gulch (x"=35.3, P<0.01) or Charleys Gulch {x"=4.14, P=0.04), 
A while Lime Gulch and Charleys Gulch were not different (x"=1.90, P=0.17). 

Growth 

In two out of four years, significantly more Arabis fecunda plants moved 
into larger size classes at Vipond Park compared to Charleys Gulch, and in 
three out of four years growth was significantly greater at Lime Gulch 
compared to Charleys Gulch (Fig. 4). When summed over all four years, there 
were significantly fewer plants moving into larger size classes at Charleys 
Gulch (x^=24.761, df=2, P<0.001), but there was no difference between Lime 
Gulch and Vipond Park (x-=l-281, P=0.26). 

Fecundity 

Over the course of the study the ratio of the number of Arabis fecunda 
plants that bloomed at an early age (<2 yr) to later (>2 yr) was 1.1 at 
Charleys Gulch, 1.75 at Lime Gulch and 4.0 at Vipond Park. Vipond park was 
^ significantly greater than both Lime Gulch (x^=17.05, P=0.001) and Charleys 



r^ 



C 



♦ 



Gulch (x^=7.72, P=0.005), but the latter two sites were not different 
(X'=0.89, P=0.345). Thus, A_^ fecunda plants at Vipond Park matured earlier in 
life than those at the other two sites. 

The number of fruits per reproductive plant varied significantly among 
sites and years (Table 3). Over the course of the study, the mean for Lime 
Gulch was 10.6, significantly lower than Charleys Gulch and Vipond Park which 
had means of 14.6 and 14.5 respectively (Table 3). The number of seeds per 
fruit also varied significantly among sites and years although differences 
were not large (Table 4). Over the course of the study, the means were 30.9, 
32.4 and 34.0 for Charleys Gulch, Lime Gulch and Vipond Park respectively. 
Only Charleys Gulch and Vipond Park were significantly different (Table 4). 
For both number of seeds per fruit and fruits per plant, there was a 
significant interaction between the site and year effects, possibly due to 
different weather conditions at the sites. 

Bolting plants 

Over the period of 1990-93 the mean percentage of reproductive plants 
that produced a bolting inflorescence was 3%, 26% and 44% for Charleys Gulch, 
Lime Gulch and Vipond Park respectively (Fig. 6). These differences were 
statistically significant for all four years (x">7.3, df=2, P<0.05). 

Bolting plants had a mean of 19.9 fruits, while axillary-flowering 
plants had a mean of 9.8 fruits, and this difference was significant (Table 
5). There were also significant effects of year, and site X year interaction, 
probably due to different weather conditions at the sites over the course of 
the study. There was also a strong interaction between bolting and year, 
suggesting that the number of fruits per plant is partially under 
environmental control. Bolting plants produced an average of 36.8 seeds per 
fruit, while axillary-flowering plants produced 29.8 seeds per fruit, and the 
difference was significant (ANOVA, F=26.4, P<0.001). Number of seeds per 

10 



\t 



* 



fruit also varied among sites in the same manner as described above. On 
average, bolting plants produce 2.5 times as many seeds as axillary flowering 
plants . 

During the period of 1991-93 at Lime Gulch, 53% of axillary flowering 
plants survived to the following year, while only 5% of bolting plants 
survived. Results for the Vipond Park population were similar, with 68% of 
axillary flowering and 16% of bolting plants surviving. Survivorship was 
significantly greater for axillary flowering plants at both sites for all 
three years (x->17.3, df=2, P<0.001). 

Germination recruirements 

Germination of Arabis f ecunda seed occurred readily at room temperature 
in the light without stratification. Site (source of seed) had no effect on 
germination; 89% and 86% of seed from Charleys Gulch and Vipond Park 
respectively germinated within eight days (ANOVA F=0.048, df=24, £=0.828). 
80% of seeds from Charleys Gulch germinated in the cold and dark after 14 
days, but only 8% of seeds from Vipond Park germinated under the same 
conditions, and this difference was highly significant {F=129.59, df=24, 
P<0.001). Seeds from Vipond Park remained dormant after being placed in a 
warm light environment for eight days. The significant site*treatment 
interaction in the full ANOVA model (Table 6) indicates that seeds from the 
two sites are genetically different. Seeds from bolting plants germinated 
better than those from axillary flowering parents under warm-light conditions 
but germinated more poorly under cold, dark conditions. The significant 
bolting X treatment interaction term in the ANOVA model suggests that seeds 
from bolting and axillary flowering plants are genetically different (Table 
6). 



11 



.4 
V 



Elasticity analysis 

Elasticities for the three sites for the four annual transitions are 
presented in Table 7. Growth and survival of plants in the non-reproductive 
stages accounted for ca. 50% of equilibrium population growth (X) at all three 
sites. Growth and survival of reproductive plants was responsible for 36% of 
X at Charleys Gulch but less than 20% at Lime Gulch and Vipond Park. On the 
other hand, recruitment from seed accounted for 34% and 36% of X at these 
latter two sites but only 16% at Charleys Gulch (Table 7). Adult 
(reproductive) growth and survival was the most important transition at 
Charleys Gulch, while recruitment was predominant at Lime Gulch and Vipond 
Park. 

Discussion 
Life history 

Arabis fecunda is a relatively short-lived perennial; only ca. half of 
the plants that establish live for more than two years, and only ca. one-third 
live for four years or more. Annual recruitment is generally high; the ratio 
of new recruits to survivors varied from 0.09 to 2.05 with means for 1989-93 
between 0.31 and 0.95. Mortality of new recruits is also high; in 1991-93, it 
varied from ca. 20-50%. Fecundity is generally high; reproductive A^ fecunda 
plants produced an average of 340-500 seeds per year. Plants that bolted 
produced ca. 2.5 times as many seeds per year as axillary flowering plants but 
had much higher mortality. Seeds become ripe in late spring or early summer 
and germinate readily without stratification. These results suggest that most 
seeds germinate in the fall, of the same year that they are produced. Seeds 
from Charleys Gulch also show high germination in the cold and dark, 
suggesting that at this site only a transient type II seed bank is formed 
(sensu Thompson and Grime 1979). On the other hand, cold/dark conditions 
induce dormancy in seeds from Vipond Park; thus, A_^ fecunda probably does have 
a long-term seed bank at this site. 



12 



Variability in life histories 

Life history theory predicts tradeoffs between traits that will maximize 
fitness for a particular environment. In particular, there is thought to be a 
negative relationship between reproduction and growth and survival. Some 
environments favor slower growth, greater age at first reproduction, smaller 
output per reproductive bout, and greater longevity. Other environments 
select for shorter lifespan, early maturity and larger reproductive output per 
bout. Early maturing, highly fecund populations have a higher intrinsic 
population growth rate. Early maturity is favored in environments where adult 
mortality is relatively high or highly variable (Stearns 1992). In plants, 
the extreme case is the annual habit. 

There was great variation in life history traits among the three 
populations studied. In most cases, the Charleys Gulch and Vipond Park 
populations occupied the two extremes of life history trait continua with the 
Lime Gulch population intermediate. For the purpose of this discussion, we 
will compare the former two populations, bearing in mind that the Lime Gulch 
population was similar to Charleys Gulch for some traits but more similar to 
Vipond Park for most. 

The Arabis fecunda population at Charleys Gulch had a lower recruitment 
rate but higher overall as well as new recruit survivorship. On average, 
plants grew more slowly, were older at first reproduction, and had lower 
annual fecundity as a result of producing fewer seeds per fruit. The Vipond 
Park population had higher recruitment, faster growth, and higher mortality. 
Annual fecundity was higher and plants became fecund at an earlier age. 
Population size was more stable at Charleys Gulch than at Vipond Park. The 
Vipond Park population demonstrated germination traits that make a long-term 
seed bank more likely than at Charleys Gulch. 



13 



A 



The frecjuency of bolting was much higher at Vipond Park, and this is 
likely the source of much of the difference between Arabis fecunda life 
histories at the two sites. Bolting plants have higher annual fecundity and 
much higher mortality than axillary flowering plants. Axillary flowering 
plants are iteroparous (perennial or polycarpic), while bolting plants 
approach the semelparous (annual or monocarpic) life history. 

Discussion of the environmental characters that cause these differences 
in Arabis fecunda life history can only be speculative. Charleys Gulch is 
warmer and likely has lower precipitation. Bare soil was more common and 
vegetation cover was lower. The bleached color of the mineral soil at 
Charleys Gulch may indicate a more extreme edaphic environment. These 
conditions may result in slower growth but lower density-dependent mortality 
which, in turn, should provide more stable population sizes and favor the 
iteroparous habit. The high elevation of the Vipond Park site may provide an 
more unstable habitat in which the semelparous habit and a long-term seed bank 
are favored (van Groenendael and Slim 1988). 

The differences in life history traits exhibited among the populations 
studied could be the result of genetic differentiation, phenotypic plasticity 
(one genotype that produces different phenotypes under different conditions) 
or both. Quantitative genetics studies are required to determine the basis of 
the variation. Leeper et al. (in press) used starch gel electrophoresis to 
investigate apportionment of genetic variation in Arabis fecunda populations, 
including the three that we studied. Of 18 putative loci scored, 17 were 
invariant; however, the one polymorphic locus had different frequencies among 
the populations, suggesting a fair degree of differentiation. Results of the 
germination studies indicate that there is genetic differentiation between the 
Charleys Gulch and Vipond Park populations. Furthermore, they suggest that 
there is a genetic difference between plants that bolt and those that do not. 



14 



i 



i 



i 



A Together these results provide evidence that differences in life history 
traits between the two sites have a genetic basis. 

Population growth and viability 

Sample populations of Arabis fecunda at Lime Gulch and Vipond Park, the 
two study sites in the southern portion of the range became larger between 
1989 and 1993. Equilibrium population growth rates (A.) at these sites were 
generally greater than or equal to one. Thus, our study provided no evidence 
that these populations are in decline. On the other hand, sample populations 
at Charleys Gulch and Birch Creek (Lesica and Shelly 1993) became smaller in 
number since 1987. Furthermore, X at Charleys Gulch was appreciably less than 
one in two out of the four years that it was measured. Our study was designed 
to elucidate demographic and life history characters and may not provide a 
robust assessment of trend. Nonetheless, our results suggest that populations 
in Ravalli County may be declining. Populations of A_^ fecunda in Ravalli 
^ County have been invaded by the aggressive exotic, Centaurea maculosa , and 

Lesica and Shelly (manuscript submitted) provide evidence that the invader has 
a negative impact on population growth rates of A_^ fecunda . Furthermore, all 
Ravalli County sites are subject to livestock grazing (Lesica 1985, 
Schassberger 1988) which may have adverse effects on A_^ fecunda (Lesica and 
Shelly 1992). Taken together, these observations suggest that A_^ fecunda 
populations in the northern portion of its range may be in jeopardy. 

Analysis of elasticity matrices indicates that Lime Gulch and Vipond 
Park populations of Arabis fecunda are heavily dependent on recruitment from 
seed to maintain population growth, while the Charleys Gulch population 
depends most on survivorship of mature individuals. This is consistent with 
the presence of germination responses promoting a long-term seed bank at 
Vipond Park but not at Charleys Gulch. Thus, populations at Lime Gulch and 
Vipond Park will be most sensitive to changes that reduce seedling 
establishment such as damping-off diseases or the introduction of aggressive 



15 



i 



< 



i 



exotics. The Charleys Gulch population should be most affected by 
disturbances that destroy adults, such as trampling or herbicide application. 
The differences in life history traits are at least partly controlled by the 
frequency of bolting and axillary flowering, and the fact that both types of 
flowering occurred in all populations suggests that there is probably ample 
variation, genetic or plastic, to compensate for any changes that may occur if 
they are not too drastic and do not occur too quickly. 

Management Considerations 
Results of our studies suggest that Arabis f ecunda populations at Lime 
Gulch and Vipond Park are stable or growing. Population growth at these sites 
depends heavily on recruitment from seed, a life history stage that is 
probably buffered by the presence of a long-term seed bank. Weed infestations 
could pose a serious problem as they can reduce recruitment of A_^ fecunda 
(Lesica and Shelly submitted) . Furthermore, weed infestations are most 
frequent in the mesic grassland and xeric forest zones in western Montana 
(Forcella and Harvey 1983), the same habitats where A_^ fecunda is most common. 
At this time, there are no serious weed infestations near any known 
populations in Beaverhead or Silver Bow counties. Nonetheless, encroachment 
by exotics is a very real potential problem. Populations of A^ fecunda should 
be regularly monitored for exotics, and roads and other disturbances that 
promote weed infestations should be minimized in these areas. 

Populations of Arabis fecunda at Charleys Gulch and Birch Creek (Lesica 
and Shelly 1993) may be declining. Results of our studies indicate that the 
Charleys Gulch population will be most sensitive to declines in the survival 
of mature plants. Centaurea maculosa is present at all Ravalli County sites, 
and this aggressive exotic does have a negative effect on A_^ fecunda 
population growth (Lesica and Shelly, submitted) . However, the main negative 
effect of C^ maculosa on A^ fecunda is to reduce recruitment, so the two 
species may be able to coexist (Lesica and Shelly, submitted) . On the other 



16 



hand, livestock are also present at the Ravalli county A_^ fecunda sites, and 
trampling by livestock or large ungulates can have an adverse effect on adult 
survival (Lesica and Shelly 1992). Negative impacts resulting from heavy 
livestock trampling and Centaurea maculosa encroachment taken together may be 
enough to result in declines of A_^ fecunda populations. 

Anthropogenic global climate change is considered a potential cause of 
species extinctions in the near future (Dobson et al. 1989, Peters 1988). 
Populations of Arabis fecunda occur throughout a wide range of elevations and 
habitats (Schassberger 1988), so it seems unlikely that climatic changes will 
have adverse effects. 

Acknowledgements 
Peter Achuff, Anne Garde, Bonnie Heidel, Lisa Roe and Jim Vanderhorst 
helped conduct field work. We are grateful to George Frost for allowing us to 
conduct our study on his ranch. This study was funded by Beaverhead National 
Forest, the U.S. Fish and Wildlife Service and The Nature Conservancy. 

Literature Cited 

Caswell, H. 1989. Matrix population models. Sinauer Associates, Sunderland, 
Massachusetts, USA. 

Daubenmire, R. 1959. A canopy-coverage method of vegetational analysis. 
Northwest Science 33: 43-64. 

Deevey, E. S. 1947. Life tables for natural populations of animals. 
Quarterly Review of Biology 22: 283-314. 

Dobson, A., A. Jolly and D. Rubenstein. 1989. The greenhouse effect and 
biological diversity. Trends in Ecology and Evolution 4: 64-68. 

de Kroon, H. , A. Plaiser, J. M. van Groenendael and H. Caswell. 1986. 
Elasticity: the relative contribution of demographic parameters to population 
growth rate. Ecology 67: 1427-1431. 

Forcella, F. and S. J. Harvey. 1983. Eurasian weed infestation in western 
Montana in relation to vegetation and disturbance. Madrono 30: 102-109. 

Hutchings, M. J., K. D. Booth, and S. Waite. 1991. Comparison of 
survivorship by the logrank test: criticisms and alternatives. Ecology 72: 
2290-2293. 



17 



Leeper, D., D. Pavek, R. Walsh and T. Mitchell-Olds. 1993. Preliminary 
report of combined demographic and genetic analyses for management of Arabis 
fecunda . In Plants and their environment in the Greater Yellowstone 
Ecosystem. National Park Service Transactions. 

Lefkovitch, L. P. 1965. The study of population growth in organisms grouped 
by stage. Biometrics 21: 1-18. 

Lesica, P. 1985. Report on the conservation status of Arabis fecunda , a 
potential candidate species. Report to the U.S. Fish and Wildlife Service, 
Office of Endangered Species, Denver, CO. 

Lesica, P. 1987. A technique for monitoring nonrhizomatous perennial plant 
species in permanent belt transects. Natural Areas Journal 7: 65-68. 

Lesica, P. 1992. Vascular and sensitive plant species inventory for the 
Highland Mountains, Deer lodge National Forest. Montana Natural Heritage 
Program, Helena. 

Lesica, P. and J. S. Shelly. 1991. Endangered, threatened and sensitive 
vascular plants of Montana. Montana Natural Heritage Program, Occasional 
Publication No. 1, Helena, Montana, USA. 

Lesica, P. and J. S. Shelly. 1992. The effects of cryptogamic soil crust on 
the population dynamics of Arabis fecunda (Brassicaceae) . American Midland 
Naturalist 128: 53-60. 

Lesica, P. and J. S. Shelly. 1993. Demographic monitoring of Arabis fecunda 
populations in the Sapphire and Beaverhead ranges, Montana. 1992 progress 
report. Unpublished report, Montana Natural Heritage Program, Helena. 

Lesica, P. and J. S. Shelly. Submitted. Demographic analysis of competitive 
effects of Centaurea maculosa on Arabis fecunda . Journal of Ecology. 

Menges, E. S. 1986. Predicting the future of rare plant populations: 
demographic monitoring and modeling. Natural Areas Journal 6: 13-25. 

Menges, E. S. 1990. Population viability analysis for an endangered plant. 
Conservation Biology 4: 52-62. 

Palmer, M. E. 1987. A critical look at rare plant monitoring in the United 
States. Biological Conservation 39: 113-127. 

Peters, R. L. 1988. Effects of global warming on species and habitats: An 
overview. Endangered Species Update 5(7): 1-8. 

Pyke, D. A. and J. N. Thompson. 1986. Statistical analysis of survival and 
removal experiments. Ecology 67: 240-245. 

Rollins, R. C. 1984. Studies in the Cruciferae of western North America II. 
Contributions to the Gray Herbarium 214: 1-18. 

Schassberger, L. A. 1988. An update of the report on the conservation status 
of Arabis fecunda , a candidate threatened species. Report to the U.S. Fish 
and Wildlife Service, Office of Endangered Species, Denver, CO. 

Silvertown, J., M. Franco, I. Pisanty and A. Mendoza. 1993. Comparative 
plant demography - relative importance of life-cycle components to the finite 
rate of increase in woody and herbaceous perennials. Journal of Ecology 81: 
465-476. 



18 



Stearns, S. C, 1992. The evolution of life histories. Oxford University 
Press, Oxford. 

Sutter, R. D. 1986. Monitoring rare plant species and natural areas-ensuring 
the protection of our investment. Natural Areas Journal 6: 3-5. 

Thompson, K. and J. P. Grime. 1979. Seasonal variation in the seed banks of 
herbaceous species in ten contrasting habitats. Journal of Ecology 67: 893- 
921. 

USDI-Fish and Wildlife Service. 1993. Endangered and threatened wildlife and 
plants; review of plant taxa for listing as endangered or threatened species; 
notice of review. Federal Register 58: 51144-51190. 

Vandermeer, J. 1978. Choosing category size in a stage projection matrix. 
Oecologia 32: 79-84. 

van Groenendael, J, M. de Kroon and H. Caswell. 1988. Projection matrices in 
population biology. Trends in Ecology and Evolution 3: 264-269. 

van Groenendael, J. M. and P. Slim. 1988. The contrasting dynamics of two 
populations of Plantaqo lanceolata classified by age and size. Journal of 
Ecology 76: 585-599. 

Werner, P. A. and H. Caswell. 1977. Population growth rates and age versus 
stage-distribution models for teasel ( Dipsacus sylvestris Huds.). Ecology 58: 
1103-1111. 

Wilson, E. O. 1988. Biodiversity. National Academy Press, Washington D.C. 

Young, T. P. 1985. Lobelia telekii herbivory, mortality and size at 
reproduction: variation with growth rate. Ecology 66: 1879-1883. 



19 



< 

# 



Table 1. Mean ground cover and canopy cover of common vascular plant species 
in Arabis fecunda monitoring transects at three study sites. 



Charleys Gulch 
East West 



Rock 
Soil 
Basal vegetation 

Agropyron spicatum 
Aristida longiseta 
Carex filifolia 
Carex rossii 
Oryzopsis hymenoides 
Poa secunda 
Stipa comata 



5 
77 
19 



2 
59 
40 



<1 
3 1 



Lime 


Gulch 


North 


South 


6 


6 


52 


58 


43 


38 


6 


6 


— 


3 


— 


5 


8 


— 


9 


2 


7 


15 



Vipond 
East 


Park 
West 


14 
43 
43 


15 

40 
48 


8 


12 


— 


2 



Artemisia frigida 
Centaurea maculosa 
Chrysopsis villosa 
Haplopappus acaulis 
Oxytropis besseyi 
Phlox muscoides 
Physaria geyeri 
Sedum lanceolatum 
Senecio canus 



30 
5 <1 



10 



19 

<1 

8 



13 

2 

11 



<1 



20 



Table 2. Stage-based transition matrices for Arabis fecunda at three sites in 1989-93. The reproductive and 
recruitment columns must be added together before solving for 1, the dominant eigenvalue (see Methods). 

Charleys Gulch 



1989-90 








From 






1991-92 








From 










Sm 


Ro 


Mu 


Rep 


Rec 






Sm 


Ros 


Mul 


Rep 


Rec 


To 














To 














Small 
















.377 


Small 




.455 


.016 





.036 


.321 


Rosette 




.391 


.375 


.136 


.076 


.434 


Rosette 




.205 


.492 





.286 


.071 


Multiple 




.044 


.025 


.182 


.057 


.076 


Multiple 







.064 


.625 


.179 





Repro 




.087 


.325 


.409 


.660 


.094 


Repro 







.286 


.250 


.286 





J.= 1 


.138 












X=0 


.898 












1990-91 








From 






1992-93 








From 










Sm 


Ro 


Hu 


Rep 


Rec 






Sm 


Ros 


Mul 


Rep 


Rec 


To 














To 














Small 




.350 


.056 


.077 





.321 


Small 




.091 











.031 


Rosette 




.150 


.556 





.286 


.071 


Rosette 




.333 


.306 





.094 


.156 


Multiple 







.074 


.539 


.159 





Multiple 







.020 


.250 


.031 


.094 


Repro 







.148 


.154 


.286 





Repro 







.204 


.250 


.653 


.281 


X=0 


.844 












i=1 


.050 
























Lime Gulch 














1989-90 








From 






1991-92 








From 










Sm 


Ro 


Mu 


Rep 


Rec 






Sm 


Ros 


Mul 


Rep 


Rec 


To 














To 














Small 




.193 


.022 


.023 





8.42 


Small 




.236 


.009 








.675 


Rosette 




.518 


.248 


.046 





8.57 


Rosette 




.382 


.307 


.021 


.065 


.398 


Multiple 




.024 


.071 


.341 





1.29 


Multiple 




.016 


.031 


.333 


.008 


.073 


Repro 




.036 


.495 


.364 


.714 


3.00 


Repro 




.033 


.425 


.396 


.301 


.114 


X=i,. 


.909 












X=1 


.009 












1990-91 








From 






1992-93 








From 










Sm 


Ro 


Mu 


Rep 


Rec 






Sm 


Ros 


Mul 


Rep 


Rec 


To 














To 














Small 




.161 


.001 


.023 


.044 


.635 


Small 




.244 


.017 


.032 


.012 


1.11 


Rosette 




.543 


.506 


.046 


.101 


.522 


Rosette 




.435 


.449 





.089 


.746 


Multiple 




.049 


.056 


.250 


.050 


.082 


Multiple 




.009 


.017 


.452 


.012 


.041 


Repro 




.025 


.269 


.523 


.327 


.044 


Repro 




.009 


.298 


.323 


.420 


.036 


i=1. 


.068 












X=^. 


.130 
























Vipond 


Park 














1989-90 








From 






1991-92 








From 










Sm 


Ro 


Hu 


Rep 


Rec 






Sm 


Ros 


Mul 


Rep 


Rec 


To 














To 














Small 




.154 


.036 


.019 


.049 


.854 


Small 




.271 


.031 


.035 


.010 


1.75 


Rosette 




.289 


.255 





.037 


.976 


Rosette 




.157 


.245 


.035 


.087 


.505 


Multiple 




.039 


.042 


.245 


.037 


.439 


Multiple 




.186 


.063 


.368 


.049 


.272 


Repro 




.173 


.442 


.491 


.598 


.622 


Repro 




.043 


.453 


.333 


.447 


.252 


i=1. 


815 












i=1. 


,357 












1990-91 








From 






1992-93 








From 










Sm 


Ro 


Mu 


Rep 


Rec 






Sm 


Ros 


Mul 


Rep 


Rec 


To 














To 














Small 




.157 


.037 


.016 





.246 


Small 




.116 


.025 


.035 


.006 


.546 


Rosette 




.326 


.244 


.079 


.100 


.322 


Rosette 




.295 


.280 


.012 


.081 


.839 


Multiple 




.079 


.089 


.413 


.043 


.147 


Multiple 




.073 


.059 


.391 


.040 


.299 


Repro 




.056 


.296 


.175 


.194 


.043 


Repro 




.024 


.271 


.138 


.333 


.052 



X=0.783 



X= 1.044 



21 



Table 3. Effect of site (population), year and their interaction on log- 
transformed number of fruits per reproductive Arabis fecunda plant in 1989-93 
by ANOVA. Means (+SE) followed by different letters are significantly 
different (P<0.001) by contrast test after ANOVA. 



Source of Variation 



df 



MS 



Site 
Year 

Site*Year 
Error 



2 

4 

8 

1495 



13, 
5. 
4. 



39 
21 

61 



0.81 



16.45 
6.40 
5.66 



<0.001 
<0.001 
<0.001 



Charleys Gulch 
14.6+0.8' 



Lime Gulch 
10.6+0.4'' 



Vipond Park 
14.5+0.5' 



Table 4. Effect of site (population), year and their interaction on log- 
transformed number of seeds per fruit for Arabis fecunda in 1989-91 and 1993 
by ANOVA. Means (+SE) followed by different letters are significantly 
different (P<0.05) by contrast test after ANOVA. 



Source of Variation 



df 



MS 



Site 
Year 

Site*Year 
Error 



2 

3 
6 

288 


234.1 

150.8 

417.9 

56.4 


4.15 0.017 
2.67 0.048 
7.41 <0.001 


Lime Gulch 




Vipond Park 


32.4+0.7'*' 




34.0+1.0'' 



Charleys Gulch 
30.9+0.6' 



22 



Table 5. Effect of bolting, site (population), year and their interactions on 
log-transformed number of fruits per Arabia fecunda plant in 1990-93 by ANOVA. 



Source of Variation 



df 



MS 



Bolting 

Site 

Year 

Bolting*Site 

Bolting*Year 

Site*year 

Error 



1 


13.67 




20. 


.76 




<0.001 


2 


1.05 




1. 


.60 




0.202 


3 


6.08 




9. 


.24 




<0.001 


2 


1.84 




2. 


,79 




0.062 


3 


7.49 




11. 


.38 




<0.001 


6 


3.03 




4. 


,60 




<0.001 


1347 


0.66 












ch 


Lime Gulch 






Vipond Park 




18.3+0. 


.9 






20, 


.9+0.8 




8.1+0. 


.3 






9. 


.8+0.5 



Bolting 

Axillary flowering 



Charleys Gulch 

17.3+3.9 
14.3+0.9 



Table 6. Effect of treatment, site (population), bolting and their 
interactions on arcsine-transformed proportion of Arabis fecunda seeds 
germinating by ANOVA. 



Source of Variation 



df 



MS 



Treatment 


1 


3. 


.83 


103.15 


<0.001 


Site 


1 


2, 


.43 


65.43 


<0.001 


Bolting 


1 


0, 


.02 


0.50 


0.484 


Treatment* Site 


1 


2, 


.23 


60.15 


<0.001 


Treatment* Bolting 


1 


0, 


.18 


4.90 


0.033 


Site*Bolting 


1 


0, 


,01 


0.28 


0.602 


Error 


41 


0, 


,04 








Warm-Light 






Cold-Dark 




Charleys Gulch 












Axillary flowering 


0.87+0.04 






0.86+0.05 




Bolting 


0.91+0.04 






0.72+0.07 




Vipond Park 












Axillary flowering 


0.86+0.04 






0.11+0.05 




Bolting 


0.87+0.07 






0.05+0.02 





23 



Table 7 Mean elasticities for Arabis fecunda stage transition matrices at 
JSieJltf fo..lS8,-,3^ T.eU«tJ„e colons «pr.se„t^.=„-^ 



seed. 







Charley 


■s Gulch 










Small 


Rosette 


From 

Multiple 


Repro 


Recruit 




To 

Small 
Rosette 
Multiple 
Repro 


.0219 
.0340 
.0010 
.0041 


.0030 
.1481 
.0163 
.1146 


.0017 
.0015 
.0806 
.0541 


.0011 
.0518 
.0287 
.2752 


.0333 
.0467 
.0113 
.0714 




Total 


.0610 


.2820 


.1379 


.3568 


.1627 








Lime 


Gulch 










Small 


Rosette 


From 

Multiple 


Repro 


Recruit 




TO 

Small 
Rosette 
Multiple 
Repro 


.0207 
.0740 
.0040 
.0186 


.0013 
.1156 
.0111 
.2005 


.0004 
.0012 
.0131 
.0340 


.0019 
.0136 
.0043 
.1327 


.0832 
.1242 
.0162 
.1396 




Total 


.1171 


.3285 


.0487 


.1525 


.3632 








Vipond Park 










Small 


Rosette 


From 

Multiple 


Repro 


Recruit 




To 
Small 
Rosette 
Multiple 
Retjro 


.0173 
.0380 
.0160 
.0389 


.0055 
.0572 
.0135 
.1580 


,0026 
.0074 
.0483 
.0695 


.0012 
.0167 
.0073 
.1651 


.0836 
.1149 
.0428 
.0965 





Total .1102 .2342 .1278 .1903 .3378 



24 



Figure 1. Number of Arabis fecunda plants at three study sites in 1989-93. 



700 
600 
500 
400 
300 
200 
100 




• Charleys 
V Lime 
T Vipond 



v- 






V 




J L 



1989 1990 1991 1992 1993 
Year 



25 



Figure 2. Annual recruitment in relationship to population size (survivors) 
of Arabia fecunda at three study sites in 1989-93. Sites with different 
letters had different recruitment rates (recruits/survivors) as determined by 
Chi-square tests (P<0.05). 



1990 



1991 



c 

O 

0) 

E 

3 



700 
600 
500 
400 
300 
200 
100 




Survivors 
Recruits 





Charleys Lime Vipond 



Charleys Lime Vipond 



1992 



1993 





Charleys Lime Vipond 



Charleys Lime Vipond 



26 



Figure 3. Survive 
study sites. 



rship curves for the 1990 Arabis fecunda cohort at three 



O 
> 

*> 

13 
in 

c 

CD 

O 
i_ 

O) 

Q_ 



100 



80 - 



50 



40 



20 - 







• Charleys 
V Lime 
T Vipond 




1990 1991 1992 1993 
Year 



27 



Figure 4. Arabis f ecunda plants moving into a larger size class or moving 
into the same or a smaller class at three study sites in 1989-93. Sites with 
different letters had different growth rates ( larger/smaller+same) as 
determined by Chi-square tests (P<0.05). 



1990 



1991 



500 



400 - 




Q- 300 - 



E 



500 



Charleys Lime Vipond 




Charleys Lime Vipond 



500 

« 400 

o 

°- 300 
"o 


- 


1992 
b 


b 


- 


Numbe 

-■ IS) 

o o 

3 O O 





1 


1 


- 



1993 



500 




Charleys Lime Vipond 



Charleys Lime Vipond 



28 



Figure 5. Number of bolting and axillary-flowering Arabis fecunda plants at 
three study sites in 1990-93. Sites with different letters had different 
proportions of bolting/axillary plants as determined by Chi-square tests 
(P<0.05) . 



1990 



1991 



c 

Q- 



E 

3 



250 



200 



150 



100 



50 



I I Axillary 
F^^ Bolting 




250 

200 h 

150 

100 

50 h 



b 
~ a 



Charleys Lime Vipond 



Charleys Lime Vipond 



1992 



1993 



250 




250 
200 
150 
100 
50 



- 






b 




c 


- 


- 


P^ 








P 


- 






o 













Charleys Lime Vipond 



Charleys Lime Vipond 



29 



Pl^j^,.., .,,.,, ..,,;, 



f>;;tr^,,,fjif:j- ... 




L