SUMMARY OF POPULATION BIOLOGY: Walsh (1992) found 

 that five sample populations of Arabis f ecunda 

 declined in 1990-91, and three of these declined 

 in 1991-92, while the other two became larger 

 (Leeper et al., in press). Leeper et al. (in 

 press) predicted that population of A^ f ecunda at 

 Birch Creek would decline and eventually become 

 extirpated based on three years of monitoring 

 data. Lesica and Shelly (1994) found that in 

 1989-93 two sample populations of A^ fecunda in 

 Beaverhead County increased in size, while one in 

 Ravalli County declined. Population survival is 

 most often controlled by uncommon events, either 

 beneficial or detrimental. Short-term studies 

 such as those reported above are probably of 

 little value for predicting extinction 

 probabilities. Results of these studies do 

 suggest that Ravalli County populations are more 

 likely to be declining. 



ECOLOGY 



COMPETITION: Arabis fecunda occurs only in 

 relatively sparse vegetation, suggesting that it 

 is sensitive to competition from other species. 

 Due to its diminutive stature, A^ fecunda is 

 probably sensitive to shading by taller plants. 



Centaurea maculosa is an aggressive Eurasian weed 

 present at all A^ fecunda sites in Ravalli County. 

 It is a taprooted perennial that is widely 

 introduced in North America where it has become a 

 serious pest of semi-arid grasslands in the 

 Pacific Northwest and intermountain valleys of the 

 Northern Rocky Mountains (Watson and Renney 1974, 

 French and Lacey 1983). Its ability to invade and 

 replace native plants is well-documented (Morris 

 and Bedunah 1984, Harris and Cranston 1979, Tyser 

 and Key 1988) . In addition, leachates of 

 Centaurea maculosa inhibit germination of grass 

 and conifer seedlings (Kelsey and Locken 1987) ; 

 however, Kelsey and Bedunah (1989) feel that 

 concentrations high enough to inhibit germination 

 are seldom found in natural environments. 

 Centaurea maculosa was introduced into western 

 Montana in the 1920 's and has since come to 

 dominate large areas of rangeland (French and 

 Lacey 1983). Like A^ fecunda , it is a rosette- 

 forming, taprooted, iteroparous perennial with an 

 average life-span of 3-5 years (Watson and Renney 

 1974, Boggs and Story 1987). The presence of C^ 

 maculosa significantly reduces the population 



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