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 



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