growth rate of A^ fecunda . mainly by reducing 

 recruitment (Lesica and Shelly, submitted) . 

 Hamilton and Mitchell-Olds (1990) found that the 

 presence of C^ maculosa reduced fecundity of A. 

 fecunda at a Ravalli County site. Results of a 

 study at Charleys Gulch and Birch Creek suggest 

 that both species may be able to co-occur if the 

 density of knapweed does not increase (Lesica and 

 Shelly, submitted) . 



Competitive effects of other species on A^ fecunda 

 are not known. 



2. FACILITATION: Cryptogamic soil crusts occur at 

 some of the Arabis fecunda sites, and Lesica and 

 Shelly (1992) demonstrated that soil crust 

 benefits A^ fecunda populations by increasing 

 survival of adult plants. 



Although there is evidence that cattle have an 

 adverse effect on A_^ fecunda populations (see 

 below), under some conditions, they may be 

 beneficial. Arabis fecunda establishes best when 

 not in competition with other plants (Lesica and 

 Shelly, submitted) , so grazing of competitors may 

 be advantageous, Exclosure studies at two sites 

 near the Big Hole River suggest that grazing may 

 sometimes have detrimental effects (Lesica 1993) . 

 At one site A^ fecunda increased in the grazing 

 exclosure, while at the other it decreased 

 relative to controls. Furthermore. Some of the 

 largest populations, such as Birch Creek and Jerry 

 Creek, are in areas that are intensely grazed. 



3. HERBIVORY: J. S. Shelly observed insect larvae in 

 the fruits of Arabis fecunda at both Lime Gulch 

 and Charleys Gulch in 1990. The identification of 

 this insect is not known. Seed predation appears 

 to be of limited extent. 



Scattered plants have been observed at Lime Gulch 

 and Canyon Creek with the upper portion of one or 

 two fruits bitten off (Lesica and Shelly, pers. 

 observation) . The source of this predation is not 

 known. 



4. PATHOGENS: A rust, Puccinia sp. was observed 

 infecting a small number of plants at Charleys 

 Gulch in 1985 (Lesica, pers. observation). Rust 

 infections appear to be rare and local. 



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