21 



5. Successional phenomena: Although Shoshonea pulvinata 

 sometimes occurs in partial shade at the edges of forests* 

 plants found in these areas appear to be less vigorous than 

 those in full light. The vast majority of plants at any one 

 site are found in open areas. These observations indicate 

 that Shoshonea prefers full or nearly full sunlight. Forest 

 encroachment of Shoshonea habitat would cause increased snow 

 cover, slower warming in spring, and lower light 

 intensities, which could, in turn, cause extirpation of the 

 species. Sites where Shoshonea pulvinata occurs are on 

 ridgetops, and on the rims above the windward side of deep 

 canyons. These sites are apparently maintained in an early 

 successional stage by their extreme exposure to wind. 



6. Dependence on dynamic aspects of biotic associations and 

 ecosystem features: Unknown. 



7. Other endangered, threatened, rare, or vulnerable species 

 occurring in habitat of this taxon: The following species 

 have a limited distribution in Montana, but are more 

 widespread elsewhere. 



Astragalus aretioides (Jones) Barneby - listed as rare 

 by Lesica et al. (1984)| listed as "state endangered" 

 (SB) by the Montana Natural Heritage Program (Shelly 

 1988). 



Hymenoxys torreyana (Nutt.) Parker - listed as rare by 

 Lesica et al. (198't); listed as "state endangered" (S2) 

 by the Montana Natural Heritage Program (Shelly 1988). 



Townsendia spathulata Nutt. - listed as "state 

 endangered" (S2) by the Montana Natural Heritage 

 Program (Shelly 1988). 



Physocarpus monoqynus (Torr.) Coult. - listed as rare 

 by Lesica et al . (198^); listed as "state status 

 unknown, possibly threatened or endangered" (SU) by the 

 Montana Natural Heritage Program (Shelly 1988). 



7. Population biology of the taxon. 



A. General summary: Known populations of Shoshonea pulvinata in 



Montana consist of three or four subpopulations separated by less 

 than 1/2 mile. Subpopulations consist of 100-1,500 plants in the 

 Pryor Mountains, and 1,000-5,000 plants in the Beartooth 

 Mountains. Small, non-reproductive plants were present at all 

 sites, indicating that successful recruitment is occurring. 

 Areas of seemingly appropriate habitat were observed to be 

 unoccupied by Shoshonea , which may indicate that the species is 

 not completely competent at colonizing new sites. The breeding 

 system of Shoshonea is unknown. On several occasions, flies in 

 the Family Syrphidae were observed on the flowers. 



