ft 



> 



35 

 8. Population ecology of the taxon. 



A. General summary: Penstemon lemhiensis appears to 

 have a close relationship with a species of pollen- 

 gathering vespid wasp. The plants are susceptible 

 to browsing, probably by deer and cattle; in some 

 populations this impact can be fairly, heavy. 

 Although P. lemhiensis shows some tolerance to 

 disturbance based on its occupation of roadbank 

 habitats, the plants are never abundant in such 

 situations, and are vulnerable to road maintenance 

 and weed control activities. In undisturbed sites, 

 it prefers more open microhabitats. These 

 observations suggest that P. lemhiensis has a low 

 tolerance for interspecific competition. 



B. Positive and neutral interactions: As described in 

 I.7.D.2.b., P. lemhiensis may have a close plant- 

 pollinator relationship with two insects, 

 especially with a vespid wasp ( Pseudomasaris 

 vespoides ) . The latter appears to be faithful to 

 Penstemon lemhiensis . and may represent its most 

 important pollinator. Other positive or neutral 

 interactions are not known. 



C. Negative interactions. 



1. Herbivores, predators, pests, parasites and 



diseases: Penstemon lemhiensis is subject to 

 moderate to heavy browsing, most likely by deer 

 and cattle. Ramstetter (1983) found the 

 percentage of browsed stalks at the Battlefield 

 (006) and Argenta (001) sites to be 23% and 

 90%, respectively. In three demographic 

 monitoring transects established in 1989 

 (French Creek (009) and Badger Pass North (019) 

 sites) , the percentage of browsed flowering 

 stems ranged from 3.0 to 47.8% (Shelly 1990b). 

 Also, Ramstetter (1983) found no plants outside 

 the Battlefield; the park is fenced, and is not 

 used for livestock grazing. Similarly, during 

 a 1986 survey by the author on the west side of 

 the Big Hole Battlefield, individuals were seen 

 growing right next to the boundary fence within 

 Park property; none were found outside the 

 fence, in an area subject to livestock grazing 

 and weed invasion. One population observed in 

 1989 (Briston Lane (025)), however, contained 

 numerous individuals in an area that had been 

 burned and grazed. This suggests that, in the 

 short term, the plants can persist in areas so 

 treated. Further studies are needed to 

 determine the long-term effects of grazing on 



