10 



to 60 acres. The total number of plants observed 

 in Montana is ca. 816, distributed across on 140 

 acres. Although the populations appeared healthy, 

 plant density is not high. 



Visits to the French Creek population in 1990 and 

 1991 revealed that one subpopulation present in 

 1990, was not present in 1991. It is possible 

 that seedlings were overlooked at this site, or 

 that weed control activities may have eliminated 

 this subpopulation. Observations should be made 

 in 1992 to confirm the absence of this 

 subpopulation . 



3. REPRODUCTIVE BIOLOGY 



a. TYPE OF REPRODUCTION: This tap-rooted 

 perennial reproduces by way of seed. 

 Chromosome counts revealed 2N = 34-36 for C. 

 subniveum (Welsh et al. 1987) . 



b. POLLINATION BIOLOGY: Bees were observed 

 pollinating Cirsium subniveum plants (pers. 

 obs.), but other insects may also serve as 

 pollinators. 



c. SEED DISPERSAL AND BIOLOGY: The wings on the 

 seeds of species in the genus Cirsium aid in 

 dispersal by wind. Dispersal usually occurs 

 in late summer and early fall. 



POPULATION ECOLOGY 



1. BIOLOGICAL INTERACTIONS 



a. COMPETITION: Cirsium subniveum occurs in 

 habitats where competition is limited by 

 harsh site conditions (loose gravelly scree) . 

 The restriction of this species to these 

 locations may be due to a lack of competitive 

 ability. 



b. HERBIVORY: Native plants in the genus 

 Cirsium support a variety of herbivorous 

 fauna including weevils, and several species 

 of moths (Turner et al . 1987a, 1987b) . In 

 addition, young rosettes are grazed by sheep 

 and cattle, but spines usually offer some 

 protection to adult plants. In either case 

 fecundity is likely to be lowered. 



