Date of Award

Spring 1-1-2011

Document Type


Degree Name

Master of Arts (MA)



First Advisor

Susan W. Beatty

Second Advisor

Timothy Seastedt

Third Advisor

Thomas T. Veblen


Native Colorado thistles are at risk of decline due to increased use by Rhinocyllus conicus, a weevil introduced to biologically control nonnative Carduus spp. R. conicus uses one third of North American Cirsium species and here we examine its relationship with high elevation thistles in Rocky Mountain National Park and on Niwot Ridge, Colorado. Transects along an elevational gradient were sampled in Rocky Mountain National Park and presence/absence of R. conicus was recorded when a native thistle was found. Thistle locations were recorded in a GIS, and we examined relationships between environmental variables and weevil presence/absence. A controlled introduction experiment was conducted at Niwot Ridge to determine if weevils were able to complete their reproductive cycle at high elevation. Results of a logistic regression indicate that R. conicus presence on native thistles in Rocky Mountain National Park is associated with elevation, such that as elevation increases, the chances of finding weevils decreases. Results of the Niwot Ridge experiment indicate that weevils are capable of reproducing at treeline. This is the first experimental study of exotic weevils at high elevation in Colorado. It is likely that R. conicus' range could expand to include more native thistles as a result of climate change and increasing global temperatures.