Comparison of ground beetle (Coleoptera: Carabidae) assemblages in rocky mountain savannas invaded and un-invaded by an exotic forb, spotted knapweed

We compared ground beetle (Carabidae) assemblages between spotted knapweed (Centaurea maculosa Lam.) -invaded (invaded) and un-invaded (native) habitats in Rocky Mountain savannas. Carabids play important roles in biotic communities and are known as a good indictor group of environmental change. Carabid species activity-abundance and diversity were estimated, and environmental measurements were taken at four transects at each of six study sites in 1999 and 2000. Data on carabid trap captures were analyzed at both the species and functional group level. We found that species belonging to specialist predator and omnivore functional groups were more abundant on transects at invaded sites, whereas generalist predator species were more abundant within native sites. Carabid species richness was similar between invaded and native sites; however, evenness was greater at invaded compared to native sites. Greater species evenness in invaded versus native sites was primarily due to an increase in activity-abundance of species in the omnivore and specialist predator functional groups and a decrease in activity-abundance of dominant species belonging to the generalist predator functional group. Our results suggest that spotted knapweed invasion results in an alteration of carabid community structure and leads to the homogenization of carabid assemblages in Rocky Mountain savannas. Biotic homogenization, the increase in taxonomic similarity of once-diverse communities, is often a direct outcome of exotic invasions and an important concern currently facing biodiversity conservation.