Introduced and native ground beetle assemblages (Coleoptera: Carabidae) along a successional gradient in an urban landscape

According to the intermediate disturbance hypothesis (IDH), species diversity should be higher at sites with intermediate levels of disturbance. We tested this hypothesis using ground beetles (Coleoptera: Carabidae) collected in pitfall traps from sites that varied in time since last disturbance. This successional gradient was embedded in an urban landscape near Montreal, Quebec. We predicted that diversity in young forests and old fields would be higher than in agricultural fields and old forests. Fifty-five species (2932 individuals) were found in 2003 and 46 species (2207 individuals) in 2004. In both years, species richness was highest from traps placed in agricultural fields. We collected nine introduced species; these had higher catch rates than the native species in both years (64.8% of total catch). When introduced species were removed from the Nonmetric Multidimensional Scaling ordination analysis, the assemblages from agricultural fields were less distinct compared to those of the other habitats, suggesting the introduced fauna is important in structuring carabid assemblages from the agricultural fields. Introduced species may play a significant role in the community composition of ground beetles in urban landscapes, and their influence may be the cause of the lack of support found for the IDH.