Forest ground beetles (Coleoptera: Carabidae) on a boreal island:: Habitat preferences and the effect of experimental removals

We used pitfall trapping to measure the species richness and relative abundance of ground beetles (Coleoptera: Carahidae) in four forest habitats on Kent Island, a 80-ha island in the Bay of Fundy, New Brunswick;, Canada. Sixteen species of ground beetles representing 11 genera were identified in the forested habitats on Kent Island; the relative paucity of ground beetle species may be a result of the island's harsh climate, dense colonies of breeding seabirds, and isolation from the mainland. Estimates of ground beetle population densities on Kent Island ranged from 50 000 to 250 000/ha. Most ground beetle species were trapped in all habitats and appeared to be habitat generalists. In a series of experiments in which we removed all ground beetles trapped daily over a 3-week period in two experimental plots, ground beetle densities remained as high as in a control plot; other ground beetles quickly moved into the experimental plots to replace beetles that had been removed. The density of ground beetles was highest in intact forest and large forest patches; in contrast, the density of invertebrates other than ground beetles (i.e., possible prey or competitors of ground beetles) was highest in open habitats: and isolated forest parches, where ground beetles were less common. Removing ground beetles from experimental plots did not result in an increase in the density of other invertebrates.