Composition and Abundance of Ground-Dwelling Coleoptera in a Fragmented and Continuous Forest

Abstract

The structure of the ground-dwelling beetle community at two forested sites in northern Delaware was compared by examining composition and abundance at the species or genus level for five target families and at the family level for all other Coleoptera. The beetle communities at an isolated 15-ha woodlot and a nearby plot of relatively continuous forest were sampled using pitfall traps during 2000 and 2001. The results showed an absence or reduced abundance of many beetle taxa in the isolated woodlot relative to the continuous forest site and elevated abundances of a few taxa. Most notably, the species richness of poorly dispersing species of carabid beetles was lower in the isolated woodlot, with 12 of 19 brachypterous species completely absent from pitfall samples. Although this study does not constitute a test of habitat fragmentation hypotheses, the data do suggest that the beetle community in the woodlot may be suffering from isolation effects. The estimated response to fragmentation was correlated with body size for the 19 most common carabid species caught, suggesting that body size may be a useful predictor of vulnerability to forest fragmentation. At least in Carabids, larger body size seems to be associated with greater susceptibility to fragmentation. A number of staphylinid beetle taxa were also significantly less abundant or absent in the isolated woodlot, as were some beetles in other trophic groups, including carrion beetles (Silphidae) and geotrupid beetles (Geotrupidae). Although it retains some faunal similarity with nearby continuous forest, the woodlot may be too isolated to sustain populations of some beetle taxa, especially large, poorly dispersing forest species.