Carabid Beetle (Coleoptera: Carabidae) Diversity in Forest Fragments of Northwestern Ohio

Abstract

American Entomologist • Volume 51, Number 4 Habitat fragmentation is a major threat to plant and animal communities worldwide (Hanski et al. 1995, Didham 1997), and species have been eliminated from areas of extreme fragmentation. Forest fragmentation is widespread. Fragmented forest landscapes typically consist of small, isolated woodland fragments that have replaced large tracts of contiguous forests. Forest-dwelling carabids are sensitive to forest fragmentation (see Davies and Margules 1998, Niemela et al. 2000, Heliola et al. 2001, Magura et al. 2001, Rainio and Niemela 2003). Because of this sensitivity to forest fragmentation, researchers have suggested that certain carabids are useful indicators of habitat alteration (Rainio and Niemela 2003). The responses of carabid species to forest fragmentation, however, are variable. Abundance of large, poorly dispersing forest specialists tends to decrease with fragmentation, whereas small, habitat-generalist carabid species possessing exceptional dispersal ability increase in abundance as forests become fragmented (Rainio and Niemela 2003). We were interested in examining the carabid communities present in forest fragments of northwestern Ohio to determine whether forest fragment size had an influence on carabid species diversity and community composition. Our hypotheses were as follows: 1. The number of carabid species and the activity density of carabids would be lower in small forest fragments than in larger forest fragments. 2. Diversity, as measured by species richness, Shannon’s index (H′) and Simpson’s index (1/ D) would be greater in large forest fragments than in small ones. 3. Forest fragments of different sizes would harbor different beetle communities, as measured by Sorensen’s similarity Index. During the spring and summer of 2000, pitfall trap grids were established in eight forest fragments of Wood and Fulton Counties of northwestern Ohio. Four of the forest fragments were categorized as small (9 to 10 ha) and four as large (20, 28, 32, and 40 ha). For each forest, 36 pitfall traps were arranged within a 100 × 100 m grid; each trap was 20 m from adjacent traps. The trap grids were positioned away from the forest fragment edges to minimize edge effects. Traps were opened for three consecutive nights every 3–4 wk from June through September in the forest fragments. Carabid specimens were curated and identified by FFP and DMP, and voucher specimens are housed in the Bowling Green State University Insect Collection. A total of 412 carabids, constituting 41 species, were caught during the study. Species accumulation curves for the small and large forest size classes (Fig. 1) indicate that species were being added as trapping progressed. Chlaenius aestivus showed the greatest activity density; 71 individuals were captured. The most widespread carabid species were Poecilus lucublandus (47) and Agonum melanarium (57); these two carabids were caught in six and seven of the eight forest fragments, respectively. Sixteen of the 41 species were caught in large and small forests. Four species were found only in small forCarabid Beetle (Coleoptera: Carabidae) Diversity in Forest Fragments of Northwestern Ohio