Species richness patterns of ground beetles (Coleoptera: Carabidae) in forest fragments

Abstract

Nineteen forest fragments were studied in the Bereg Plain, Hungary, and SW Ukraine. This area contains natural forest patches, mainly of oak and hornbeam. The aim of this study was to analyse the effect of fragmentation on the species richness of ground beetles (Coloptera: Carabidae) living in natural forest fragments. Ground beetles present in the forest patches were categorized into generalists, forest specialists and edge-preferring species. For these categories we analysed the relationship between species richness and fragment area. Our research hypothesis was that the edge-preferring species and generalist species (species that occur also in the surrounding matrix) modifies the species-area relationship of the fragments causing a high species richness in the small forest fragments (spurious diversity).

We found that forest specialist species richness was correlated positively with forest patch size as predicted by the classical bio-geography. Forest patch size and the number of generalist species showed a marginally significant negative relationship, indicating that generalist species were more important in smaller patches. Edge-preferring species were shown to influence the species-area relationship; we found that the number of edge-preferring species increased with the edge:area ratio. Or findings revealed that both generalist and edge-preferring species distort the species-area relationship; matrices surrounding the forest fragments provide colonists that do not necessarily distinguish the fragment from the matrix and can survive and reproduce there. We also found that edge-preferring species can further distort the species-area relationship, as smaller fragments have larger edge:core ratios.