Respective roles of recent hedges and forest patch remnants in the maintenance of ground-beetle (Coleoptera : Carabidae) diversity in an agriculturallandscape

We compared three kinds of habitats: small remnants of native forests, rece nt hedges and barley crops, in order to investigate their respective roles in the maintenance of carabid-beetle diversity in a 950-ha area of an inten sive agricultural landscape. Carabid faunas in remnants differed weakly fro m these found in hedges and crops. In particular, small remnants had few ty pical forest carabid species and a large number of open-area or ubiquitous species. Different approaches in the measurement of alpha and beta -diversi ty (classical indices, and additive partitioning of Simpson's index) showed similar results: hedges supported a high alpha -diversity but habitat type s were quite similar overall, with weak differences between open and closed or disturbed and undisturbed habitats. A comparison of species dispersal powers in the various habitat types showe d that species with a low dispersal power were rare in all habitats. Howeve r, wing development measured on two dimorphic species revealed, surprisingl y, that brachypterous individuals were mainly present in hedges, which were expected a priori to be more disturbed, than remnants hence less suitable for the establishment of populations with a low dispersal power. These results suggest that small remnants do not behave as 'climax' habitat s in this intensive agricultural landscape, probably because of their small size and strong isolation. We discuss the interest of new undisturbed habi tats, such as recent hedges, for the maintenance of carabid diversity at bo th the local and landscape scale.