Effects of newly planted hedges on ground-beetle diversity (Coleoptera, Carabidae) in an agricultural landscape

The diversity of ground-beetle communities (Coleoptera, Carabidae) was stud ied to assess the short-term impact of new hedges planted in an intensive a gro-ecosystem. Hedges represent a new and undisturbed habitat for those pol yphagous predators and may provide increased prey availability. Carabids we re sampled with pitfall traps in a hedge and an adjacent cultivated field d uring the whole activity period of these insects to assess the effect of di stance from the hedge on species diversity. Fenced pitfall traps were also used to estimate absolute population densities. Several diversity indices w ere calculated at various sampling levels (total area, distance treatment, trap). Kendall's coefficient of rank correlation between communities at adj acent distances showed that the greatest changes in species relative abunda nces occurred close to the hedge. Indices of species richness, dominance co ncentration, equitability and Fisher's a all indicated a significant decrea se in species diversity with increasing distance from the hedge. These tren ds are explained by two complementary factors. First, the number of species decreased significantly with distance from the centre of the hedge. Second , the various species had different spatial patterns of total capture and a bsolute density. Four groups of species can thus be distinguished: species restricted to the hedge, species preferring the hedge, species preferring t he crop, and species unaffected by the hedge. The respective roles of small -scale abiotic changes in habitat structure and differences in prey availab ility are discussed.