Local and large scale determinants of biodiversity in winter wheat fields

Abstract

Factors acting at various scales may affect biodiversity, demanding analyses at multiple spatial scales to understand how community richness is determined. Here, a hierarchical approach was used to test the contribution of region, landscape heterogeneity, local management (organic vs. conventional) to the species richness and abundance of arthropods in cereals. The study was conducted in three regions of Western and Central Germany: Leine Bergland, Soester Boerde and Lahn-Dill Bergland. 54 paired organic and conventional winter wheat fields were compared. Field pairs were located in areas ranging from structurally simple to structurally complex landscapes. In spring and summer 2003 epigeic insects were sampled using pitfall traps and the insect community of thistles Cirsium arvense was monitored using experimental thistle plots. Linear mixed models were used to determine the relationship between diversity and abundance of arthropods and the spatial factors region, landscape heterogeneity, as well as local management and location within field. Landscape heterogeneity was a significant predictor of diversity for spiders and thistle herbivores, while organic management positively affected both detritivorous staphylinid beetles and thistle herbivores. More species of epigeic arthropods were found in field edges and in heterogeneous landscapes. Analyses of beta diversity showed similar patterns as those conducted for alpha diversity. In addition the importance of beta diversity depended on taxon and decreased with dispersal ability. Our study suggests that organic farming benefits some arthropod groups but not others, and that promoting heterogeneity in land use at landscape scales is one of the keys to increase biodiversity in agroecosystems.