Effects of landscape connectivity on the spatial distribution of insect diversity in agricultural mosaic landscapes

Abstract

European agricultural landscapes are mosaics of intensively cultivated areas and semi-natural elements. Although comprising only a small fraction of the total area, semi-natural elements provide habitat for most of the landscape biodiversity. Agricultural intensification has increasingly fragmented semi-natural elements and species numbers are in decline. Insights into the effects of landscape structure on species’ distributions within and among semi-natural habitats are needed to conserve biodiversity in agricultural landscapes more effectively. We investigated the landscape- and habitat-specific diversity partitions of wild bees, true bugs, and carabid beetles in two differently structured agricultural landscapes in Switzerland. In each landscape, we partitioned the total species diversity (γ) into its additive components within (αP) and among patches (βP) and among habitats (βH). In the landscape characterized by a patchy, isolated distribution of habitat elements, among-patch diversity (βP) explained 44% of the total species richness (γ) and was significantly higher than expected under a random distribution of samples among habitat patches; in the landscape with higher habitat connectivity, among-patch diversity (βP) comprised 32% of the total species richness (γ) and did not differ from the random expectation. Habitat-specific within-patch contributions to species richness were similarly low across habitat types (αP=23–24%) in the patchy landscape, whereas in the more connected landscape within-patch partitions tended to be higher and differed among habitat types (αP=22–38%). Functionally different groups of bees, true bugs, and carabids also responded differently to landscape structure in a manner that was consistent with known differences in resource specialization and dispersal ability. Differences in diversity partitions among landscapes and taxa indicate the need for flexible conservation strategies. Conservation of habitat-specific diversity may require more habitat patches in landscapes that have lower habitat connectivity and low within-patch diversity (αP) than in landscapes with higher within-patch diversity (αP).