Does the surrounding landscape heterogeneity affect the butterflies of insular grassland reserves? A contrast between composition and configuration

Landscape homogenisation represents one of the gravest threats to the biodiversity of intensively farmed landscapes. In such landscapes, many species persist within remnants of (semi)natural habitats, such as in the steppe grasslands of Southern Moravia, SE Czech Republic. We investigated how the butterfly fauna of insular grassland reserves is affected by the heterogeneity of the surrounding farmland. We followed two lines of evidence, one based on species richness, the other on species community composition, considering two aspects of landscape heterogeneity, composition (amount of land cover types) and configuration (geometry of land cover patches). After statistically correcting for individual reserves characteristics, and within-reserves biotope composition, we found that reserves amidst heterogeneous landscapes contained more species. With increasing buffers around the reserves, the strength of the effects decreased for landscape composition, and increased for landscape configuration. Similar patterns applied for the butterfly assemblage composition, but in a rather subtle manner, not reflecting a specialist versus generalist dichotomy. However, more red-listed species inclined towards reserves amidst heterogeneous matrices. The species most tightly associated with heterogeneous landscapes were those whose populations likely span across multiple patches of relatively rare biotopes, whereas those indifferent to configuration were either those persisting at isolated sites, or those utilising common biotope types outside the reserves. The importance of landscape configuration suggests that relatively cheap restoration measures aimed at compartmentalisation the currently huge farmland units may substantially contribute to preserving biodiversity in intensively farmed regions.