Landscape composition and configuration differently affect trap-nesting bees, wasps and their antagonists

Abstract

Intensification of agriculture reduces heterogeneity at local and landscape levels and thereby impact biodiversity and ecosystem processes. We studied a host-antagonist system of cavity-nesting bees, wasps and their antagonists and hypothesised that hosts and antagonists show different responses to local land-use intensity, the diversity of landscape in terms of composition and the spatial structure of landscape in terms of configuration.In a highly replicated study, we established nesting resources on 95 grasslands in three geographic regions across Germany and measured species richness and abundance of hosts (bees and wasps) and their antagonists, and rates of parasitism. For each site, we quantified local land-use intensity as well as landscape heterogeneity in terms of composition and configuration at spatial scales ranging from 250m to 2000m.Increasing landscape heterogeneity enhanced species richness, abundance and parasitism rate, whereas local land-use intensity only marginally negatively affected total abundance. Bee and wasp abundance as well as wasp species richness were enhanced by landscape composition at 250m, whereas their antagonists were enhanced by landscape configuration at 1500m.In conclusion, landscape composition and configuration affect trophic levels differently and are more relevant than local land-use intensity. Solitary bees and wasps, which offer important pollination and pest control services, could be supported by enhancing landscape diversity, while their antagonists could benefit from measures that promote landscape connectivity. Hence, scale-dependent and trophic group specific conservation management schemes are required, that address different components of landscape heterogeneity to enhance functional diversity and trophic interactions in agricultural landscapes.