Land-use intensity determines grassland Orthoptera assemblage composition across a moisture gradient

Abstract

Two of the main principles of global and national conservation strategies consist in focusing on the most species-rich and most vulnerable ecosystems. In this study, we investigated the Orthoptera species assemblages of species-rich grasslands in the southern Black Forest, one of 30 German biodiversity hotspots. Across a moisture gradient, we considered the three dominant grassland types within the study area: (i) dry, (ii) mesic and (iii) wet grasslands. In order to analyze the drivers of biodiversity in a landscape of high conservation value, we related (i) differences in Orthoptera assemblage composition between the three grassland types and (ii) the relationship of Orthoptera assemblage composition within each grassland type to environmental conditions. In our study, we detected considerable variation in land-use intensity which dropped from high in mesic to low in dry and again to near-zero in wet grasslands. Land-use intensity was the only predictor of Orthoptera species richness in the multivariable Generalized Linear Mixed-effects Models. The mean number of both all and threatened species was highest in the grassland type with low land-use intensity, dry grasslands, differing from those of mesic (high land-use intensity) and wet (mostly abandoned) grasslands. Additionally, dry grasslands had the highest number of all, threatened and exclusive indicator species. Both (i) intensive land use in mesic grasslands and (ii) abandonment of land use in wet grasslands led to a homogenization of the habitat structures and the species assemblages. In contrast, dry grasslands with low land-use intensity and high habitat heterogeneity were hotspots of Orthoptera species richness.