Get larger or grow longer wings? Impacts of habitat area and habitat amount on orthopteran assemblages and populations in semi-natural grasslands

Abstract

Context: Habitat loss and fragmentation are major threats to biodiversity and can change community composition, species traits and intraspecific morphology. Calcareous grasslands are hotspots of diversity for plants and invertebrates in Europe, but habitat area and habitat amount declined strongly over the last century. Objectives: It is controversially discussed how habitat area and habitat amount independently affect species assemblages, traits and morphology. Methods: With variable transects we recorded orthopteran assemblages on 22 calcareous grasslands along independent gradients of habitat area and habitat amount in a 1 km matrix. We measured male body size and wing length of two abundant grasshopper species. Results: Orthopteran assemblages showed positive species–area and abundance–area relationships with habitat area and (extenuated) with habitat amount. We found a stronger effect of habitat area reduction on specialists and endangered species, compared to generalists and non-threatened species. The species Chorthippus biguttulus and Gomphocerippus rufus had a larger body size (fitness-related trait) in landscapes with high habitat area and habitat amount. Grasshoppers had longer wings in relation to body size (dispersal-related trait) in landscapes with a low amount of habitat. Conclusions: Our findings emphasize the value of large patches and landscapes with high habitat amount to (i) enhance species richness and abundances, (ii) protect threatened species, (iii) ensure long term survival of habitat-specialists and (iv) preserve individuals with high fitness traits (large body size). Conservation strategies for Orthoptera should focus on large habitats and areas with a high habitat amount.