Habitat availability and climate warming drive changes in the distribution of grassland grasshoppers

Abstract

Land use and climate change are considered the major drivers of current insect declines. However, in intensively used agricultural landscapes the impacts of both on Orthoptera (hereinafter termed `grasshoppers') are still poorly understood. We analysed grasshopper assemblages in two grassland types (patches, N = 63 and verges, N = 118) by comparing two surveys - one in 1995 and one in 2012 - in an agricultural landscape of the NW-German Lowland. Despite the short time period between the two surveys, we detected strong changes in environmental conditions and grasshopper assemblages. In contrast to grassland verges, grassland patches suffered from severe habitat loss. More than a quarter of all grassland patches were converted to other biotope types, in particular, arable fields cropped with maize. Additionally, summer temperatures rose by 1.1 degrees C. Species richness and the Community Temperature Index also increased in grassland patches and verges. By contrast, the Community Farmland Index decreased. The ongoing cultivation of maize as a bioenergy crop was responsible for a severe loss of grassland patches leading to a homogenization at the landscape level. However, due to the high connectivity of grasslands, thermophilous and generalistic grasshopper species with both low and high dispersal ability were able to track global warming. Based on our study, (i) the availability of suitable habitats and (ii) climate warming were the major drivers of grasshopper assemblage shifts. With the ongoing loss of grassland patches, grassland verges become increasingly important not only as dispersal corridors, but also as refuges for biodiversity.