Effects of land-use and climate change on grasshopper assemblages differ between protected and unprotected grasslands

Abstract

Land-use and climate change are considered the major drivers of recent insect loss. Orthoptera (hereinafter termed ‘grasshoppers’) are the main arthropod consumers in grasslands and, hence, are important elements for supporting ecosystem services. However, for intensively-used agricultural landscapes, it is largely unknown to what extent both factors have affected grasshopper assemblages in protected (nature reserves) and unprotected grasslands.Here, we analysed species richness of grasshopper assemblages in protected (n = 14) and unprotected grasslands (n = 49) by comparing two surveys—one in 1995 and one in 2012—of a landscape with intensive agriculture in the NW-German Lowland. The observed changes were associated with the Community Farmland Index (CFI) and the Community Temperature Index (CTI) in order to disentangle possible effects of land-use and climate change on assemblage shifts.Between the two surveys, environmental conditions substantially changed. Summer temperatures increased by 1.1°C, and grasslands suffered from a severe loss of patches. However, the latter only occurred in unprotected grasslands. Here, 35% of the patches were converted to other biotope types, in particular maize fields as a result of the expansion of bioenergy-crop cultivation. In the grasslands still existing in 2012, irrespective of its protection status, species richness usually increased, except for species with low dispersal ability in unprotected grasslands. By contrast, the development of the CFI and CTI clearly varied between the two grassland types. In protected grasslands, neither the CFI nor the CTI changed. However, in unprotected grasslands, the CFI decreased but the CTI increased.Land-use change has led to a biotic homogenisation at the landscape level and within unprotected grassland patches. Additionally, our study highlights that the legal designation of grasslands as a nature reserve successfully prevents the conversion of grasslands. Overall, well-managed grasslands in nature reserves play a vital role for the conservation of grasshopper biodiversity.