Summer drought affects abundance of grassland grasshoppers differently along an elevation gradient

Abstract

Orthoptera (hereinafter termed `grasshoppers') are of great functional significance since they are the main arthropod consumers in grasslands and an important food source for medium-sized insectivorous vertebrates. However, research investigating the effects of extreme weather events on the abundance of grasshoppers has lacked thus far. Here, we studied the effects of summer drought on grasshopper abundance in temperate semi-natural grasslands with low land-use intensity. We considered calcareous and mesic grasslands; per type, we randomly selected 27 plots. Our study revealed distinct differences in habitat characteristics between plots of calcareous and mesic grasslands. Overall, calcareous grasslands had a more heterogeneous and shorter vegetation than mesic grasslands. Consequently, species richness was higher in calcareous grasslands. By contrast, grasshopper abundance did not differ between the two types. Summer temperature was the key driver of grasshopper abundance. Abundance was lowest in grasslands that were situated at lower elevations with higher summer temperatures and that were characterised by the strongest effects of summer drought. Its influence even overrode the differences in habitat characteristics between calcareous and mesic grasslands. Extreme weather events, such as summer droughts, are expected to become more frequent due to global warming. Accordingly, suitable conservation strategies that increase the resistance and resilience of temperate semi-natural grasslands and their insect assemblages against summer drought are highly needed. Based on our study, increasing habitat heterogeneity seems to be the most effective way to mitigate the negative effects of summer drought.