Re-surveys reveal biotic homogenization of Orthoptera assemblages as a consequence of environmental change

Aim Biodiversity loss is a major global challenge. While population trends of vertebrates are well documented, insect declines have not been sufficiently studied. We aim to identify changes in Orthoptera assemblages and the underlying drivers with a focus on land-use and climate change. Location Central Europe. Time period 2018 to 2020. Methods We resurveyed 199 study sites in which Orthoptera assemblages had been recorded between 1986 and 1999. Results Our results show a significant increase in species per site (alpha-diversity), but simultaneously a homogenization of Orthoptera assemblages (decreasing Sorensen's beta-diversity). Highly mobile species significantly increased in site occupancy compared to species with low mobility. Some Orthoptera species showed significant altitudinal range shifts, including species with positive trends (i.e. expansion to higher altitudes) and negative trends (i.e. extinction at lower altitudes). Abandonment of extensively used grassland sites and the associated afforestation had negative effects on Orthoptera, underlining the importance of extensive grassland management. Protected areas had a high efficacy for conservation as trends in site occupancy were generally more positive in protected areas than in unprotected sites. Main conclusions Our results provide insights into the patterns and drivers of orthopteran assemblage turnover, including major effects of agricultural land-use change and climate change. These results are essential for implementing and adapting conservation action, as they show that traditional land-use practices, protected areas and reduction of nitrogen input are important to preserve Orthoptera. The results also show that climate change is driving both range expansion and retraction of species. Therefore, insect monitoring is critical to understanding insect population trends and implementing the necessary actions.