Recent environmental change shapes biotic homogenisation of Orthoptera and Mantodea communities in semi-dry grasslands

Semi-dry grasslands are among the most species-rich ecosystems in Europe. However, many grassland remnants are undergoing gradual habitat degradation due to climate change, atmospheric nitrogen deposition, and the relaxation or abandonment of traditional management. While declines of specialised insects have repeatedly been reported, the extent to which these drivers promote long-term community reorganisation and biotic homogenisation remains poorly understood. Using a nationwide resurvey of 221 semi-dry grassland patches across Germany, spanning two to three decades, we investigated long-term changes in Orthoptera and Mantodea communities. We quantified changes in species richness, community composition, and beta diversity, and related these patterns to major global change drivers. Despite an increase in total species richness, these communities became increasingly homogenised, as indicated by declining beta diversity. Community reorganisation was characterised by pronounced winner-loser dynamics, with highly mobile generalists and thermophilous species expanding, whereas threatened species, low-mobility habitat specialists, and species associated with High Nature Value farmland declined. Winner species richness increased particularly in warm and dry regions, under elevated atmospheric nitrogen deposition, and outside protected areas. By contrast, low-mobility habitat specialists and threatened species persisted most successfully in structurally heterogeneous habitats. High shrub cover was negatively associated with both winners and losers, indicating an overall deterioration of habitat suitability. Our findings demonstrate that environmental change does not necessarily reduce species richness but can profoundly reorganise communities through selective filtering of species. Maintaining habitat heterogeneity with appropriate management strategies is therefore crucial for buffering biodiversity loss under ongoing global change.