Authors: Martínez-Nuñez, Carlos; Neff, Felix;Obrist, Martin K.;Gossner, Martin;Bollmann, Kurt;Herzog, Felix;Knop, Eva;Luka, Henryk;Cahenzli, Fabian;Albrecht, Matthias;

There is growing concern about the human-induced loss of arthropod diversity, abundance and biomass. However, we still know little about the main drivers of long-term changes across different arthropod groups, land-use types and spatial scales.
Here, we analysed data of 1.73 million arthropods (i.e., carabid beetles and spiders) belonging to 877 species that were collected using 51,250 pitfall traps across 44 years (1974‒2018) in Switzerland. We examined inter-annual trends in their diversity, abundance and biomass at different spatial scales and across six major land-use types, and we explored the potential drivers (i.e., climate change, land-use intensity and urbanization) causing these trends.
We found fundamentally distinct trends across land-use types that were relatively consistent for both groups. There were moderate local arthropod diversity declines in ruderal habitats and croplands, increases in grasslands and woody linear structures, and non-significant changes in forests or wetlands. Importantly, regional richness in ruderal habitats and croplands declined sharply, highlighting community homogenization as a major process threatening arthropod diversity. Furthermore, urbanization was an important landscape-scale driver of the observed declines.
Our results show that local land-use as well as urbanization at landscape scale drive long-term arthropod changes, and that regional community processes contribute significantly to its decline.