Increasing stability of northern Austrian Lepidoptera populations over three decades

Abstract Agricultural intensification has led to landscape homogenisation across major parts of Europe and to reduced diversity in flora and fauna. In Central Europe, the species composition of major insect groups is increasingly dominated by a few ecologically generalist and mobile species. So far, however, the degree of stability of population sizes in today's anthropogenic landscapes in comparison to the pre‐Anthropocene has hardly been analysed. Here, we studied large museum records of Lepidoptera from northern Austria spanning the years 1990–2022 to infer trends in the stability of population sizes. On average, population dynamics decreased and stability increased significantly over time. This trend was most pronounced in lowland regions, where agricultural intensification transformed the former heterogeneous landscapes into intensively managed grasslands and fields. Community structures are now dominated by ubiquitous species. Habitat specialist species existing in isolated patches particularly decreased over time. A metapopulation structure appeared to have a stabilising effect on population dynamics. We conclude that reduced diversity and altered community composition might not only stem from selective population decline but also from altered patterns of population stochasticity. Higher population stability was associated with faunal homogenisation. Precise butterfly sensitivity analyses require long‐term data on average population sizes and on community composition.