Abstract
Over the last century, intensification and conversion of land use has caused habitat destruction and species extinctions throughout Europe. However, these extinctions can be delayed by time lag effects, i.e., extinction debts, which are typically measured by species richness. The aim of this study was to investigate whether such extinction debts can be detected in dung beetles of the Pannonian region of Austria and the Czech Republic, where extensive pasture systems were converted into intensive agricultural areas. We modeled the impact of this land use change and the use of anthelmintics as an additional stressor on both dung beetle species richness and individual abundance. We found that the use of veterinary anthelmintics significantly reduces dung beetle species richness and that historic land cover data from the 19th century best explained not only current dung beetle species richness, but showed even stronger effects on individual abundance. This suggest that population declines may precede species extinctions, potentially masking the true extent of biodiversity loss in short-term studies. Biodiversity assessments using only species richness may therefore underestimate ongoing species losses, as they don't account for temporal trends in population size. Our findings further underscore the necessity of incorporating historical land-use data when assessing biodiversity trends and conservation strategies, as well as the need for long-term ecological monitoring to capture delayed responses to environmental change. Moreover, the observed impact of anthelmintics on dung beetle communities calls for reconsideration of veterinary practices to mitigate their unintended consequences on biodiversity. Overall, the results add a crucial temporal dimension to understanding insect declines, reinforcing that past land-use decisions shape present and future biodiversity in complex and often underestimated ways.