1. Landscape simplification and habitat fragmentation may cause severe declines of less mobile and habitat specialist species and lead to biotic homogenization of species communities, but large-scale empirical evidence on biotic homogenization remains sparse.
2. We sampled butterfly and day-active geometrid moth communities within 134 differently fragmented landscapes in Finland situated in five geographical regions. Overall species richness was partitioned into alpha and beta diversity and butterflies were assigned a species-specific mobility rank and habitat specificity score based on published ecological trait classifications.
3. Alpha and beta diversity of butterflies and geometrid moths decreased with increasing agricultural intensity, independently of geographical position. The responses were either linear or nonlinear with accelerating decrease of diversity when arable field cover exceeded 60%.
4. Mobility rank and percentage generalists of butterfly communities increased linearly with increasing field cover.
5. In landscapes with high agricultural intensity (>60% field coverage), the decrease in beta diversity of butterflies was strongly associated with an increasing proportion of habitat generalists and increasing average mobility in the butterfly communities. However, there was no such relationship in landscapes with low or moderate agricultural intensity.
6. Synthesis and applications. We demonstrate that biotic homogenization caused by land-use change arises as a consequence of the loss of habitat specialists and poor dispersers in intensively cultivated landscapes with simplified landscape structure. Agri-environment schemes will therefore be inefficient in protecting high beta diversity unless they explicitly increase habitat availability and connectivity for habitat specialists and poor dispersers.