The type of forest edge governs the spatial distribution of different-sized ground beetles

Worldwide human-induced habitat fragmentation intensifies the emergence of forest edges. In addition to these edges, there are edges evolved by natural processes. Edge-maintaining processes (natural vs. anthropogenic) fundamentally determine edge responses, and thus edge functions. Species with various traits show fundamentally different edge response, therefore the trait-based approach is essential in edge studies. We evaluated the edge effect on the body size of ground beetles in forest edges with various maintaining processes. Our results, based on 30 published papers and 221 species, showed that natural forest edges were impenetrable for small species, preventing their dispersal into the forest interiors, while both the medium and the large species penetrated across these edges and dispersed into the forest interiors. Anthropogenic edges maintained by continued human disturbance (agriculture, forestry, urbanisation) were permeable for ground beetles of all size, allowing them to invade the forest interiors. Overwintering type (overwintering as adults or as larvae) was associated with body size, since almost two-thirds of the small species, while slightly more than a third of both the medium and the large species were adult overwintering. Based on this, size-dependent permeability of natural edges may be related to overwintering type, which basically determines species tolerance to human disturbance.