Pervasive impact of large-scale edge effects on a beetle community

Habitat edges are a ubiquitous feature of modern fragmented landscapes, but a tendency for researchers to restrict sampling designs to relatively small spatial scales means that edge effects are known to influence faunal communities over small spatial scales of only 20-250 m. However, we found striking changes in the abundance and community composition of 769 New Zealand beetle species (approximate to 26,000 individuals) across very long edge gradients. We show that almost 90% of species respond significantly to habitat edges and that the abundances of 20% of common species were affected by edges at scales >250 m. Moreover, as many as one in eight common species had edge effects that appeared to penetrate as far as 1 km into habitat patches. Even 1 km inside forest, beetle communities differed in species richness, beta-diversity (spatial turnover), and composition from the deep forest interior. Spatially explicit models of fragmented landscapes have shown that such large-scale edge effects can lead to an 80% reduction in the population size of interior forest species in even very large fragments. Moreover, such large-scale edge effects can drive species that inhabit central habitat core which are among the most threatened species in fragmented landscapes-to local extinction from habitat fragments and protected areas. In a global analysis of protected areas, we show that kilometer-scale edge effects may compromise the ability of more than three-quarters of the world's forested reserves to conserve the community biostructures that are unique to forest interiors.