Is β-diversity of Amazonian ant and dung beetles communities elevated at rainforest edges?

Aim: Thousands of kilometres of rainforest edges are created every year through forest fragmentation, but we have little knowledge of the impacts of edges on spatial patterns of species turnover and nestedness components of β-diversity. Location: A quasi-experimental landscape in the north-east Brazilian Amazon. Methods: We sampled dung beetles and ants using a sampling design based on a fractal series of equilateral triangles that naturally allows examination at multiple spatial scales. We sampled two edge types (primary-secondary and primary-Eucalyptus forest) and three control sites immersed in primary, secondary and Eucalyptus forest. We measured β-diversity between communities across the primary forest-matrix edge and within communities at up to 1 km from the forest edge. We examined β-diversity at multiple scales by partitioning the dissimilarity matrix into fractal orders representing inter-point distances of ~32, ~100, ~316 and ~1,000 m and into turnover and nestedness components. Results: Turnover but not nestedness was greater across the primary-Eucalyptus forest than primary-secondary forest edge. There was spillover of species across edges in both directions. Across edges and within controls, turnover was the main driver of β-diversity. Within community, β-diversity was increased for dung beetles at large scales (~300–1,000 m) at both edge types. This increase, however, was driven by elevated nestedness. Levels of β-diversity were affected even ~300 m into habitat interiors, but appeared to be at control levels by 1 km. Main conclusions: The effects of edges on the spatial dynamics of community composition penetrated far beyond the typical distances at which forest structure and microclimate are altered. This indicates that for a significant proportion of Amazonian communities, the underlying processes determining diversity may be impacted by deforestation.