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

Abstract

Aim: thousands of kilometres of rainforest edges are created every year throughforest fragmentation, but we have little knowledge of the impacts of edges on spa-tial patterns of species turnover and nestedness components of b-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 afractal series of equilateral triangles that naturally allows examination at multiplespatial scales. We sampled two edge types (primary-secondary and primary-Eucalyp-tus forest) and three control sites immersed in primary, secondary and Eucalyptusforest. We measured b-diversity between communities across the primary forest-matrix edge and within communities at up to 1 km from the forest edge. We exam-ined b-diversity at multiple scales by partitioning the dissimilarity matrix into fractalorders representing inter-point distances of ~32, ~100, ~316 and ~1,000 m and intoturnover 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 acrossedges in both directions. Across edges and within controls, turnover was the maindriver of b-diversity. Within community, b-diversity was increased for dung beetlesat large scales (~300–1,000 m) at both edge types. This increase, however, was dri-ven by elevated nestedness. Levels of b-diversity were affected even ~300 m intohabitat interiors, but appeared to be at control levels by 1 km. Main conclusions: the effects of edges on the spatial dynamics of community com-position penetrated far beyond the typical distances at which forest structure andmicroclimate are altered. This indicates that for a significant proportion of Amazo-nian communities, the underlying processes determining diversity may be impactedby deforestation.