Quantifying edge effects: the role of habitat contrast and species specialization

Abstract

Edge effect is a key process influencing populations and communities, particularly in tropical and subtropical fragmented forests. A general analytical framework has been proposed to quantify the strength of the edge effects (extent and magnitude); however, factors determining the later remain poorly explored. We took advantage of recent advances to explore the response of dung beetle species and assemblages to ecotones which differ in environmental dissimilarity in the Southern Atlantic forest of Argentina. Using baited pitfall traps and automatic sensors, we estimated dung beetle abundance, microclimatic conditions and vegetation structure along five different forest-plantations transects. At the assemblages level, the majority of species showed either edge avoidance or preference; however, the response depended on the environmental dissimilarity between habitats (plantation and native forest) and varied from a neutral response on mature plantations (low contrast ecotone) to edge avoidance on recent ones (high contrast ecotone). At species level, the degree of habitat specialization explains the differential response of species to edge effects; more specialized species showed stronger edge response while generalist species showed softer or neutral responses. Environmental dissimilarity between confronted habitats and species specialization explain the quantitative component of edge effects on species and assemblages. The explanatory and predictive power of theoretical models dealing with edge effects and functional connectivity will gain through the incorporation of the results of this study. This is particularly important on highly fragmented landscapes, such as the Atlantic forest, where edge effect is probably one the most important mechanisms affecting native species and communities.