Edge effect in assemblages of dung beetles (Coleoptera: Scarabaeidae) in forest remnants of an andean landscape

In fragmented landscapes, the composition, diversity, and abundance of communities of various groups of organisms change from the edge inward the forest. To assess such changes in dung beetle assemblages, transects were established perpendicular to the edge in remnants of forest immersed in a heterogeneous matrix. The transects were in three types of edge: Forest-pastures, forest-natural regeneration and forest-highway, each with eight sampling stations at 0, 30, 60, 90, 120 and 150 m from the edge towards the inside, and 30 and 60 m from the edge towards the matrix. At each station, we set up a pitfall trap baited with human excrement. Six environmental variables were evaluated. The changes in the assemblage of dung beetles were dependent of the edge type and became noticeable to maximum 3o m into the forest; however, stations from 60 to 150 m inward did not show significant changes in these parameters. The percentage of light, indirect measure of plant cover, was the most influential variable on the number of species, individuals and biomass of beetles. Although dung beetles appear to be less affected by the edge effect than other groups it is necessary to consider that 25 % of species avoid the edge and that only a few species can move through the matrix, which can have consequences on the ecological function and the viability of their populations in the long term.