Edge effects in fragmented landscapes: Pattern and processes

Abstract

Edge effects consist of environmental changes on the boundaries of forest remnants, affecting all levels of biological organization. These changes can increase or decrease species abundance near edges. Although important patterns of variation in the direction and intensity of edge effects have been detected, the mechanisms underlying these patterns need to be better explored. This thesis sought to better understand some of the mechanisms explaining variation in edge effects globally and locally. Here we used null models to infer the importance of local environmental variables and species functional traits determining their response to edges. In the first chapter, our meta-analysis showed that tropical communities are more subjected to edge effects leading to a reduction in species richness near the edges, and that communities subject to historical disturbances are subject to milder negative edge effects than communities not subject to these disturbances. The second chapter showed that, in a forest reserve in the Atlantic Forest, forest mammals have their response to edges determined by hunting, and that considering the stochastic distribution of individuals of a species does not help to explain their response to edges. Furthermore, considering this stochastic distribution did not change the effects of environmental variables in qualitative and quantitative terms. The third chapter showed that stochastic models based on the random placement of home ranges underestimate the negative edge effects on species. Specifically, this chapter showed that species with a more specialized diet tend to deviate less from stochastic predictions, and that the impact of the edge effect tends to be more underestimated in diet generalists. In general, this study shows that the response of species to edges is mainly driven by ecological factors related to the environment and the natural history of the species, while environmental variations at a global scale are also important moderators of the direction and intensity of these effects.