Primate Densities in the Atlantic Forest of~Southeast Brazil: The Role of Habitat Quality and Anthropogenic Disturbance

Abstract

Studies of variation in abundance within a species’ geographic range provide the connection between the disciplines of ecology and biogeography. Empirical studies of various taxonomic groups show that density of a given species is unevenly distributed in space, with few “hotspots” and many “coldspots”, where abundance is orders of magnitude lower (Brown et al. 1995). The typical explanation for this pattern is spatial variation in habitat suitability. In other words, variation in density is generated by how closely sites correspond to a species’ niche (Brown et al. 1995). Like many ecological patterns, the correspondence between primate density and habitat suitability can be investigated at several spatial scales (Wiens 1989; Levin 1992). For example, coarse-scale studies comparing densities of howler monkeys (Alouatta spp.) across the Neotropics have shown that howler density is largely a function of primary productivity (Peres 1997). Fine-scale studies comparing neighboring forest fragments have also reported variation in howler density, but in this case the pattern is frequently attributed to anthropogenic pressure (Hirsh et al. 1994; Cullen et al. 2001; Chiarello 2003; Martins 2005). In general, human impact on other primates can be direct via hunting, or indirect through habitat disturbance and fragmentation. However, some species thrive in disturbed habitats (Chiarello 1993, 2003; Rylands et al. 1993; Strier et al. 2000). This fact complicates the task of predicting changes in primate density across a gradient in land use. In the present chapter, we investigate the synergistic effects of environmental and anthropogenic factors on the density of five primate genera that inhabit the Atlantic forest of southeast Brazil. Our goal is not to produce distribution maps, but rather to: (i) synthesize available census information for the region; (ii) compare the genera’s responses to anthropogenic impact; and (iii) map areas of high