Initial effects of fragmentation on the density of three neotropical primate species in two lowland forests of Colombia

Abstract

Fragmentation and habitat destruction are 2 factors driving the current decline of mammal populations. Spider monkeys Ateles spp. are some of the first neotropical mammals to go extinct after fragmentation, as they (1) are large-bodied, specialized frugivores that require large areas to subsist, (2) are preferred targets for local hunters, (3) have slow reproductive cycles, and (4) rarely move between adjacent forest fragments. Brown spider monkeys A. hybridus are Critically Endangered, and most of their historical habitat has either been cleared or is seriously fragmented. We conducted census surveys at 2 areas in Colombia (Las Quinchas and San Juan) in order to compare the population density of brown spider monkeys, red howler monkeys Alouatta seniculus, and whitefronted capuchins Cebus albifrons in both continuous forest and recently fragmented forest in each of these 2 areas. We found a higher density of brown spider monkeys and red howler monkeys in recent fragments at both sites, while differences were not consistent for white-fronted capuchins. We suggest that these patterns could be explained by the constrained ability of spider monkeys and howler monkeys to move between forest fragments and to exploit impacted or degraded areas. In the absence of hunting, the immediate effects of fragmentation on spider monkeys seem to lead to a sudden increase in population density as a result of a decreasing forested area, while maintaining population numbers relatively stable. Longer-term research will lead to the identification of the proximate factors leading to the generalized pattern of local extinction of spider monkey populations in small isolated fragments.