Life on the edge: gastrointestinal parasites from the forest edge and interior primate groups

Humans are responsible for massive changes to primate habitats, and one unanticipated consequence of these alterations may be changes in host-parasite interactions. Edges are a ubiquitous aspect of human disturbance to forest landscapes. Here we examine how changes associated with the creation of edges in Kibale National Park, Uganda, alter the parasite community that is supported by two species of African colobines: the endangered red colobus (Piliocolobus tephrosceles) and the black-and-white colobus (Colobus guereza). An analysis of 822 fecal samples from edge and forest interior groups revealed no difference in the richness of parasite communities (i.e., the number of parasite species recovered from the host's fecal sample). However, for both species the proportion of individuals with multiple infections was greater in edge than forest interior groups. The prevalence of specific parasites also varied between edge and forest interior groups. Oesophagostomum sp., a potentially deleterious parasite, was 7.4 times more prevalent in red colobus on the edge than in those in the forest interior, and Entamoeba coli was four times more prevalent in red colobus on the edge than in animals from the forest interior. Environmental contamination with parasites (measured as parasite eggs/gm feces) by red colobus from the edge and forest interior differed in a similar fashion to prevalence for red colobus, but it did not differ for black-and-white colobus. For example, egg counts of Oesophagostomum sp. were 10 times higher in red colobus from the edge than in those from the interior. The less severe infections in the black-and-white colobus relative to the red colobus may reflect the fact that black-and-white colobus raid agricultural crops while red colobus do not. This nutritional gain may facilitate a more effective immune response to parasites by the black-and-white colobus. The fact that animals on the edge are likely not nutritionally stressed raises an intriguing question as to what facilitates the elevated infections in edge animals. We speculate that interactions with humans may be linked to the observed patterns of infections, and hence that understanding the ecology of infectious diseases in nonhuman primates is of paramount importance for conservation and potentially for human-health planning.