Effects of resource availability and social aggregation on the species richness of raccoon endoparasite infracommunities

Within populations the contact rate of hosts and infectious parasites is mediated by the interactions of resource availability, host density, and host behavior. Fluctuations in host density can result in the loss or extinction of a parasite population as contact rates between parasites and susceptible individuals drop below thresholds of parasite population persistence. Less understood is how changes in resources and the behavioral ecology of host populations aff ect parasites. We used food provisioning to experimentally assess the eff ects of resource availability and of inducing host aggregation on the endoparasite community of free-ranging raccoons. Twelve independent raccoon populations were subjected to diff erential resource provisioning for two years: a clumped food distribution to aggregate hosts (n  5 populations), a dispersed food distribution to add food without aggregating hosts (n  3), and a no food treatment (n 4). Remote cameras indicated that aggregation sizes were three to four times greater in aggregated versus non-aggregated populations. We considered endoparasites with direct and indirect life cycles separately and determined the best-fi t models of parasite species richness in relation to host aggregation, food supplements, and host age and sex. Social aggregation had a negligible impact on the species richness of directly or indirectly transmitted parasites. However, food additions decreased the number of indirectly transmitted parasite species by 35% in the oldest age classes. Th ese results suggest that while resource availability can infl uence the transmission of indirectly transmitted parasites, an examination of additional factors will be necessary to understand the role of host contact and factors that shape the community structure of endoparasites in natural environments.