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

Abstract

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 affect parasites. We used food provisioning to experimentally assess the effects of resource availability and of inducing host aggregation on the endoparasite community of free‐ranging raccoons. Twelve independent raccoon populations were subjected to differential 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‐fit 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. These results suggest that while resource availability can influence 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.

Baylisascaris procyonis roundworm infection patterns in raccoons (Procyon lotor) from Missouri and Arkansas, USA

“…Baylisascaris procyonis has been reported from Missouri (Monello & Gompper, 2011;Page et al, 2016). Prevalence in central Missouri based on fecal surveys was 9 -20 %, with the variance a function of the study population (Monello & Gompper, 2011).…”

“…Previous work on B. procyonis in regions the parasite has recently invaded (e.g. Robel et al, 1989;Monello & Gompper, 2011) have not fully documented the variance in intensity among individual hosts. Yet such variance can be a fundamental tenet of Baylisascaris-raccoon interactions.…”

“…Problematically, documentation of the relative size of B. procyonis infrapopulations (that is, the inten-sity of infection of parasitized hosts; Bush et al, 1997) is poorly known from regions where the parasitic nematode is newly reported. For instance, in Missouri the parasite is known to occur and in Arkansas the parasite has only recently been reported (Monello & Gompper, 2011;Al-Warid et al, in review), but there is little information on measures of intensity in the region. Understanding the overall pattern of B. procyonis prevalence and intensity in a region is a necessary fi rst step in assessing the potential health risks for humans, domestic animals and wildlife.…”

“…For instance, Evans (2002) reported visceral, ocular, and neural larva migrans caused by B. procyonis in 26 species of birds and mammals from a single locale in California. Similarly, populations of the Allegheny woodrat (Neotoma magister), a species of conservation concern, are believed to be at risk due to severe population-scale impacts of B. procyonis infection (Page, 2013). Raccoons are the defi nitive host for B. procyonis.…”

“…Yet such variance can be a fundamental tenet of Baylisascaris-raccoon interactions. For instance, Page et al (2016) included raccoon specimens collected from Missouri as part of a larger study from the Upper Midwest that reported overall prevalence of 36 % and mean intensity of 15.8, but signifi cant overdispersion such that a relatively small proportion of hosts (7 %) had larger (>50) B. procyonis infrapopulations. More fully documenting aggregation patterns in raccoons could help formulate a more effective strategy for control of parasite transmission (e.g.…”