Infection at an ecotone: cross‐system foraging increases satellite parasites but decreases core parasites in raccoons

Ecotones can increase free‐living species richness, but little is known about how parasites respond to ecotones. Here, we use parasite communities in raccoons (Procyon lotor) to test the hypothesis that parasite communities can be divided into core and satellite species, each with fundamentally different responses to ecotones. We used published parasite surveys to classify parasites as common core or rare satellite species, and then surveyed raccoons in coastal California to examine how proximity to two aquatic ecotones altered parasite communities. Raccoons near ecotones had more satellite and fewer core parasite species. Specifically, the marine ecotone increased parasite diversity by adding satellite species to a persistent core community, whereas the freshwater ecotone shifted the community from core to satellite species without a net change in parasite richness. We hypothesize that increased parasite richness at the marine ecotone resulted from increased diet diversity, but that raccoons were sinks for some parasites. Increased exposure to rare parasites at ecotones has implications for wildlife health and provides insight into observed associations between ecotones and emerging disease. Whether field to forest, desert to river, or ocean to land, ecotones can be biodiversity hotspots because edge effects mix species from two systems and create opportunities for species that depend on habitat diversity (Odum 1971, Kark 2013). On the other hand, ecotones might be hard to adapt to, penalizing some species that straddle two systems (Kunin 1998, Kark and van Rensburg 2006). Because host diversity begets parasite diversity and ecotones likely foster novel host interactions (Hechinger and Lafferty 2005), these transitional habitats should also affect parasite communities (Lanfranchi et al. 2016). This could have implications for host health, particularly where changing climate and anthropogenic impacts shift ecotone boundaries (Despommier et al. 2006). Although free‐living community responses to ecotones have been extensively examined (Kark 2013), ecotone effects on parasite communities are less understood (Despommier et al. 2006). Edge habitats can alter infection risk. For example, forest edges are the preferred habitat for brood‐parasitic Brown‐headed Cowbirds in North America (Howell et al. 2007) and are also associated with increased coccidian infection in European rodents (Svobodova et al. 2004). Increased infection can also occur at the interface between aquatic and terrestrial habitats, as seen for human cholera and schistosomiasis (Despommier et