Parasites are integral to ecosystem functioning yet often overlooked. Improved understanding of host-parasite associations is important, particularly for wide-ranging species for which host range shifts and climate change could alter host-parasite interactions and their effects on ecosystem function.

Among the most widely distributed mammals with diverse diets, grey wolves (Canis lupus) host parasites that are transmitted among canids and via prey species. Grey wolf-parasite associations may therefore influence the population dynamics and ecological functions of both wolves and their prey. Our goal was to identify large-scale processes that shape host-parasite interactions across populations, with the grey wolf as a model organism.

By compiling data from various studies, we examined the faecal prevalence of gastrointestinal parasites in six wolf populations from two continents in relation to wolf density, diet diversity, and other ecological conditions.

As expected, we found that the faecal prevalence of parasites transmitted directly to wolves via contact with other canids or their excreta was positively associated with wolf density. Contrary to our expectations, the faecal prevalence of parasites transmitted via prey was negatively associated with prey diversity. We also found that parasite communities reflected landscape characteristics and specific prey items available to wolves.

Several parasite taxa identified in this study, including hookworms and coccidian protozoans, can cause morbidity and mortality in canids, especially in pups, or in combination with other stressors. The density-prevalence relationship for parasites with simple lifecycles may reflect a regulatory role of gastrointestinal parasites on wolf populations. Our result that faecal prevalence of parasites was lower in wolves with more diverse diets could provide insight into the mechanisms by which biodiversity may regulate disease. A diverse suite of predator-prey interactions could regulate the effects of parasitism on prey populations and mitigate the transmission of infectious agents, including zoonoses, spread via trophic interactions.

These data were collected as part of three previously published studies (see Related Works). The data come from the identification of gastrointestinal parasite larval stages (i.e., eggs, oocysts, sporocysts, and nematode larvae) using coprological methods in wolf feces. Samples came from the Abruzzo, Lazio and Molise National Park (PNALM) in Italy, Mercantour National Park (MNP) in France, the Northern Range of Yellowstone National Park (YNP) in the United States, the Great Bear Rainforest (GBR) on the west coast of Canada, and Riding Mountain National Park (RMNP) and Duck Mountain Provincial Park and Forest (DMPPF) in Canada.