Long-distance animal movements such as seasonal migration are widespread across animal taxa and can affect host-parasite interactions in multiple ways. Migration can increase exposure to diverse parasites, but can also reduce infection risk through escape from contaminated habitats or culling of infected individuals. These mechanisms have been demonstrated at the population level in single-host/single-parasite interactions, but whether these mechanisms apply to other movement modes such as nomadism, and whether they influence parasite diversity across diverse host taxa, is largely unknown. We gather data on the movement strategies (migratory, resident, and nomadic) and the parasite assemblages of 93 ungulate species (orders Artiodactyla and Perissodactyla). Using a comparative approach, we investigate the relationship between long-distance movement and parasite species richness and prevalence across these host species, as well as the ecological processes underlying this relationship.
Results/Conclusions
We find that species that migrate have higher parasite species richness than those that do not, even after accounting for other factors known to influence parasite diversity, such as study effort, host body size and host geographic range area. We propose that multiple (non-exclusive) mechanisms underlie this pattern: (i) infection risk increases as animals that sample more diverse habitats are exposed to more parasites; (ii) the social aggregation and large group sizes that facilitate migration increase transmission among hosts; and (iii) migration allows parasites to experience environments favorable to transmission year-round (a novel hypothesis we refer to as “environmental tracking”). In contrast, we find little support for the hypotheses of migratory escape and culling, possibly due to characteristics particular to ungulates, or to the larger spatial and taxonomic scales of this study relative to previous investigations. Our findings also highlight the importance of considering the potential effects of environmental change on future dynamics of parasitism in migratory animals.