Evidence for the Vacated Niche Hypothesis in Parasites of Invasive Mammals.

Species redistribution and invasion are becoming increasingly common due to climate change and anthropogenic impacts. Understanding the resultant shifts in host-parasite associations is important for anticipating disruptions to host communities, disease cycles, and conservation efforts. In this paper, we bring together the enemy release and vacated niche hypotheses to relate parasite acquisition and retention, two distinct yet intertwined processes that play out during host invasion. Using the Global Mammal Parasite Database, we test for net enemy release based on differences in parasite species richness, and we develop a novel taxonomic null modeling approach to demonstrate that parasites fill vacated niches. We find evidence of net enemy release, and our taxonomic null models indicate replacement of lost parasites by taxonomically similar acquired ones, over and above what might be expected by chance. Our work suggests that both enemy release and vacated niche hypotheses provide valuable frameworks through which to understand and predict changing host-parasite associations, which may include insights on how climate change and anthropogenic influences perturb and reorganize communities and ecosystems.