Land use and wetland spatial position jointly determine amphibian parasite communities.

Land use change is one of the most commonly cited contributing factors to infectious disease emergence, yet the mechanisms responsible for such changes and the spatial scales at which they operate are rarely identified. The distributions of parasites with complex life cycles depend on interactions between multiple host species, suggesting the net effects of land use on infection patterns may be difficult to predict a priori. Here, we used an information-theoretic approach to evaluate the importance of land use and spatial scale (local, watershed, and regional) in determining the presence and abundance of multi-host trematodes of amphibians. Among 40 wetlands and 160 hosts sampled, trematode abundance, species richness, and the presence and abundance of pathogenic species were strongly influenced by variables at the watershed and regional scales. Based on model averaging results, overall parasite richness and abundance were higher in forested wetlands than in agricultural areas; however, this pattern was influenced by a wetland's proximity to the Mississippi Flyway at the regional scale. These patterns likely reflect the activity of trematode definitive hosts, such as mammals and especially birds, such that infections decreased with increasing distance from the Mississippi River. Interestingly, despite lower mean infections, agricultural wetlands had higher variances and maximum infections. At the wetland scale, phosphorus concentrations and the abundances of intermediate hosts, such as snails and larval amphibians, positively affected parasite distributions. Taken together, these results contribute to our understanding of how altered landscapes affect parasite communities and inform further research on the environmental drivers of amphibian parasite infections.