Using hierarchical, multi-response models to disentangle coexposure and parasite interactions across multiple scales in wetland amphibian communities
Results/Conclusions: Each pathogen varied substantially in prevalence and mean abundance among sites, host species, and individuals. At the site scale, Ranavirus and R. ondatrae mean abundances correlated negatively (r = - 0.38, credible interval [-0.62,-0.11]), suggesting the presence of an unmeasured site-level variable driving opposing patterns of exposure for these two parasites. However, after accounting for the (co)variation among sites and species, we found positive mean correlations for two of three pathogen pairs at the individual host level. Ranavirus was positively correlated with both R. ondatrae (r = 0.23, CI[0.03,0.42]) and Bd abundance (r = 0.21, CI[0.001, 0.41]), suggesting that these pathogens may interact to facilitate infection, for example by increasing host susceptibility or reducing hosts ability to clear infections. We found no strong correlations in mean abundance among the five host species. Finally we illustrate how including additional predictors such as individual size or the density of intermediate hosts can indicate and account for sources of co-exposure at different scales of analysis. Overall, these results illustrate how appropriately formulated and parametrized hierarchical models can be used to assess patterns of coinfection across scales and to enable stronger inference about potentially interacting pathogens.