Data from: Population density, not host competence, drives patterns of disease in an invaded community

Generalist parasites can strongly influence interactions between native
and invasive species. Host competence can be used to predict how an
invasive species will affect community disease dynamics; the addition of a
highly competent, invasive host is predicted to increase disease. However,
densities of invasive and native species can also influence the impacts of
invasive species on community disease dynamics. We examined whether
information on host competence alone could be used to accurately predict
the effects of an invasive host on disease in native hosts. We first
characterized the relative competence of an invasive species and a native
host species to a native parasite. Next, we manipulated species
composition in mesocosms and found that host competence results did not
accurately predict community dynamics. While the invasive host was more
competent than the native, the presence of the native (lower competence)
host increased disease in the invasive (higher competence) host. To
identify potential mechanisms driving these patterns, we analyzed a
two-host, one-parasite model parameterized for our system. Our results
demonstrate that patterns of disease were primarily driven by relative
population densities, mediated by asymmetry in intra- and interspecific
competition. Thus, information on host competence alone may not accurately
predict how an invasive species will influence disease in native species.