Host community structure can shape pathogen outbreak dynamics through a phylogenetic dilution effect.

Abstract Biodiversity loss and anthropogenic alterations to species communities are impacting the frequency and magnitude of disease emergence events. These changes may be related through mechanisms in which biodiversity either increases (amplifies) or decreases (dilutes) disease prevalence. Biodiversity effects can be direct, when contacts among competent hosts are replaced by contacts with sink hosts, or indirect through regulation of host abundances. Here, we introduce a multi-host compartmental disease model, weighting host competences by their evolutionary relatedness. Using simulations, and estimating community disease outbreak potential (R0), we show how differences in phylogenetic structure can switch host communities from diluting to amplifying a disease, even when species richness is unchanged. We illustrate our model using empirical data describing the relationship between phylogenetic distances separating hosts and their likelihood of disease sharing. Our study demonstrates how host evolutionary histories can drive disease dynamics through a phylogenetic dilution effect.