Community phylogenetic structure shapes pathogen outbreak potential in an epidemiological multi-host model

Biodiversity loss and anthropogenic alterations to species communities are impacting disease emergence events. These trends may be related through mechanisms in which biodiversity either increases (amplification) or decreases (dilution) diseases among hosts. Biodiversity effects can be direct, when contacts with competent hosts are replaced by sink hosts, or indirect through regulation of abundances and depend on the disease-competence of the added host. Here, we introduce a multi-host compartmental disease model, weighting host competence by their evolutionary history. We explore two scenarios: (1) where the probability of transmission depends on the evolutionary distance between the transmitting and recipient hosts, and (2) where transmission depends on the evolutionary distance from the receiving host to the primary host of the pathogen. Using simulations, and estimating the host community outbreak potential ( R ₀ ), we show how differences in phylogenetic structure can switch host communities from diluting to amplifying a disease, even when species richness is unchanged. Common ecophylogenetic metrics of community structure that capture variation in the pairwise distances among hosts, are able to explain >90% of the variation in R ₀ across simulations. Our study provides a simple illustration of how host evolutionary histories can drive disease dynamics.