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

Biodiversity loss and anthropogenic modifications 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 the regulation of host abundances.Here, we introduce a multihost compartmental disease model, weighting host competences by their evolutionary relatedness. Our model simulates host communities with substitutive and additive assembly patterns and frequency‐ and density‐dependent pathogen transmission modes, from which we estimate the community disease outbreak potential R0.Simulations show how differences in phylogenetic structure can switch host communities from diluting to amplifying a disease, even when species richness is unchanged. We additionally show that phylogenetic dilution can occur simultaneously with (classic) amplification through species richness.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. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]