How Does Interspecific Host Competition Alter the Amplification and Dilution of Disease?

Abstract:

For pathogens that infect multiple host species, the loss or addition of one host species in a community can affect levels of disease in other host species.  Predictions about whether increased host biodiversity increases (amplifies) or decreases (dilutes) disease in a focal host are limited because current theory does not account for interspecific host competition.  Using epidemiological models, I explore how interspecific host competition alters whether increased host biodiversity amplifies or dilutes disease.  Using a 2-host, 1-pathogen model parameterized to an experimental daphniid-fungal system, I show that between-host competition, not host competence, drove patterns of amplification/dilution in native and invasive hosts.  I then generalize these results by showing that increased interspecific competition promotes dilution for pathogens with environmental transmission (e.g., pathogens transmitted by spores) and pathogens with frequency or density dependent direct transmission.  I also identify how the affects of interspecific competition are influenced by the pathogen transmission mechanism, e.g., density dependent direct transmission requires the highest levels of competition for dilution.  This work is a step towards a unified theory on amplification/dilution of environmentally and directly transmitted pathogens.