The context dependent effects of host competence, competition, and the pathogen transmission mode on disease prevalence

Biodiversity in communities is changing globally, including the gain and loss of host species in host-pathogen communities. Increased host diversity can cause infection prevalence in a focal host to increase (amplification) or decrease (dilution).  However, it is unclear what general rules govern the context dependent effects, in part because theories for pathogens with different transmission modes have developed largely independently.  Using a two-host model, we explore how the pathogen transmission mode and characteristics of a second host (disease competence and competitive ability) influence disease prevalence in a focal host.  Our work shows how the theories for pathogens with environmental transmission, density-dependent direct transmission, and frequency-dependent direct transmission can be unified.  Our work also identifies general rules about how host and pathogen characteristics affect amplification/dilution.  For example, higher competence hosts promote amplification, unless ...