Comparing the effects of host species richness on different metrics of disease

Abstract

Changes in host species richness can increase or decrease the risk of infection and levels of disease in communities. In this study, I review theoretical predictions for direct and environmental transmission pathogens about how host additions and removals affect three commonly used metrics of disease: the pathogen community reproduction number (R0), focal host infection prevalence (the proportion of infected individuals), and focal host infected density. I extend this body of theory by applying sensitivity analysis to a multihost mathematical model and exploring how variation in non-focal host competence (i.e., the ability to transmit a pathogen), non-focal host density, and the pathogen transmission mechanism affect each disease metric. My results yield insight about which biological mechanisms cause host additions and removals to increase or decrease each disease metric, and they identify when and why metrics respond differently (e.g., responses in focal host infection prevalence and infected density can differ when there are large changes in focal host density). My results explain and unify theoretical prior predictions about host species richness-disease relationships. I discuss areas of future research where advances in theory could help explain empirical relationships between host biodiversity and disease.