In the face of global biodiversity loss, we must understand the mechanisms by which biodiversity increases or decreases infectious disease spread. For environmentally transmitted parasites, changing biodiversity can alter the dose of parasites that hosts encounter in the environment. However, predicting the impact of biodiversity on environmentally transmitted parasites proves challenging, because infection rate, infected host mortality, and the rate at which infected hosts transmit parasites all change non-linearly with parasite exposure dose—a pattern that biodiversity/disease theory does not currently take into account. To understand the implications of dose-response relationships for biodiversity-disease patterns, we first performed a meta-analysis on published dose-infectivity experiments to quantify the proportion of synergistic, mass-action, or antagonistic dose-infectivity relationships. We then explored the impact of competitor host density on the infection prevalence of a focal host in two host, one parasite models parameterized with multiple dose-infectivity, dose-transmission, and dose-mortality relationships.
Results/Conclusions
We found that the majority of experiments in our analysis showed antagonistic dose-infectivity relationships, which in our model weakened biodiversity-disease patterns via negative feedback loops. Additionally, positive dose-mortality relationships resulted in hosts that traditionally dilute disease (non-competent, strong competitors) amplifying disease, and vice versa. This suggests that without taking dose-response relationships into account, we may incorrectly predict the impact of biodiversity on environmentally transmitted parasites.