Alternative Host Traits and Transient Dynamics of Focal Host Infection Prevalence

Environmental changes driven by climate change and anthropogenic activity are altering the composition of host communities in host-pathogen systems through the loss or introduction of host species, which can impact disease levels in other host species. Although previous work has identified that host species that strongly or weakly spread disease are expected to increase or decrease disease levels in other hosts, respectively, it remains unclear how disease levels change in the transient period of host community composition changes. In this study, we analyze an ordinary differential equation model representing two hosts that share an environmentally-transmitted pathogen to identify how the disease and non-disease traits of a lost host impact disease levels in the remaining host. By simulating our model using parameter sets spanning a broad area of parameter space, we find that short- and long-term changes in focal host disease levels occur in the same direction when the two hosts have dissimilar abilities to spread disease, but that focal host disease levels can change nonmonotonically when hosts have similar abilities to spread disease and the lost host is a sufficiently strong competitor. Additionally, using both local and global sensitivity analysis, we identify that the lost host's birth rate, interspecific competitive ability, pathogen shedding rate, and pathogen uptake rate must be measured precisely when predicting the change in focal host disease levels, while precise measurement of the lost host's infection capacity, recovery rate, and disease mortality rate is only critical in some circumstances.