Managing invasive wildlife pathogens on the margin

The literature on managing invasive pathogens has focused considerable attention on a pathogen’s basic reproductive ratio, R0, and related measures of host-density thresholds and host reservoir status. The conventional wisdom is these measures inform disease management according to a two-step process: (i) identify which hosts are reservoirs for the disease, and (ii) for each reservoir host, calculate the host-density threshold, which is used to guide management. We illustrate that conventional measures of thresholds and reservoir statuses do not fully guide the intertemporal allocation of management efforts across controls and host populations in a way that either maximizes effectiveness of minimizes control costs. We offer alternative measures of host-density thresholds and reservoir status so that they become relevant for marginal analysis, the basis for decision theory. We find host-density thresholds are endogenous and time-varying, as is a host’s reservoir status. Disease control is therefore achieved by simultaneously managing a population’s density, its threshold, and the reservoir status of other populations. Understanding these thresholds within a marginal analysis framework enables managers to better assess the tradeoffs necessary in multiple-host disease management. The approach is applicable to a wide range of invasion problems where eradication is of interest.