When to stop managing or surveying cryptic threatened species

Abstract

Threatened species become increasingly difficult to detect as their populations decline. Managers of such cryptic threatened species face several dilemmas: if they are not sure the species is present, should they continue to manage for that species or invest the limited resources in surveying? We find optimal solutions to this problem using a Partially Observable Markov Decision Process and rules of thumb derived from an analytical approximation. We discover that managing a protected area for a cryptic threatened species can be optimal even if we are not sure the species is present. The more threatened and valuable the species is, relative to the costs of management, the more likely we are to manage this species without determining its continued persistence by using surveys. If a species remains unseen, our belief in the persistence of the species declines to a point where the optimal strategy is to shift resources from saving the species to surveying for it. Finally, when surveys lead to a sufficiently low belief that the species is extant, we surrender resources to other conservation actions. We illustrate our findings with a case study using parameters based on the critically endangered Sumatran tiger (Panthera tigris sumatrae), and we generate rules of thumb on how to allocate conservation effort for any cryptic species. Using Partially Observable Markov Decision Processes in conservation science, we determine the conditions under which it is better to abandon management for that species because our belief that it continues to exist is too low. . Even the persistence of large mammals, like the Sumatran rhinoceros, Dicerorhinus sumatrensis, can be uncertain in particular locations (8). Managers of cryptic threatened species are prone to 2 sorts of error. First, it is possible, if not likely, that some reserves are being managed to conserve a species that has already disappeared or become functionally extinct (e.g., the Ivory-billed woodpecker, Campephilus principalis) (9, 10). The second possible error is that managers could give up on a species too soon, failing to invest in sufficient surveying to be sufficiently sure further management is unwarranted. Managers of protected areas need to know how long they should continue investing in conservation management without strong evidence that the species is still present and when to shift their resources from saving a species to looking for that species, that is, surveying. Ultimately, if their belief in the persistence of the species continues to decline, when should managers surrender resources to another conservation problem?The problem of how best to allocate conservation resources can be couched in terms of a trade-off between managing, surveying, or doing nothing (surrendering and redistributing resources to other problems). Whether to invest scarce management resources and time in surveying may be a difficult decision for managers to make, although some may argue that expenditure on determining the presence of a potentially viable population is a prerequis...

General rules for managing and surveying networks of pests, diseases, and endangered species

“…As demonstrated in Chadès et al (9), the problem of when to stop managing and surveying a single population of cryptic species is dependent on the relative cost of survey and management, the cost of the infection, the benefits of eradication, and the efficiency of management and surveillance determine the switching points (9). To avoid rerunning the POMDP algorithms for every network studied, we build on this work and derive an analytic approximation by transforming our network POMDP problem into a single POMDP.…”

“…Most pests, diseases, and threatened species cannot be detected perfectly (9). Apparently susceptible nodes may, in fact, be infected.…”

“…The problem of how to allocate management and surveillance effort has been studied for a single cryptic population (8)(9)(10). For example, Regan et al (8) determined when to stop monitoring an invasive plant with a long-lived seed bank.…”

“…For example, Regan et al (8) determined when to stop monitoring an invasive plant with a long-lived seed bank. Chadès et al (9) determined when to stop managing or surveying cryptic threatened species. However, none of these works have accounted for multiple populations, spatial dispersal, or risk of reinfestation over time.…”

Managing biotic interactions for ecological intensification of agroecosystems

“…Markov Decision Process (MDP) or Partially Observed Markov Decision Process (POMDP) have been used to propose new management strategies for conservation (Chadès et al, 2008) and agriculture (Tixier et al, 2013b). These mathematical models provide a framework, taking account of the cost-benefit trade-offs, for sequential decision-making when there is a high level of uncertainty.…”