How Viable Is Population Viability Analysis?

Abstract

Population viability analysis (PVA) uses data in a model to estimate the risk of extinction for a population. Ideally, PVA would assess and integrate the effects of all factors affecting the persistence of a population, which are usually stated as the demographic, genetic, environmental, and catastrophic risks and the interactions between them. This goal, however, is still beyond our capabilities. Three types of PVA have been developed: analytical and both custom and generic simulation models. Each type has strengths and weaknesses. PVAs have been criticized because (1) they are a single-species technique, (2) they omit risk sources that are difficult to estimate, (3) they are sometimes inappropriate for endangered species management, and (4) they project current conditions long into the future. In spite of its limitations, PVA is useful in a variety of situations as long as we emphasize our limited abilities as scientific prophets and make uncertainties explicit. When PVA is used to estimate relative risk, it may be acceptable to omit some risk factors. However, some applications of PVA require the estimation of absolute extinction risk, and in these cases, the estimate of extinction risk should attempt to include all sources of risk and uncertainty. Even in an era when management emphasizes an ecosystem perspective, some species will need individual attention. We predict that PVA will continue to evolve as a useful tool for single-species management.