Population Viability Analysis

Abstract

Population viability analysis (PVA) refers to the set of ideas, theoretical models, and conceptual and computational tools ecologists use to understand extinction risk and to forecast future scenarios of population growth and decline. PVA focuses on four phenomena that affect extinction risk of small populations: demographic stochasticity, environmental stochasticity, Allee effects, and inbreeding depression. PVAs fall into two categories. Analytical models are idealized mathematical models of population dynamics and are used to understand general principles of extinction risk. Computational models are more complex and are used to perform risk assessment for endangered populations. The cost of this complexity is relinquishing intuitive understanding of the drivers of population fluctuations. Simple examples of each class of models are illustrated with data on grizzly bear population fluctuations in Yellowstone National Park. Advances in PVA methodology have been rapid and continued progress promises to improve population management for threatened and endangered populations.