Models for management of wildlife populations: lessons from spectacled bears in zoos and grizzly bears in Yellowstone

Models of population dynamics are frequently used in the management and conservation of wildlife populations. They provide a powerful method of quantitatively assessing a population’s risk of decline and determining the potential to reverse the decline. Models from recent studies of managed populations are presented. The first model simulates the spectacled bear populations maintained in American Zoo and Aquarium Association (AZA) zoos. The second model simulates the grizzly bear population in the Greater Yellowstone Ecosystem (GYE). The article concludes with a discussion of system dynamics modeling in the larger context of population dynamics modeling. Copyright © 2004 John Wiley & Sons, Ltd. Syst. Dyn. Rev. 20, 163–178, (2004) Quantitative models of population dynamics are essential tools for conservation and management of endangered and threatened species (Beissinger and Westphal 1998; Beissinger and McCullough 2002; Morris and Doak 2002). They are used as general predictive tools for assessing a population’s risk of extinction or potential for growth. With sensitivity, elasticity, and perturbation analyses, users can assess the impact of changes in demographic rates on a population’s growth or decline (Mills and Lindberg 2002). Through such analyses the model can be used to assess the impact of management actions, to indicate which variables are most critical for prioritized data collection, and ultimately to guide allocation of conservation resources. Population models focus on understanding the demographic processes influencing population growth through births, deaths, immigration and emigration. The models show how the demography is influenced by external factors such as environmental fluctuations and by management actions. We work within two systems closely influenced by management actions. In captive populations maintained in AZA institutions, for example, mortality is influenced by veterinary care, diet, and protection from predation. Reproduction is influenced by controlling access of breeding animals to each other or by contraception. In the grizzly bear population of the GYE, managers can influence the demographics by garbage cleanup practices or by limiting human access to prime habitat where grizzly bears would prefer to feed. Managers can also influence the grizzly bear demographics more directly by the removal or killing of the “nuisance bears” that have become conditioned to human Lisa Faust is a