Impacts of Spatial and Environmental Heterogeneity on Grizzly Bear Demographics in the Greater Yellowstone Ecosystem: A Source–Sink Dynamic with Management Consequences

By necessity, grizzly bear demographic models have largely ignored spatial considerations (McLellan 1989, Eberhardt et al. 1994, Eberhardt 1995, Hovey and McLellan 1996). However, ignoring spatial heterogeneity is equivalent to assuming that individuals live in a homogeneous environment and that all members of the population experience the same environmental conditions at any point in time (Pulliam 1996). Knight et al. (1988) were probably the first to recognize the potential effect of habitat heterogeneity on grizzly bear survival and impacts of sink habitats on long-term conservation of the species (see also Doak 1995). These sinks, associated with human activity and development, represented locations where grizzly bears obtained anthropogenic foods and suffered high rates of mortality. Schwartz et al. (2006c) and Haroldson et al. (2006) demonstrated that simple spatial indices of residency were consistently important correlates of survival. To understand the implications of geographically heterogeneous survival, we explored life tables corresponding to hypothetical grizzly bear populations whose residency varied from living entirely within Yellowstone National Park (InYNP), to entirely outside of YNP but within the U.S. Fish and Wildlife Service–designated RZ (OutYNP), and beyond the borders of the RZ (OutRZ), using survival rates of the top models of dependent and independent bears (Haroldson et al. 2006, Schwartz et al. 2006c). These 3 zones correspond to distinct management approaches, although they doubtless ignore finerscale correlates of survival. We further explored consequences of these simulations and discuss them in the context of source–sink theory, deviations from the theory, and implications for management. Additionally, we incorporate significant temporal covariates into our models and explore impacts of temporal heterogeneity (food availability) on population demographics.