Life history analysis for black bears (Ursus americanus) in a changing demographic landscape

We used matrix population models to evaluate the relative importance of different vital rates to population growth (λ) for female black bears on the Southeastern Coastal Plain (SCP) of the United States, and to determine whether reductions in subadult and adult survival due to ongoing habitat fragmentation and human disturbance will cause shifts in the relative importance of vital rates. Additionally, we evaluated how well predictions made by Heppell et al. [Ecology 81 (2000) 654] concerning elasticity patterns for mammals apply to black bears over realistic variation in vital rates, and how much correlations between vital rates will influence their relative effects on λ. We generated 500 model replicates based upon different combinations of vital rate values for each of nine scenarios, where scenarios represented different combinations of reduction in survival and level of correlation among vital rates. Elasticity analysis indicated that adult survival, and litter size of three- and four-year-old females are most important to λ in 99.3 and 0.7% of all replicates, respectively; the few replicates with higher elasticity for litter size occurred in scenarios with some type of correlation among vital rates; of these, 21 (70.0%) occurred in scenarios with 20% reductions in subadult and adult survival. Results from elasticity analysis, indicating the strong and consistent effect of adult survival, are also supported by results from regression analysis. In all scenarios, the regressions of λ on the vital rates showed that adult survival accounted for the majority of variation in λ. Our results suggest that adult survival should be the primary target of conservation and management strategies. Ongoing human impacts on subadult and adult survival reduce the frequency of conditions in which populations on the SCP are stable or increasing. Without conservation strategies that reverse this trend, local extinctions will become more likely, and recovery of at-risk populations will be more difficult to achieve.