Are black bears declining in Montana? Inference from multiple data sources in the face of uncertainty
Year of Award
Doctor of Philosophy (PhD)
Fish and Wildlife Biology
Department or School/College
College of Forestry and Conservation
Vanessa Ezenwa, Mark Hebblewhite, L. Scott Mills, Michael Mitchell
black bear, demography, harvest, population dynamics, spatial variation, Ursus americanus
University of Montana
Carnivores are managed both to maintain populations and reduce conflict with humans, but data-based decision-making is difficult due to the expense of data collection. When new fieldwork is impossible, we can benefit from available data in assessing populations. I used demographic and harvest data to assess the population status of black bears (Ursus americanus) in Montana.
I conducted a hierarchical Bayesian meta-analysis of black bear demographic studies to evaluate geographic structuring and estimate vital rates and population growth rate. Adult survival is higher in the west than the east, but the reverse is true for fecundity. The mean population growth rate is 0.97 (0.93, 1.00) in the west, but variability among populations suggests many are increasing.
I analyzed the sex and age of bears harvested in Montana, 1985-2005, to estimate harvest rate and population size. The harvest rate of females is 4.3% and the total population is 30-40000. Montana's population is stable or increasing.
I modeled discrete and continuous spatial variation in population growth rate with varying movement and habitat distributions. In order for the entire population to be stable, fewer than 20% of individuals can disperse, which is reasonable based on the literature. Landscapes with 20-30% source habitat were generally able to sustain populations.
I applied a similar approach to brown bears (U. arctos) in British Columbia, where management of salmon and bears occur independently despite the reliance of brown bears on salmon. I conducted a demographic meta-analysis and used several models and parameter combinations to evaluate the consequences of salmon reduction and bear harvest. While both affect populations, bear harvest has a more dramatic effect.
My research highlights the application of available data when new fieldwork is not feasible. Both intensive, demographic data and extensive data, like statewide harvest information, are useful in evaluating population status and management actions.
Beston, Julie Ann, "Are black bears declining in Montana? Inference from multiple data sources in the face of uncertainty" (2010). Graduate Student Theses, Dissertations, & Professional Papers. 53.
© Copyright 2010 Julie Ann Beston