Brown bear population vital rates

Identifying mechanisms of population change is fundamental for conserving
small and declining populations and determining effective management
strategies. Few studies, however, have measured the demographic components
of population change for small populations of mammals (< 50
individuals). We estimated vital rates and trends in two adjacent but
genetically distinct, threatened brown bear (Ursus arctos) populations in
British Columbia, Canada, following the cessation of hunting. One
population had approximately 45 resident bears but had some genetic and
geographic connectivity to neighbouring populations, while the other
population had < 25 individuals and was isolated. We estimated
population-specific vital rates by monitoring survival and reproduction of
telemetered female bears and their dependent offspring from 2005 to 2018.
In the larger, connected population, independent female survival was 1.00
(95% CI: 0.96-1.00) and the survival of cubs in their first year was 0.85
(95% CI: 0.62-0.95). In the smaller, isolated population, independent
female survival was 0.81 (95% CI: 0.64-0.93) and first-year cub survival
was 0.33 (95% CI: 0.11-0.67). Reproductive rates did not differ between
populations. The large differences in age-specific survival estimates
resulted in a projected population increase in the larger population (λ =
1.09; 95% CI: 1.04-1.13) and population decrease in the smaller population
(λ = 0.84; 95% CI: 0.72-0.95). Low female survival in the smaller
population was the result of both continued human-caused mortality and an
unusually high rate of natural mortality. Low cub survival may have been
due to inbreeding and the loss of genetic diversity common in small
populations, or to limited resources. In a systematic literature review,
we compared our population trend estimates with those reported for other
small populations (< 300 individuals) of brown bears. Results
suggest that once brown bear populations become small and isolated,
populations rarely increase and, even with intensive management, recovery
remains challenging.