Abstract
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 neighboring 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.
Highlights
Many of the world's terrestrial large carnivore populations are declining (Ripple et al, 2014)
Between 2005 and 2018, we captured and collared 25 independent female brown bears in the McGillvary Mountains (n = 16) and North Stein-Nahatlatch (n = 9) populations resulting in survival and reproductive data for 43.1 and 26.0 bear-years in each population, respectively
We used data from telemetered individuals in two adjacent but distinct brown bear populations in British Columbia, Canada, to measure the demographic components of population change following the elimination of human-caused mortality from legal hunting
Summary
Many of the world's terrestrial large carnivore populations are declining (Ripple et al, 2014). The principal causes of decline are habitat loss, habitat fragmentation, as well as human- caused mortality from legal harvest, conflict with humans for safety or livestock, and persecution Or synergistically, these factors erode the geographic ranges of species, contracting and fragmenting populations, leaving increased interface edges and population isolates (Henschel et al, 2014; Kenney et al, 2014; Proctor et al, 2012; van Oort et al, 2011). Reasons for variable outcomes of recovery efforts in brown bears remain poorly understood but may be related to the small size and increasing isolation of remnant populations. The larger, higher density McGillvary Mountains population, with some genetic and demographic connectivity to other large populations, was estimated to increase at 2% each year while the adjacent, small (
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