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Brown bear population vital rates

Citation

McLellan, Michelle (2022), Brown bear population vital rates, Dryad, Dataset, https://doi.org/10.5061/dryad.h44j0zpjb

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 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.

Methods

ch_survival.txt: This dataset is the monthly survival and monitoring data of independent (not with mother) female grizzly bears. It is formatted for processing in Rmark with monthly intervals for 7 months and one 5 month interval for winter. Each year from 2005-2018.

transition_reproductive_state.txt: Transitions between reproductive state for collared adult female grizzly bears in two adjacent populations. AA -alone to alone; AC - alone to with cubs; CY- with cubs to with yearlings; CA - with cubs to alone; Y-A yearling to alone; Y-T yearling to with two-year-old offspring; T-A with two-year-old offspring to alone or older offspring. 

coy_survial.txt: Dependent offspring survival in the first year of life and litter membership by population.

yearling_survival.txt: Dependent offspring survival in the second year of life by population.

primiparity.txt: Monitoring and reproduction of primiparous female grizzly bears by population. For each age, data show whether they had their first litter or not and whether they were removed from the sample by mortality or because their reproductive fate was unknown (i.e. radio-collar dropped).

interbirth_interval.txt: Interbirth interval of parous female grizzly bears by population. For each year following a reproductive event whether another reproductive event was observed until the female reproduced or they were removed from the sample by mortality or because their reproductive fate was unknown (i.e. radio-collar dropped).

Usage Notes

The data is complete.