Abstract 329 – Demography of American black bears (Ursus americanus) in a semiarid environment

Brenden Orocu, Cambria Armstrong, Janene Auger, Hal L. Black, Randy T. Larsen,
Brock R. McMillan, Mark C. Belk

American black bears (Ursus americanus) have a widespread distribution in North America.
However, demography of American black bears in semiarid environments, which compose a
significant portion of the geographic range, is poorly understood. Our objective was to
characterize fecundity and survival rates and to estimate population growth rate (λ), stable
stage distribution and reproductive value for black bears in semiarid environments, and to
compare these vital rates to populations in mesic environments where most of our current
understanding lies. We conducted a long-term mark-recapture study of black bears in semiarid
eastern Utah. We monitored fecundity and survival rates of 5 life stages (cub; yearling;
subadult, 2–4 years old; prime-aged adult, 4–14; and old adult, 15+) from 1991 to 2017. We
used a matrix transition model to estimate λ, reproductive value, and stable age distribution.
We performed sensitivity and elasticity analyses to determine which parameters were most
influential to λ. Average annual survival rate was 0.62 (95% CI: 0.54–0.70), 0.56 (0.46–0.66),
0.80 (0.68–0.92), 0.87 (0.79–0.95), 0.87 (0.69–1.0), for cub, yearling, subadult, prime-aged
adult, and old adult, respectively. Our estimate of λ was 0.96 (0.82–1.10), indicative of a stable
population and comparable to black bears in mesic areas. Cub and yearling survival are
relatively low and adult survival is relatively high compared to other populations. Adults make
up the majority of the population and have the highest reproductive value, and survival of
adults had the highest elasticity contribution to our estimated λ. Population dynamics of black
bears in our semiarid environment appear to function within the range of bears in other
ecozones, but bears in our study exhibit relatively higher survival of adults and greater longevity
compared to other populations. It is not clear if this pattern of adult dominance in the life
history is due to the semiarid environment or a different factor.