Reproductive data collected during a period of 11 years are presented for a low-density black bear (Ursus americanus) population occupying marginal habitat along the Susitna River. These data are contrasted with data from higher-density populations on the Kenai Peninsula also in south-central Alaska (Schwartz and Franzmann 1991), thought to occupy better habitat. Low reproductive and recruitment rates and high cub mortality rates were found in the Susitna population. Mean litter size was 2.1 for newborn cubs (range = 1-4), and 1.9 for yearlings, and sex ratio for cubs or yearlings were not different from 50:50 (P > 0.10). Mean age of first reproduction was 5.9 years (range = 5-7), recruitment interval was 2.7 years (range = 2-5), birth interval was 2.03 years (range 1-4), and 59% of newborn cubs survived for 1 year (survivorship = 0.54, 95% CI = 0.42-0.66). A large proportion of adult females were without cubs following an apparent berry crop failure and again 5 years later. This generated pulses of cubs produced 2-3 years and 6-7 years after the berry crop failure. First year survivorship in the Susitna population was lower than in the 2 Kenai populations studied by Schwartz and Franzmann (1991) (P = 0.06 and < 0.01). The parameters in the 3 Alaskan populations that varied in response to different environmental conditions were first year survivorship, recruitment interval, and age at first reproduction; litter size was not responsive. For purposes of population modeling, recruitment interval will usually be a more useful statistic than birth interval because of early mortality of entire litters. In the Susitna area, black bear productivity and calculated consumption rates of moose calves were similar to findings in the least productive Kenai population. The Susitna data were consistent with the hypothesis of Schwartz and Franzmann (1991) that productivity in Kenai bears was dependent on calf consumption rates during spring.
- Volume 9
- Issue
- Pages 263-273
- Publication Date 1 January 1994
- DOI 10.2307/3872710
- File Size 505.69 KB
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