We used harvested, stochastic population models for grizzly bears (Ursus arctos) and polar bears (U. maritimus) to illustrate the propensity for male-biased harvesting to reduce mean male age and numbers of sexually mature males for species with relatively low reproductive potential. We compared our results with those obtained from caribou (Rangifer tarandus), an annually reproducing species with relatively high reproductive potential. Differences in the rate at which mean ages and numbers of sexually mature males were reduced by harvesting was a function of differences in species life history of species, but also the extent to which young animals were protected from hunting. For example, the length of each species' reproductive cycle (we modeled 1 year for caribou, 2 years for bears) determined the degree to which sex-biased harvest was also age-biased. Proportionately more young bears were protected from harvest than young caribou due to the multiannual, rather than annual, parental care afforded young bears (we assumed all females with accompanying offspring were invulnerable to harvest). This additional age-bias in the hunt served to direct offtake toward adult males; consequently, as male selectivity in the kill increased, mean ages of bears declined at rates that were higher than for caribou. For species with low reproductive potential, we believe there is a real possibility that persistence probabilities may be overestimated if, after prolonged sex-selective harvest, lack of sexually mature males in the population impairs fecundity. We encourage further development of population models that incorporate potentially negative, hunting-induced impacts on reproduction. In particular, we support the development of models that link the mean age of males or frequency of adult males in a population to the rate at which females are successfully mated.
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