Possible negative effects of adult male mortality on female grizzly bear reproduction

We studied 2 grizzly bear (Ursus arctos) populations to test 3 hypotheses on the effects of adult male mortality on female reproduction. The "no effect" hypothesis predicts that reproduction should be higher in the population with superior overall diet quality, regardless of mortality of adult males. The "increased reproduction" hypothesis predicts that reproduction should be higher in the hunted population because of lowered numbers of competitive or cannibalistic adult males. The "decreased reproduction" hypothesis predicts that reproduction should be lower in the hunted population because of increased immigration by potentially infanticidal, nonsire males with subsequent reduced survival of cubs, and/or increased sexual segregation resulting in reduced production of cubs. Reproduction rates were 0.46 in a hunted population in Kananaskis, Alberta and 0.74 in non-hunted populations in the Selkirk Mountains of Idaho and British Columbia. Mean litter size was smaller in Kananaskis than in the Selkirks (1.40 vs 2.22) but age at first parturition was earlier in Kananaskis (5.50 vs 7.30 years). Mean birth intervals were not different between populations. Age of mothers, overall diet quality, and total population density were nor associated with differences in litter size and age at first reproduction, but adult female avoidance (sexual segregation) of nonsire immigrant males and associated food-rich habitats were. Our results are inconsistent with the "no effect" and "increased reproduction" hypotheses but consistent with the "decreased reproduction" hypothesis. Higher hunting mortality of older males coincided with higher numbers of potentially infanticidal, immigrant males in Kananaskis. Adult females avoided those males and their food-rich habitats in Kananaskis and female reproduction appeared to suffer as a result. (C) 2000 Elsevier Science Ltd. All rights reserved.