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Correlates with body size and mass in yearling brown bears (Ursus arctos)

Authors

  • B. Dahle,

    1. Department for Ecology and Natural Resource Management, Norwegian University of Life Sciences, Ås, Norway
    2. Department of Biology, Programme for Experimental and Population Ecological Research, University of Oslo, Oslo, Norway
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  • A. Zedrosser,

    1. Department for Ecology and Natural Resource Management, Norwegian University of Life Sciences, Ås, Norway
    2. Department of Wildlife Biology and Game Management, University of Natural Resources and Applied Life Sciences, Vienna, Austria
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  • J. E. Swenson

    1. Department for Ecology and Natural Resource Management, Norwegian University of Life Sciences, Ås, Norway
    2. Norwegian Institute for Nature Research, Tungasletta, Trondheim, Norway
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Correspondence
Bjørn Dahle, Department of Biology, University of Oslo, Postbox 1066 Blindern, NO-0316 Oslo, Norway. Tel: +47 22 85 45 88; Fax: +47 22 85 47 26
Email: bjorn.dahle@bio.uio.no

Abstract

Body size and mass have a strong effect on an individual's fitness, and conditions experienced early in life may affect survival to adulthood, age and size at maturation, and reproductive success. For this reason, body size and mass of 226 yearling brown bears Ursus arctos were analysed in relation to maternal size, litter size, sex, multilocus heterozygosity, population density and cohort in two study areas in Sweden. Body mass of yearlings varied from 8 to 48 kg (=24.5±0.5se). Yearling body size and mass were positively related to maternal size and negatively related to litter size. Males were on average 2.6% larger and 7.8% heavier than females. Population density negatively affected both size and mass of yearlings. Yearling body size and mass varied among cohorts, but data on food availability were not available to evaluate the relationship between food availability and size and mass of yearlings. Maternal age and multilocus heterozygosity did not seem to influence yearling body size or mass. Body mass of yearlings varied within litters, especially in litters with three offspring, where the heaviest yearling was on average 29.5±2.8% (se) heavier than the lightest one. This suggests that competition among offspring increases with litter size, thereby having a pronounced negative effect on the smallest offspring. Survival of subadult brown bears from ages 1 to 3 increased with increasing yearling body size.

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