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Brown bear body mass and growth in northern and southern Europe

Abstract

We tested six hypotheses to explain expected geographical differences in body masses of 1,771 brown bears (Ursus arctos) from northern and southern Europe (Sweden and Norway compared with Slovenia and Croatia): Bergmann’s rule, the fasting endurance hypothesis, and the dietary meat hypothesis, which predicted larger bears in the north; and hypotheses stressing the role of high primary productivity, high population density, low seasonality, and length of the growing season, which predicted larger bears in the south. Although brown bear populations in North America vary greatly in body mass, we found no significant difference in body mass between the two European populations using a new analytical approach incorporating modeled age-standardized body masses in linear models, when correcting for sex and season. The greater variation in North America may be due primarily to the presence of large bears that feed on salmon (Oncorhynchus spp.), which does not occur in Europe. Asymptotic body masses were 115 ± 9 (SE) kg in spring and 141 ± 9 kg in autumn for southern females, 248 ± 25 and 243 ± 24 kg for southern males, 96 ± 2 and 158 ± 4 kg for northern females, and 201 ± 4 and 273 ± 6 kg for northern males, respectively. Northern bears gained more body mass before hibernation and lost more during hibernation than southern bears, probably because hibernation was twice as long in the north. Northern bears gained and southern bears lost mass during the spring, perhaps due to the greater availability and use of protein-rich food in spring in the north. As reproductive success in bears is correlated with adult female body mass in interpopulation comparisons, brown bears may have relatively similar reproductive rates throughout Europe, although minimum age at primiparity and litter interval are lower in the south.

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Acknowledgments

We especially thank Steinar Engen, who designed our model and gave us statistical advice, Petra Kaczensky for providing data on denning dates in Slovenia, and Andrew Derocher and Nigel Yoccoz for useful comments on earlier versions of the manuscript. The Scandinavian Brown Bear Research Project has been supported by the Swedish Environmental Protection Agency, Norwegian Directorate for Nature Management, Swedish Association for Hunting and Wildlife Management, WWF-Sweden, Research Council of Norway, and several private foundations. The bear research in Slovenia was funded by the Ministry of Education, Science and Sports and by the Ministry of Agriculture and Forestry. Teeth (P1) for ageing have been extracted by the district wildlife officers of the State Forest Service during the course of regular inspections of dead brown bears. The studies of brown bears in Croatia have been supported by the Croatian Ministry for Science and Technology, the National Geographic Society, the International Association for Bear Research, and Management (Bevins Fund), as well as by local forestry offices.

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Correspondence to Jon E. Swenson.

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Communicated by Jean-Michel Gaillard.

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Swenson, J.E., Adamič, M., Huber, D. et al. Brown bear body mass and growth in northern and southern Europe. Oecologia 153, 37–47 (2007). https://doi.org/10.1007/s00442-007-0715-1

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Keywords

  • Body growth
  • Ursus arctos
  • Europe