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.

Geographic and temporal correlations of mammalian size reconsidered: a resource rule

“…No correlation of body size with latitude occurs in this species in Europe and North America (Kojola and Laitala 2001;Meiri et al 2004Meiri et al , 2007Swenson et al 2007) because the occurrence of salmon spawning areas is not correlated with latitude (Meiri et al 2007). However, an overwhelming seasonally available protein and fat load in the form of five species of reproducing salmon (Oncorhynchus spp.)…”

“…However, an overwhelming seasonally available protein and fat load in the form of five species of reproducing salmon (Oncorhynchus spp.) occurs on Kodiak island, which facilitates a large mass in its bears (Hilderbrand et al 1999;Swenson et al 2007). Clearly, resource abundance is pivotal in determining bear size.…”

The dietary habits of the Brown bear (Ursus arctos) in western Greece

“…Of the domestic ungulates, only sheep were likely to be preferred by foraging brown bears. However obtaining fresh meat is essential for bears to obtain adequate energy to grow in size and deposit fat (Swenson et al 2007). …”

Body length and mass growth of the brown bear (Ursus arctos) in northern Canada: model selection based on information theory and ontogeny of sexual size dimorphism

“…Historically, the most common approach in modeling growth of the brown bear is to select a priori the von Bertalanffy function and fit it to the data (Kingsley et al 1983(Kingsley et al , 1988Zedrosser et al 2006Zedrosser et al , 2007Swenson et al 2007). Inference and estimation of growth parameters and their precision are based solely on that fitted model.…”