Geographic expansion of an increasing brown bear population: evidence for presaturation dispersal
Article first published online: 25 DEC 2001
Journal of Animal Ecology
Volume 67, Issue 5, pages 819–826, September 1998
How to Cite
Swenson, J. E., Sandegren, F. and SO-Derberg, A. (1998), Geographic expansion of an increasing brown bear population: evidence for presaturation dispersal. Journal of Animal Ecology, 67: 819–826. doi: 10.1046/j.1365-2656.1998.00248.x
- Issue published online: 25 DEC 2001
- Article first published online: 25 DEC 2001
- brown bear;
- population expansion;
- presaturation dispersal;
- Ursus arctos
1. The distribution of brown bears (Ursus arctos L.) expanding into suitable habitat in Sweden following near extermination was estimated using harvest data from the period 1981–93. Core areas were defined as female concentration areas, where 90% of the hunter-killed females were taken.
2. Three predictions were tested, based on results of earlier bear dispersal studies, which show that females are extremely philopatric. Prediction 1: the relative density of females declines more rapidly from the centre of a core area towards the edge than for males. Prediction 2: males dominate in the peripheral areas, especially males in the age of most active dispersal (2–4 years of age). Prediction 3: females in the periphery are found closer to the edge of the core area than males.
3. The results of the present study supported Predictions 1 and 2, but not Prediction 3. This indicates that males were more prone to disperse from the core areas than females. However, females that did disperse did not differ from males in distance from the core areas, and females were found up to 80–90 km from them. Such long-distance female dispersal has apparently not been previously documented in other bear populations that are stable or declining. The results strongly suggest that presaturation dispersal, i.e. dispersal occurring before the carrying capacity of the habitat has been reached, is occurring in this increasing population. This phenomenon might be more common in increasing populations of large mammals than was previously thought. Regarding conservation of bears, this result is positive for gene flow and metapopulation dynamics and negative for livestock losses in formerly bear-free areas.
4. Core and peripheral areas can be identified based on the age and sex of shot bears. This allowed us to classify Norway as a peripheral area. Bear density appears difficult to estimate near an expansion front because of large differences in densities over short distances.