Life history aspects of European brown bears

An organism`s life history is its lifetime pattern of growth, reproduction and mortality, formed by a long-term evolutionary process, but may also result from an immediate response of an organism to the environment to which it is exposed. This project deals with the European brown bear (Ursus arctos) and its life history parameters. Bears are controversial in regard to their conservation and management. They compete with man for livestock and game animals, thus causing economic damages, and even occasionally wound or kill people. Wise management can only be built on sound biological knowledge of the species. Most of today`s management of European brown bears is built on North American experiences and examples. But life-history parameters may show substantial differences between Europe and North America. Eurasian brown bear populations have generally higher population growth rates and higher mean litter sizes than North American interior populations and European bears mature earlier, separate earlier, but stay smaller than North American brown bears. On the other hand, North American interior individuals are more aggressive. Centuries of heavy hunting pressure on brown bears by man may have affected the selection of certain life-history traits in Europe. Contrary to North American bear populations, European bears have survived for centuries in a heavily managed landscape, coping with a dense human population and heavy human persecution. In this project we evaluate the influence of maternal size on a female`s and her offsprings` long term reproductive success, the factors influencing paternal long term mating success, and litter survival in relation to litter size, infanticide and different reproductive strategies.The important topic of dispersal will be evaluated concerning female dispersal in relation to life history traits (body size, body growth, density dependency and genetic variability). Further on, the variation of life history strategies in North America, northern Europe and south-eastern Europe will be investigated in relation to ecological and anthropomorphic factors. The project aims at providing results that break new scientific ground as well as improve the basis for management and conservation decisions.

This project dealt with several life history aspects of the brown bear Ursus arctos, especially in its Swedish habitats. An organism`s life history is its lifetime pattern of growth, reproduction, life expectancy, and mortality. Body size is important for the reproductive success of both male and female brown bears and also for the survival chance of young bears. We evaluated the determinants of yearling and adult female body size and found that yearling size was determined by maternal size, food conditions, litter size, and population density. Adult female body size varied with food conditions and population density. Larger males produced more offspring annually, and larger females seemed to be able to defend their offspring better against infanticidal (= cub-killing) males. Other factors positively related to male annual reproductive success were increasing age and population density. However we found also evidence for female mate selection: female brown bears chose to mate with males in their vicinity, but among these males the most heterozygous, less inbred, and largest males were more often the father to the female`s next litter. The probability of cub loss due to infanticide decreased with increasing litter size. This was in accordance with the maternal investment theory, because the litter-size related willingness to defend offspring against infanticidal males was the most deciding factor for cub losses. Dispersal in brown bears was found to be inversely density-dependent, i.e. dispersal decreased with increasing population density. Males had a higher dispersal probability than females; 94% of the males and 41% of the females dispersed from their natal area. Male brown bears dispersed to avoid inbreeding. Female litter mates seemed to compete for philopatry (staying at home), suggesting that a dominance hierarchy among female litter mates based on body size may cause the subdominant or smaller sister to disperse. However philopatric females reproduced later than females that dispersed outside their mother`s home range, probably due to reproductive suppression by the mother. Primiparous mothers also had smaller litters and lost more offspring due to infanticide than multiparous mothers. Evidence for an apparent case of human induced life-history change in brown bears was found insofar, as populations with a long history of human persecution (> 50 generations) showed a greater reproductive investment relative to body mass than populations with a shorter history (< 15 generations). As a result, populations with a long history of exploitation are the world`s most productive, which may explain why many of these populations (Europe) have responded more positively to changes in management in recent times (like a more sustainable hunting, or full protection) than most other populations (North America, Asia).