The social system of a “nonsocial” species, the brown bear

Brown bears are a nonterritorial and solitary species, i.e. they do not defend an exclusive territory against conspecifics. Instead, they live in overlapping home ranges - areas that are not defended and in which animals live for the majority of their lives. The brown bear has a polygamous mating system, i.e. both sexes mate with several partners. The mating season is in spring and early summer, and both sexes roam over large areas to find reproductive partners. Males commonly compete for access to females, and fights can inflict severe injuries or cause death. Male competition for reproductive success can result in sexually selected infanticide (SSI), a reproductive strategy in which males kill dependent conspecific offspring for obtaining mating opportunities. Young bears disperse at one and a half to two years of age. Males typically disperse very long distances, up to several hundred kilometres. In contrast, female dispersal distances are short, on average 10-25 km. Female brown bears commonly form matrilineal assemblages (i.e. spatial clusters of related females), with home range overlap correlated with relatedness. Hunting greatly affects the social system of brown bears in Scandinavia. The removal of conspecifics through hunting creates vacancies on the landscape, and surviving bears shift their home ranges toward these vacancies, which increases the probability of SSI and negatively affects population growth rate.