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• W2126189558 abstract "This thesis deals with two main aspects of brown bear Ursus arctos reproductive strategies. First, it seeks to understand strategies of maternal care and how these affect the size and fate of offspring. Second it focuses on how home range size relates to ecological factors and reproductive strategies. All these aspects were studied using empirical data from a long-term study of brown bears in southcentral and northern Sweden.Size of offspring is an important life history variable, because it might affect their survival and extend into adulthood and affect their reproductive success. Yearling body size and mass were positively related to maternal body size and negatively related to litter size. Males were larger and heavier than females, suggesting that mothers invest more in their male offspring, in accordance with the sex allocation theory for polygynous species. Further, yearling body mass showed a pronounced variance among cohorts, probably a result of variable food abundance among years. Yearling size and mass did not differ between the southern and northern study area. No significant relationship was found between population density and yearling body mass, but population density was probably below carrying capacity. Subadult bears (1-3 years-old) that died (excluding human caused mortalities) tended to be smaller as yearlings than subadults that did not die.Length of maternal care, i.e. the interval between successfully raised litters, is the most important factor explaining the variation in reproductive rates among brown bear populations, making it an interesting life history trait. In southcentral Sweden 95% of the litters separated from their mother as yearlings and the rest as two-year-olds. In northern Sweden litters separated as yearlings (53%), two-year-olds (44%) and three-year-olds (3%). In northern Sweden the probability of yearling litters staying with their mother for a second year decreased with increasing yearling body mass, and was higher for litters with 2 offspring than for litters with 1 or 3-4 offspring. Staying with their mothers for a second year had a positive effect on mass gain in yearlings and this effect was most pronounced in litters with 2 offspring. Body mass of 2-year-olds was not related to age of weaning and our results suggested that keeping offspring for an additional year mainly compensated for low yearling body mass. In the southern study area we examined the behavior of family groups during family breakup. With few exceptions, all yearlings within a litter separated at the same time. Yearlings separated from their mothers during the mating season in May-early July, and most family breakups occurred with an adult male present. Our results suggest that termination of maternal investment was not initiated by the offspring. Because yearling body mass did not differ between the study areas, body mass itself can not explain why many females cared for their yearlings for a second year in the northern study area. Although cohort effects on yearling body mass was evident in both study areas, prolonged care for small offspring in the northern study area probably reduced the cohort effect by the age of 2 year.Abandonment of dependent offspring has been related to poor nutritional conditions, but also to unusual small broods/litters. We modeled the number of offspring recruited to the population when female brown bears varied their behavior regarding abandoning single cubs to evaluate whether there might be a selective advantage of abandoning single cubs. In the southern subpopulation, with a 2-year reproductive cycle, females would not gain by abandoning single-cub litters, whereas in the northern subpopulation, females with a 3-year reproductive cycle would gain marginally (about 2%) by doing so. Females with single-cub litters did not seem to abandon single cubs after leaving the den, but we were not able to judge whether females abandoned single cubs shortly after birth. In the southern subpopulation, where sexually selected infanticide (SSI) was suggested to be a major agent of cub mortality, the probability of loosing one or more cubs from a litter decreased with litter size. In the northern subpopulation, where cub mortality was low and SSI less common, the probability of loosing one or more cubs from a litter increased with litter size. Our results support the maternal investment theory, that mothers invest in offspring defense in positive relation to the number of offspring. Protecting cubs from males is costly for mothers, as they tended to be killed more often by conspecifics than females without cubs. Excluding human caused mortality, intraspecific predation is the most important cause of mortality in brown bears.Staying with their mother did not significantly reduce intraspecific predation among yearlings, suggesting that the benefit for yearlings by staying for second year is mainly increased growth rate. The number of adult males that died 3 years previously and whether an adult male died 2 years previously explained part of the variation of the number of female yearlings killed. This was similar to the results previous reported for cub mortality, further pointing out that killing of adult males might has a strong demographic effect. In polygynous mammals the size of male home ranges has been considered to be determined by the distribution of females and the size of female ranges has been considered to be determined by the spatial distribution of food. On a large geographical scale home range size reported for brown bear populations was negatively related to food availability. However, for the Scandinavian populations we rejected the hypothesis that home range size is proportional to individuals’ metabolic needs, because this hypothesis was not able to explain the larger annual or seasonal ranges in males than estrous females nor the differences among females of different reproductive categories. Males and estrous females increased their ranges in the mating season, suggesting a roam-to-mate strategy in both sexes. Roaming behavior of estrous females may be a strategy to consort several males for mate selection and to hide paternity as a counterstrategy against sexually selected infanticide, apparently the most important cause of cub mortality. Females with cubs, on the other hand, decreased their ranges during the mating season, probably to avoid contact with infanticidal males, because the presence of small cubs was not able to explain the small ranges used in the mating season. The size of annual ranges was negatively related to population density along a population density gradient not related to food availability, probably because movements are restricted by conspecifics at higher population density." @default.
• W2126189558 created "2016-06-24" @default.
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• W2126189558 date "2003-01-01" @default.
• W2126189558 modified "2023-10-18" @default.
• W2126189558 title "Reproductive strategies in Scandinavian brown bears" @default.
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