Male reproductive strategy explains spatiotemporal segregation in brown bears

Abstract

1. Spatiotemporal segregation is often explained by the risk for offspring predation or by differences in physiology, predation risk vulnerability or competitive abilities related to size dimorphism.2. Most large carnivores are size dimorphic and offspring predation is often intraspecific and related to nonparental infanticide (NPI). NPI can be a foraging strategy, a strategy to reduce competition, or a male reproductive strategy. Spatiotemporal segregation is widespread among large carnivores, but its nature remains poorly understood.3. We evaluated three hypotheses to explain spatiotemporal segregation in the brown bear, a size-dimorphic large carnivore in which NPI is common; the ‘NPI – foraging/competition hypothesis', i.e. NPI as a foraging strategy or a strategy to reduce competition, the ‘NPI – sexual selection hypothesis’, i.e. infanticide as a male reproductive strategy and the ‘body size hypothesis’, i.e. body-size-related differences in physiology, predation risk vulnerability or competitive ability causes spatiotemporal segregation. To test these hypotheses, we quantified spatiotemporal segregation among adult males, lone adult females and females with cubs-of-the-year, based on GPS-relocation data (2006–2010) and resource selection functions in a Scandinavian population.4. We found that spatiotemporal segregation was strongest between females with cubs-of-the-year and adult males during the mating season. During the mating season, females with cubs-of-the-year selected their resources, in contrast to adult males, in less rugged landscapes in relative close proximity to certain human-related variables, and in more open habitat types. After the mating season, females with cubs-of-the-year markedly shifted their resource selection towards a pattern more similar to that of their conspecifics. No strong spatiotemporal segregation was apparent between females with cubs-of-the-year and conspecifics during the mating and the postmating season.5. The ‘NPI – sexual selection hypothesis’ best explained spatiotemporal segregation in our study system. We suggest that females with cubs-of-the-year alter their resource selection to avoid infanticidal males. In species exhibiting NPI as a male reproductive strategy, female avoidance of infanticidal males is probably more common than observed or reported, and may come with a fitness cost if females trade safety for optimal resources.

Alaskan brown bears (Ursus arctos) aggregate and display fidelity to foraging neighborhoods while preying on Pacific salmon along small streams

“…Female brown bears are thought to be less sensitive to human presence than males, and may even use humans as shields against infanticidal males (Rode et al., ; Steyaert et al., , ). Because the bears in our study system are exposed to researchers, hunters, and residents of the nearby town of Aleknagik, we expected to find elevated female abundance and detectability relative to males.…”

Infanticide as a male reproductive strategy has a nutritive risk effect in brown bears

“…The study area encompassed approximately 13000 km 2 , and the bear density was approximately 30 individuals per 1000 km 2 [6]. …”

Selenium in brown bears (Ursus arctos) from Croatia: Relation to cadmium and mercury

“…The enhanced fat metabolism likely contributes to the higher Hg levels found in females, together with assumed higher food intake relative to body mass during the hyperphagic period in order to ensure parturition. Also, the foraging and behavioural habits of females with cubs shift towards becoming more cautious, [53] undoubtedly influencing the quality, quantity and choice of food. We cannot propose an impact direction (more/less) of the above factor on element content in bears.…”