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Published on: March 13, 2011
Interspecific resource partitioning in sympatric ursids
Jerrold L Belant1, Knut Kielland, Erich H Follmann
1Department of Biology and Wildlife, University of Alaska, Fairbanks 99775, USA. Jerry_Belant@nps.gov
Summary
Brown bears dominate salmon resources, restricting black bears
Area of Science:
- Ecology
- Wildlife Biology
- Conservation Biology
Background:
- Species interactions shape realized niches, influencing resource partitioning.
- Resource partitioning among sympatric ursids (bears) has been inferred but not directly demonstrated.
- Understanding interspecific competition is crucial for wildlife management and conservation.
Purpose of the Study:
- To demonstrate resource partitioning between sympatric brown bears (Ursus arctos) and American black bears (U. americanus).
- To assess the relationship between diet, body condition, and reproduction in these two bear species.
- To investigate the role of brown bears in constraining the niche of black bears.
Main Methods:
- Isotopic analysis of blood and claw keratin to estimate assimilated diets.
- Monitoring body condition (fat, lean mass, total mass) and reproductive rates.
- Field study conducted in south-central Alaska from 1998-2000.
Main Results:
- Brown bears predominantly consumed salmon (>53% annually), while black bears consumed 0-25% salmon.
- Black bears reduced salmon consumption during low salmon years, likely due to brown bear deterrence.
- Brown bear body size and condition were linked to salmon availability; black bear condition and reproduction were directly related to assimilated salmon.
- Salmon consumption improved body condition, reducing lean mass catabolism during hibernation and enhancing subsequent spring condition and black bear reproduction.
Conclusions:
- Brown bears constrain the fundamental niche of black bears through resource partitioning, particularly of salmon.
- Reduced salmon access forces black bears to rely on less nutritious food sources, negatively impacting their body condition and reproductive success.
- Interspecific competition for key resources like salmon can significantly influence population dynamics and reproductive output in sympatric carnivore species.
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