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Interspecific resource partitioning in sympatric ursids

机译：同胞小种间的种间资源划分

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The fundamental niche of a species is rarely if ever realized because the presence of other species restricts it to a narrower range of ecological conditions. The effects of this narrower range of conditions define how resources are partitioned. Resource partitioning has been inferred but not demonstrated previously for sympatric ursids. We estimated assimilated diet in relation to body condition (body fat and lean and total body mass) and reproduction for sympatric brown bears (Ursus arctos) and American black bears (U. americanus) in southcentral Alaska, 1998-2000. Based on isotopic analysis of blood and keratin in claws, salmon (Oncorhynchus spp.) predominated in brown bear diets (> 53% annually) whereas black bears assimilated 0-25% salmon annually. Black bears did not exploit salmon during a year with below average spawning numbers, probably because brown bears deterred black bear access to salmon. Proportion of salmon in assimilated diet was consistent across years for brown bears and represented the major portion of their diet. Body size of brown bears in the study area approached mean body size of several coastal brown bear populations, demonstrating the importance of salmon availability to body condition. Black bears occurred at a comparable density (mass: mass), but body condition varied and was related directly to the amount of salmon assimilated in their diet. Both species gained most lean body mass during spring and all body fat during summer when salmon were present. Improved body condition (i.e., increased percentage body fat) from salmon consumption reduced catabolism of lean body mass during hibernation, resulting in better body condition the following spring. Further, black bear reproduction was directly related to body condition; reproductive rates were reduced when body condition was lower. High body fat content across years for brown bears was reflected in consistently high reproductive levels. We suggest that the fundamental niche of black bears was constrained by brown bears through partitioning of food resources, which varied among years. Reduced exploitation of salmon caused black bears to rely more extensively on less reliable or nutritious food sources (e.g., moose [Alces alces], berries) resulting in lowered body condition and subsequent reproduction.
机译：一个物种的基本生态位很少得到实现，因为其他物种的存在将其限制在较窄的生态条件范围内。条件范围的缩小定义了如何划分资源。已经对资源分区进行了推断，但先前并未针对同胞的ursids进行过证明。我们估算了1998-2000年在阿拉斯加中部的同伴棕熊（Ursus arctos）和美洲黑熊（U. americanus）的身体状况（体脂，瘦肉和总体重）和生殖的同化饮食。根据对爪中血液和角蛋白的同位素分析，棕熊饮食中的鲑鱼（Oncorhynchus spp。）占主导地位（每年> 53％），而黑熊每年则吸收0-25％的鲑鱼。黑熊在一年内没有产卵低于平均产卵量，这可能是因为棕熊阻止了黑熊获取鲑鱼。棕熊在同化饮食中的鲑鱼比例多年来保持一致，并代表其饮食的主要部分。研究区域内棕熊的体型接近几个沿海棕熊种群的平均体型，这表明鲑鱼获取对身体状况的重要性。黑熊的密度可比（质量：质量），但身体状况各不相同，并且与饮食中所吸收的鲑鱼数量直接相关。当出现鲑鱼时，这两个物种在春季都获得了最瘦的体重，而在夏季则获得了所有的脂肪。鲑鱼消费改善了身体状况（即增加了身体脂肪百分比），从而减少了冬眠期间瘦体重的分解代谢，从而使下一个春天的身体状况更好。此外，黑熊繁殖与身体状况直接相关。当身体状况降低时，生殖率降低。棕熊多年来的高身体脂肪含量反映在持续的高繁殖水平上。我们认为，黑熊的基本利基市场是通过分配食物资源来限制黑熊的，而食物资源的分配因年份而异。减少对鲑鱼的利用导致黑熊更广泛地依赖较不可靠或营养不良的食物来源（例如，驼鹿[Alces alces]，浆果），从而导致身体状况降低和随后的繁殖。

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