Niche theory predicts that closely related and ecologically similar species with overlapping distribution ranges can coexist through resource partitioning, that limits interspecific competition. However, studies examining the mechanisms promoting coexistence of top predators at a large geographical scale are still scant. Here, we describe the foraging ecology of three sympatric owl species [Northern long-eared owl (Asio otus), Tawny owl (Strix aluco), Eurasian eagle owl (Bubo bubo)] in the Mediterranean Basin. We review 160 studies reporting diet information (212,236 vertebrate preys) and investigate among-species differences in diet metrics (diversity, evenness, prey size and proportion of mammals) and their variation along geographical and environmental gradients. Moreover, we test whether diet metrics differ in presence or absence of the other predators. All the three species mainly rely on small mammals, but they significantly differ in diet metrics. The smallest predator (i.e., long-eared owl) shows a higher level of specialism on small mammals (highest proportion but lowest diversity of mammals in the diet) compared to the larger ones. In addition, mean prey size significantly increases with predator body size (long-eared owl < tawny owl < eagle owl). Finally, interspecific competition results in an increase of diet diversity and evenness in the long-eared owl, and species’ diet also varies in response to environmental factors. The three species thus segregate along several dietary niche axes over a large spatial scale and according to both morphological characteristics (i.e., body size) and environmental variables. Such dietary niche segregation may adaptively buffer interspecific competition costs, ultimately allowing coexistence.

中文翻译：

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地中海盆地顶级掠食者行会的营养生态位隔离

生态位理论预测，分布范围重叠的密切相关且生态相似的物种可以通过资源分配共存，从而限制种间竞争。然而，研究促进大地理范围内顶级捕食者共存的机制的研究仍然很少。在这里，我们描述了地中海盆地三种同域猫头鹰物种[北方长耳猫头鹰（Asio otus）、黄褐色猫头鹰（Strix aluco）、欧亚雕鸮（Bubo bubo）]的觅食生态。我们回顾了 160 项报告饮食信息的研究（212,236 种脊椎动物猎物），并调查了饮食指标（多样性、均匀性、猎物大小和哺乳动物比例）的物种间差异及其随地理和环境梯度的变化。此外，我们还测试了饮食指标在其他掠食者存在或不存在时是否有所不同。这三个物种主要依赖小型哺乳动物，但它们的饮食指标存在显着差异。与较大的捕食者相比，最小的捕食者（即长耳猫头鹰）对小型哺乳动物表现出更高水平的专业性（饮食中哺乳动物的比例最高，但多样性最低）。此外，平均猎物尺寸随着捕食者身体尺寸的增加而显着增加（长耳猫头鹰<黄褐色猫头鹰<雕鸮）。最后，种间竞争导致长耳鸮的饮食多样性和均匀性增加，并且物种的饮食也会因环境因素而变化。因此，这三个物种根据形态特征（即体型）和环境变量，在大空间范围内沿几个饮食生态位轴分离。这种饮食生态位隔离可以适应性地缓冲种间竞争成本，最终实现共存。