Otterbeck Andreas, Lindén Andreas, Roualet Éric
Department of Biosciences, University of Oslo, Blindern, P.O. Box 1066, 0316, Oslo, Norway,
Oecologia. 2015 Sep;179(1):129-37. doi: 10.1007/s00442-015-3320-8. Epub 2015 May 6.
Predatory species' usage of different prey types is affected by both prey availability and selectivity. The diet during the breeding season may affect the reproductive success of individual pairs. We studied the prey use of a small reversed size-dimorphic raptor, the Eurasian sparrowhawk Accipiter nisus, with respect to prey weight on two organizational levels. Using 13 years of data from southern Norway, we related reproductive output of individual breeding events to prey size taken. Further, we assessed the regional variation in prey usage between five Fennoscandian populations. This was done by fitting optimum-type functions to the prey species' numbers or relative predation risks. Pairs that successfully completed the season with more fledglings displayed less variation in prey size, suggesting a possible adaptive benefit of diet specialism, or possibly a correlative effect due to higher prey availability or lower female hunting effort. This finding contrasts with earlier raptor studies, which have suggested benefits of dietary (and hence nutritional) diversity. Indeed, our results might be limited to nutritionally substitutable prey items. We also found a tendency suggesting that older females raised more fledglings than 1-year-old females. In the population-level analysis, we found that optimum-type functions with constant width and spatially variable average best described the relationship between relative predation risk and log weight. This can reflect local conditions, such as prey availability. Our findings and new methodological tools could apply to a broader spectrum of predators. They also highlight the role of viewing usage or choice of prey at several spatial scales.
掠食性物种对不同猎物类型的利用受到猎物可获得性和选择性的影响。繁殖季节的饮食可能会影响个体配对的繁殖成功率。我们从两个组织层面研究了一种体型大小反转的小型猛禽——欧亚雀鹰（Accipiter nisus）对猎物重量的猎物利用情况。利用挪威南部13年的数据，我们将个体繁殖事件的繁殖产出与所捕获猎物的大小联系起来。此外，我们评估了五个芬诺斯堪的亚种群之间猎物利用的区域差异。这是通过将最优类型函数拟合到猎物种类数量或相对捕食风险来完成的。成功育雏数量更多的配对所捕获猎物大小的变化较小，这表明饮食专业化可能具有适应性益处，或者可能是由于猎物可获得性较高或雌鸟捕猎努力较低而产生的相关效应。这一发现与早期猛禽研究形成对比，早期研究表明饮食（以及营养）多样性有益处。事实上，我们的结果可能仅限于营养可替代的猎物种类。我们还发现一种趋势，即年龄较大的雌鸟比1岁雌鸟养育的雏鸟更多。在种群水平分析中，我们发现宽度恒定且空间平均可变的最优类型函数最能描述相对捕食风险与对数重量之间的关系。这可以反映当地条件，例如猎物可获得性。我们的发现和新的方法工具可以应用于更广泛的捕食者。它们还强调了在多个空间尺度上观察猎物利用或选择的作用。
