Department of Animal Behaviour, University of Bielefeld, Bielefeld, Germany.
PLoS One. 2010 Dec 6;5(12):e15229. doi: 10.1371/journal.pone.0015229.
Intraguild predation (IGP) is widespread but it is often neglected that guilds commonly include many layers of dominance within. This could obscure the effects of IGP making unclear whether the intermediate or the bottom mesopredator will bear higher costs from the emergence of a new top predator.
METHODOLOGY/PRINCIPAL FINDINGS: In one of the most extensive datasets of avian IGP, we analyse the impact of recolonization of a superpredator, the eagle owl Bubo bubo on breeding success, territorial dynamics and population densities of two mesopredators, the northern goshawk Accipiter gentilis and its IG prey, the common buzzard Buteo buteo. The data covers more than two decades and encompass three adjacent plots. Eagle owls only recolonized the central plot during the second decade, thereby providing a natural experiment. Both species showed a decrease in standardized reproductive success and an increase in brood failure within 1.5 km of the superpredator. During the second decade, territory dynamics of goshawks was significantly higher in the central plot compared to both other plots. No such pattern existed in buzzards. Goshawk density in the second decade decreased in the central plot, while it increased in both other plots. Buzzard density in the second decade rapidly increased in the north, remained unchanged in the south and increased moderately in the center in a probable case of mesopredator release.
CONCLUSIONS/SIGNIFICANCE: Our study finds support for top-down control on the intermediate mesopredator and both top-down and bottom-up control of the bottom mesopredator. In the face of considerable costs of IGP, both species probably compete to breed in predator-free refugia, which get mostly occupied by the dominant raptor. Therefore for mesopredators the outcome of IGP might depend directly on the number of dominance levels which supersede them.
种内捕食（IGP）很普遍，但人们常常忽略的是， guild 通常包含许多层次的支配关系。这可能会掩盖 IGP 的影响，使得不清楚新出现的顶级捕食者会使中间还是底层的中型捕食者承担更高的成本。
方法/主要发现：在鸟类 IGP 最广泛的数据集之一中，我们分析了超级捕食者鹰鸮 Bubo bubo 重新定殖对繁殖成功率、领地动态和两种中型捕食者北方游隼 Accipiter gentilis 及其 IGP 猎物普通鵟 Buteo buteo 的种群密度的影响。数据涵盖了二十多年，包括三个相邻的地块。鹰鸮仅在第二个十年重新定殖于中心地块，从而提供了一个自然实验。两个物种在离超级捕食者 1.5 公里内的标准繁殖成功率都降低，并且雏鸟成活率增加。在第二个十年中，与其他两个地块相比，中心地块中游隼的领地动态明显更高。在普通鵟中不存在这种模式。第二个十年中，中心地块中游隼的密度下降，而在其他两个地块中则增加。第二个十年中，北方的普通鵟密度迅速增加，南方保持不变，中心适度增加，可能是中型捕食者释放的结果。
结论/意义：我们的研究支持了对中间中型捕食者的自上而下的控制，以及对底部中型捕食者的自上而下和自下而上的控制。面对相当大的 IGP 成本，这两个物种可能会竞争在没有捕食者的避难所中繁殖，而这些避难所大多被占优势的猛禽占据。因此，对于中型捕食者来说，IGP 的结果可能直接取决于超越它们的支配层次的数量。
