Data from: Intraguild predation leads to cascading effects on habitat choice, behaviour and reproductive performance

Intraguild predation (IGP) is a commonly recognized mechanism influencing the community structure of predators, but the complex interactions are notoriously difficult to disentangle. The mesopredator suppression hypothesis predicts that a superpredator may either simultaneously repress two mesopredators, restrain the dominant one and thereby release the subdominant mesopredator, or elicit different responses by both mesopredators. We show the outcome arising from such conditions in a three-level predator assemblage (Eurasian eagle owl Bubo bubo L., northern goshawk Accipiter gentilis L. and common buzzard Buteo buteo L.) studied over 25 years. In the second half of the study period, the eagle owl re-colonized the study area, thereby providing a natural experiment of superpredator introduction. We combined this set-up with detailed GIS analysis of habitat use and a field experiment simulating intrusion by the superpredator into territories of the subdominant mesopredator, the buzzard. Although population trends were positive for all three species in the assemblage, the proportion of failed breeding attempts increased significantly in both mesopredators after the superpredator re-colonized the area. We predicted that superpredator-induced niche shifts in the dominant mesopredator may facilitate mesopredator coexistence in superpredator-free refugia. We found significant changes in nesting habitat choice in goshawk, but not in buzzard. Since competition for enemy-free refugia and the rapid increase in population density may have constrained niche shifts of the subdominant mesopredator, we further predicted behavioural changes in response to the superpredator. The field experiment indeed showed a significant increase in aggressive response of buzzards towards eagle owl territory intrusion over the course of 10 years, probably due to phenotypic plasticity in the response towards superpredation risk. Overall, our results show that intraguild predation can be a powerful force of behavioural change, simultaneously influencing habitat use and aggressiveness in predator communities. These changes might help to buffer mesopredator populations against the negative effects of intraguild predation.

集团内捕食（intraguild predation, IGP）是公认的影响捕食者群落结构的关键机制，但其复杂的相互作用向来难以厘清。中级捕食者抑制假说预测，顶级捕食者可同时对两类中级捕食者产生压制作用：或是通过抑制优势中级捕食者，从而释放从属中级捕食者；或是引发两类中级捕食者产生不同的响应。我们针对由欧亚雕鸮*Bubo bubo* L.、苍鹰*Accipiter gentilis* L.与普通鵟*Buteo buteo* L.组成的三级捕食者类群开展了长达25年的研究，以此阐明此类情境下的生态结果。在研究周期的后半段，欧亚雕鸮重新定居至研究区域，为顶级捕食者引入的自然实验提供了理想场景。我们结合该实验设置，开展了详细的栖息地利用地理信息系统（Geographic Information System, GIS）分析，并设置野外实验，模拟顶级捕食者入侵从属中级捕食者——普通鵟的领地。尽管该类群中所有三个物种种群趋势均呈正向增长，但在顶级捕食者重新定居研究区域后，两类中级捕食者的繁殖失败尝试的比例均显著上升。我们曾提出假设：顶级捕食者诱导的优势中级捕食者生态位分化，或可在无顶级捕食者的避难所中促进中级捕食者的共存。研究发现，苍鹰的筑巢栖息地选择发生了显著变化，而普通鵟则未出现此类改变。由于对无天敌避难所的竞争以及种群密度的快速增长，或已限制了从属中级捕食者的生态位分化，我们进一步预测，这些物种会对顶级捕食者产生行为响应。野外实验确实证实，在10年的研究周期内，普通鵟对欧亚雕鸮领地入侵的攻击性响应显著增强，这或许源于其应对顶级捕食风险的行为表型可塑性。总体而言，我们的研究结果表明，集团内捕食可成为驱动行为改变的强大力量，同时影响捕食者群落的栖息地利用与攻击性水平。此类变化或有助于缓冲中级捕食者种群免受集团内捕食的负面影响。