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）是一类公认的影响捕食者群落结构的机制，但其复杂的相互作用却极难厘清。中级捕食者抑制假说预测，顶级捕食者可通过两种方式作用于两类中级捕食者：同时抑制两者，或通过压制优势中级捕食者从而释放次优势中级捕食者，亦或引发两类中级捕食者产生不同的响应。本研究基于一项长达25年的野外监测，揭示了三级捕食者群落（欧亚雕鸮*Bubo bubo* L.、苍鹰*Accipiter gentilis* L.及普通鵟*Buteo buteo* L.）在上述情境下的响应结果。在研究周期的后半段，欧亚雕鸮重新定居本研究区域，这为顶级捕食者引入的自然实验提供了绝佳场景。研究团队结合该自然实验场景，开展了针对生境利用的精细地理信息系统（Geographic Information System, GIS）分析，以及一项模拟顶级捕食者入侵次优势中级捕食者（普通鵟）领地的野外控制实验。尽管群落内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率均出现显著上升。我们曾提出假说：顶级捕食者引发的优势中级捕食者生态位偏移，或可促进无顶级捕食者避难所内的中级捕食者共存。研究结果显示，苍鹰的营巢生境选择出现了显著变化，而普通鵟则未表现出此类改变。鉴于对无天敌避难所的竞争以及种群密度的快速增长可能限制了次优势中级捕食者的生态位偏移，我们进一步预测其会产生针对顶级捕食者的行为响应。野外控制实验结果证实：在10年的监测周期内，普通鵟对欧亚雕鸮领地入侵的攻击性响应显著增强，这一现象或源于其应对顶级捕食风险的表型可塑性（phenotypic plasticity）。综上，本研究结果表明，集团内捕食可成为驱动捕食者群落行为改变的强劲动力，同时影响其生境利用与攻击性水平。这类变化或有助于缓冲中级捕食者种群免受集团内捕食带来的负面影响。