Data from: Do intraspecific or interspecific interactions determine responses to predators feeding on a shared size-structured prey community?

1. Coexistence of predators that share the same prey is common. This is still the case in size structured predator communities where predators consume prey species of different sizes (interspecific prey responses) or consume different size classes of the same species of prey (intraspecific prey responses). 2. A mechanism has recently been proposed to explain coexistence between predators that differ in size but share the same prey species, emergent facilitation, which is dependent on strong intraspecific responses from one or more prey species. Under emergent facilitation predators can depend on each other for invasion, persistence or success in a size structured prey community. 3. Experimental evidence for intraspecific size-structured responses in prey populations remain rare and further questions remain about direct interactions between predators that could prevent or limit any positive effects between predators (e.g. intraguild predation). 4. Here we provide a community wide experiment on emergent facilitation including natural predators. We investigate both the direct interaction between two predators that differ in body size (fish vs. invertebrate predator) and the indirect interaction between them via their shared prey community (zooplankton). 5. Our evidence supports the most likely expectation of interactions between differently sized predators, that intraguild predation rates are high and interspecific interactions in the shared prey community dominate the response to predation (i.e. predator-mediated competition). The question of whether emergent facilitation occurs frequently in nature requires more empirical and theoretical attention, specifically to address the likelihood that its pre-conditions may co-occur with high rates of intraguild predation.

1. 共享同一猎物的捕食者共存现象十分普遍。在体型结构化捕食者群落（size structured predator communities）中亦是如此：此类群落内的捕食者或捕食不同物种种群的猎物（即种间猎物响应（interspecific prey responses）），或捕食同一物种种群内不同体型等级的猎物（即种内猎物响应（intraspecific prey responses））。
2. 近期有研究提出了一种可解释体型不同但共享同一猎物种群的捕食者共存现象的机制——涌现促进作用（emergent facilitation），该机制依赖于一种或多种猎物种群的强烈种内响应。在涌现促进作用机制下，体型结构化猎物种群中的捕食者可借助彼此实现入侵、存续或种群成功扩张。
3. 目前，关于猎物种群体型结构化种内响应的实验证据仍较为匮乏，且捕食者间的直接相互作用是否会抑制或削弱捕食者间的正向效应（如集团内捕食（intraguild predation）），相关问题仍有待解答。
4. 本研究开展了一项涵盖天然捕食者的全群落水平实验，以探究涌现促进作用。我们同时研究了两类体型迥异的捕食者（鱼类与无脊椎动物捕食者）间的直接相互作用，以及二者通过共享的猎物群落（浮游动物（zooplankton））产生的间接相互作用。
5. 本研究结果支持关于体型不同的捕食者间相互作用的主流预期：集团内捕食发生率较高，且共享猎物群落内的种间相互作用主导了捕食响应（即捕食者介导的竞争（predator-mediated competition））。关于涌现促进作用在自然环境中是否普遍存在的问题，仍需更多实证与理论研究予以关注，尤其是需明确其发生前提是否常与高发生率的集团内捕食共存。