Keystone predation can be a determinant of community structure, including species diversity, but factors underlying “keystoneness” have been minimally explored. Using the system in which the original keystone, the sea star Pisaster ochraceus, was discovered, we focused on two potential (but overlapping) determinants of keystoneness: intrinsic traits or state variables of the species (e.g., size, density), and extrinsic environmental parameters (e.g., prey productivity) that may provide conditions favorable for keystone predator evolution. Using a comparative‐experimental approach, with repeated field experiments at multiple sites across a variable coastal environment, we tested predation rates, or how quickly predators consumed prey, and predation effects, or community response to predator presence or absence. We tested five hypotheses: (H₁) predation rates and effects will vary in space but not time; (H₂) per population predation rates will vary primarily with individual traits and population variables; (HJHH₃) per capita predation rates will vary only with individual traits; (H₄) predation effects will vary with traits, variables, and external drivers; and (H₅) as predicted by the keystone predation hypothesis, diversity will vary unimodally with predation pressure. As hypothesized, predation rates differed among sites but not over time (H₁), and in caging exclusion experiments, predation effect varied with both intrinsic and extrinsic factors (H₄). Unexpectedly, predation rates varied with both intrinsic and extrinsic (H₂, per population), or only with extrinsic (H₃, per capita) factors. Further, in large‐plot exclusion experiments, predation effect was most closely associated with individual traits (contra H₄). Finally, taxon diversity varied unimodally with proxies of predation pressure (sessile prey abundance) and was sensitive to extrinsic factors (mussel growth, temperature, and upwelling, H₅). Hence, keystoneness depended on predator individual traits, predator population variables, and environmental parameters. However, temporal differences in caging experiments suggested that environmental characteristics underlying prey dynamics may be preeminent. Compared to prior experiments, predation was weaker with low prey input compared to periods with high prey input. Collectively, our results suggest that keystone predator evolution depends on the coalescence of species‐specific characteristics, and environmental parameters favoring high prey productivity. Our approach may be a model for future studies exploring the generality of keystoneness.

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重点捕食：基于特征还是由外在过程驱动？使用比较实验方法进行评估

梯形石捕食可以决定群落结构，包括物种多样性，但是对“梯形”的基础因素却很少进行研究。使用原始的系统在其中的基石，海星Pi鱼被发现时，我们专注于关键性的两个潜在（但重叠）决定因素：物种的内在特征或状态变量（例如大小，密度），以及可能提供有利于关键性条件的外部环境参数（例如猎物生产力）捕食者的进化。我们采用比较实验的方法，在变化多端的沿海环境中的多个地点进行了重复的野外实验，测试了捕食率，捕食者消耗猎物的速度，捕食效果或社区对捕食者存在与否的反应。我们检验了五个假设：（H ₁）捕食率和影响在空间上会变化，但在时间上不会变化；（高₂）每个人口的捕食率将主要随个人特征和人口变量而变化；（HJHH ₃）人均被捕食率仅因个体特征而异；（H ₄）捕食效果会随着特质，变量和外部驱动因素而变化；和（H ₅）由基石捕食假说所预测，多样性将随捕食压力单峰变化。如假设的那样，不同地点的捕食率有所不同，但不会随时间变化（H ₁），在笼排除实验中，捕食效果随内在因素和外在因素而变化（H ₄）。出乎意料的是，捕食率随内在和外在因素（H ₂（按人口计算），或仅包含外部因素（人均H ₃）。此外，在大图排除实验中，捕食效果与个体性状最相关（H ₄相反）。最后，分类群多样性随捕食压力（无柄猎物的丰度）的代理而单峰变化，并且对外部因素（贻贝的生长，温度和上升流，H ₅）敏感。）。因此，关键性取决于捕食者的个体特征，捕食者种群变量和环境参数。但是，笼养实验的时间差异表明，猎物动态的潜在环境特征可能是杰出的。与先前的实验相比，低猎物输入的捕食能力比高猎物输入的捕食能力弱。总体而言，我们的结果表明，梯形捕食者的进化取决于物种特定特征的结合以及有利于高猎物生产力的环境参数。我们的方法可能是将来研究梯形的普遍性的模型。