Data from: Reefscapes of fear: predation risk and reef heterogeneity interact to shape herbivore foraging behavior

Predators can exert strong direct and indirect effects on ecological communities by intimidating their prey. The nature of predation risk effects is often context dependent, but in some ecosystems these contingencies are often overlooked. Risk effects are often not uniform across landscapes or among species. Indeed, they can vary widely across gradients of habitat complexity and with different prey escape tactics. These context-dependencies may be especially important for ecosystems such as coral reefs that vary widely in habitat complexity and have species-rich predator and prey communities. With field experiments using predator decoys of the black grouper (Mycteroperca bonaci), we investigated how reef complexity interacts with predation risk to affect the foraging behavior and herbivory rates of large herbivorous fishes (e.g., parrotfishes and surgeonfishes) across four coral reefs in the Florida Keys (USA). In both high and low complexity areas of the reef we measured how herbivory changed with increasing distance from the predator decoy to examine how herbivorous fishes reconcile the conflicting demands of avoiding predation vs. foraging within a reefscape context. We show that with increasing risk, herbivorous fishes consumed dramatically less food (ca. 90 %) but fed at a faster rate when they did feed (ca. 26 %). Furthermore, we show that fishes foraging closest to the predator decoy were 40 % smaller than those that foraged at further distances. Thus, smaller individuals showed muted response to predation risk compared to their larger counterparts, potentially due to their decreased risk to predation or lower reproductive value (i.e., the asset protection principle). Habitat heterogeneity mediated risk effects differently for different species of herbivores, with predation risk more strongly suppressing herbivore feeding in more complex areas and for individuals at higher risk of predation. Predators appear to create a reefscape of fear that changes the size structure of herbivores towards smaller individuals, increases individual feeding rates, but suppresses overall amounts of primary producers consumed, potentially altering patterns of herbivory, an ecosystem process critical for healthy coral reefs.

捕食者可通过威慑猎物，对生态群落产生强烈的直接与间接效应。捕食风险效应的本质往往具有情境依赖性，但在部分生态系统中，这类情境依赖性常被研究者忽视。捕食风险效应在不同景观或物种种群间往往并不统一，事实上，其差异可随生境复杂度梯度以及猎物不同的逃逸策略发生显著变化。这类情境依赖性对于生境复杂度差异显著、捕食者与猎物群落物种丰富度极高的珊瑚礁等生态系统而言，尤为关键。本研究借助黑石斑鱼（*Mycteroperca bonaci*）捕食诱饵开展野外实验，在美国佛罗里达礁岛群的四处珊瑚礁生境中，探究了珊瑚礁复杂度与捕食风险的交互作用如何影响大型植食性鱼类（如鹦嘴鱼、刺尾鱼）的觅食行为与植食速率。在珊瑚礁的高、低复杂度区域内，本研究均测量了植食速率随与捕食诱饵距离增加的变化规律，以此探究植食性鱼类在珊瑚礁景观语境下，如何协调规避捕食与觅食这两项相互冲突的生存需求。研究结果显示，随着捕食风险升高，植食性鱼类的食物摄取量大幅下降（约90%），但当其觅食时，单次进食速率会提升约26%。此外，研究发现，距捕食诱饵最近区域觅食的鱼类个体，其体型比远距离觅食的个体小40%。由此可见，相较于大型个体，小型个体对捕食风险的响应更为平缓，这可能源于小型个体面临的捕食风险更低，或是其繁殖价值更低（即资产保护原理）。生境异质性对不同植食动物物种的风险效应存在差异化调控：在复杂度更高的区域，以及捕食风险更高的个体中，捕食风险对植食动物觅食行为的抑制作用更强。捕食者似乎构建了一片"恐惧礁景"：该景观会使植食动物的体型结构向小型个体偏移，提升单个个体的进食速率，但会抑制被取食的初级生产者总生物量，进而可能改变植食作用模式——而植食作用是维持健康珊瑚礁的关键生态过程。