Department of Zoology, Melbourne University, Parkville, VIC, 3010, Australia.
Oecologia. 2013 Jun;172(2):387-97. doi: 10.1007/s00442-012-2508-4. Epub 2012 Nov 3.
Predicting the consequences of predator biodiversity loss on prey requires an understanding of multiple predator interactions. Predators are often assumed to have independent and additive effects on shared prey survival; however, multiple predator effects can be non-additive if predators foraging together reduce prey survival (risk enhancement) or increase prey survival through interference (risk reduction). In marine communities, juvenile reef fish experience very high mortality from two predator guilds with very different hunting modes and foraging domains-benthic and pelagic predator guilds. The few previous predator manipulation studies have found or assumed that mortality is independent and additive. We tested whether interacting predator guilds result in non-additive prey mortality and whether the detection of such effects change over time as prey are depleted. To do so, we examined the roles of benthic and pelagic predators on the survival of a juvenile shoaling zooplanktivorous temperate reef fish, Trachinops caudimaculatus, on artificial patch reefs over 2 months in Port Phillip Bay, Australia. We observed risk enhancement in the first 7 days, as shoaling behaviour placed prey between predator foraging domains with no effective refuge. At day 14 we observed additive mortality, and risk enhancement was no longer detectable. By days 28 and 62, pelagic predators were no longer significant sources of mortality and additivity was trivial. We hypothesize that declines in prey density led to reduced shoaling behaviour that brought prey more often into the domain of benthic predators, resulting in limited mortality from pelagic predators. Furthermore, pelagic predators may have spent less time patrolling reefs in response to declines in prey numbers. Our observation of the changing interaction between predators and prey has important implications for assessing the role of predation in regulating populations in complex communities.
预测捕食者生物多样性丧失对猎物的影响需要了解多种捕食者之间的相互作用。捕食者通常被认为对共同猎物的生存有独立和累加的影响；然而，如果捕食者一起觅食降低了猎物的生存（风险增强）或通过干扰增加了猎物的生存（风险降低），则多个捕食者的影响可能是非累加的。在海洋群落中，幼年珊瑚鱼受到两种捕食者群体的极高死亡率的影响，这两种捕食者群体具有非常不同的狩猎模式和觅食领域——底栖和浮游捕食者群体。以前的少数捕食者操纵研究发现或假设死亡率是独立和累加的。我们测试了相互作用的捕食者群体是否会导致非累加的猎物死亡率，以及随着猎物的消耗，这种效应的检测是否会随时间而变化。为此，我们在澳大利亚菲利普港湾的人工斑块礁上，检查了底栖和浮游捕食者对幼年集群浮游动物食性温带珊瑚鱼 Trachinops caudimaculatus 生存的作用，为期 2 个月。我们在最初的 7 天观察到了风险增强，因为集群行为使猎物处于捕食者觅食领域之间，没有有效的避难所。在第 14 天，我们观察到了累加死亡率，并且不再检测到风险增强。在第 28 天和第 62 天，浮游捕食者不再是死亡的主要来源，累加性几乎微不足道。我们假设猎物密度的下降导致了集群行为的减少，使猎物更频繁地进入底栖捕食者的领域，从而导致来自浮游捕食者的有限死亡。此外，浮游捕食者可能会因为猎物数量的减少而减少在珊瑚礁上巡逻的时间。我们对捕食者和猎物之间不断变化的相互作用的观察对评估捕食在调节复杂群落中种群方面的作用具有重要意义。
