Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California 93106, USA.
Ecology. 2010 Dec;91(12):3563-71. doi: 10.1890/09-2174.1.
The indirect, ecosystem-level consequences of ocean fishing, and particularly the mechanisms driving them, are poorly understood. Most studies focus on density-mediated trophic cascades, where removal of predators alternately causes increases and decreases in abundances of lower trophic levels. However, cascades could also be driven by where and when prey forage rather than solely by prey abundance. Over a large gradient of fishing intensity in the central Pacific's remote northern Line Islands, including a nearly pristine, baseline coral reef system, we found that changes in predation risk elicit strong behavioral responses in foraging patterns across multiple prey fish species. These responses were observed as a function of both short-term ("acute") risk and longer-term ("chronic") risk, as well as when prey were exposed to model predators to isolate the effect of perceived predation risk from other potentially confounding factors. Compared to numerical prey responses, antipredator behavioral responses such as these can potentially have far greater net impacts (by occurring over entire assemblages) and operate over shorter temporal scales (with potentially instantaneous response times) in transmitting top-down effects. A rich body of literature exists on both the direct effects of human removal of predators from ecosystems and predators' effects on prey behavior. Our results draw together these lines of research and provide the first empirical evidence that large-scale human removal of predators from a natural ecosystem indirectly alters prey behavior. These behavioral changes may, in turn, drive previously unsuspected alterations in reef food webs.
海洋捕捞的间接的、生态系统层面的后果，特别是其驱动机制，人们还知之甚少。大多数研究都集中在密度介导的营养级联上，在这种情况下，捕食者的移除会交替地导致较低营养级的丰度增加和减少。然而，级联也可能是由猎物觅食的地点和时间驱动的，而不仅仅是由猎物的丰度决定的。在太平洋中部偏远的北莱恩群岛上，从渔业密度的大幅梯度变化中，包括一个几乎原始的基线珊瑚礁系统，我们发现，捕食风险的变化会在多个猎物鱼类物种的觅食模式中引发强烈的行为反应。这些反应是根据短期（“急性”）风险和长期（“慢性”）风险以及当猎物暴露于模型捕食者时观察到的，以将感知到的捕食风险的影响与其他潜在的混杂因素隔离开来。与数量上的猎物反应相比，这些如捕食防御行为反应可能具有更大的净影响（通过发生在整个集合体上），并且在传递自上而下的影响方面具有更短的时间尺度（可能具有即时的反应时间）。关于人类从生态系统中移除捕食者的直接影响以及捕食者对猎物行为的影响，已经有大量的文献。我们的研究结果将这些研究结合起来，并提供了第一个经验证据，表明人类从自然生态系统中大规模移除捕食者会间接改变猎物的行为。这些行为变化可能反过来导致以前未被怀疑的珊瑚礁食物网的改变。
