Biology Department, San Diego State University, 5500 Campanile Drive, San Diego, San Diego, CA, 92182, USA.
Hopkins Marine Station, Department of Biology, Stanford University, 120 Ocean View Blvd, Pacific Grove, CA, 93950, USA.
Oecologia. 2022 Aug;199(4):859-869. doi: 10.1007/s00442-022-05225-5. Epub 2022 Jul 30.
Prey state and prey density mediate antipredator responses that can shift community structure and alter ecosystem processes. For example, well-nourished prey at low densities (i.e., prey with higher per capita predation risk) should respond strongly to predators. Although prey state and density often co-vary across habitats, it is unclear if prey responses to predator cues are habitat-specific. We used mesocosms to compare the habitat-specific responses of purple sea urchins (Strongylocentrotus purpuratus) to waterborne cues from predatory lobsters (Panulirus interruptus). We predicted that urchins from kelp forests (i.e., in well-nourished condition) tested at low densities typically observed in this habitat would respond more strongly to predation risk than barren urchins (i.e., in less nourished condition) tested at high densities typically observed in this habitat. Indeed, when tested at densities associated with respective habitats, urchins from forests, but not barrens, reduced kelp grazing by 69% when exposed to lobster risk cues. Barren urchins that were unresponsive to predator cues at natural, high densities suddenly responded strongly to lobster cues when conspecific densities were reduced. Strong responses of low densities of barren urchins persisted across feeding history (i.e. 0-64 days of starvation). This suggests that barren urchins can respond to predators but typically do not because of high conspecific densities. Because high densities of urchins in barrens should weaken the non-consumptive effects of lobsters, urchins in these habitats may continue to graze in the presence of predators thereby providing a feedback that maintains urchin barrens.
被捕食状态和被捕食密度调节着捕食者的防御反应，这些反应会改变群落结构并改变生态系统过程。例如，低密度（即，个体被捕食风险较高）的营养良好的猎物应该对捕食者做出强烈反应。尽管猎物的状态和密度通常在不同的栖息地中共同变化，但尚不清楚猎物对捕食者线索的反应是否具有栖息地特异性。我们使用中观模型来比较紫海胆（Strongylocentrotus purpuratus）对来自掠食性龙虾（Panulirus interruptus）的水传播线索的栖息地特异性反应。我们预测，在这种栖息地中通常观察到的低密度（即营养良好）的海胆对捕食风险的反应会比在这种栖息地中通常观察到的高密度（即营养较差）的海胆更强烈。事实上，当在与各自栖息地相关的密度下进行测试时，来自森林的海胆（但不是荒地的海胆）在暴露于龙虾风险线索时，减少了 69%的海带摄食。当同种密度降低时，对捕食者线索无反应的荒地海胆突然对龙虾线索做出强烈反应。在整个摄食历史（即 0-64 天的饥饿）中，低密度荒地海胆的强烈反应都持续存在。这表明，荒地海胆可以对捕食者做出反应，但由于同种密度高，通常不会这样做。由于荒地中海胆的高密度应该会削弱龙虾的非消耗性影响，因此这些栖息地中的海胆可能会在捕食者存在的情况下继续摄食，从而提供一种反馈，维持海胆荒地的存在。
