Predator presence affects activity patterns but not food consumption or growth of juvenile corkwing wrasse (Symphodus melops)

Data and analysis script for: Norin et al (in prep) Predator presence affects activity patterns but not food consumption or growth of juvenile corkwing wrasse (Symphodus melops)<br>Please see readme file.<br>Abstract: Indirect effects of predators can manifest themselves as changes in prey behaviour and physiology. Reduced prey activity is a common behavioural response to predation risk, generally resulting in reduced foraging and growth. Given that digestion requires energy, it has been suggested that prey will choose to eat smaller meals under predation risk to reserve a larger portion of the aerobic metabolic scope they have available for energetically demanding tasks more critical than digestion, such asescape. To test this prediction, we quantified food consumption and growth of juvenile corkwing wrasses (Symphodus melops) over 11 days in the presence or absence of a predator (Atlantic cod, Gadus morhua). We then quantified behaviour and food consumption of the same wrasses in behavioural arenas with a predator present. All food consumption data were examined in the context of the aerobic scope that would have been available during the digestive period. Overall, there was no effect ofpredator exposure on food consumption or growth, yet predator-exposed wrasses were more consistent in their daily food consumption, lending some support to our prediction of prey bet-hedging on meal size under predation risk. The lack of a clear pattern may have resulted from a relatively low percentage of aerobic scope (~20-27%) beingoccupied by digestion, such that fish retained ample aerobic scope for activities other than digestion. In the subsequent behavioural trials, predator-exposed wrasses weremore active and spent more time near the cod than predator-naïve wrasses, suggesting the former had habituated to predation threat and were more risk-taking.Our results highlight the complex and often counter-intuitive effects that predator presence can have on prey populations beyond direct consumption.

本数据集与分析脚本配套的研究为：Norin 等人（待刊）《捕食者存在可改变幼年濑鱼（Symphodus melops，corkwing wrasse）的活动模式，但不影响其摄食与生长》<br>详见说明文档（readme file）<br>摘要：捕食者的间接效应可通过猎物的行为与生理变化体现。猎物活动水平降低是应对捕食风险的常见行为响应，通常会导致觅食与生长速率下降。鉴于消化过程需要消耗能量，有假说提出猎物在捕食风险下会选择摄入更少的食物，以保留更多的需氧代谢范围（aerobic metabolic scope），用于完成比消化更具能量需求且更为关键的行为，例如逃逸。为验证该假说，我们设置了有无捕食者（大西洋鳕鱼，Gadus morhua）的对照组，在11天周期内量化了幼年濑鱼的摄食与生长情况；随后，我们在配备捕食者的行为测试竞技场（behavioural arenas）中，对同一批濑鱼的行为与摄食模式进行了量化。所有摄食数据均结合消化时段内可获得的需氧代谢范围进行了分析。整体而言，捕食者暴露处理对濑鱼的摄食与生长无显著影响，但经捕食者暴露的个体其每日摄食量更为稳定，为我们的假说提供了一定的支持。未观测到显著效应的原因可能是：消化过程仅占用了相对较低比例的需氧代谢范围（约20%~27%），因此鱼类仍保留了充足的需氧代谢范围用于开展消化以外的其他活动。在后续的行为测试中，经捕食者暴露的个体相较于未经历捕食暴露的个体（predator-naïve）更为活跃，且更常待在鳕鱼附近，这表明前者已对捕食威胁产生了习惯化，表现出更高的风险偏好。本研究结果表明，捕食者的存在对猎物种群产生的影响往往复杂且违背直觉，远超直接捕食所带来的效应。