Mechanisms and functions of collective anti-predatorresponses

与独居时相比，形成群体或鱼群的动物受益于较低的捕食风险。除了作为一个群体的一部分带来的好处外，一些动物物种--包括蜜蜂、鱼类和有蹄类动物--已经被证明在应对捕食者的攻击时积极地进行集体行为。例如，群体中的个体可能会对捕食者的攻击做出突然惊吓的反应，远离感知到的威胁。少数个体的惊吓反应可能会扩散到群体中的其他成员，导致整个群体的连锁反应。惊吓通常是一种空间逃生策略，但在一些物种中，人们发现个体在不离开危险区域的情况下，会重复进行类似惊吓的行为。这些行为的波浪式传播可能会迷惑和抑制攻击捕食者，但几乎没有经验证据表明它们有效地降低了捕食率，或者个体如何集体实现如此高度协调的行为。这项研究项目旨在调查重复的、类似惊吓的集体行为发生的最终功能和最接近的机制。作为一个研究系统，我选择了适应硫磺的活鱼(Poecilia属和Gambusia属)，它们通过集体潜水行为对鸟类的捕食做出反应。这些鱼栖息在墨西哥富含硫的几乎是缺氧的水域中，自然地被限制在水体富含氧气的表层。在这里，它们以极高的密度出现，并暴露在鸟类的高捕食率下。一旦受到攻击，这些鱼就会表现出一种独特的集体逃生反应，在再次潜水之前，个体会迅速潜水，并在初始位置附近重新浮出水面。这种运动导致重复的、波浪状的图案在水面上扩散。通过将对自然捕食事件的现场观察与高度受控的实验和基于个人的计算机模型相结合，我的目标是调查(A)波浪状潜水行为是否以及如何发挥作用以减轻鸟类的捕食，(B)鱼类如何在不断变化的环境需求中适应它们的潜水行为，以及(C)在混合物种鱼群中，后者如何受到物种相互作用的影响。我将理论与实证分析相结合的创新方法，将有助于发展对集体行为的强有力和整体的描述。

Animals that form groups or shoals benefit from a lower risk of predation than what they would face when being alone. Beyond the beneficial effects of simply being part of a group, several animal species - including bees, fish and ungulates - have been shown to actively perform collective behaviours in response to attacking predators. For example, individuals within a group may respond to attacking predators with a sudden startle movement away from the perceived threat. The startle responses of a few individuals may then spread to other members of the group, resulting in a cascading chain-reaction of the entire group. Startles usually function as a spatial escape strategy, but in some species individuals have been found to perform repeated, startle-like behaviours without leaving the area of danger. The wave-like propagation of these behaviours may confuse and inhibit attacking predators, but there is little empirical evidence that they effectively reduce predation rates, or how individuals collectively achieve such highly coordinated behaviours. This research project aims to investigate both the ultimate function and the proximate mechanisms underlying the occurrence of repeated, startle-like collective behaviours. As a study system, I selected sulphur-adapted live-bearing fishes (genera Poecilia and Gambusia) that respond to bird predation by performing collective diving behaviour. Inhabiting sulphur-rich, almost anoxic waters in Mexico, these fish are naturally constrained to the water’s well-oxygenated surface layer. Here, they occur at greatdensities and are exposed to high rates of bird predation. Upon attack, these fish exhibit a unique collective escape response, whereby individuals quickly dive and resurface near their initial location, before diving again. This motion results in a repeated, wave-like pattern spreading over the water surface. By combining field observations of natural predation events with highly-controlled experiments and individual-based computer models, I aim to investigate (A) whether and if, how wave-like diving behaviour functions to mitigate bird predation, (B) how fish adapt their diving behavior in the face of changing environmental demands, and (C) how the latter is affected by species interactions in mixed-species fish shoals. My innovative approach to combine theory alongside empirical analyses will serve todevelop a robust and holistic characterization of collective behaviour.