Mechanisms and functions of collective anti-predatorresponses

形成群体或鱼群的动物比单独生活时面临的捕食风险更低。除了作为一个群体的一部分所带来的好处之外，一些动物物种——包括蜜蜂、鱼类和有蹄类动物——已经被证明在面对捕食者的攻击时，会积极地采取集体行为。例如，一个群体中的个体可能会对攻击的捕食者做出反应，突然离开感知到的威胁。少数个体的惊吓反应可能会传播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，个体被发现在不离开危险区域的情况下重复进行类似惊吓的行为。这些行为的波状传播可能会迷惑和抑制攻击的捕食者，但很少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这种高度协调的行为。本研究项目旨在研究重复发生的类似惊吓的集体行为的最终功能和近似机制。作为一个研究系统，我选择了适应含硫的活鱼（Poecilia属和Gambusia属），它们通过集体潜水行为对鸟类捕食做出反应。这些鱼生活在富含硫、几乎缺氧的墨西哥水域，它们天生就被限制在含氧良好的水表层。在这里，它们的密度很大，暴露在鸟类捕食率很高的环境中。一旦受到攻击，这些鱼会表现出独特的集体逃跑反应，在再次潜入之前，它们会迅速潜入并在最初的位置附近浮出水面。这种运动在水面上形成了一种重复的波浪状图案。通过将自然捕食事件的实地观察与高度控制的实验和基于个体的计算机模型相结合，我的目标是研究(A)波浪状潜水行为是否以及如何减轻鸟类捕食，(B)面对不断变化的环境需求，鱼类如何适应其潜水行为，以及(C)混合物种鱼群中物种相互作用如何影响后者。我将理论与实证分析结合起来的创新方法，将有助于形成对集体行为的有力而全面的描述。

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.