Data from: Initiation and spread of escape waves within animal groups

The exceptional reactivity of animal collectives to predatory attacks is thought to be owing to rapid, but local, transfer of information between group members. These groups turn together in unison and produce escape waves. However, it is not clear how escape waves are created from local interactions, nor is it understood how these patterns are shaped by natural selection. By startling schools of fish with a simulated attack in an experimental arena, we demonstrate that changes in the direction and speed by a small percentage of individuals that detect the danger initiate an escape wave. This escape wave consists of a densely packed band of individuals that causes other school members to change direction. In the majority of cases, this wave passes through the entire group. We use a simulation model to demonstrate that this mechanism can, through local interactions alone, produce arbitrarily large escape waves. In the model, when we set the group density to that seen in real fish schools, we find that the risk to the members at the edge of the group is roughly equal to the risk of those within the group. Our experiments and modelling results provide a plausible explanation for how escape waves propagate in nature without centralized control.学界普遍认为，动物集群对捕食者攻击的卓越反应能力，源于群体成员间快速且局限于局部的信息传递。此类集群会同步转向，并产生逃逸波（escape waves）。然而，目前尚不明确逃逸波如何通过局部交互产生，也不清楚这类模式是如何被自然选择塑造的。本研究通过在实验场地中施加模拟攻击以惊扰鱼群，证实了仅占小比例的感知到危险的个体，通过改变自身运动方向与速度即可引发逃逸波。该逃逸波由一群密集聚集的个体组成，它们会带动其余鱼群成员改变运动方向。在多数场景下，此类逃逸波会贯穿整个集群。本研究借助仿真模型证实，仅依靠局部交互，该机制即可生成任意规模的逃逸波。在模型中，当我们将集群密度设置为真实鱼群的密度水平时，发现集群边缘个体所面临的风险，与集群内部个体的风险大致相当。本研究的实验与建模结果，为自然界中无集中式控制的逃逸波传播机制提供了合理的解释。