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.动物群体对捕食者攻击的卓越应激反应，通常被认为源于群体成员间快速且局限于局部的信息传递。这类群体能够同步转向，并形成逃逸波（escape waves）。然而，目前尚不清楚逃逸波如何通过局部交互产生，也未明晰此类群体模式是如何经自然选择塑造的。本研究通过在实验场域（experimental arena）中施加模拟攻击以惊扰鱼群，证实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。该逃逸波由高密度聚集的个体集群组成，会促使其余鱼群成员改变运动方向。在大多数情况下，该逃逸波会传遍整个鱼群。我们借助模拟模型证实，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，当我们将群体密度设置为真实鱼群的密度水平时，发现群体边缘个体所面临的风险，与群体内部个体的风险大致相当。本研究的实验与建模结果，为自然状态下逃逸波如何在无集中式控制的条件下传播提供了合理的解释。