鸟群中的无标度相关
Scale-free correlations in bird flocks
摘要：
从鸟群到鱼群，动物群体对环境扰动的反应似乎常常是一致的。大多数关于动物集体行为的研究都旨在了解一个全球有序的国家是如何从简单的行为规则中产生的。较少的努力致力于了解集体反应的起源，即群体作为一个整体对其环境的反应方式。然而，集体反应是幸存者适应的关键，特别是当强大的捕食压力存在时。在这里，我们认为，动物群体的集体反应是通过无标度的行为相关性。通过重建大群椋鸟中单个鸟类的三维位置和速度，我们测量了不同鸟类的速度波动在多大程度上相互关联。我们发现，这种空间相关性的范围没有一个恒定的值，但它的规模与线性规模的羊群。这一结果表明，行为相关性是无标度的：一只动物行为状态的变化会影响该组中所有其他动物的行为状态，并受到该组中所有其他动物的影响，无论该组有多大。无标度相关性最大限度地扩展了个体的有效感知范围，从而弥补了个体间直接相互作用的短程性质，并增强了对扰动的整体反应。我们的研究结果表明，羊群行为的关键系统，准备最大限度地响应环境扰动。
英文摘要：
From bird flocks to fish schools, animal groups often seem to react to environmental perturbations as if of one mind. Most studies in collective animal behaviour have aimed to understand how a globally ordered state may emerge from simple behavioural rules. Less effort has been devoted to understanding the origin of collective response, namely the way the group as a whole reacts to its environment. Yet collective response is the adaptive key to survivor, especially when strong predatory pressure is present. Here we argue that collective response in animal groups is achieved through scale-free behavioural correlations. By reconstructing the three-dimensional position and velocity of individual birds in large flocks of starlings, we measured to what extent the velocity fluctuations of different birds are correlated to each other. We found that the range of such spatial correlation does not have a constant value, but it scales with the linear size of the flock. This result indicates that behavioural correlations are scale-free: the change in the behavioural state of one animal affects and is affected by that of all other animals in the group, no matter how large the group is. Scale-free correlations extend maximally the effective perception range of the individuals, thus compensating for the short-range nature of the direct inter-individual interaction and enhancing global response to perturbations. Our results suggest that flocks behave as critical systems, poised to respond maximally to environmental perturbations.
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