Curr Biol. 2012 Jul 24;22(14):R561-2. doi: 10.1016/j.cub.2012.05.008.
Flocking is a striking example of collective behaviour that is found in insect swarms, fish schools and mammal herds. A major factor in the evolution of flocking behaviour is thought to be predation, whereby larger and/or more cohesive groups are better at detecting predators (as, for example, in the 'many eyes theory'), and diluting the effects of predators (as in the 'selfish-herd theory') than are individuals in smaller and/or dispersed groups. The former theory assumes that information (passively or actively transferred) can be disseminated more effectively in larger/cohesive groups, while the latter assumes that there are spatial benefits to individuals in a large group, since individuals can alter their spatial position relative to their group-mates and any potential predator, thus reducing their predation risk. We used global positioning system (GPS) data to characterise the response of a group of 'prey' animals (a flock of sheep) to an approaching 'predator' (a herding dog). Analyses of relative sheep movement trajectories showed that sheep exhibit a strong attraction towards the centre of the flock under threat, a pattern that we could re-create using a simple model. These results support the long-standing assertion that individuals can respond to potential danger by moving towards the centre of a fleeing group.
集群是一种引人注目的集体行为模式，存在于昆虫群、鱼群和哺乳动物群中。集群行为进化的一个主要因素被认为是捕食，较大和/或更具凝聚力的群体更善于发现捕食者（例如，在“多眼理论”中），并且比较小和/或分散的群体中的个体更能稀释捕食者的影响（如“自私羊群理论”）。前者的理论假设，信息（被动或主动传递）可以在更大/更具凝聚力的群体中更有效地传播，而后者则假设，在大群体中个体存在空间优势，因为个体可以改变它们相对于同伴和任何潜在捕食者的空间位置，从而降低捕食风险。我们使用全球定位系统（GPS）数据来描述一群“猎物”动物（一群羊）对逼近的“捕食者”（一只牧羊犬）的反应。对相对羊运动轨迹的分析表明，羊在受到威胁时会强烈地向羊群中心吸引，这种模式我们可以使用一个简单的模型来重现。这些结果支持了一个长期以来的观点，即个体可以通过向逃离群体的中心移动来应对潜在的危险。
