Predator Attack Strategy and Prey Behaviour Drive Individual Predation Risk in Schooling Prey

Abstract

Predation is one of the main drivers of animal grouping. However, predation risk is not shared equally within groups. Despite long-standing theoretical work and strong empirical insights, very little work has examined the real-time dynamics of predators attacking groups of prey nor quantified the features that predict prey predation risk and survival. Here we used high resolution tracking of Northern pike (Esox lucius) attacking large schools of prey (golden shiner fish, Notemigonus crysoleucas) to get a mechanistic quantification of predation at every stage of the attack. We found that pike tended to attack the groups head-on, but did so stealthily, often striking only when partly within the school. From the predator’s perspective, relative position to the prey was the most important feature, with shiners very close and directly in front of the pike being most at risk. From the prey’s perspective, we found that central individuals, with relatively low local neighbour density and alignment, face increased risk. While the majority of attacks were successful, escape was associated with individuals achieving high maximum movement speeds, relative to others. Our study highlights both predator attack strategy and prey behaviour are key factors underlying the predation risk of grouping prey, and our results contradict the long-held assertion arising from Hamilton’s “selfish herd” concept that central positions are safer. To ultimately understand the cost-benefits that underly the evolution of animal grouping it is thus key to consider the multifaceted, and dynamical, nature of predator-prey relationships.