Predator confusion is sufficient to evolve swarming behaviour

Abstract

Swarming behaviors in animals have been exten-sively studied due to their implications for the evo-lution of cooperation, social cognition, and predator-prey dynamics. An important goal of these studies is discerning which evolutionary pressures favor the formation of swarms. One hypothesis is that swarms arise because the presence of multiple moving prey in swarms causes confusion for attacking predators, but it remains unclear how important this selective force is. Using an evolutionary model of a predator-prey system, we show that predator confusion pro-vides a sufficient selection pressure to evolve swarm-ing behavior in prey. Furthermore, we demonstrate that the evolutionary effect of predator confusion on prey could in turn exert pressure on the structure of the predator’s visual field, favoring the frontally ori-ented, high-resolution visual systems commonly ob-served in predators that feed on swarming animals. Finally, we provide evidence that when prey evolve swarming in response to predator confusion, there is a change in the shape of the functional response curve describing the predator’s consumption rate as prey density increases. Thus, we show that a relatively simple perceptual constraint—predator confusion— could have pervasive evolutionary effects on prey be-havior, predator sensory mechanisms, and the ecolog-ical interactions between predators and prey.