Abstract
Swarming behaviours in animals have been extensively
studied owing to their implications for the evolution
of cooperation, social cognition and predator–prey
dynamics. An important goal of these studies is
discerning which evolutionary pressures favour 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 provides a
sufficient selection pressure to evolve swarming
behaviour 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, favouring the frontally
oriented, high-resolution visual systems commonly
observed 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 behaviour, predator sensory mechanisms and the
ecological interactions between predators and prey.
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