Abstract
A common hypothesis about the origins of collective behaviour suggests that animals might live and move in groups to increase their chances of surviving predator attacks. This hypothesis is supported by several studies that use computational models to simulate natural evolution. These studies, however, either tune an ad-hoc model to ‘reproduce’ collective behaviour, or concentrate on a single type of predation pressure, or infer the emergence of collective behaviour from an increase in prey density. In nature, prey are often targeted by multiple predator species simultaneously and this might have played a pivotal role in the evolution of collective behaviour. We expand on previous research by using an evolutionary rule-based system to simulate the evolution of prey behaviour when prey are subject to multiple simultaneous predation pressures. We analyse the evolved behaviour via prey density, polarization, and angular momentum. Our results suggest that a mixture of antagonistic external pressures that simultaneously steer prey towards grouping and dispersing might be required for prey individuals to evolve dynamic parallel movement.
Highlights
Results from studies of collective behaviour are useful for scientists from many different research fields–from biology, physics and medicine, to computer science[1,2,3,4,5]
As groups of animals in nature move in many different regimes[12,33] and different predation pressures are countered by different responses of prey groups, we can hypothesise that the type of predation tactic has an influence on the type of collective behaviour that evolves
As these responses are experience dependant[51,52], we can hypothesise that if collective behaviour evolved as an anti-predator response it might as well have been shaped by the predation pressures the prey faced
Summary
Results from studies of collective behaviour are useful for scientists from many different research fields–from biology, physics and medicine, to computer science[1,2,3,4,5]. The confusion effect hypothesis states that a predator attacking a group of visually similar prey might have a hard time tracking and capturing its target[14,19,20,21,22,23]. The dilution of risk hypothesis suggests that the chance of a single prey being selected as the predator’s target is lower in larger groups[26]. Kunz et al.[20] evolved artificial neural networks to show that the presence of a confusable predator might be a sufficient condition for prey individuals to evolve collective behaviour. A similar result was achieved by Olson et al.[21,22], who in addition showed that predators may reduce the benefits of prey grouping by attacking peripheral targets and that grouping evolves when the predators attack prey individuals that are located nearby. A recent study by Biswas et al.[32] suggests that the dilution of risk is the most prominent factor for the evolution of clumping and not the confusion effect as suggested by previous research
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