Evolution of Swarming Behavior Is Shaped by How Predators Attack

Abstract

Animal grouping behaviors have been widely studied due to their implications for understanding social intelligence, collective cognition, and potential applications in engineering, artificial intelligence, and robotics. An important biological aspect of these studies is discerning which selection pressures favor the evolution of grouping behavior. In the past decade, researchers have begun using evolutionary computation to study the evolutionary effects of these selection pressures in predator-prey models. The selfish herd hypothesis states that concentrated groups arise because prey selfishly attempt to place their conspecifics between themselves and the predator, thus causing an endless cycle of movement toward the center of the group. Using an evolutionary model of a predator-prey system, we show that how predators attack is critical to the evolution of the selfish herd. Following this discovery, we show that density-dependent predation provides an abstraction of Hamilton's original formulation of "domains of danger." Finally, we verify that density-dependent predation provides a sufficient selective advantage for prey to evolve the selfish herd in response to predation by coevolving predators. Thus, our work corroborates Hamilton's selfish herd hypothesis in a digital evolutionary model, refines the assumptions of the selfish herd hypothesis, and generalizes the domain of danger concept to densitydependent predation.

A Balanced Mixture of Antagonistic Pressures Promotes the Evolution of Parallel Movement

“…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. Using a comparable technique, a similar result was achieved by Olson et al 2122,. 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.…”

“…The selfish herd hypothesis suggests that animals form groups in order to reduce their individual domain of danger161718. The confusion effect hypothesis states that a predator attacking a group of visually similar prey might have a hard time tracking and capturing its target141920212223. The many eyes hypothesis suggests that as the size of the group increases the amount of time an individual has to scan the environment decreases2425.…”

“…In the studies that investigated the evolution of collective behaviour under various predation tactics17212232 researchers were mostly interested in whether prey individuals start to group or not (i.e. whether as a result of the artificial evolution the prey density increased or decreased).…”

“…We let prey individuals evolve their behaviour while experiencing predation from a) predators for which grouping might be a natural response and b) predators for which dispersing might be a natural response. According to previous research there are several predation tactics that pressure prey individuals to evolve grouping behaviour20212232. Two of these are a) attack prey individuals located at the periphery of the prey group (P, periphery) and b) attack the nearest prey individual (N, nearest).…”

Information-Theoretic Neuro-Correlates Boost Evolution of Cognitive Systems

“…The standard substrate for neuro-evolution are Artificial Neural Networks (ANNs, see e.g., [20]), but we use here a different substrate ("Markov networks" or "Markov Brains") that has proven to be adept at behavioral decision-making tasks [21][22][23][24][25][26][27][28]. In contrast to ANNs in which neurons are continuous-valued and non-firing, neurons in Markov brains (MBs) are digital with only two states: quiescent or firing.…”