Collective response to local perturbations: how to evade threats without losing coherence

• Published in: Physical biology Vol. 20; no. 3; pp. 35003 - 35025
• Main Authors: Loffredo, Emanuele, Venturelli, Davide, Giardina, Irene
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 11.04.2023; Institute of Physics: Hybrid Open Access
• Subjects: active matter; Animals; Behavior, Animal - physiology; collective behavior; dynamical response; flocking; Humans; Models, Biological; Physics; dynamical response; flocking; active matter; collective behavior; Collective behavior; Flocking; Active matter; Dynamical response
• ISSN: 1478-3975; 1478-3967; 1478-3975
• DOI: 10.1088/1478-3975/acc5cc

Living groups move in complex environments and are constantly subject to external stimuli, predatory attacks and disturbances. An efficient response to such perturbations is vital to maintain the group’s coherence and cohesion. Perturbations are often local, i.e. they are initially perceived only by few individuals in the group, but can elicit a global response. This is the case of starling flocks, that can turn very quickly to evade predators. In this paper, we investigate the conditions under which a global change of direction can occur upon local perturbations. Using minimal models of self-propelled particles, we show that a collective directional response occurs on timescales that grow with the system size and it is, therefore, a finite-size effect. The larger the group is, the longer it will take to turn. We also show that global coherent turns can only take place if i) the mechanism for information propagation is efficient enough to transmit the local reaction undamped through the whole group; and if ii) motility is not too strong, to avoid that the perturbed individual leaves the group before the turn is complete. No compliance with such conditions results in the group’s fragmentation or in a non-efficient response.