Communication and Collective Consensus Making in Animal Groups via Mechanical Interactions

Mechanical constraints have strong influence on the dynamics, and structure of granular aggregations. The contact forces within dense suspensions of active particles may give rise to intriguing phenomena including anomalous density fluctuations, long-range orientational ordering, and spontaneous pattern formation. Various authors have proposed that these physical phenomena contribute to the ability of animal groups to move coherently. Our systematic numerical simulations confirm that spontaneous interactions of elongated individuals can trigger oriented motion in small groups. They are however insufficient in bigger ones, despite their significant imprint on the group’s internal structure. It is also demonstrated that preferred directions of motion of a minority of group members can be communicated to others solely by mechanical interactions. These findings strengthen the link between pattern formation in active nematics, and the collective decision making of social animals.