All Together Now: Activity Synchrony and Social Cohesion in Group-Living Animals

Abstract A central problem all group-living animals face is how to maintain group cohesion during the course of the day in the face of forces that drive animals apart. When activity schedules become desynchronised, groups will inevitably fragment as animals drift apart. To explore the impact that individual differences in activity scheduling might have for group cohesion, we here explore the consequences having different activity schedules has for social cohesion. By modeling a group as a set of semi-coupled oscillators, we show that, all else equal, the members of the group will become less and less coupled across the active day until the group devolves and breaks apart, setting an upper limit on the size of group that can be maintained as a coherent entity given a particular level of correlation in members' activity schedules. We then show that when social bonding creates a stickiness, or gravitational pull, between pairs of individuals, fragmentation is reduced. We argue that large, stable social groups are only possible when some form of social bonding has evolved.