The emergence of leaders and followers in foraging pairs when the qualities of individuals differ

Abstract

BackgroundForaging in groups offers animals a number of advantages, such as increasing their likelihood of finding food or detecting and avoiding predators. In order for a group to remain together, there has to be some degree of coordination of behaviour and movement between its members (which may in some cases be initiated by a decision-making leader, and in other cases may emerge as an underlying property of the group). For example, behavioural synchronisation is a phenomenon where animals within a group initiate and then continue to conduct identical behaviours, and has been characterised for a wide range of species. We examine how a pair of animals should behave using a state-dependent approach, and ask what conditions are likely to lead to behavioural synchronisation occurring, and whether one of the individuals is more likely to act as a leader.ResultsThe model we describe considers how the energetic gain, metabolic requirements and predation risks faced by the individuals affect measures of their energetic state and behaviour (such as the degree of behavioural synchronisation seen within the pair, and the value to an individual of knowing the energetic state of its colleague). We explore how predictable changes in these measures are in response to changes in physiological requirements and predation risk. We also consider how these measures should change when the members of the pair are not identical in their metabolic requirements or their susceptibility to predation. We find that many of the changes seen in these measures are complex, especially when asymmetries exist between the members of the pair.ConclusionAnalyses are presented that demonstrate that, although these general patterns are robust, care needs to be taken when considering the effects of individual differences, as the relationship between individual differences and the resulting qualitative changes in behaviour may be complex. We discuss how these results are related to experimental observations, and how the model and its predictions could be extended.

Collective decision-making in white-faced capuchin monkeys

“…For example, the quantity of ingested food could lead to a physiological state requiring consequent movement and the search for food. Thus, the initiator and the followers have a probability of movement that depends on each personal physiological condition or each energy-level reserve (Rands et al 2008). The propensity of group members to follow could intervene in the success of a start attempt, although the initiator is unable to measure it.…”

Where Next? Group Coordination and Collective Decision Making by Primates

“…When individuals face a choice between 2 mutually exclusive options (activities or target destinations), the individuals with the highest energetic requirements are predicted to initiate a change in activity and lead the group when there is an advantage to remaining coordinated Rands et al 2008;Sueur et al 2010b). Leadership by a single individual can therefore emerge as a consequence of heterogeneity within groups King et al 2009;Pillot et al 2010).…”

Leaders, followers, and group decision-making

“…Examining the problem of coordinating periods of foraging and resting, models by Rands and colleagues 9,18 provide a straightforward resolution to the problem of group coordination where individuals' interests differ. They use a game-theoretic, state-dependent, individual-based approach to model the foraging behavior of a pair of animals.…”