The Effects of Dominance on Leadership and Energetic Gain: A Dynamic Game between Pairs of Social Foragers

Although social behaviour can bring many benefits to an individual, there are also costs that may be incurred whenever the members of a social group interact. The formation of dominance hierarchies could offer a means of reducing some of the costs of social interaction, but individuals within the hierarchy may end up paying differing costs dependent upon their position within the hierarchy. These differing interaction costs may therefore influence the behaviour of the group, as subordinate individuals may experience very different benefits and costs to dominants when the group is conducting a given behaviour. Here, a state-dependent dynamic game is described which considers a pair of social foragers where there is a set dominance relationship within the pair. The model considers the case where the subordinate member of the pair pays an interference cost when it and the dominant individual conduct specific pairs of behaviours together. The model demonstrates that if the subordinate individual pays these energetic costs when it interacts with the dominant individual, this has effects upon the behaviour of both subordinate and the dominant individuals. Including interaction costs increases the amount of foraging behaviour both individuals conduct, with the behaviour of the pair being driven by the subordinate individual. The subordinate will tend to be the lighter individual for longer periods of time when interaction costs are imposed. This supports earlier suggestions that lighter individuals should act as the decision-maker within the pair, giving leadership-like behaviours that are based upon energetic state. Pre-existing properties of individuals such as their dominance will be less important for determining which individual makes the decisions for the pair. This suggests that, even with strict behavioural hierarchies, identifying which individual is the dominant one is not sufficient for identifying which one is the leader. Author Summary: Dominance hierarchies could offer interacting animals a quick way to settle disputes without having to use too much effort. However, individuals may pay a price for acknowledging their position within the hierarchy, which could influence how they choose to behave within the group. Consequently, the actions of the group may be shaped by the effects of the hierarchy on each of the group’s members. I consider the behaviour of a pair that consists of a dominant and a subordinate individual, where the subordinate pays an energetic cost when it interacts with the dominant. I show that having to pay this cost affects the behaviour of the pair. I also demonstrate that, although a social hierarchy is imposed, the behaviour of the pair is not determined by the dominance relationship, but is instead influenced by the energetic reserves of the pair, where the decision-maker may just be whoever is the hungriest.