Dominance Hierarchy - Determining The Outcome of Conflict

Determining The Outcome of Conflict

Patterns of animal conflict reveal important insights into the evolution of behavior and the influence of behavior on relationships that develop in a social group. Pair-wise interactions have been observed to promote social hierarchies within groups of animals where individuals with successful agonistic behaviors often achieve dominance. These behaviors, which include aggression, threats, displays, and fighting, are indicative of competition over resources, such as food or mates. However, they may vary based on the situation and position of the individuals involved.

Animal decisions regarding involvement in conflict are defined by the interplay between the costs and benefits of agonistic behaviors. When initially developed, game theory, the study of optimal strategies during pair-wise conflict, was grounded in the false assumption that animals engaged in conflict were of equal fighting ability. Modifications, however, have provided increased focus on the differences between the fighting capabilities of animals and raised questions about their evolutionary development. These differences are believed to determine the outcomes of fights, their intensity, and animal decisions to submit or continue fighting. The influence of aggression, threats, and fighting on the strategies of individuals engaged in conflict has proven integral to establishing social hierarchies reflective of dominant-subordinate interactions

The asymmetries between individuals have been categorized into three types of interactions. 1. Resource-holding potential: Animals that are better able to defend resources often win without much physical contact. 2. Resource value: Animals more invested in a resource are likely to invest more in the fight despite potential for incurring higher costs. 3. Intruder retreats: When participants are of equal fighting ability and competing for a certain territory, the resident of the territory is likely to end as the victor because he values the territory more. This can be explained further by looking at the example of the common shrews. If one participant believes he is the resident of the territory, he will win when the opponent is weaker or food is scarce. However, if both shrews believe they are the true territory holder, the one with the greater need for food, and therefore, one that values the resource more, is most likely to win.

As expected, the individual who emerges triumphant is rewarded with the dominant status, having demonstrated his/her physical superiority. However, the costs incurred to the defeated, which include loss of reproductive opportunities and quality food, can hinder the individual’s fitness. In order minimize these losses, animals generally retreat from fighting or displaying fighting ability unless there are obvious cues indicating victory. These often involve characteristics that provide an advantage during agonistic behavior, such as size of body, displays, etc. Red stags, for example, engage in exhausting roaring contests to exhibit their strength (Huntingford). However, such an activity would impose more costs than benefits for unfit stags, and compel them to retreat from the contest. Larger stags have also been known to make lower-frequency threat signals, acting as indicators of body size, strength, and dominance.

Engaging in agonistic behavior can be very costly and thus there are many examples in nature of animals who achieve dominance in more passive ways. In some, the dominance status of an individual is clearly visible, eliminating the need for agonistic behavior. In wintering bird flocks, white-crowned sparrows display a unique white plumage; the higher the percentage of the crown that consists of white feathers, the higher the status of the individual. For other animals, the time spent in the group serves as a determinant of dominance status. Pack members of gray wolves, for example, need the time to reach the top of the ladder. Rank may also be acquired from maternal dominance rank. In rhesus monkeys, offspring gain dominance status based on the rank of the mother—the higher ranked the mother, the higher ranked the offspring will be (Yahner). Similarly, the status of a male Canada goose is determined by the rank of his family. Although dominance is determined differently in each case, it is influenced by the relationships between members of social groups.

These observed interactions reflect the battle for resources. The association between resource availability and agonistic behavior suggests that animal conflict is adaptive by enabling competition and exploitation of available food and mates. The outcome of these interactions results in important social patterns that define hierarchies and, therefore, future access to resources.