What is a Dominance Hierarchy?

In many species of animals, pairs of individuals within small groups set up fairly stable dominance relationships. In a dominance relationship, one of the individuals, “the dominant”, is consistently aggressive toward the other, “the subordinate”, but the subordinate rarely attacks the dominant. Aggressive acts vary by species. In chickens, for example, dominants peck subordinates, and in fish, they bite and chase them. There are also subtle kinds of behaviors, which stop just short of physical aggression, by which the dominant can threaten the subordinate. For example, a dominant fish may only have to initiate a short, fast swim toward the subordinate, while a dominant hen may just need to raise her head above that of the subordinate to demonstrate a threat and not have to follow through with an actual peck.

A dominance hierarchy, or pecking order, is the network, the collection, of all the dominance relationships in a group. In small groups, under some 8 or 10 members, dominance hierarchies often take what is called a “linear” structure in many different kinds of animals. In a linear structure, one individual dominates all the others, a second dominates all but the top individual, and so on down to the last individual. Linear hierarchies are common in some insects and reptiles, and in many fish, birds, and mammals, including human preschoolers. While a linear ranking of the individuals may seem like the only possibility, other kinds of hierarchy structures do sometimes form, at least for short periods of time.

The rank of an individual in its hierarchy can have important consequences. For example, higher ranking individuals may have better access to food when it is in short supply, suffer less predation, experience lower levels of stress, and have better functioning immune systems.

(To see some cichlid fish forming a dominance hierarchy, click on the video below.)