Dominance hierarchy

In the zoological field of ethology, a dominance hierarchy (formerly and colloquially called a pecking order) is a type of social hierarchy that arises when members of animal social groups interact, creating a ranking system. Different types of interactions can result in dominance depending on the species, including ritualized displays of aggression or direct physical violence.^[2]

In social living groups, members are likely to compete for access to limited resources and mating opportunities. Rather than fighting each time they meet, individuals of the same sex establish a relative rank, with higher-ranking individuals often gaining more access to resources and mates. Based on repetitive interactions, a social order is created that is subject to change each time a dominant animal is challenged by a subordinate one.

In eusocial animals, whether mammals or insects, aggressive interactions often lead to the suppression of reproduction in non-dominant individuals. Such interactions may be ritualised, and an individual's resulting rank in the dominance hierarchy may be advertised to other individuals by visual or chemical cues. Suppression operates in some species on the reproductive hormones of non-dominant individuals. Dominance hierarchies exist in many bird species, first observed in the domestic chicken, where the hierarchy is maintained by pecking with the beak.

There is a spectrum of social organisations in different species, from a full despotic hierarchy to a relatively egalitarian system in species with little intraspecific competition. Dominance varies, too, depending on the context or resource, and on group size.