In biology, 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. A dominant higher-ranking individual is sometimes called an alpha, and the submissive lower-ranking individual a beta. Different types of interactions can result in dominance depending on the species, including ritualized displays of aggression or direct physical violence. In social living groups, members are likely to compete for access to limited resources and mating opportunities. Rather than fighting each time they meet, relative rank is established between individuals of the same sex, 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. Definitions Dominance is an individual's preferential access to resources over another based on coercive capacity based on strength, threat, and intimidation, compared to prestige (persuasive capacity based on skills, abilities, and knowledge). A dominant animal is one whose sexual, feeding, aggressive, and other behaviour patterns subsequently occur with relatively little influence from other group members. Subordinate animals are opposite; their behaviour is submissive, and can be relatively easily influenced or inhibited by other group members. Dominance For many animal societies, an individual's position in the dominance hierarchy corresponds with their opportunities to reproduce. In hierarchically social animals, dominant individuals may exert control over others. For example, in a herd of feral goats it is a large male that is dominant and maintains discipline and coherence of the flock. He leads the group but shares leadership on a foraging expedition with a mature she-goat who will normally outlast a succession of dominant males. However, earlier work showed that leadership orders in goats was not related to age or dominance. In sheep, position in a moving flock is highly correlated with social dominance, but there is no definite study to show consistent voluntary leadership by an individual. In birds, dominant individuals preferentially select higher perches to put themselves in the best position to detect and avoid predators, as well as to display their dominance to other members of their own species. It has been suggested that decision-taking about the actions of the group is commonly dissociated from social dominance. When individuals seek high rank Given the benefits and costs of possessing a high rank