Dominance Hierarchy

Predominance chain of importance emerges when individuals from a social gathering collaborate, frequently forcefully, to make a positioning framework. In social living gatherings, individuals are prone to vie for access to constrained assets and mating open doors. Instead of battle every time they meet, relative connections are framed between individuals from the same sex. These dreary communications lead to the making of a social request that is liable to change every time an overwhelming creature is tested by a subordinate one.

Systems

An image depicting the social orders a social group may demonstrate. In an egalitarian society, all members are equal, and relative ranking is not assigned. In a linear hierarchy (pecking order), each member is assigned a rank relative to one another, creating a linear distribution of power. In a despotic hierarchy, one member is assigned dominance while all other members are subordinate.

This manifestation of intrasexual conflict can be observed in one of two systems. The social order can be either egalitarian or despotic. In a linear ranking system (often referred to as a pecking order), every member of the gender is recognized as either dominant or submissive relative to every other member, creating a linear distribution of rank. For example, groups of spotted hyenas and brown hyenas both demonstrate linear dominance. In a despotic system, one member is considered dominant while all others members of the living group are equally submissive. Examples of despotic social systems are found in meerkats, wolves, male gorillas, Neolamprologus pulcher, and African wild dogs.

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.

  • Resource-holding potential: Animals that are better able to defend resources often win without much physical contact.
  • Resource value: Animals more invested in a resource are likely to invest more in the fight despite potential for incurring higher costs.
  • 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.

Dominance

Benefits

Reproductive success

In primates, one of the most widely studied hierarchal groups, many studies have found a positive relationship between high rank and reproductive success. In baboons, higher-ranking males have the highest reproductive success due to increased female acquisition. Also, female baboons benefit from increased rank because high-ranking females produce more surviving offspring.

Bonnet macaques demonstrate another example of increased reproductive success from high rank. High-ranking males have more access to fertile females and consequently partake in most of the mating within the group, demonstrated by one population in which only three males were responsible for over 75% of mating. In this population, males often vary in their rank, and as they gain rank, they gain more time spent exclusively with fertile females; the opposite relationship is seen as males drop in rank. In many primates, including bonnet macaques and rhesus monkeys, the offspring of high-ranking individuals have better fitness and thus an increased rate of survival. This is most likely a function of two factors. The first is that high-ranking males mate with high-ranking females. Assuming their high rank is correlated with higher fitness and fighting ability, this trait will be conferred to their offspring. The second factor is that higher-ranking parents probably provide better protection to their offspring and thus ensure higher survival rates.

In rodents, the highest-ranking male frequently sires the most offspring. The same pattern is found in most carnivores, such as the dwarf mongoose. The dwarf mongoose lives in a social system with one dominant pair. The dominant female produces all or almost all of the offspring in the living group, and the dominant male has first access to her during her oestrus period. In red deer, the males who experienced winter dominance, resulting from greater access to preferred foraging sites, had higher ability to get and maintain larger harems during the mating season.

In many monogamous bird species, the dominant pairs tend to get the best territories, which in turn promote offspring survival and adult health. In dunnocks, a species of birds that experiences many mating systems, sometimes individuals will form a group that will have one dominant male who achieves all of the mating in the group.

In the monogynous bee species Melipona subnitida it is noted that the queen wants to maintain reproductive success, and does so by preventing workers from caring for their cells, pushing or hitting them using her antennae. Workers additionally have been noted to display aggression towards males, claiming priority over the cells when males try to use them to place eggs. This species further demonstrates the conflict between hierarchy and reproductive success.

Foraging success

Another benefit to high-ranking individuals is increased foraging success and access to food resources. During times of water shortage the highest-ranking vervet females have greater access than subordinates females to water in tree holes. In chacma baboons, the high-ranking males have the first access to vertebrate prey that has been caught by the group, and in yellow baboons the dominant males feed for longer without being interrupted.

In many bird species the dominant individuals have higher rates of food intake including dark-eyed juncos and oystercatchers. The dominant individuals in these groups fill themselves up first and fill up more quickly, so they spend less time foraging, which reduces the risk of predation. Thus they have increased survival because of increased nutrition and decreased predation.

Costs

Despite the benefits to being of a high rank in a hierarchal group, there are also costs which offset these benefits. The most common costs to high-ranking individuals are higher metabolic rates and higher levels of stress hormones. In great tits and pied flycatchers, high-ranking individuals experience higher resting metabolic rates and therefore need to consume more food in order to maintain fitness and activity levels compared to subordinates in their groups. The energetic costs of defending territory, mates, and other resources can be very consuming and cause high-ranking individuals, who spend more time in these activities, to lose body mass over long periods of dominance. Therefore, their physical condition decreases the longer they spend partaking in these high-energy activities, and they lose rank as a function of age.

In wild male baboons, the highest ranking male, also known as the alpha, experiences high levels of both testosterone and glucocorticoid, which indicates that high-ranking males undergo higher levels of stress which reduces fitness. Reduced health and longevity occurs because these two hormones have immunosuppressant activity, which reduces survival and presents opportunities for parasitic infestation and other health risks. This reduced fitness due to the alpha position results in individuals maintaining high rank for shorter periods of time and having an overall reduced health and longevity from the physical strain and costs of the position.

When to seek high rank

Given the benefits and costs of possessing a high rank within a hierarchal group, there are certain characteristics of individuals, groups, and environments that determine whether an individual will benefit from a high rank. Individual characteristics include whether or not high rank gives them access to valuable resources such as mates and food. Individuals will often weigh the cost of the resource against factors including their age, intelligence, experience, and physical fitness, which can determine the costs to gaining rank.

Hierarchy results as an accumulation of individual interaction, group dynamics, and sharing of resources, therefore group size and composition can affect the dominance decisions of high-ranking individuals and hierarchy type. For example, in a large group with many males, it may be very challenging for the highest-ranking male to dominate all the mating opportunities, so some mate sharing probably exists. These occasional mating opportunities available to subordinates reduce the likelihood of subordinates challenging the dominant male – mating is no longer an all-or-nothing game and the scraps are enough to placate most subordinates. Another aspect that can determine dominance hierarchies is the environment. In populations of Kenyan vervets, high-ranking females have higher foraging success when the food resources are clumped, but when food is distributed throughout an area they lose their advantage because subordinate females can acquire food with less risk of encountering a dominant female.

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