Dominance Hierarchy
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biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
, a dominance hierarchy (formerly and colloquially called a pecking order) is a type of social
hierarchy A hierarchy (from Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an important ...
that arises when members of animal
social groups In the social sciences, a social group can be defined as two or more people who interact with one another, share similar characteristics, and collectively have a sense of unity. Regardless, social groups come in a myriad of sizes and varieties ...
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 Sex is the biological distinction of an organism between male and female. Sex or SEX may also refer to: Biology and behaviour *Animal sexual behaviour **Copulation (zoology) **Human sexual activity **Non-penetrative sex, or sexual outercourse ** ...
, 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 within a hierarchical group, there are certain characteristics of individuals, groups, and environments that determine whether an individual will benefit from a high rank. These include whether or not high rank gives them access to valuable resources such as mates and food. Age, intelligence, experience, and physical fitness can influence whether or not an individual deems it worthwhile to pursue a higher ranking in the hierarchy, which often comes at the expense of conflict. Hierarchy results from interactions, group dynamics, and sharing of resources, so group size and composition affect the dominance decisions of high-ranking individuals. For example, in a large group with many males, it may be difficult for the highest-ranking male to dominate all the mating opportunities, so some mate sharing probably exists. These opportunities available to subordinates reduce the likelihood of a challenge to the dominant male: mating is no longer an all-or-nothing game and the sharing is enough to placate most subordinates. Another aspect that can determine dominance hierarchies is the environment. In populations of Kenyan
vervet monkey The vervet monkey (''Chlorocebus pygerythrus''), or simply vervet, is an Old World monkey of the family Cercopithecidae native to Africa. The term "vervet" is also used to refer to all the members of the genus ''Chlorocebus''. The five distinct ...
s, 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.


Benefits


Foraging success

A benefit to high ranking individuals is increased
foraging Foraging is searching for wild food resources. It affects an animal's Fitness (biology), fitness because it plays an important role in an animal's ability to survive and reproduce. Optimal foraging theory, Foraging theory is a branch of behaviora ...
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 baboon The chacma baboon (''Papio ursinus''), also known as the Cape baboon, is, like all other baboons, from the Old World monkey family. It is one of the largest of all monkeys. Located primarily in southern Africa, the chacma baboon has a wide vari ...
s, 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. Such species include
dark-eyed junco The dark-eyed junco (''Junco hyemalis'') is a species of junco, a group of small, grayish New World sparrows. This bird is common across much of temperate North America and in summer ranges far into the Arctic. It is a very variable species, much ...
s and
oystercatcher The oystercatchers are a group of waders forming the family Haematopodidae, which has a single genus, ''Haematopus''. They are found on coasts worldwide apart from the polar regions and some tropical regions of Africa and South East Asia. The ...
s. 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.


Reproductive success

In primates, a well-studied group, high rank brings reproductive success, as seen in a 1991 meta-analysis of 32 studies. A 2016 study determined that higher status increased reproductive success amongst men, and that this did not vary by type of subsistence (foraging, horticulture, pastoralism, agriculture). This contradicts the "egalitarian hypothesis", which predicts that status would affect reproductive success more amongst foragers than amongst nonforagers. High-ranking
bonnet macaque The bonnet macaque (''Macaca radiata''), also known as zati,Chambers English Dictionary is a species of macaque endemic to southern India. Its distribution is limited by the Indian Ocean on three sides and the Godavari and Tapti Rivers, along wi ...
males have more access to fertile females and consequently partake in most of the matings within the group; in one population, three males were responsible for over 75% of matings. In this population, males often vary in rank. As their rank improves, they gain more exclusive time with fertile females; when their rank decreases, they get less time. In many primates, including bonnet macaques and
rhesus monkey The rhesus macaque (''Macaca mulatta''), colloquially rhesus monkey, is a species of Old World monkey. There are between six and nine recognised subspecies that are split between two groups, the Chinese-derived and the Indian-derived. Generally b ...
s, 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. Amongst rhesus macaques, higher ranking males sired more offspring, though the alpha male was never the one to sire the most offspring, with that instead being a high-ranking but not top male. The complex relationship between rank and reproduction in this species is likely explained by the fact that rhesus macaques queue, rather than fight, for dominance, meaning that the alpha male is not necessarily the strongest or most attractive male. 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 common dwarf mongoose (''Helogale parvula'') is a mongoose species native to Angola, northern Namibia, KwaZulu-Natal in South Africa, Zambia and East Africa. It is part of the genus ''Helogale'', along with the Ethiopian dwarf mongoose. Char ...
. 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 This is a glossary of terms used in the descriptions of ants. A B D E F G H M N O P Q R S T U W See also ...
bee species ''
Melipona subnitida ''Melipona subnitida'' is a neotropical bee species in the Apidae family found in the dry areas of Northeastern Brazil. This species of stingless bees practices single mating, monogynous habits. This species nests in hollow trunks of living tree ...
'', the queen seeks to maintain reproductive success by preventing workers from caring for their cells, pushing or hitting them using her antennae. Workers display aggression towards males, claiming priority over the cells when males try to use them to place eggs.


Costs of being dominant

There are costs to being of a high rank in a hierarchical group which offset the benefits. The most common costs to high-ranking individuals are higher metabolic rates and higher levels of stress hormones. In
great tit The great tit (''Parus major'') is a passerine bird in the tit family Paridae. It is a widespread and common species throughout Europe, the Middle East, Central Asia and east across the Palearctic to the Amur River, south to parts of North Af ...
s 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.


Interpersonal complementarity hypothesis

The interpersonal complementarity hypothesis suggests that obedience and authority are reciprocal, complementary processes. That is, it predicts that one group member's behaviours will elicit a predictable set of actions from other group members. Friendly behaviours are predicted to be met with friendly behaviours, and hostile behaviours are predicted to be reciprocated with similar, hostile behaviours. When an individual acts in a dominant, authoritative manner in a group, this behaviour tends to prompt submissive responses from other group members. Similarly, when group members display submissive behaviour, others feel inclined to display dominant behaviours in return. Tiedens and Fragale (2003) found that hierarchical differentiation plays a significant role in liking behaviour in groups. Individuals prefer to interact with other group members whose power, or status behaviour complements their own. That is to say, group members who behave submissively when talking to someone who appears to be in control are better liked, and similarly individuals who display dominant behaviours (e.g., taking charge, issuing orders) are more liked when interacting with docile, subservient individuals.


Subordinance


Benefits

There are a number of benefits to being subordinate. Subordination is beneficial in agonistic conflicts where rank predicts the outcome of a fight. Less injury will occur if subordinate individuals avoid fighting with higher-ranking individuals who would win a large percentage of the time - knowledge of the pecking order keeps both parties from incurring the costs of a prolonged fight. In hens it has been observed that both dominants and subordinates benefit from a stable hierarchical environment because fewer challenges means more resources can be dedicated to laying eggs. In groups of highly related individuals, kin selection may influence the stability of hierarchical dominance. A subordinate individual closely related to the dominant individual may benefit more genetically by assisting the dominant individual to pass on their genes. Alpha male savanna baboons have high levels of
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
and stress; over a long period of time, this can lead to decreased fitness. The lowest ranking males also had high stress levels, suggesting that it is the beta males that gain the most fitness, avoiding stress but receiving some of the benefits of moderate rank. The mating tactics of savanna baboons are correlated with their age. Older, subordinate males form alliances to combat higher-ranking males and get access to females. Fighting with dominant males is a risky behavior that may result in defeat, injury or even death. In bighorn sheep, however, subordinates occasionally win a fight for a female, and they father 44% of the lambs born in the population. These sheep live in large flocks, and dominance hierarchies are often restructured each breeding season.
Burying beetle Burying beetles or sexton beetles, genus ''Nicrophorus'', are the best-known members of the family Silphidae (carrion beetles). Most of these beetles are black with red markings on the elytra (forewings). Burying beetles are true to their name ...
s, which have a social order involving one dominant male controlling most access to mates, display a behavior known as sneak copulation. While one male at a carcass has a 5:1 mating advantage, subordinate males will tempt females away from the carcass with pheromones and attempt to copulate, before the dominant male can drive them forcefully away. In
flat lizard ''Platysaurus'' is a genus of lizards, commonly known as flat lizards for their flat backs, in the family Cordylidae. Geographic range All species in the genus ''Platysaurus'' live in isolated populations in southern Africa. They are found in ...
s, young males take advantage of their underdeveloped secondary sex characteristics to engage in sneak copulations. These young males mimic all the visual signs of a female lizard in order to successfully approach a female and copulate without detection by the dominant male. This strategy does not work at close range because the chemical signals given off by the sneaky males reveal their true nature, and they are chased out by the dominant.


Costs to subordinates

Subordinate individuals suffer a range of costs from dominance hierarchies, one of the most notable being reduced access to food sources. When a resource is obtained dominant individuals are first to feed as well as taking the longest time. Subordinates also lose out in shelter and nesting sites. Brown hyenas, which display defined linear dominance in both sexes, allow subordinate males and females decreased time of feeding at a carcass. In
toque monkey The toque macaque (; ''Macaca sinica'') is a reddish-brown-coloured Old World monkey endemic to Sri Lanka, where it is known as the ''rilewa'' or ''rilawa'' ( Sinhala: රිළවා), (hence "rillow" in the ''Oxford English Dictionary''). Its n ...
s subordinates are often displaced from feeding sites by dominant males. Additionally, they are excluded from sleeping sites, and they suffer reduced growth and increased mortality. Subordinate individuals often demonstrate a huge reproductive disadvantage in dominance hierarchies. Among brown hyenas, subordinate females have less opportunity to rear young in the communal den, and thus had decreased survival of offspring when compared to high-ranking individuals. Subordinate males have far less copulations with females compared to the high-ranking males. In
African wild dogs The African wild dog (''Lycaon pictus''), also called the painted dog or Cape hunting dog, is a wild canine which is a native species to sub-Saharan Africa. It is the largest wild canine in Africa, and the only extant member of the genus '' L ...
which live in social packs separated into male and female hierarchies, top ranking alpha females have been observed to produce 76-81% of all litters.


Mitigating the costs

Subordinate animals engage in a number of behaviors in order to outweigh the costs of low rank. Dispersal is often associated with increased mortality and subordination may decrease the potential benefits of leaving the group. In the
red fox The red fox (''Vulpes vulpes'') is the largest of the true foxes and one of the most widely distributed members of the Order (biology), order Carnivora, being present across the entire Northern Hemisphere including most of North America, Europe ...
it has been shown that subordinate individuals, given the opportunity to desert, often do not due to the risk of death and the low possibility that they would establish themselves as dominant members in a new group.


Conflict over dominance

Animal decisions regarding involvement in conflict are defined by the interplay between the costs and benefits of agonistic behaviors. When initially developed,
game theory Game theory is the study of mathematical models of strategic interactions among rational agents. Myerson, Roger B. (1991). ''Game Theory: Analysis of Conflict,'' Harvard University Press, p.&nbs1 Chapter-preview links, ppvii–xi It has appli ...
, 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 A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
, 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 shrew The common shrew (''Sorex araneus''), also known as the Eurasian shrew, is the most common shrew, and one of the most common mammals, throughout Northern Europe, including Great Britain, but excluding Ireland. It is long and weighs , and has ve ...
s. 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, the 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 their 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 to 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 stag Jim Beam is an American brand of bourbon whiskey produced in Clermont, Kentucky, by Beam Suntory. It is one of the best-selling brands of bourbon in the world. Since 1795 (interrupted by Prohibition in the United States, Prohibition), seven gene ...
s, for example, engage in exhausting roaring contests to exhibit their strength. 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 sparrow The white-crowned sparrow (''Zonotrichia leucophrys'') is a species of passerine bird native to North America. A medium-sized member of the New World sparrow family, this species is marked by a grey face and black and white streaking on the uppe ...
s 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. Rank may also be acquired from maternal dominance rank. In
rhesus monkey The rhesus macaque (''Macaca mulatta''), colloquially rhesus monkey, is a species of Old World monkey. There are between six and nine recognised subspecies that are split between two groups, the Chinese-derived and the Indian-derived. Generally b ...
s, 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 The Canada goose (''Branta canadensis''), or Canadian goose, is a large wild goose with a black head and neck, white cheeks, white under its chin, and a brown body. It is native to the arctic and temperate regions of North America, and it is o ...
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.


Regulation mechanisms

Individuals with greater hierarchical status tend to displace those ranked lower from access to space, to
food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is inge ...
and to
mating In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. ''Fertilization'' is the fusion of two gametes. ''Copulation'' is the union of the sex organs of two sexually reproduc ...
opportunities. Thus, individuals with higher
social status Social status is the level of social value a person is considered to possess. More specifically, it refers to the relative level of respect, honour, assumed competence, and deference accorded to people, groups, and organizations in a society. Stat ...
tend to have greater
reproductive success Reproductive success is an individual's production of offspring per breeding event or lifetime. This is not limited by the number of offspring produced by one individual, but also the reproductive success of these offspring themselves. Reproduct ...
by mating more often and having more resources to invest in the survival of
offspring In biology, offspring are the young creation of living organisms, produced either by a single organism or, in the case of sexual reproduction, two organisms. Collective offspring may be known as a brood or progeny in a more general way. This ca ...
. Hence, hierarchy serves as an intrinsic factor for population control, ensuring adequate resources for the dominant individuals and thus preventing widespread starvation.
Territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
behavior Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...
enhances this effect.


In eusocial animals

The suppression of reproduction by dominant individuals is the most common mechanism that maintains the hierarchy. In eusocial mammals this is mainly achieved by aggressive interactions between the potential reproductive females. In eusocial insects, aggressive interactions are common determinants of reproductive status, such as in the
bumblebee A bumblebee (or bumble bee, bumble-bee, or humble-bee) is any of over 250 species in the genus ''Bombus'', part of Apidae, one of the bee families. This genus is the only extant group in the tribe Bombini, though a few extinct related gener ...
''
Bombus bifarius ''Bombus bifarius'', the two-form bumblebee, is a species of eusocial bumblebee of the subgenus ''Pyrobombus''. ''B. bifarius'' inhabits mountainous regions of western North America, primarily the states of Colorado and Utah. Its common name refe ...
'', the
paper wasp Paper wasps are Vespidae, vespid wasps that gather fibers from dead wood and plant stems, which they mix with saliva, and use to construct nests made of gray or brown papery material. Some types of paper wasps are also sometimes called umbrell ...
''
Polistes annularis ''Polistes annularis'' (''P. annularis'') is a species of paper wasp found throughout the eastern half of the United States. This species of red paper wasp is known for its large size and its red-and-black coloration and is variably referred to ...
'' and in the ants ''
Dinoponera australis ''Dinoponera australis'' is a species of ant notable for its lack of distinct queen caste. Subspecies ''Dinoponera australis'' is divided into three subspecies: * ''Dinoponera australis australis'' Emery, 1901 * ''Dinoponera australis bucki' ...
'' and '' D. quadriceps''. In general, aggressive interactions are ritualistic and involve antennation (drumming), abdomen curling and very rarely mandible bouts and stinging. The winner of the interaction may walk over the subordinated, that in turn assumes a prostrated posture. To be effective, these regulatory mechanisms must include traits that make an individual rank position readily recognizable by its nestmates. The composition of the
lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...
layer on the cuticle of social insects is the clue used by nestmates to recognize each other in the colony, and to discover each insect's reproductive status (and rank). Visual cues may also transmit the same information. Paper wasps ''
Polistes dominulus The European paper wasp (''Polistes dominula'') is one of the most common and well-known species of social wasps in the genus ''Polistes''. Its diet is more diverse than those of most ''Polistes'' species—many genera of insects versus mainly ca ...
'' have individual "facial badges" that permit them to recognize each other and to identify the status of each individual. Individuals whose badges were modified by painting were aggressively treated by their nestmates; this makes advertising a false ranking status costly, and may help to suppress such advertising. Other behaviors are involved in maintaining reproductive status in social insects. The removal of a thoracic
sclerite A sclerite (Greek , ', meaning "hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instead it refers most commonly ...
in ''
Diacamma ''Diacamma'' is a genus of queenless ants belonging to the subfamily Ponerinae. It is distributed from India to Australia and contains about 24 species. Biology A queen caste does not exist in ''Diacamma''. Unique to this genus, all workers ...
'' ants inhibits ovary development; the only reproductive individual of this naturally queenless genus is the one that retains its sclerite intact. This individual is called a
gamergate Gamergate may refer to: * Gamergate (ant), a worker ant that can store sperm and reproduce sexually * Gamergate (harassment campaign), targeting women in the video game industry * Lt. Gamergate, a character in the ''Adventure Time'' episode " Den ...
, and is responsible for mutilating all the newly emerged females, to maintain its social status. Gamergates of ''
Harpegnathos saltator ''Harpegnathos saltator'', sometimes called the Indian jumping ant or Jerdon's jumping ant, is a species of ant found in India. They have long mandibles and have the ability to leap a few inches. They are large-eyed and active predators that hu ...
'' arise from aggressive interactions, forming a hierarchy of potential reproductives. In the
honey bee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current co ...
''
Apis mellifera The western honey bee or European honey bee (''Apis mellifera'') is the most common of the 7–12 species of honey bees worldwide. The genus name ''Apis'' is Latin for "bee", and ''mellifera'' is the Latin for "honey-bearing" or "honey carrying", ...
'', a pheromone produced by the queen mandibular glands is responsible for inhibiting ovary development in the
worker caste Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping genera ...
. "
Worker policing Worker policing is a behavior seen in colonies of social hymenopterans (ants, bees, and wasps) whereby worker females eat or remove eggs that have been laid by other workers rather than those laid by a queen. Worker policing ensures that the o ...
" is an additional mechanism that prevents reproduction by workers, found in bees and ants. Policing may involve
oophagy Oophagy ( ) sometimes ovophagy, literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek (, "egg") and classical Greek (, ...
and immobilization of workers who lay eggs. In some ant species such as the
carpenter ant Carpenter ants (''Camponotus'' spp.) are large () ants indigenous to many forested parts of the world. They build nests inside wood consisting of galleries chewed out with their mandibles or jaws, preferably in dead, damp wood. However, unlik ...
''
Camponotus floridanus ''Camponotus floridanus'', or Florida carpenter ant, is a species of ant in the genus '' Camponotus''. First described as ''Formica floridana'' by Buckley in 1866, the species was moved to '' Camponotus'' by Mayr in 1886. The ant is widespread i ...
'', eggs from queens have a peculiar chemical profile that workers can distinguish from worker laid eggs. When worker-laid eggs are found, they are eaten. In some species, such as '' Pachycondyla obscuricornis'', workers may try to escape policing by shuffling their eggs within the egg pile laid by the queen.


Hormonal control

Modulation of
hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
levels after
hibernation Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most ...
may be associated with dominance hierarchies in the social order of the paper wasp (''
Polistes dominulus The European paper wasp (''Polistes dominula'') is one of the most common and well-known species of social wasps in the genus ''Polistes''. Its diet is more diverse than those of most ''Polistes'' species—many genera of insects versus mainly ca ...
''). This depends on the queen (or foundress), possibly involving specific hormones. Laboratory experiments have shown that when foundresses are injected with
juvenile hormone Juvenile hormones (JHs) are a group of acyclic sesquiterpenoids that regulate many aspects of insect physiology. The first discovery of a JH was by Vincent Wigglesworth. JHs regulate development, reproduction, diapause, and polyphenisms.The chem ...
, responsible for regulating growth and development in insects including wasps, the foundresses exhibit an increase in dominance. Further, foundresses with larger
corpora allata In insect physiology and anatomy, the corpus allatum (plural: corpora allata) is an endocrine gland that generates juvenile hormone; as such, it plays a crucial role in metamorphosis. Surgical removal of the corpora allata (an allatectomy) can cau ...
, a region of the female wasp brain responsible for the synthesis and secretion of juvenile hormone, are naturally more dominant. A follow-up experiment utilized 20-hydroxyecdysone, an
ecdysone Ecdysone is a prohormone of the major insect molting hormone 20-hydroxyecdysone, which is secreted from the prothoracic glands. It is of steroidal structure. Insect molting hormones (ecdysone and its homologues) are generally called ecdysteroids. ...
known to enhance maturation and size of
oocytes An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female g ...
. The size of the oocytes plays a significant role in establishing dominance in the paper wasp. Foundresses treated with 20-hydroxyecdysone showed increased dominance compared to those treated with juvenile hormone, so 20-hydroxyecdysone may play a larger role in establishing dominance (Roseler ''et al.'', 1984). Subsequent research however, suggests that juvenile hormone is implicated, though only on certain individuals. When injected with juvenile hormone, larger foundresses showed more mounting behaviors than smaller ones, and more oocytes in their
ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
. Naked mole-rats ('' Heterocephalus glaber'') similarly have a dominance hierarchy dependent on the highest ranking female (queen) and her ability to suppress critically important reproductive hormones in male and female sub-dominants. In sub-dominant males, it appears that
luteinizing hormone Luteinizing hormone (LH, also known as luteinising hormone, lutropin and sometimes lutrophin) is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone (GnRH) ...
and
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
are suppressed, while in females it appears that the suppression involves the entire suppression of the
ovarian cycle The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that make pregnancy possible. The ovarian cycle controls the production and release of eggs a ...
. This suppression reduces sexual
virility Virility (from the Latin ''virilitas'', manhood or virility, derived from Latin ''vir'', man) refers to any of a wide range of masculine characteristics viewed positively. Virile means "marked by strength or force". Virility is commonly associ ...
and behavior and thus redirects the sub-dominant's behavior into helping the queen with her offspring, though the mechanisms of how this is accomplished are debated. Former research suggests that
primer Primer may refer to: Arts, entertainment, and media Films * ''Primer'' (film), a 2004 feature film written and directed by Shane Carruth * ''Primer'' (video), a documentary about the funk band Living Colour Literature * Primer (textbook), a t ...
pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s secreted by the queen cause direct suppression of these vital reproductive hormones and functions however current evidence suggests that it is not the secretion of pheromones which act to suppress reproductive function but rather the queen's extremely high levels of circulating testosterone, which cause her to exert intense dominance and
aggressiveness Aggression is overt or covert, often harmful, social interaction with the intention of inflicting damage or other harm upon another individual; although it can be channeled into creative and practical outlets for some. It may occur either reacti ...
on the colony and thus "scare" the other mole-rats into submission. Research has shown that removal of the queen from the colony allows the reestablishment of reproductive function in sub-dominant individuals. To see if a priming pheromone secreted by the queen was indeed causing reproductive suppression, researchers removed the queen from the colony but did not remove her bedding. They reasoned that if a primer pheromones were on the bedding then the sub-dominant's reproductive function should continue to be suppressed. Instead however, they found that the sub-dominants quickly regained reproductive function even in the presence of the queen's bedding and thus it was concluded that primer pheromones do not seem to play a role in suppressing reproductive function.
Glucocorticoid Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every vertebr ...
s, signaling molecules which stimulate the
fight or flight response The fight-or-flight or the fight-flight-or-freeze response (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first des ...
, may be implicated in dominance hierarchies. Higher ranking individuals tend to have much higher levels of circulating glucocorticoids than
subdominant In music, the subdominant is the fourth tonal degree () of the diatonic scale. It is so called because it is the same distance ''below'' the tonic as the dominant is ''above'' the tonicin other words, the tonic is the dominant of the subdomina ...
individuals, the opposite of what had been expected. Two core hypotheses attempt to explain this. The first suggests that higher ranking individuals exert more
energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
and thus need higher levels of glucocorticoids to mobilize
glycogen Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. The polysaccharide structure represents the main storage form of glucose in the body. Glycogen functions as one o ...
for energy use. This is supported by the fact that when food availability is low,
cortisol Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone. It is produced in many animals, mainly by the ''zona fasciculata'' of the adrenal cortex in the adrenal gland ...
levels increase within the dominant male. The second suggests that elevated
stress hormones Stress hormones are secreted by endocrine glands to modify one's internal environment during times of stress. By performing various functions such as mobilizing energy sources, increasing heart rate, and downregulating metabolic processes which a ...
are a result of social factors, particularly when the hierarchy is in transition, perhaps resulting in increased aggression and confrontation. As a result, the dominant individual fights more and has elevated glucocorticoids during this period. Field studies of
olive baboon The olive baboon (''Papio anubis''), also called the Anubis baboon, is a member of the family Cercopithecidae Old World monkeys. The species is the most wide-ranging of all baboons, being native to 25 countries throughout Africa, extending fr ...
s in
Kenya ) , national_anthem = "Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...
seem to support this, as dominant individuals had lower cortisol levels in a stable hierarchy than did subdominant individuals, but the reverse was true at unstable times.


Brain pathways and hierarchy

Several areas of the brain contribute to hierarchical behavior in animals. One of the areas that has been linked with this behavior is the
prefrontal cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA46, ...
, a region involved with decision making and social behavior. High social rank in a hierarchical group of mice has been associated with increased excitability in the medial prefrontal cortex of pyramidal
neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
s, the primary excitatory cell type of the brain. High ranking macaques have a larger rostral prefrontal cortex in large social groups.
Neuroimaging Neuroimaging is the use of quantitative (computational) techniques to study the structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive manner. Incre ...
studies with computer stimulated hierarchal conditions showed increased activity in the
ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...
and dorsolateral prefrontal cortex, one processing judgment cues and the other processing status of an individual. Other studies have determined that lesions to the prefrontal cortex (when the area is severed to disrupt functioning to observe its role in behavior) led to deficits in processing social hierarchy cues, suggesting this area is important in regulating this information. Although the prefrontal cortex has been implicated, there are other downstream targets of the prefrontal cortex that have also been linked in maintaining this behavior. This includes the
amygdala The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...
through lesion studies in rats and primates which led to disruption in hierarchy, and can affect the individual negatively or positively depending on the subnuclei that is targeted. Additionally, the dorsal medial PFC-medial dorsal
thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...
connection has been linked with maintenance of rank in mice. Another area that has been associated is the
dorsal raphe nucleus The dorsal raphe nucleus is located on the midline of the brainstem and is one of the raphe nuclei. It has rostral and caudal subdivisions. * The rostral aspect of the ''dorsal'' raphe is further divided into interfascicular, ventral, ventrolatera ...
, the primary
serotonergic Serotonergic () or serotoninergic () means "pertaining to or affecting serotonin". Serotonin is a neurotransmitter. A synapse is serotonergic if it uses serotonin as its neurotransmitter. A serotonergic neuron ''produces'' serotonin. A substance is ...
nuclei (a neurotransmitter involved with many behaviors including reward and learning). In manipulation studies of this region, there were changes in fighting and affiliative behavior in primates and crustaceans.


In specific groups


Female dominance in mammals

Female-biased dominance occurs rarely in mammals. It occurs when all adult males exhibit submissive behavior to adult females in social settings. These social settings are usually related to feeding, grooming, and sleeping site priority. It is observed consistently in hyenas,
lemur Lemurs ( ) (from Latin ''lemures'' – ghosts or spirits) are Strepsirrhini, wet-nosed primates of the Superfamily (biology), superfamily Lemuroidea (), divided into 8 Family (biology), families and consisting of 15 genera and around 100 exist ...
s and the
bonobo The bonobo (; ''Pan paniscus''), also historically called the pygmy chimpanzee and less often the dwarf chimpanzee or gracile chimpanzee, is an endangered great ape and one of the two species making up the genus '' Pan,'' the other being the comm ...
. The
ring-tailed lemur The ring-tailed lemur (''Lemur catta'') is a large strepsirrhine primate and the most recognized lemur due to its long, black and white ringed tail. It belongs to Lemuridae, one of five lemur families, and is the only member of the ''Lemur'' ge ...
is observed to be the most prominent model of female dominance. There are three basic proposals for the evolution of female dominance: # The Energy Conservation Hypothesis: males subordinate to females to conserve energy for intense male-male competition experienced during very short breeding seasons # Female behavioral strategy: dominance helps females deal with the unusually high reproductive demands; they prevail in more social conflicts because they have more at stake in terms of fitness. # Male behavioral strategy: males defer as a parental investment because it ensures more resources in a harsh unpredictable climate for the female, and thus, the male's future offspring. In lemurs, no single hypothesis fully explains female social dominance at this time and all three are likely to play a role. Adult female lemurs have increased concentrations of
androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This inc ...
s when they transition from non-breeding to breeding seasons, increasing female aggression. Androgens are greater in pregnant female lemurs, which suggests that organizational androgens might influence the developing offspring. Organizational androgens play a role in "explaining female social dominance" in
ring-tailed lemur The ring-tailed lemur (''Lemur catta'') is a large strepsirrhine primate and the most recognized lemur due to its long, black and white ringed tail. It belongs to Lemuridae, one of five lemur families, and is the only member of the ''Lemur'' ge ...
s, as androgens are associated with aggressive behavior in young females. Females that were "exposed to greater concentrations of maternal ndrostenedionelate in fetal development were less likely to be aggressed against postnatally, whereas females that were...exposed to greater concentrations of maternal estosterone..were more likely to receive aggression postnatally." Dominance rank in female
chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
s is correlated with
reproductive success Reproductive success is an individual's production of offspring per breeding event or lifetime. This is not limited by the number of offspring produced by one individual, but also the reproductive success of these offspring themselves. Reproduct ...
. Although a high rank is an advantage for females, clear linear hierarchies in female chimpanzees have not been detected. In "masculinized" female mammals like the
spotted hyena The spotted hyena (''Crocuta crocuta''), also known as the laughing hyena, is a hyena species, currently classed as the sole extant member of the genus ''Crocuta'', native to sub-Saharan Africa. It is listed as being of least concern by the IUC ...
(''Crocuta crocuta''), androgens (i.e. specifically, androstenedione and testosterone) are "implicated in the organization and activation of...nonreproductive behavioral traits, including aggression, social dominance, rough-and-tumble play, and scent marking" For aggressively dominant female
meerkat MeerKAT, originally the Karoo Array Telescope, is a radio telescope consisting of 64 antennas in the Meerkat National Park, in the Northern Cape of South Africa. In 2003, South Africa submitted an expression of interest to host the Square Kilom ...
s (''Suricata suricatta''), they have "exceptionally high concentrations" of androgens, "particularly during gestation".


Birds

The concept of dominance, originally called "pecking order", was described in birds by
Thorleif Schjelderup-Ebbe Thorleif Schjelderup-Ebbe (12 November 1894 in Kristiania – 8 June 1976 in Oslo) was a Norwegian zoologist and comparative psychologist. He was the first person to describe a pecking order of hens. Career Thorleif Schjelderup-Ebbe was at the ag ...
in 1921 under the German terms ''Hackordnung'' or ''Hackliste'' and introduced into English in 1927. In his 1924 German-language article, he noted that "defense and aggression in the hen is accomplished with the
beak The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food ...
". This emphasis on pecking led many subsequent studies on fowl behaviour to use it as a primary observation; however, it has been noted that
rooster The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adult m ...
s tend to leap and use their claws in conflicts. Wild and feral chickens form relatively small groups, usually including no more than 10 to 20 individuals. It has been shown that in larger groups, which is common in farming, the dominance hierarchy becomes less stable and aggression increases. Dominance hierarchies are found in many species of bird. For example, the
blue-footed booby The blue-footed booby (''Sula nebouxii'') is a marine bird native to subtropical and tropical regions of the eastern Pacific Ocean. It is one of six species of the genus '' Sula'' – known as boobies. It is easily recognizable by its distinct ...
brood of two chicks always has a dominance hierarchy due to the asynchronous hatching of the eggs. One egg is laid four days before the other, and incubation starts immediately after laying, so the elder chick is hatched four days before the younger chick and has a four-day head start on growth. The elder, stronger chick almost always becomes the dominant chick. During times of food shortage, the dominant chick often kills the subordinate chick by either repeatedly pecking or by ousting the younger chick from the nest. The brood hierarchy makes it easier for the subordinate chick to die quietly in times of food scarcity, which provides an efficient system for booby parents to maximize their investment.


Eusocial insects

In insect societies, only one to few individuals members of a colony can reproduce, whereas the other colony members have their reproductive capabilities suppressed. This conflict over reproduction in some cases results in a dominance hierarchy. Dominant individuals in this case are known as queens and have the obvious advantage of performing reproduction and benefiting from all the tasks performed by their subordinates, the worker caste (foraging, nest maintenance, nest defense, brood care and thermal regulation). According to
Hamilton's rule Kin selection is the evolutionary strategy that favours the reproductive success of an organism's relatives, even when at a cost to the organism's own survival and reproduction. Kin altruism can look like altruistic behaviour whose evolution ...
, the reproduction costs of the worker caste are compensated by the contribution of workers to the queen's reproductive success, with which they share genes. This is true not only for the popular social insects (
ants Ants are Eusociality, eusocial insects of the Family (biology), family Formicidae and, along with the related wasps and bees, belong to the Taxonomy (biology), order Hymenoptera. Ants evolved from Vespoidea, vespoid wasp ancestors in the Creta ...
,
termites Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blattod ...
, some bees and
wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. Th ...
s), but also for the
naked mole-rat The naked mole-rat (''Heterocephalus glaber''), also known as the sand puppy, is a burrowing rodent native to the Horn of Africa and parts of Kenya, notably in Somali regions. It is closely related to the blesmols and is the only species in the ...
''Heterocephalus glaber''. In a laboratory experiment, Clarke and Faulkes (1997) demonstrated that reproductive status in a colony of ''H. glaber'' was correlated with the individual's ranking position within a dominance hierarchy, but aggression between potential reproductives only started after the queen was removed. The social insects mentioned above, excluding termites, are
haplodiploid Haplodiploidy is a sex-determination system in which males develop from unfertilized eggs and are haploid, and females develop from fertilized eggs and are diploid. Haplodiploidy is sometimes called arrhenotoky. Haplodiploidy determines the se ...
. Queen and workers are diploid, but males develop from haploid genotypes. In some species, suppression of
ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...
development is not totally achieved in the worker caste, which opens the possibility of reproduction by workers. Since nuptial flights are seasonal and workers are wingless, workers are almost always non-breeders, and (as
gamergate Gamergate may refer to: * Gamergate (ant), a worker ant that can store sperm and reproduce sexually * Gamergate (harassment campaign), targeting women in the video game industry * Lt. Gamergate, a character in the ''Adventure Time'' episode " Den ...
ants or laying worker bees) can only lay unfertilised eggs. These eggs are in general viable, developing into males. A worker that performs reproduction is considered a "cheater" within the colony, because its success in leaving descendants becomes disproportionally larger, compared to its sisters and mother. The advantage of remaining functionally sterile is only accomplished if every worker assume this "compromise". When one or more workers start reproducing, the "social contract" is destroyed and the colony cohesion is dissolved. Aggressive behavior derived from this conflict may result in the formation of hierarchies, and attempts of reproduction by workers are actively suppressed. In some wasps, such as ''
Polistes fuscatus ''Polistes fuscatus'', whose common name is the dark or northern paper wasp, is widely found in eastern North America, from southern Canada through the southern United States. It often nests around human development. However, it greatly prefers a ...
'', instead of not laying eggs, the female workers begin being able to reproduce, but once being under the presence of dominant females, the subordinate female workers can no longer reproduce. In some wasp species such as Liostenogaster flavolineata there are many possible queens that inhabit a nest, but only one can be queen at a time. When a queen dies the next queen is selected by an age-based dominance hierarchy. This is also true in the species ''
Polistes instabilis ''Polistes instabilis'', a type of paper wasp, is a neotropical, eusocial wasp (family Vespidae) that can be found in tropical and subtropical areas such as Central America and South America. It can be easily identified with its characteristic y ...
'', where the next queen is selected based on age rather than size. ''
Polistes exclamans ''Polistes exclamans'', the Guinea paper wasp, is a social wasp and is part of the family Vespidae of the order Hymenoptera. It is found throughout the United States, Mexico, the Bahamas, Jamaica and parts of Canada. Due to solitary nest foundin ...
'' also exhibits this type of hierarchy. Within the dominance hierarchies of the ''
Polistes versicolor ''Polistes versicolor'', also known as the variegated paper wasp or yellow paper wasp, is a subtropical social wasp within ''Polistes'', the most common genus of paper wasp. It is the most widely distributed of South American wasp species and is ...
'', however, the dominant-subordinate context in the yellow paper wasps is directly related to the exchange of food. Future foundresses within the nest compete over the shared resources of nourishment, such as protein. Unequal nourishment is often what leads to the size differences that result in dominant-subordinate position rankings. Therefore, if during the winter aggregate, the female is able to obtain greater access to food, the female could thus reach a dominant position. In some species, especially in ants, more than one queen can be found in the same colony, a condition called
polygyny Polygyny (; from Neoclassical Greek πολυγυνία (); ) is the most common and accepted form of polygamy around the world, entailing the marriage of a man with several women. Incidence Polygyny is more widespread in Africa than in any o ...
. In this case, another advantage of maintaining a hierarchy is to prolong the colony lifespan. The top ranked individuals may die or lose fertility and "extra queens" may benefit from starting a colony in the same site or nest. This advantage is critical in some ecological contexts, such as in situations where nesting sites are limited or dispersal of individuals is risky due to high rates of predation. This polygynous behavior has also been observed in some eusocial bees such as ''
Schwarziana quadripunctata ''Schwarziana quadripunctata'' is a small, stingless bee found in a stretch of the South American Amazon from Goiás, Brazil, through Paraguay, to Misiones, Argentina.Michener, C.D. (2007). ''The Bees of the World''. Baltimore: Johns Hopkins Uni ...
''. In this species, multiple queens of varying sizes are present. The larger,
physogastric Physogastrism or physogastry is a characteristic of certain arthropods (mostly insects and mites), where the abdomen is greatly enlarged and membranous. The most common examples are the "queens" of certain species of eusocial insects such as termi ...
, queens typically control the nest, though a "dwarf" queen will take its place in the case of a premature death.


Variations


Spectrum of social systems

Dominance hierarchies emerge as a result of
intersexual Intersex people are individuals born with any of several Sexual characteristics, sex characteristics including chromosome patterns, gonads, or sex organ, genitals that, according to the Office of the United Nations High Commissioner for Hum ...
and intrasexual selection within groups, where competition between individuals results in differential access to resources and mating opportunities. This can be mapped across a spectrum of social organization ranging from egalitarian to despotic, varying across multiple dimensions of cooperation and competition in between. Conflict can be resolved in multiple ways, including aggression, tolerance, and avoidance. These are produced by social decision-making, described in the "relational model" created by the zoologist
Frans De Waal Franciscus Bernardus Maria "Frans" de Waal (born October 29, 1948) is a Dutch primatologist and ethologist. He is the Charles Howard Candler Professor of Primate Behavior in the Department of Psychology at Emory University in Atlanta, Georgia, ...
. In systems where competition between and within the sexes is low, social behaviour gravitates towards tolerance and egalitarianism, such as that found in woolley spider monkeys. In despotic systems where competition is high, one or two members are dominant while all other members of the living group are equally submissive, as seen in Japanese and rhesus macaques,
leopard geckos ''Eublepharis'' is a genus of terrestrial geckos native to eastern and southwestern Asia. The genus was first described by the British zoologist John Edward Gray in 1827. The etymology of their name is 'eu' = good (=true) , 'blephar' = eyelid, a ...
, dwarf hamsters,
gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...
s, the cichlid ''
Neolamprologus pulcher ''Neolamprologus pulcher'' is a species of cichlid endemic to Lake Tanganyika where it prefers locations with plenty of sedimentation. The common name for ''N. pulcher'' is the daffodil cichlid. This species can reach a length of TL. It can ...
'', and
African wild dog The African wild dog (''Lycaon pictus''), also called the painted dog or Cape hunting dog, is a wild canine which is a native species to sub-Saharan Africa. It is the largest wild canine in Africa, and the only extant member of the genus '' Ly ...
. Linear ranking systems, or "pecking orders", which tend to fall in between egalitarianism and despotism, follow a structure where every member of the group is recognized as either dominant or submissive relative to every other member. This results in a linear distribution of rank, as seen in
spotted hyena The spotted hyena (''Crocuta crocuta''), also known as the laughing hyena, is a hyena species, currently classed as the sole extant member of the genus ''Crocuta'', native to sub-Saharan Africa. It is listed as being of least concern by the IUC ...
s and brown hyenas.


Context dependency

Dominance and its organisation can be highly variable depending on the context or individuals involved. In
European badgers The European badger (''Meles meles''), also known as the Eurasian badger, is a badger species in the family Mustelidae native to almost all of Europe. It is classified as least concern on the IUCN Red List as it has a wide range and a large stabl ...
, dominance relationships may vary with time as individuals age, gain or lose social status, or change their reproductive condition. Dominance may also vary across space in
territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
animals as territory owners are often dominant over all others in their own territory but submissive elsewhere, or dependent on the resource. Even with these factors held constant, perfect dominance hierarchies are rarely found in groups of any great size, at least in the wild. Dominance hierarchies in small herds of domestic horses are generally linear hierarchies whereas in large herds the relationships are triangular. Dominance hierarchies can be formed at a very early age.
Domestic pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus s ...
lets are highly
precocious Precocious refers to earlier-than-normal development, as in a "precocious child". The term may also refer to: Films *''A Precocious Girl'' (German title: ''Csibi, der Fratz aka Früchtchen''), a 1934 Austrian comedy film *'' Precocious Youth'' (G ...
and within minutes of being born, or sometimes seconds, will attempt to suckle. The piglets are born with sharp teeth and fight to develop a teat order as the anterior teats produce a greater quantity of milk. Once established, this teat order remains stable with each piglet tending to feed from a particular teat or group of teats. Dominance–subordination relationships can vary markedly between breeds of the same species. Studies on
Merino The Merino is a breed or group of breeds of domestic sheep, characterised by very fine soft wool. It was established in Spain near the end of the Middle Ages, and was for several centuries kept as a strict Spanish monopoly; exports of the bree ...
s and Border Leicesters sheep revealed an almost linear hierarchy in the Merinos but a less rigid structure in the Border Leicesters when a competitive feeding situation was created.


Species with egalitarian/non-linear hierarchies

Although many group-living animal species have a hierarchy of some form, some species have more fluid and flexible social groupings, where rank does not need to be rigidly enforced, and low-ranking group members may enjoy a wider degree of social flexibility. Some animal societies are "democratic", with low-ranking group members being able to influence which group member is leader and which one is not. Sometimes dominant animals must maintain alliances with subordinates and grant them favours to receive their support in order to retain their dominant rank. In chimpanzees, the alpha male may need to tolerate lower-ranking group members hovering near fertile females or taking portions of his meals. Other examples can include Muriqui monkeys. Within their groups, there is abundant food and females will mate promiscuously. Because of this, males gain very little in fighting over females who are, in turn, too large and strong for males to monopolize or control, so males do not appear to form especially prominent ranks between them, with several males mating with the same female in view of each other. This type of mating style is also present in manatees, removing their need to engage in serious fighting. Among female elephants, leadership roles are not acquired by sheer brute force, but instead through seniority, and other females can collectively show preferences for where the herd can travel. In hamadryas baboons, several high-ranking males will share a similar rank, with no single male being an absolute leader. Female bats also have a somewhat fluid social structure, in which rank is not strongly enforced. Bonobos are matriarchal, yet their social groups are also generally quite flexible, and serious aggression is quite rare between them. In olive baboons, certain animals are dominant in certain contexts, but not in others. Prime age male olive baboons claim feeding priority, yet baboons of any age or sex can initiate and govern the group's collective movements.


See also

*
Sociobiology Sociobiology is a field of biology that aims to examine and explain social behavior in terms of evolution. It draws from disciplines including psychology, ethology, anthropology, evolution, zoology, archaeology, and population genetics. Within t ...
*
Sociality Sociality is the degree to which individuals in an animal population tend to associate in social groups (gregariousness) and form cooperative societies. Sociality is a survival response to evolutionary pressures. For example, when a mother wasp ...


References


Further reading


Theme issue of Philosophical Transactions B
on 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies' (2022) {{DEFAULTSORT:Dominance Hierarchy Ethology Hierarchy