Dominance hierarchy
Encyclopedia
A dominance hierarchy is the organization of individuals in a group that occurs when competition for resources leads to aggression. Schjelderup-Ebbe, who studied the often-cited example of the pecking order
in chickens, found that such social structures lead to more stable flocks with reduced aggression among individuals.
Dominance hierarchies can be despotic or linear
. In a despotic hierarchy, only one individual is dominant, while the others are all equally submissive. In a linear hierarchy, for example, in the above cited pecking order
of chickens, each individual dominates all individuals below him and not those above him.
Dominance hierarchies
occur in most social animal species that normally live in groups, including primates. Dominance hierarchies have been extensively studied in fish
, birds, and mammals. Dominance hierarchies can be simple linear structures, which often arise from the physical differences among individuals in a group in relation to their access to resources. They are also influenced by the complex social interactions among individuals in the group.
), in isolation, until a hierarchy can be deduced. The process of deducing the hierarchy involves the construction of a dominance matrix, in which wins/ties are expressed in relation to each member of the group.
Recently, it has been postulated that paired interactions alone can not account for the emergence of dominance hierarchies. This is because in nature, such paired interactions rarely occur in isolation. Thus, a relatively new concept has now emerged in animal behavior: the study of socially embedded dyads. Such phenomena as the audience effect
, the context-dependent audience effect in Betta fish (Betta splendens), the observer effect, and the winner-loser effect, may play important roles in the formation of dominance hierarchies in social groups. Furthermore, it has been argued that the social group forms a complex signaling network: interactions that occur among just two individuals of the group are in turn affected by other signals transmitted by individuals in direct communication with them. In many animals, these putative signals can include postural changes, as well as changes in “state” (such as color changes).
Individuals with greater hierarchical status tend to displace those ranked lower from access to space, to food
and to mating
opportunities. Thus, individuals with higher social status
tend to have greater reproductive success
by mating more often and having more resources to invest in the survival of offspring
.
Hence it serves as an intrinsic factor for population control, insuring adequate resources for the dominant individuals and thus preventing widespread starvation. Territorial
behavior
enhances this effect.
These hierarchies are not fixed and depend on any number of changing factors, among them are age
, gender
, body size, intelligence, and aggressiveness.For instance, in linear hierarchies the top ranked individual (“alpha”) is usually replaced by its direct subordinate (“beta”), that assume its role in the group and gain the same benefits. In eusocial species, decrease of fertility is among the main reasons for ranking displacement.
, 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 to the popular social insects (ants, termites, some bees and wasps), but also for the naked mole rat
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.
Social insects above mentioned, excluding termites, are haplodiploidy. Queen and workers are diploid, but males develop from haploid genotypes. In some species, suppression of ovary
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 usually virgin and only able to lay eggs that are not inseminated. These eggs are in general viable, developing into males. A worker that perform 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 species, especially in ants, more than one queen can be found in the same colony, a condition called Polygyny. 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 of 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.
Bombus bifarius, the paper wasp
Polistes annularis
and in the ants Dinoponera australis
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 on the substrate. This stereotyped behavior
is common in social insects, especially within ponerine ants
, and was also observed in interactions of naked mole rats.
In order 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 layer present on the cuticle of social insects is usually the clue used by nestmates to recognize each other in the colony and to access information regarding the reproductive status of each one (and therefore its rank in the hierarchy). However, another recent finding suggest that visual cues may also transmit the same information. The paper wasp Polistes dominulus have individual facial marks ("facial badges") that permit them to recognize each other and to identify the hierarchy/reproductive status of each individual. Individuals that have their badges modified by painting were aggressively treated by their nestmates, suggesting that advertising a false ranking status is a costly behavior and it is suppressed in these wasps.
In addition, other behaviors have been demonstrated to be involved in the maintenance of reproductive status in social insects. The removal of a thoracic sclerite
in Diacamma ants inhibit ovary development and the only reproductive individual of this naturally queenless genus is the one that retains its sclerite intact. This individual is called gamergate and is responsible for mutilating all the newly emerged females, to maintain its social status. Gamergates of Harpegnathos saltator arise from aggressive interactions, forming a hierarchy of potential reproductives.
In the honey bee
Apis mellifera, pheromone produced by the queen mandibular glands is responsible for inhibiting ovary development in the worker caste. “Worker policing” is an additional mechanism that prevents reproduction by workers, found in bees and ants. Policing may involve oophagy and immobilization of egg-layers from the worker caste. In some ant species such as the carpenter ant Camponotus floridanus, 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.
s, lemur
s and the bonobo
. 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.
There are three basic proposals for the evolution of female dominance:
Since these original proposals, scientists like Peter Kappeler have modified and integrated other ideas. However, in the case of lemurs, there is no single hypothesis that can fully explain female social dominance
at this time and all three are likely to play a role.
, tribe
or clan
, work organizations, politics
, etc. in normal and abnormal social situations. It is not clear how much of dominance hierarchy in humans is due to the intrinsic biology
of our brains, derived from evolution
, and how much is due to cultural
factors.
Pecking order
Pecking order or just peck order is the colloquial term for a hierarchical system of social organization in chickens. It was first described from the behaviour of poultry by Thorleif Schjelderup-Ebbe in 1921 under the German terms Hackordnung or Hackliste' ...
in chickens, found that such social structures lead to more stable flocks with reduced aggression among individuals.
Dominance hierarchies can be despotic or linear
Linear
In mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...
. In a despotic hierarchy, only one individual is dominant, while the others are all equally submissive. In a linear hierarchy, for example, in the above cited pecking order
Pecking order
Pecking order or just peck order is the colloquial term for a hierarchical system of social organization in chickens. It was first described from the behaviour of poultry by Thorleif Schjelderup-Ebbe in 1921 under the German terms Hackordnung or Hackliste' ...
of chickens, each individual dominates all individuals below him and not those above him.
Dominance hierarchies
Hierarchy
A hierarchy is an arrangement of items in which the items are represented as being "above," "below," or "at the same level as" one another...
occur in most social animal species that normally live in groups, including primates. Dominance hierarchies have been extensively studied in fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, birds, and mammals. Dominance hierarchies can be simple linear structures, which often arise from the physical differences among individuals in a group in relation to their access to resources. They are also influenced by the complex social interactions among individuals in the group.
Mechanisms that regulate the formation of hierarchies in animals
The most basic interaction that establishes a Dominance Hierarchy is the dyad, or paired interaction among individuals. To study the formation of hierarchies, scientists have often used the dyadic method, in which two individuals are forced to interact isolated from others. All individuals in the group are paired with each other (i.e. a round-robinRound-robin tournament
A round-robin tournament is a competition "in which each contestant meets all other contestants in turn".-Terminology:...
), in isolation, until a hierarchy can be deduced. The process of deducing the hierarchy involves the construction of a dominance matrix, in which wins/ties are expressed in relation to each member of the group.
Recently, it has been postulated that paired interactions alone can not account for the emergence of dominance hierarchies. This is because in nature, such paired interactions rarely occur in isolation. Thus, a relatively new concept has now emerged in animal behavior: the study of socially embedded dyads. Such phenomena as the audience effect
Audience effect
The audience effect is the impact that a passive audience has on a subject performing a task. It was first formally noted in various psychology studies in the early 20th century...
, the context-dependent audience effect in Betta fish (Betta splendens), the observer effect, and the winner-loser effect, may play important roles in the formation of dominance hierarchies in social groups. Furthermore, it has been argued that the social group forms a complex signaling network: interactions that occur among just two individuals of the group are in turn affected by other signals transmitted by individuals in direct communication with them. In many animals, these putative signals can include postural changes, as well as changes in “state” (such as color changes).
Individuals with greater hierarchical status tend to displace those ranked lower from access to space, to food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
and to mating
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
opportunities. Thus, individuals with higher social status
Social status
In sociology or anthropology, social status is the honor or prestige attached to one's position in society . It may also refer to a rank or position that one holds in a group, for example son or daughter, playmate, pupil, etc....
tend to have greater reproductive success
Reproductive success
Reproductive success is defined as the passing of genes onto the next generation in a way that they too can pass those genes on. In practice, this is often a tally of the number of offspring produced by an individual. A more correct definition, which incorporates inclusive fitness, is the...
by mating more often and having more resources to invest in the survival of offspring
Offspring
In biology, offspring is the product of reproduction, of a new organism produced by one or more parents.Collective offspring may be known as a brood or progeny in a more general way...
.
Hence it serves as an intrinsic factor for population control, insuring adequate resources for the dominant individuals and thus preventing widespread starvation. Territorial
Territory (animal)
In ethology the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics...
behavior
Ethology
Ethology is the scientific study of animal behavior, and a sub-topic of zoology....
enhances this effect.
These hierarchies are not fixed and depend on any number of changing factors, among them are age
Ageing
Ageing or aging is the accumulation of changes in a person over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline...
, gender
Gender
Gender is a range of characteristics used to distinguish between males and females, particularly in the cases of men and women and the masculine and feminine attributes assigned to them. Depending on the context, the discriminating characteristics vary from sex to social role to gender identity...
, body size, intelligence, and aggressiveness.For instance, in linear hierarchies the top ranked individual (“alpha”) is usually replaced by its direct subordinate (“beta”), that assume its role in the group and gain the same benefits. In eusocial species, decrease of fertility is among the main reasons for ranking displacement.
Dominance hierarchies in 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 result 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). Accordingly to Hamilton’s ruleKin selection
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...
, 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 to the popular social insects (ants, termites, some bees and wasps), but also for the naked mole rat
Naked Mole Rat
The naked mole rat , also known as the sand puppy or desert mole rat, is a burrowing rodent native to parts of East Africa and the only species currently classified in the genus Heterocephalus...
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.
Social insects above mentioned, excluding termites, are haplodiploidy. Queen and workers are diploid, but males develop from haploid genotypes. In some species, suppression of ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
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 usually virgin and only able to lay eggs that are not inseminated. These eggs are in general viable, developing into males. A worker that perform 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 species, especially in ants, more than one queen can be found in the same colony, a condition called Polygyny. 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 of 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.
Regulatory mechanisms in eusocial organisms
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 between sexuals are common determinants of reproductive status, such as in the bumblebeeBumblebee
A bumble bee is any member of the bee genus Bombus, in the family Apidae. There are over 250 known species, existing primarily in the Northern Hemisphere although they are common in New Zealand and in the Australian state of Tasmania.Bumble bees are social insects that are characterised by black...
Bombus bifarius, the paper wasp
Paper wasp
Paper wasps are -long wasps that gather fibers from dead wood and plant stems, which they mix with saliva, and use to construct water-resistant nests made of gray or brown papery material...
Polistes annularis
Polistes annularis
Polistes annularis is a species of paper wasp which lives in North America.-Description:Unusually for a North American Polistes, P. annularis shows little sexual dimorphism in coloration. It resembles Polistes metricus, which differs from P. annularis in a number of ways, including the coloration...
and in the ants Dinoponera australis
Dinoponera australis
Dinoponera australis is a species of ant notable for its lack of distinct queen caste. Studies have shown that fat storage in this species is related to the division of labour in the colony and non-reproductive indiviuals are characterized with a lower lipid count than reproductives....
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 on the substrate. This stereotyped behavior
Stereotypy
A stereotypy is a repetitive or ritualistic movement, posture, or utterance, found in people with mental retardation, autism spectrum disorders, tardive dyskinesia and stereotypic movement disorder. Stereotypies may be simple movements such as body rocking, or complex, such as self-caressing,...
is common in social insects, especially within ponerine ants
Ponerinae
Ponerinae is a subfamily of ants in the Poneromorph subfamilies group, with about 1,600 species in 28 extant genera, including Dinoponera gigantea - one of the world's largest species of ant....
, and was also observed in interactions of naked mole rats.
In order 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 layer present on the cuticle of social insects is usually the clue used by nestmates to recognize each other in the colony and to access information regarding the reproductive status of each one (and therefore its rank in the hierarchy). However, another recent finding suggest that visual cues may also transmit the same information. The paper wasp Polistes dominulus have individual facial marks ("facial badges") that permit them to recognize each other and to identify the hierarchy/reproductive status of each individual. Individuals that have their badges modified by painting were aggressively treated by their nestmates, suggesting that advertising a false ranking status is a costly behavior and it is suppressed in these wasps.
In addition, other behaviors have been demonstrated to be involved in the maintenance of reproductive status in social insects. The removal of a thoracic sclerite
Sclerite
A sclerite is a hardened body part. The term is used in various branches of biology for various structures including hardened portions of sponges, but it is most commonly used for the hardened portions of arthropod exoskeletons....
in Diacamma ants inhibit ovary development and the only reproductive individual of this naturally queenless genus is the one that retains its sclerite intact. This individual is called gamergate and is responsible for mutilating all the newly emerged females, to maintain its social status. Gamergates of Harpegnathos saltator arise from aggressive interactions, forming a hierarchy of potential reproductives.
In the honey bee
Honey bee
Honey bees are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis...
Apis mellifera, pheromone produced by the queen mandibular glands is responsible for inhibiting ovary development in the worker caste. “Worker policing” is an additional mechanism that prevents reproduction by workers, found in bees and ants. Policing may involve oophagy and immobilization of egg-layers from the worker caste. In some ant species such as the carpenter ant Camponotus floridanus, 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.
Female dominance in mammals
Female-biased dominance occurs rarely in mammals, and it is only observed consistently in hyenaHyena
Hyenas or Hyaenas are the animals of the family Hyaenidae of suborder feliforms of the Carnivora. It is the fourth smallest biological family in the Carnivora , and one of the smallest in the mammalia...
s, lemur
Lemur
Lemurs are a clade of strepsirrhine primates endemic to the island of Madagascar. They are named after the lemures of Roman mythology due to the ghostly vocalizations, reflective eyes, and the nocturnal habits of some species...
s and the bonobo
Bonobo
The bonobo , Pan paniscus, previously called the pygmy chimpanzee and less often, the dwarf or gracile chimpanzee, is a great ape and one of the two species making up the genus Pan. The other species in genus Pan is Pan troglodytes, or the common chimpanzee...
. 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.
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
- 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.
- 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.
Since these original proposals, scientists like Peter Kappeler have modified and integrated other ideas. However, in the case of lemurs, there is no single hypothesis that can fully explain female social dominance
Social dominance orientation
Social dominance orientation is a personality trait which predicts social and political attitudes, and is a widely used Social Psychological scale. SDO is conceptualised as a measure of individual differences in levels of group-based discrimination and domination; that is, it is a measure of an...
at this time and all three are likely to play a role.
Humans
Dominance hierarchies, though often more subtle, can be observed in human societies and are important for understanding the organization of familyFamily
In human context, a family is a group of people affiliated by consanguinity, affinity, or co-residence. In most societies it is the principal institution for the socialization of children...
, tribe
Tribe
A tribe, viewed historically or developmentally, consists of a social group existing before the development of, or outside of, states.Many anthropologists use the term tribal society to refer to societies organized largely on the basis of kinship, especially corporate descent groups .Some theorists...
or clan
Clan
A clan is a group of people united by actual or perceived kinship and descent. Even if lineage details are unknown, clan members may be organized around a founding member or apical ancestor. The kinship-based bonds may be symbolical, whereby the clan shares a "stipulated" common ancestor that is a...
, work organizations, politics
Politics
Politics is a process by which groups of people make collective decisions. The term is generally applied to the art or science of running governmental or state affairs, including behavior within civil governments, but also applies to institutions, fields, and special interest groups such as the...
, etc. in normal and abnormal social situations. It is not clear how much of dominance hierarchy in humans is due to the intrinsic biology
Nature versus nurture
The nature versus nurture debate concerns the relative importance of an individual's innate qualities versus personal experiences The nature versus nurture debate concerns the relative importance of an individual's innate qualities ("nature," i.e. nativism, or innatism) versus personal experiences...
of our brains, derived from evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
, and how much is due to cultural
Culture
Culture is a term that has many different inter-related meanings. For example, in 1952, Alfred Kroeber and Clyde Kluckhohn compiled a list of 164 definitions of "culture" in Culture: A Critical Review of Concepts and Definitions...
factors.
See also
- SociobiologySociobiologySociobiology is a field of scientific study which is based on the assumption that social behavior has resulted from evolution and attempts to explain and examine social behavior within that context. Often considered a branch of biology and sociology, it also draws from ethology, anthropology,...
- Social organization
- HypergamyHypergamyHypergamy is the act or practice of seeking a spouse of higher socioeconomic status, or caste status than oneself....
- Hierarchical organizationHierarchical organizationA hierarchical organization is an organizational structure where every entity in the organization, except one, is subordinate to a single other entity. This arrangement is a form of a hierarchy. In an organization, the hierarchy usually consists of a singular/group of power at the top with...
- Evolution of intelligence
- Pecking orderPecking orderPecking order or just peck order is the colloquial term for a hierarchical system of social organization in chickens. It was first described from the behaviour of poultry by Thorleif Schjelderup-Ebbe in 1921 under the German terms Hackordnung or Hackliste' ...
Books with this theme
- Lord of the FliesLord of the FliesLord of the Flies is a novel by Nobel Prize-winning author William Golding about a group of British boys stuck on a deserted island who try to govern themselves, with disastrous results...
by William GoldingWilliam GoldingSir William Gerald Golding was a British novelist, poet, playwright and Nobel Prize for Literature laureate, best known for his novel Lord of the Flies... - Life of PiLife of PiLife of Pi is a fantasy adventure novel by Yann Martel published in 2001. The protagonist, Piscine Molitor "Pi" Patel, an Indian boy from Pondicherry, explores issues of spirituality and practicality from an early age...
by Yann MartelYann MartelYann Martel is a Canadian author best known for the Man Booker Prize-winning novel Life of Pi.-Early life:Martel was born in Salamanca, Spain where his father was posted as a diplomat for the Canadian government. He was raised in Costa Rica, France, Mexico, and Canada...