Concept 18: Communication & Social Organisation
Success Criteria & Vocabulary
Click this drop-down menu to see the Success Criteria.
Describe agonistic behaviour as a consequence of intraspecific competition.
Explain the role of hierarchies, territories, and home ranges in allocating resources and reducing aggression.
Describe reproductive behaviours (courtship, mating systems, parental care, and pair bonding) and explain their adaptive advantage.
Click this drop-down menu to see the list of Vocabulary.
Behaviour: An organism's interactive response to its environment.
Gene: Section of DNA that codes for a protein a
Concept 18: Support Notes
Communication is the transmission of understood information between individuals, usually of the same species. It is essential to species survival and reproductive success. Effective communication enables animals to avoid predators, coordinate FORAGING and hunting activity, maintain social behaviours, and attract mates. Messages can be passed between animals using a range of signals that may be visual, chemical, auditory, or tactile. The type of signal used depends on the activity pattern and habitat of the animals, e.g. sound carries well in a dense forest.
Many animals convey information to other members of the species through body coverings and adornment, as well as through gestures and body language. Visual displays can signal threat, show submission, attract a mate, and even exert control over a social group.
Many animals are bioluminsecent. The glow they produce can be used as a signal to others of their species, such as fireflies signalling to a mate. Some deep sea fish use bioluminescence to signal other fish in the school.
Some =animals produce a stunning visual display to attract a mate. The plumage of some birds can be extremely colourful and elaborate, such as the peacock, the birds of paradise, and the lyrebird.
Some animals produce scents that are carried by the wind. Scientists may advertise for a mate or warn neighbouring competitors to keep out of a territory. IN some cases, mammals use their urine and faeces to mark territorial boundaries. Sniffing genitals is common among mammals.
Sound may be used to communicate over great distances. Birds keep rivals away and advertise for mates with song. Fin whales send messages over thousands of kilometres of ocean. Calls by mammals may attract mates, keep in touch with group members or warn away competitors.
Body position or facial expression
Social species with DOMINANCE HIERARCHIES (e.g. wolves) use facial expressions to communicate.
Touch may be a part of a cooperative or an aggressive interaction. Grooming behaviour between members of a primate group communicates social bonding. Vibrations sent along a web by a male spider signal to a potential mate not to eat him.
Animals may be solitary, form loosely associated groups, or form complex groups with clear social structures. Each behaviour has advantages and disadvantages.
No animal lives completely alone. At some stage in their lives, all animals must interact with others of their species (e.g. to reproduce or through competitive interactions for food or resources). Generally, animals are classed as being solitary, in unstructured social groups, or in structured social groups.
Solitary animals spend the majority of their lives alone, often in defended territories. They may only seek out others of their own species for breeding. Offspring are often driven away shortly after they become independent.
Solitary life is often an advantage when resources are scarce or scattered over a large area. Solitary animals include many of the cat family (e.g. tiger, bears, and various invertebrates).
Unstructured social groups
Many animals form loose associations but do not interact socially. Each animal is acting for its own benefit with little or no direct cooperation between them. Schools of fish, flocks of birds, and some herding animals exhibit this unstructured social grouping.
Unstructured social groups provide protection from predators by reducing the possibility of being preyed upon individually. There may also be benefits during feeding and moving.
Structured social groups
Some species form complex social structures often based around a family group. Some involve DOMINANCE HIERARCHIES in which individuals in the group are ranked socially.
Dominance hierarchies help distribute resources and maintain social structure. In some species (e.g. ants and bees), group members are divided in to castes with specific roles. Some produce offspring or help raise young, others may be workers or help with defending the colony.
Advantages of large social groupings
Protection from adverse physical factors and predators.
Assembly for mate selection
Locating and obtaining food.
Defence of resources against other groups.
Division of labour amongst specialist.
Richer learning environment.
Population regulation (e.g. breeding restricted to a dominant pair).
Possible disadvantages of large social groupings
Increased competition for resources between group members as group size increases.
Increased chance of the spread of disease and parasites.
Interference with reproduction, e.g. infanticide by non-parents or cheating in parental care (as in BROOD PARASITES) so that non-parents may unknowingly raise another's offspring.
In social groups, members of the group interact regularly. Social species organise themselves in a way that divides resources and roles between group members. All behaviour has its roots in an individual's underlying genetic programme, but these INNATE BEHAVIOURS are often modified by learning through experience (LEARNED BEHAVIOURS), particularly social interactions. The behavioural adaptations of organisms contribute to their fitness (survival and successful reproduction) and so are the products of NATURAL SELECTION.
Many animals live in cooperative groups for all or part of their lives. Structured social species are those where individuals live together in an organised fashion and can be divided into EUSOCIAL and PRESOCIAL GROUPS. Social groups divide resources and activities between them, and are mutually dependent on each other.
EUSOCIAL animals are those which a single female produces the offspring and non-reproductive individuals care for the young.
They have the highest form of social organisation. Individuals are divided into different castes with specific roles. In most cases, a queen produces all the young and members of the group are normally directly related to the queen.
Non-reproductive members of the group may be involved in care of the young, FORAGING, or defense of the nest site. Examples include ants, honey bees, termites, and naked mole rats.
PRESOCIAL live in large groups based around a single breeding pair and relatives (e.g. aunts/older siblings) may help raise the young.
These groups often form HIERARCHIES where the breeding pair are the most dominant. There may also be separate hierarchies for male and female group members. Examples include canine species that live in packs (e.g. wolves), many primates, and some birds.
The number of males in a social group varies between species. In equines (horses), a single stallion controls a group of mares. young males are driven away when they are old enough. In elephants, the group is led by a matriarch, and the herd relies on her to make decisions in a crisis.
Concept 19: Cooperative Behaviours within Social Groups
COOPERATIVE behaviour is where two or more individuals work together to achieve a common goal such as defence, FORAGING, or rearing young. By working together, members of a group increase each other's chances of survival. However, the level of help depends on the level of relatedness.
Types of cooperative behaviour include:
Working together in defence decreases individual risk and increases the chances of a successful defence. Group defence is a key strategy for survival in social or herding mammals. Forming groups during an attack by a predator decreases the chances of being singled out, while increasing the chances of a successful defence.
Group defence in Musk Oxen
Musk oxen must find novel ways to protect themselves from predators. There is often no natural cover, so they must make their own barrier in the form of a defensive circle.
When wolves (their most common predator) attack, they shield the young inside the circle. Lone animals have little chance of surviving an attack as wolves hunt in packs.
Red Colobus Monkey Defence
Red colobus monkeys are a common target during chimpanzee hunts. They counter these attacks by fleeing (especially females with young), hiding, or mounting a group defence.
The group defence is usually the job of the males and the more defenders there are, the greater the likelihood of the defence being successful.
Group attack is often used for hunting for food, but may be used by some species for raiding nests or territories in order to gain access to new resources (e.g. space or workers).
Group attacks may be highly organised with individuals taking specific roles. Working together in attack can help increase the chance of success especially if roles are allocated between the attacking members.
The Gombe Chimpanzee War
Group attacks between members of the same species and even the same social groups do occur. They usually involve disputes over resources or territory, but may be due simply to rifts in social groups.
One of the most well recorded and startling examples of group fighting is the Gombe Chimpanzee War. Observed by Jane Goodall, the violence began in 1974, after a split in a group of chimpanzees in the Gombe Stream National Park, in Tanzania. The group divided into two, the Kasakela in the northern part of the former territory and the Kahama in the south.
Over the course of four years, the Kasakela systematically destroyed the Kahama, killing all six makes and one female, and kidnapping three more females. The Kasakela then took over the Kahama territory.
However, ironically, the territorial gains made by the Kasakela were quickly lost as their new territory bordered a larger more powerful group of chimpanzees, the Kalande. After a few violent skirmishes along this border, the Kasakela were pushed back into their former territory.
Cooperating to gather food can be much more efficient than finding it alone. It increases the chances of finding food or capturing prey. Cooperative hunting will evolve in a species if there is a sustained benefit to the participants, the benefit for a single hunter is less than that of the benefit of hunting in a group, and cooperation within the group is guaranteed.
Example in Ants
Cooperative foraging in ants often involves division of labour. Leaf-cutter ants harvest parts of leaves and use them to cultivate a fungus, which they eat. Workers that tend the fungus gardens have smaller heads than foragers, which cut and transport the leaves. Similarly, army ants have several
Example in Honey Bees
Honeybees forage for nectar, gathering it from flowers and taking it back to the nest. If a particularly good nectar source is found, the bee will perform one of two dances when it returns to the nest. If the source is distant, the bee performs the waggle dance. If the food source is very close (less than 50 m) the honeybee will perform a round dance. The honeybees dances simulate other workers to leave the hive and search for a food source.
Altruism & Kin Selection
ALTRUISM is an extreme form of cooperative behaviour in which one individual disadvantages itself for the benefit of another. Altruism is often seen in highly social animal groups. Most often the individual who is disadvantaged receives benefit in some non-material form (e.g. increased probability of passing on genes onto the next generation).
Altruism in Honeypot Ants
Honeypot ants of central Ausralia have a special group of workers called 'repletes'. These never leave the nest, but stay in underground galleries where they seve as vessels for storing a rich food supply.
Regular workers that have been foraging for honeydew and nectar return to the next where they regurgitate food from their crops to feed the replete. The replete will continue to accept these offerings until its abdomen has swollen to the size of a pea. The repletes become so swollen that their movements are restricted to clinging to the ceiling where many hundreds of them hang in a row.
When the dry season arrives and food supplies become scarce, workers return to the repletes, stimulating them to regurgitate droplets of honey.
Altruism in Gunnison's Prairie Dogs
Gunnison's prairie dogs live in large communities called towns in the grasslands of western Norther America. The towns are divided into territories which may have up to 20 individuals in them. During foraging, above-ground individuals may produce alarm calls if a predator approaches, at which nearby prairie dogs will move to cover. However, whether or not an alarm call is given depends on the relatedness of the individuals receiving the call to the individual giving it. Gunnison's prairie dogs put themselves at risk when giving an alarm call by attracting the attention of the predator.
KIN SELECTION is altruistic behaviour towards relatives. In meerkats, individuals from earlier litters remain in the colony to care for new pups instead of breeding themselves. They help more often when more closely related.
Are honey bees altruistic?
Each female worker in the colony:
Sacrifices her life to defend the colony against danger.
Produces no eggs.
Raises the young of the queen.
Kin selection explains the behaviour:
Honey been males (drones) are haploid and females are diploid.
Workers therefore all have the same male genes and half the queen's genes.
Workers are more closely related to each other than they would be to their own daughters.
Therefore, caregiving behaviour of sisters will increase faster than genes promoting investment in offspring.
Black-backed jackals live in the brushland of Africa.
Monogamous pairs (single male and female parents) hunt cooperatively, share food and defend territories.
Offspring from the previous year's litter frequently help rear their siblings by regurgitating food for the lactating mother and for the pups themselves.
Concept 20: Intraspecific Competition
Aggression is a complex phenomenon often associated with competition for resources, but it also includes predatory behaviour. Agonistic behaviour is a more precise term, which refers specifically to conflict situations between members of the same species.
AGONISTIC BEHAVIOUR includes all aspects of conflict, such as threats, submissions, chases, and physical combat, but it excludes predatory aggression. Agonistic behaviour is usually highly ritualised so that it is not easily misinterpreted. The ritualisation has an important role in reducing the risk of physical conflict and injury.
Aggression can occur between different species when they are competing for the same resources. For example, agression can be seen when vultures are competing with hyenas for a carcass.
Many primates and birds form DOMINANCE HIERARCHIES established by agonistic behaviour. Once the hierarchy is in place, little effort is required to maintain order in the group.
Disputes between zebra stallions can get serious. The fighting is less ritualised than in many species and the force of the kick from the hind legs can cause serious injury. Face to face fighting may also result in serious bite injuries.
INTRASPECIFIC COMPETITION is a form of competition in which individuals of the same species compete for the same resource.
Consequence: Scramble Competition & Contest Competition
In SCRAMBLE COMPETITION, all individuals in the population have equal access to a limited resource and many individuals may starve. This limits population growth and can tightly constrain the life cycle events of some species.
Social Hierarchy and Contest Competition
In social groups, access to resources may be determined by the social HIERARCHY.
The most dominant individuals have priority access to food, but low ranked individuals must contest the remainder and may miss out or may be forced to leave the group.
Consequence: Dominance Hierarchies
Hierarchies in Pukekos
Hierarchies in social birds can be determined by identifying the winners and losers in conflict situations.
In contrast to most other bird species which form mating pairs, pukeko cooperate as a group with coordinated activities. More than two birds will defend territory, court and mate, lay in, incubate and defend a single nest, and feed and care for chicks. Most social animals establish a strict ranking order or hierarchy (sometimes called a pecking order) to reduce fighting between group members.
During activities such as feeding, some pukeko in close contact situations may avoid contact by taking food a short distance away from the others before eating. Other members of the group (the winners), chase away losers that come too close. In any encounter between two birds there is a winner and a loser.
The social organisation of a stable group is dependent on the fact that these birds act at all times in accordance with their status. Chicks are initiated into the hierarchy at a very early age.
Hierarchies in Baboons
Baboons have a highly developed social structure with a dominance hierarchy.
Dominance hierarchies are most commonly seen in males, who are not related and aggressively compete over higher positions and access to females.
Females also have hierarchies but these are often based on mother-daughter relationships.
Once established, hierarchies are usually maintained by gestures, facial expressions (e.g. yawning to show canine teeth), and ritual aggression. Fighting usually occurs when one male wishes to increase his status and rise in the hierarchy.
Olive baboons (Papio anubis) live in the savannah regions of Africa and have a highly organised and complex social structure. Within a troop of baboons, an orderly hierarchy promotes division of labour within the group, reduces conflict, and maximises the efficiency with which the group can serach for food and defend itself against predators and other troops.
The adult males are distinguished by their large size and well developed manes. Females with babies are positioned near the centre for protection. The two females in oestrus move in consort with the most dominant males. All males (with the exception of the dominant males) tend to be positioned on the edges of the group. Should any threat be encountered in their march, the dominant males will move to the front, with the subordinate males in support. The females, adolescents, and babies move to the rear, away from the threat.
Consequence: Territories, Home Ranges, & Leks
A TERRITORY is the area occupied by an animal and defended against intruders. Territories may be large and multi-purpose for feeding, mating, and rearing young, or they may be small and for a single purpose, e.g. mating grounds called LEKS.
Blue duck pairs occupy and defend exclusive territories in the same stretch of river year after year.
Territory size depends on many factors including resource availability, the social behaviour of the animal, and the energy expended to defend it.
Gannet territories consist of the nest and the area immediately around the nest. The home range consists of the ocean covered when searching for food.
A LEK is an aggregation of males engaging in competitive displays. Males defend their lek territories, which are usually established seasonally.
Females select males based on their display or position of the lek. Highly ranked males occupy the middle of the group with lower ranked individuals on the periphery.
Benefits/advantages of territorial behaviour:
Protection in numbers
Mates can be easily found
Young survive more easily
More parental care
Natural selection (strongest birds have better defended territories, raise stronger offspring).
Decreased aggression in group
Costs/disadvantages of territorial behaviour:
Large investment of energy to gain and maintain a territory
Intraspecific competition (Between different cooperative groups of the same species)
Some individuals may not be able to gain/maintain territory therefore not breed
Small nesting sites and close proximity to other animals can spread diseases.
Benefits must outweigh costs
HOME RANGES are usually much larger than territories. They are not defended and may overlap with the home ranges of other members of the species. This means that even solitary animals can remain in contact with others. The size of a home range depends on the resource density. Home ranges are larger when resources are scarce.
Behaviours associated with breeding, such as COURTSHIP and territorial behaviours, are adaptations to ensure reproductive success. Breeding pairs often establish territories to ensure reliable access to resources during breeding, while ritualised courtship behaviours reduce conflict between the sexes so that mating is achieved without injury.
Do females choose mates?
Mate choice (or intersexual selection) occurs where members of one biolgical sex choose mates of the other sex to mate with. Where there is mate choice, one sex competes with same-sex members and the other sex chooses. This competition often involves elaborate rituals, calls, and displays to the choosing sex.
Females usually are more invested in offspring so their mate choice is important and they are often the choosy sex. Female preference for certain features, e.g. eyes on peacocks tail, is thought to be behind the elaborate structures and displays that have evolved in many species (e.g. peafowl).
Courtship refers to the behaviour of animals just before, during, and just after mating. Courtship is a way for both male and female to evaluate the health, strength, and potential fitness of a possible mate.
A potential mate may initially be attracted by a call (e.g. male frog calling). The caller may then perform a more intricate display once the responder arrives. In other cases, the male's call and display may be the same performance.
Sometimes the male may attract a mate by offering a git of food. This is relatively common in insects, such as empid flies.
Female empid flies are aggressive hunters, so males have to be careful about how they approach them.
Ritualised courtship behaviour by the male helps him to be accepted by the female as a mate. The male's gift of food for the female pacifies her during mating and is a crucial component of mating success.
In birds, song is an important mechanism for attracting a mate and proclaiming ownership of a territory. The song also acts as a reproductive isolating mechanism, as differences between the songs of two species enables individuals to recognize their own species and mate only with them.
Kakapo are a LEK species and males attempt to attract a mate to their lek (breeding territory) by producing a low frequency booming sound during the breeding season that can be heard over many kilometres of forest. When a female arrives the male begins a display which he spreads his wings and rocks side to side.
Although courtship rituals may be complex, they are very stereotyped and not easily misinterpreted. Males display, usually through exaggerated physical posturing, and the females then select their mates.
Many birds like albatrosses, form life-long bonds and renew these every year by displaying to each other when they arrive at breeding grounds.
Reproductive Strategies: R and K Selection, & Parental Care
The way in which an animal allocates its reproductive effort is part of its reproductive strategy. Effort can be expended in producing offspring or caring for them or both. Different strategies carry different costs and benefits.
R-SELECTED species produces many offspring and invests in very little to no parental care.
K-SELECTED species produces few offspring and invests a significant amount of parental care.
At one extreme, most invertebrates expend their total reproductive effort in producing eggs and sperm and there is no parental care. At the other extreme, mammals invest heavily in a small number of offspring and the parental cost is substantial. Between this continuum, with some animals adopting alternative strategies, such as brood parasitism. No strategy is necessarily 'better' than any other. They are different solutions to the problem of successful reproduction.
Little or no parental care
Large number of offspring produced.
Reproductive effort per offspring is low.
Little or no parental care of offspring.
Reproductive effort is put into producing the offspring, not parental care.
Examples: most fish, amphibians, reptiles, and invertebrates.
Many invertebrates allocate their reproductive effort to producing offspring and there is no parental care.
Broadcast spawners such as clams and corals, release millions of gametes into the water. Very few of the larvae will survive.
This is the most common reproductive strategy in the oceans and is typical of most marine invertebrates and many fish.
Many amphibians are also broadcast spawners although there are many exceptions, including New Zealand's native frogs in which the males carry the offspring on their backs.
Reproductive effort per offspring is high.
Moderate to substantial care of offspring.
Large reproductive effort put into raising offspring to a less vulnerable stage.
Examples: most birds and mammals, some fish.
Both mammals and birds are well known for their high levels of parental investment.
Other vertebrates, such as some amphibians, fish, and reptiles also provide care until the offspring are capable of fending for themselves.
Bird parents are required to incubate their eggs in next and then feed the chicks until they are independent.
Although most mammals give birth to well developed offspring, they are dependent on their mother for nourishment via suckling milk, as well as learning behaviours essential to their survival.
Moderate number of offspring.
Reproductive effort per offspring is moderate to low.
Rely on others to raise young.
Risk of egg loss is mitigated by distributing eggs amongst a number of hosts.
Examples: some birds, insects, and fish.
Brood parasitism is adopted by some birds, notably cuckoos and cowbirds. The brood parasite removes an egg from the nest of a host species and lays one of its own in its place.
To reduce of eggs being discovered and destroyed, the eggs are spread around a large number of hosts.
Most bird brood parasites have short incubation times, so the egg hatches before those of the host and the imposter will eliminate all or most of the host's eggs/nestlings. The host then raises the parasite chick as if it were its own, even when the chick is larger and differs in appearance.
The strategy is not without risk - only about half of the parasite's young survive.
Reproductive Strategy: Mating System
A mating system describes which males mate with which females, under which circumstances. Different mating systems offer different reproductive advantages to the individuals involved and are determined in part by the social structure of the species. Each particular mating system is usually associated with a certain pattern of parental care and is closely tied to the resources available for breeding.
The significance of reproductive investment
Producing offspring demands enormous amounts of energy and risk. In many vertebrate species, reproductive is almost entirely up to the female (males contributing only sperm) but in other species, the male also provides support (e.g. by defending a territory or providing food for the female).
Because the female is most heavily invested in the offspring, it is important that she has the best possible reproductive outcome each time she mates, and the mate choice is critical. In general, females have a limited reproductive and can only produce so many eggs or offspring in a lifetime. For example, a human female produces one egg a month for about 40 years, a maximum of ~480 eggs in a lifetime. Given that gestation and breastfeeding (which suppresses ovulation) may take two years, only about 20 children can be raised in the average lifetime.
Males on the other hand, have less investment in offspring. They produce sperm continuously and put no direct energy into the offspring until at least birth or egg laying. Potentially, males could fertilise unlimited numbers of females and so produce far more young without any additional effort.
These differences in reproductive investment have been important in the evolution of mating systems, e.g. monogamy, with animals adopting strategies that maximise reproductive success in their particular physical and social environment.
In kaka, both parents are needed to successfully rear the chicks. Monogamy is a common mating system, when biparental care is needed for offspring survival.