53 Cooperative Behaviour

Key Idea: Cooperative behaviour is where two or more individuals work together to achieve a common goal. It increases the probability of survival for all individuals involved. Cooperative behaviour involves behaviour in which two or more individuals work together to achieve a common goal such as defence, food acquisition, or rearing young. Examples include hunting as a team (e.g. wolf packs, chimpanzee hunts), responding to the actions of others with the same goal (e.g. migrating mammals), or acting to benefit others (e.g. mobbing in small birds). Cooperation occurs most often between members of the same species. 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 genes onto the next generation).

Coordinated behavior is used by many social animals for the purpose of both attack (group hunting) and defense. Cooperation improves the likelihood of a successful outcome, e.g. a successful kill. Animals may move en masse in a coordinated way and with a common goal, as in the mass migrations of large herbivores. Risks to the individual are reduced by the group behavior. Kin selection is altruistic behavior 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.

Evidence of cooperation between species

Many small birds species will cooperate to attack a larger predatory species, such as a hawk, and drive it off. This behaviour is called mobbing. It is accompanied by mobbing calls, which can communicate the presence of a predator to other vulnerable species, which benefit from and will become involved in the mobbing.

One example is the black-capped chickadee, a species that often forms mixed flocks with other species. When its mobbing calls in response to a screech owl were played back, at least ten other species of small bird were attracted to the area and displayed various degrees of mobbing behaviour. The interspecific communication helps to coordinate the community anti-predator mobbing behaviour.

1. (a) What is altruism?

(b) Why would altruism be more common when individuals are related?

2. How do cooperative interactions enhance the survival of both individuals and the group they are part of?

3. What evidence is there that unrelated species can act cooperatively? Why would they do this?

Are honeybees 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

Workers: female diploid The queen's daughters will share identical genes from the father and will share half the genes from the queen. Drone: male haploid

Kin selection explains the behaviour

` honeybee 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 care-giving behaviour of sisters will increase faster than genes promoting investment in offspring.

Honeypot ants

Honeypot ants of central Australia have a special group of workers called 'repletes'. These never leave the nest, but stay in underground galleries where they serve as vessels for storing a rich food supply. Regular workers that have been foraging for honeydew and nectar return to the nest 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 (normally it is the size of a grain of rice). The repletes become so swollen that their movements are restricted to clinging to the gallery 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, coaxing them to regurgitate droplets of honey.

Greg Hume at en.wikipedia CC 2.5

4. (a) How does kin selection account for the evolution of apparently altruistic behaviour?

(b) Do you think such behaviour is truly self sacrificing? Explain:

5. How are honeypot ant repletes an extreme form of cooperation?