58 Conflict in Social Groups

Key Idea: Aggressive behaviour encompasses conflict over resources as well as predatory behaviour. Agonistic behaviour specifically refers to non-predatory competitive behaviour between conspecifics (individuals of the same species). 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. In the photograph above, vultures are competing with hyaenas for a carcass.

Lions live in small prides of related females and one or two males. The dominant male's position may be challenged by nomadic males. Such challenges involve serious fighting with the winner displacing the loser from the pride. Fighting between social groups (e.g chimpanzee troops) can be extremely serious, even fatal. The fighting is usually over the defence or invasion of territories and resources.

DoC

Hooker’s (New Zealand) sea lion forms breeding colonies on several sub-Antarctic islands. A bull will set up a territory on one of the breeding beaches, defend it against challenges from other bulls, and attract females as mates to the site.

1. Distinguish between aggressive behaviour and agonistic behaviour:

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.

2. Describe how the following behaviours reduce the risk of injury to individuals in a population:

(a) Dominance hierarchies:

(b) Ritual aggression:

Briefly describe the adaptive advantage of each of the types of aggression in the table in the column provided.

4. Explain why, in social species, aggression between conspecific groups (e.g. one group invading another's territory) is often less ritualised and more inclined to lead to injury than aggression between individuals within the same social group.

5. Infanticide occurs in lions and Indian langur monkeys, and involves killing all the infants sired by other males.

(a) Describe the conditions under which this behaviour would occur:

(b) Explain the adaptive value of this behaviour in terms of natural selection:

Type of aggression Description

Territorial

Dominance

Sexual

Parental Exclusion of others (usually of the same species) from some physical space.

Control of the behaviour of another member of the same species.

Threats and physical abuse of rivals, usually by males, to obtain or retain mates.

Attacks on intruders when the young are present and threatened.

Parent/offspring Disciplinary action by parent against offspring (mammals).

Predatory Act of predation, possibly including cannibalism.

Adaptive advantage

Anti-predatory Defensive attack by prey on predator.

Sibling Attack by one sibling on another to exclude them from the litter/nest.

Competitive Attack on a competitor to drive it away from a resource such as food.