WikiFindings

Conflicts between animals may be decided by which is bigger, but also by some ‘convention’, such as who found a resource first, that enables animals to avoid fighting too much

Background

Natural selection will have made animals that make choices that maximise their fitness. Animals often must decide whether to contest a resource (such as food) with another individual, which often involves a risk of injury or death. Biologists use game theory to predict choices when the best choice depends on what others are doing. Many potential contests are ‘asymmetric’, meaning that the individual differ in how valuable the resource is, how strong or well-armed they are, or which found the resource first. These different asymmetries lead to different predictions about what animals should do when we find the ‘evolutionarily stable strategy’ (ESS). A population of individuals using the ESS cannot be 'invaded' by an initially rare mutant adopting any other strategy.

Findings

In a situation where one individual finds a resource first, the difference between them has no effect on fighting ability. However, if fighting is costly, then we expect a convention to evolve where prior ownership is respected. The situation may change if the owner has more to lose than the newcomer has to gain, but the behaviour of animals should be the same. In a situation where the individuals differ in size or fighting ability, the smaller should always back down if the risk of injury is high, but fight if it is small. This convention should be used even if size doesn’t mean the outcome is certain; there is always more fights in the future so individuals should save themselves.

Implications

In a situation where one individual finds a resource first, the difference between them has no effect on fighting ability. However, if fighting is costly, then we expect a convention to evolve where prior ownership is respected. The situation may change if the owner has more to lose than the newcomer has to gain, but the behaviour of animals should be the same. In a situation where the individuals differ in size or fighting ability, the smaller should always back down if the risk of injury is high, but fight if it is small. This convention should be used even if size doesn’t mean the outcome is certain; there is always more fights in the future so individuals should save themselves.