WikiFindings

An evolutionary model suggests animals consider the proportion of fighters to decide whether to fight, because like in reality (but unlike in simple models) territory owners win

Background

One common feature of animal contests is that the owners of territories are more likely to win contest. This competitive asset is called the prior residence effect. Why are owners more likely to win fights than the intruders? We can study animal contests with hawk-dove games where two individuals have access to one territory, and can either fight (play “hawk”) or submit (play “dove”). Standard studies do not represent nature accurately because they find a paradoxical solution: intruders fight and owners let them take their territory. One major factor that influences one’s decisions is the behaviour of others. Yet, in the simple hawk-dove game, we assume outcomes do not change as a function of the frequency at which different strategies are expressed in the population. In nature, as more individuals play dove, playing hawk may become better, so a feedback of the environment influences which strategies individuals use.

Findings

The model aims to explain the prior-residence effect. It does not assume the cost and value of fighting (for instance) are constant. Instead, these parameters change in the population in function of the frequency of individuals who choose to fight: more frequent fights decrease the value of the territory, because it is more likely to be usurped. The model predicts the prior-residence effect when fighting is risky. The owner is not assumed to be more likely to win, and animals cannot assess the fighting abilities of others, yet the residents are more aggressive. An asymmetry of strategies emerges. So even if animals are not able to assess others’ resource holding potential, the first resident (‘the owner’) is more likely to win. Animals adjust their decisions to fight or not in function of the frequency of fights in the population.

Implications

This model shows it is possible to obtain predictions that match observations when we do not assume all the costs and benefits of the behaviour from the start. When the benefit changes, individuals modify their behaviour. The authors suggest that this asymmetry in the propensity to fight between owner and intruder occurs even without differences in fighting abilities. We still need to test if the convention of resident winning is caused by frequency-dependence. Applying this method to other models might reap interesting insights in other questions of animal behaviour and evolutionary biology.