Resolution of evolutionary conflicts: costly behaviours enforce the evolution of cost-free competition

A resolution model for evolutionary conflicts of interest is proposed. We a ssume that two conflicting parties originally have different evolutionarily stable strategies (ESS) with respect to a continuous variable, but that on ly one value of the variable is simultaneously possible. Individuals from t he two parties meet in antagonistic encounters. The side that invests more in the antagonistic behaviours mediating the conflict is able to adjust the variable in its preferred direction. It is shown that the extent of the co nflict - that is, the difference between the ESS values of the parties - de creases with increases in investment to antagonistic behaviours. The precon dition for this is that the total conflict cost increases with the intensit y and frequency of the antagonistic encounters, and that these factors in t urn are related to how much the variable is adjusted. The conflict costs th en result in a change of ESS level that forces the stronger party to alter its preferred level of the conflict variable. Behaviours that give control in the conflict escalate in an 'arms race', which eventually leads to a com promise solution with one ESS shared by the parties and with a small or no realized cost of conflict behaviour. This result contrasts with the traditi onal view of evolutionary conflicts, that expressed costs of antagonistic b ehaviours are necessary for evolutionarily stable resolutions. The model is applied to sexual conflicts, where a stable resolution may result in which apparent conflict behaviours are suppressed, although both parties are rea dy to engage in costly conflicts. In an explicit model of the compromise re solution of a parent-offspring conflict over parental investment, we demons trate that the conflict may be resolved so that offspring do not beg. At th e solution, parents provide an amount of care intermediate between the orig inal ESS level of the parents and offspring, and the new parental and offsp ring ESS levels are identical.