Beyond replicator dynamics: From frequency to density dependent models of evolutionary games

• Published in: Journal of theoretical biology 2018-10, Vol.455, p.232-248
• Main Authors: Křivan, Vlastimil, Galanthay, Theodore E., Cressman, Ross
• Format: Article
• Language: English
• Subjects: Contest competition; Evolutionary game theory; Exploitative competition; Hawk–Dove game; Pair formation; Population dynamics
• ISSN: 0022-5193; 1095-8541
• DOI: 10.1016/j.jtbi.2018.07.003

Highlights•A new approach to the theory of two-player symmetric evolutionary games where pairs are formed by the mass action principle is developed.•This theory explicitly considers the duration of interactions between the two players and their status as singles between interactions.•When applied to the Hawk–Dove game, this theory shows that Hawks and Doves can coexist in two different states when interaction times between two Hawks are long enough.•We show how interaction times between pairs and the existence of singles lead to density dependence in game dynamics (e.g., the replicator dynamics) that are density independent otherwise.•The ms shows the link between frequency dependent dynamics of evolutionary game theory and density dependent models of population dynamics. Game theoretic models of evolution such as the Hawk–Dove game assume that individuals gain fitness (which is a proxy of the per capita population growth rate) in pair-wise contests only. These models assume that the equilibrium distribution of phenotypes involved (e.g., Hawks and Doves) in the population is given by the Hardy–Weinberg law, which is based on instantaneous, random pair formation. On the other hand, models of population dynamics do not consider pairs, newborns are produced by singles, and interactions between phenotypes or species are described by the mass action principle. This article links game theoretic and population approaches. It shows that combining distribution dynamics with population dynamics can lead to stable coexistence of Hawk and Dove population numbers in models that do not assume a priori that fitness is negative density dependent. Our analysis shows clearly that the interior Nash equilibrium of the Hawk and Dove model depends both on population size and on interaction times between different phenotypes in the population. This raises the question of the applicability of classic evolutionary game theory that requires all interactions take the same amount of time and that all single individuals have the same payoff per unit of time, to real populations. Furthermore, by separating individual fitness into birth and death effects on singles and pairs, it is shown that stable coexistence in these models depends on the time-scale of the distribution dynamics relative to the population dynamics. When explicit density-dependent fitness is included through competition over a limited resource, the combined dynamics of the Hawk–Dove model often lead to Dove extinction