Promotion of cooperation with loyalty-based reward in the spatial prisoner's dilemma game

Memory and reward have been proved as effective mechanisms for maintaining cooperation among selfish individuals. In this article, this study proposes a reward mechanism based on historical loyalty, that is, an individual who adhere to the cooperation strategy for a period of time will get additional reward. Accordingly, the reward for a loyal cooperator is undertaken by neighboring defectors equally. The results on prisoner's dilemma game show that, with appropriate loyalty threshold and reward factors, the cooperation level can be greatly enhanced. In addition, the time evolution of cooperator density and the spatial distribution of cooperators and defectors are also studied. © 2020