Dominant strategy in repeated games on networks

TL;DR

This paper introduces a new strategy, CSDT, for repeated games on networks that can dominate other strategies by balancing cooperation and tolerated defection, with its effectiveness influenced by network structure and dynamics.

Contribution

The paper proposes the CSDT strategy that dominates others in networked populations and explores how network structure and the inclusion of ALLD influence its evolution.

Findings

CSDT can dominate other strategies in networked populations.

Tolerance limits of CSDT vary with network and game parameters.

Including ALLD enhances CSDT evolution and suppresses vulnerable strategies.

Abstract

Direct reciprocity, stemming from repeated interactions among players, is one of the fundamental mechanisms for understanding the evolution of cooperation. However, canonical strategies for the repeated prisoner's dilemma, such as Win-Stay-Lose-Shift and Tit-for-Tat, fail to consistently dominate alternative strategies during evolution. This complexity intensifies with the introduction of spatial structure or network behind individual interactions, where nodes represent players and edges represent their interactions. Here, we propose a new strategy, ``Cooperate-Stay-Defect-Tolerate" (CSDT), which can dominate other strategies within networked populations by adhering to three essential characteristics. This strategy maintains current behaviour when the opponent cooperates and tolerates defection to a limited extent when the opponent defects. We demonstrate that the limit of tolerance of CSDT can vary with the network structure, evolutionary dynamics, and game payoffs. Furthermore, we find that incorporating the Always Defect strategy (ALLD) can enhance the evolution of CSDT and eliminate strategies that are vulnerable to defection in the population, providing a new interpretation of the role of ALLD in direct reciprocity. Our findings offer a novel perspective on how cooperative strategy evolves on networked populations.