Evolution of cooperation on networks under continuous removal and addition of nodes

The robustness of cooperation clusters formed on complex networks has been intensively studied. In this paper, we numerically investigate the robustness of cooperation in prisoner´s dilemma played on scale-free networks, where the network topologies are changed by continuous removal and addition of nodes. Each of removal and addition can be either random or intentional. We therefore have four different strategies in changing network topology: random removal and random addition (RR), random removal and preferential addition (RP), targeted removal and random addition (TR), and targeted removal and preferential addition (TP). We found that cooperation clusters are most fragile against TR, while they are most robust even in high temptation coefficients for defect against RP. These results imply that the robustness of cooperation clusters increases in accordance with increasing the number of cooperating hubs and that a huge variety of individuals is needed to maintain global cooperation in a social network in the real world where each individual represented by a node constantly comes and leaves.