Effects of group size and noise on cooperation in population evolution of dynamic groups

Abstract: In a large population, the agents temporally form group of the Public Goods Game (PGG) one after another, and size of one group is randomly distributed at $g\in [g_l,g_h]$. Players in it have two strategies to be chosen to cooperate, or to defect for playing the PGG. Based on this structure we investigate the evolution of cooperation in PGG as a function of the noise level underlying strategy adoptions with the group size distribution. In the process of the evolution, the payoffs of cooperators(defectors) have related to the strategy selection implemented by the death-birth process. With a smaller group size $g$, different noise value $K$ induces different dynamic behavior with the increase of multiplication factor $r$. These cooperative behavior can be analytically solved. For a greater group size $g$, the system finally evolve to the bistable state(AllC and hybrid state with cooperators and defectors)starting from different initial concentrations of cooperation. The numerical computation also fit well with the simulation results. We focus on the bistable phenomenon in the equilibrium for a given value of $K$ and a greater group size when the intrusion of one C(D)-player into D(C)-population is investigated from upwards(downwards) branch after experiencing a unstable cooperative evolution. Here, the hysteresis phenomenon can be observed. Further, when one D-player invades into the C-population, the critical value $r_c$ can be obtained in the simulation and the mathematical relationship between the critical value $r_c$ and noise $K$ is analysed.