Coordination in a skeptical two-group population

Journal of Economic Interaction and Coordination - This paper explores a situation in which a population split into two groups attempts to achieve the socially efficient outcome of a coordination...     

A public good model with lotteries in large groups

We analyze the effect of a large group on a public goods model with lotteries. We show that as populations get large, and with preferences in which people only care about their private consumptions and the total supply of the public good, the level of contributions converges to the one given by voluntary contributions. With altruistic preferences of the warm-glow type, the contributions converge to a level strictly higher than those given by voluntary contributions, but in general they do not yield first-best levels. Our results are important to clarify why in general governments do not rely on lotteries for a large part of the revenue creation for public good provision. They are also useful to understand why lottery proceeds are earmarked to worthy causes, where warm glow is likely to be larger.     

Heterogeneity in the resistance to learning

In this paper we analyze the effect of heterogeneity in the recently introduced “resistance to learning” (Jiménez et al. in Eur Phys J B 71:273–280, 2009a). In the context of the spatial Continuous Prisoner’s Dilemma, the resistance to learning has become a key mechanism for the emergence and maintenance of cooperation in a wide range of cost regimes. We extend the model to the case in which different individuals may have different levels of resistance. From non-cooperative initial states, the existence of heterogeneity in the resistance affects the cooperative behavior of unconditional imitators. These unconditional imitators, i.e., fast learners or individuals without resistance can achieve due to their interactions with gradual learners significant levels of cooperation. Our results confirm in one of its form the impact of heterogeneity and its role as a fundamental mechanism in promoting the emergence of cooperation.     

The shared reward dilemma on structured populations

In this paper we study the recently introduced “shared reward dilemma” (Cuesta et al. in J Theor Biol 251:253–263, 2008) in the presence of a structure governing the interactions among the population. The shared reward dilemma arises when the prisoner’s dilemma is supplemented with a second stage in which a fixed reward is equally distributed among all cooperators. We first extend our previous results on the equilibrium structure of this game to the case of a one-shot game taking place on a regular network. Subsequently, we consider an evolutionary version of the game on both lattices and random networks. We show that the evolutionary game on graphs exhibits important differences with the case of well-mixed populations. In particular, there exists an important parameter range in which the cooperation is boosted and a single cooperator can invade a population of defectors. We study the dependence of the cooperation levels on the neighborhood size, finding that on random networks the level of cooperation reached decreases as the neighborhood size increases. Moreover, square lattices favor cooperation more than random networks, and on them cooperation may be almost full for certain parameter regions even for large neighborhood sizes. Further, we show that the effect of the population structure is never detrimental for cooperation. We interpret our results in terms of weak versus strong temptation and discuss the nontrivial issues involved in trying to promote cooperation exogenously by means of such a reward mechanism.