Preservation of the value of rice paddy fields: Investigating how to prevent farmers from abandoning the fields by means of evolutionary game theory.

The evolution of group cooperation is still an evolutionary puzzle and has been studied from the perspective of not only evolutionary ecology but also social sciences. Some socio-ecological problems are caused by collapse of group cooperation. By applying theoretical studies about the evolution of cooperation, we can elucidate what causes the problems and find solutions. One of the appropriate examples is maintaining rice paddy field landscapes, which are a grand spectacle in Asia, and some are UNESCO world heritage sites. These magnificent landscapes and the associated biodiversity are at risk of abandonment for social and financial reasons. Rice paddy fields can be preserved not only by regular cultivation, which requires farmers to invest effort in cultivation, but also by the maintenance of common facilities such as irrigation canals. To investigate how this landscape might be preserved, we developed an agent-based model in which each farmer makes two types of efforts: an effort for land cultivation and an effort for collective action such as common facility maintenance. Additionally, we consider the side effects of rice production such as field deterioration from abandonment and water use competition. These factors determine the utility of each player who imitates the level of efforts necessary to invest in land cultivation and common facility maintenance of one with higher utility. This decision-making of each player can be described by the evolutionary game theory. We find that maintenance effort promotes cultivation effort, but not vice versa, even though we usually consider that each farmer's cultivation effort makes rice field landscape sustainable. We also find that if players and their near neighbors are responsible for maintaining their common facilities together, they continue to maintain them and cultivate, but if all players are responsible for maintaining all facilities in the whole farmland, players are likely to quit facility maintenance and stop cultivation. Competition for water use among all players, however, promotes cultivation more than competition among neighbors only. Therefore, rice paddy field landscapes can be sustainable if neighbors, but not the whole players, are responsible for maintaining their common facilities and cooperate together, and if the water usage of all players, but not neighbors, influences the productivity of each rice field.

Social evolution leads to persistent corruption.

Cooperation can be sustained by institutions that punish free-riders. Such institutions, however, tend to be subverted by corruption if they are not closely watched. Monitoring can uphold the enforcement of binding agreements ensuring cooperation, but this usually comes at a price. The temptation to skip monitoring and take the institution's integrity for granted leads to outbreaks of corruption and the breakdown of cooperation. We model the corresponding mechanism by means of evolutionary game theory, using analytical methods and numerical simulations, and find that it leads to sustained or damped oscillations. The results confirm the view that corruption is endemic and transparency a major factor in reducing it.

The Persistence of a Local Dialect When a National Standard Language is Present: An Evolutionary Dynamics Model of Cultural Diversity.

In recent decades, cultural diversity loss has been a growing issue, which can be analyzed mathematically through the use of the formalism of the theory of cultural evolution. We here study the evolutionary dynamics of dialects in order to find the key processes for mitigating the loss of language diversity. We define dialects as different speech systems of the same language which are mutually intelligible. Specifically, we focus on the survival of a local dialect when competing against a national standard language, with the latter giving an advantage in occupational and economic contexts. We assume individuals may use different dialects, in response to two different situations: they may use the national language in a formal workplace, while they may use a local dialect in family or close friend meetings. We consider the choice of a dialect is guided by two forces: (1) differential attractiveness of the local/standard language and (2) willingness to speak the same dialect (conformity factor) inside a private group. We found that the evolutionary outcome critically depends on how conformity works. Conformity enhances the effect of differential attractiveness between the local dialect and the standard language if conformity works favoring only those states in which all speakers use the same dialect (unanimity pressure model), but conformity has no effect at all if it works in proportion to the fraction among peers (peer pressure model).

Exploiting a cognitive bias promotes cooperation in social dilemma experiments.

The decoy effect is a cognitive bias documented in behavioural economics by which the presence of a third, (partly) inferior choice causes a significant shift in people's preference for other items. Here, we performed an experiment with human volunteers who played a variant of the repeated prisoner's dilemma game in which the standard options of "cooperate" and "defect" are supplemented with a new, decoy option, "reward". We show that although volunteers rarely chose the decoy option, its availability sparks a significant increase in overall cooperativeness and improves the likelihood of success for cooperative individuals in this game. The presence of the decoy increased willingness of volunteers to cooperate in the first step of each game, leading to subsequent propagation of such willingness by (noisy) tit-for-tat. Our study thus points to decoys as a means to elicit voluntary prosocial action across a spectrum of collective endeavours.

Games of corruption in preventing the overuse of common-pool resources.

Maintaining human cooperation in the context of common-pool resource management is extremely important because otherwise we risk overuse and corruption. To analyse the interplay between economic and ecological factors leading to corruption, we couple the resource dynamics and the evolutionary dynamics of strategic decision making into a powerful analytical framework. The traits of this framework are: (i) an arbitrary number of harvesters share the responsibility to sustainably exploit a specific part of an ecosystem, (ii) harvesters face three strategic choices for exploiting the resource, (iii) a delegated enforcement system is available if called upon, (iv) enforcers are either honest or corrupt, and (v) the resource abundance reflects the choice of harvesting strategies. The resulting dynamical system is bistable; depending on the initial conditions, it evolves either to cooperative (sustainable exploitation) or defecting (overexploitation) equilibria. Using the domain of attraction to cooperative equilibria as an indicator of successful management, we find that the more resilient the resource (as implied by a high growth rate), the more likely the dominance of corruption which, in turn, suppresses the cooperative outcome. A qualitatively similar result arises when slow resource dynamics relative to the dynamics of decision making mask the benefit of cooperation. We discuss the implications of these results in the context of managing common-pool resources.

Cultural evolution of hinoeuma superstition controlling human mate choice: The role of half-believer.

In this study, we used a cultural dynamic model to explain the persistence of the hinoeuma superstition in traditional Japan. Men with this superstition avoid marrying women born in a hinoeuma year (or hinoeuma-women). Parents avoided childbirth during the last hinoeuma year out of the concern that their daughter would have trouble finding a husband in the future, and this resulted in a large drop in the number of babies born in 1966. A previous theoretical analysis of the hinoeuma superstition considered two alternative cultural factors: believers and nonbelievers. In the present study, we considered a third cultural factor, the half-believer. A man that is a half-believer accepts a hinoeuma-woman as his wife, but parents that are half-believers avoid childbirth during hinoeuma years. With these three cultural factors, there are two possible outcomes for the population. In the first outcome, [1] non-believers become extinct, with the population consisting of believers and half-believers; some men refuse hinoeuma-women as their mate choice, and most parents attempt to avoid childbirth during hinoeuma years. In the second outcome, [2] believers become extinct, and the remaining population consists of non-believers and half-believers; no man refuses hinoeuma-women, and some parents avoid childbirth in hinoeuma years to prevent potential harm to their daughters. If birth control fails at a steady rate, believers will become extinct eventually. The superstition is more likely to be maintained if the mother has a stronger influence on the beliefs of her children than the father.

Agent-based mapping of credit risk for sustainable microfinance.

By drawing analogies with independent research areas, we propose an unorthodox framework for mapping microfinance credit risk--a major obstacle to the sustainability of lenders outreaching to the poor. Specifically, using the elements of network theory, we constructed an agent-based model that obeys the stylized rules of microfinance industry. We found that in a deteriorating economic environment confounded with adverse selection, a form of latent moral hazard may cause a regime shift from a high to a low loan payment probability. An after-the-fact recovery, when possible, required the economic environment to improve beyond that which led to the shift in the first place. These findings suggest a small set of measurable quantities for mapping microfinance credit risk and, consequently, for balancing the requirements to reasonably price loans and to operate on a fully self-financed basis. We illustrate how the proposed mapping works using a 10-year monthly data set from one of the best-known microfinance representatives, Grameen Bank in Bangladesh. Finally, we discuss an entirely new perspective for managing microfinance credit risk based on enticing spontaneous cooperation by building social capital.

Games of corruption: how to suppress illegal logging.

Corruption is one of the most serious obstacles for ecosystem management and biodiversity conservation. In particular, more than half of the loss of forested area in many tropical countries is due to illegal logging, with corruption implicated in a lack of enforcement. Here we study an evolutionary game model to analyze the illegal harvesting of forest trees, coupled with the corruption of rule enforcers. We consider several types of harvesters, who may or may not be committed towards supporting an enforcer service, and who may cooperate (log legally) or defect (log illegally). We also consider two types of rule enforcers, honest and corrupt: while honest enforcers fulfill their function, corrupt enforcers accept bribes from defecting harvesters and refrain from fining them. We report three key findings. First, in the absence of strategy exploration, the harvester-enforcer dynamics are bistable: one continuum of equilibria consists of defecting harvesters and a low fraction of honest enforcers, while another consists of cooperating harvesters and a high fraction of honest enforcers. Both continua attract nearby strategy mixtures. Second, even a small rate of strategy exploration removes this bistability, rendering one of the outcomes globally stable. It is the relative rate of exploration among enforcers that then determines whether most harvesters cooperate or defect and most enforcers are honest or corrupt, respectively. This suggests that the education of enforcers, causing their more frequent trialing of honest conduct, can be a potent means of curbing corruption. Third, if information on corrupt enforcers is available, and players react opportunistically to it, the domain of attraction of cooperative outcomes widens considerably. We conclude by discussing policy implications of our results.

Graduated punishment is efficient in resource management if people are heterogeneous.

In natural resource managements, people often overcome tragedy of commons by developing an institution that punishes selfish actions, thus enhancing pro-social behavior. Elinor Ostrom reported that many successful communities apply graduated punishment--the punishment level gradually increases with the amount of harm of the selfish action. This observation is apparently in conflict with a theoretical study of public good game supporting a severe and strict punishment. Here, we study the conditions in which graduated punishment enforces cooperation most efficiently. If people follow a quantal response equilibrium, the optimal punishment is a jump from no punishment to a high level of punishment then increases little with the societal harm, which is inconsistent with the graduated punishment concept. We find that the graduated punishment is the most efficient rule if there is a small probability that player's action is reported incorrectly and if players are heterogeneous in their sensitivity to utility (or payoff) difference. We derive a mathematical formula for the optimal punishment when people's sensitivity to utility difference follows an exponential distribution. When the magnitude of harm is large, the optimal punishment increases in proportion to the square root of the societal harm, thus confirming the efficiency of the graduated punishment.

Optimal investment for enhancing social concern about biodiversity conservation: a dynamic approach.

To maintain biodiversity conservation areas, we need to invest in activities, such as monitoring the condition of the ecosystem, preventing illegal exploitation, and removing harmful alien species. These require a constant supply of resources, the level of which is determined by the concern of the society about biodiversity conservation. In this paper, we study the optimal fraction of the resources to invest in activities for enhancing the social concern y(t) by environmental education, museum displays, publications, and media exposure. We search for the strategy that maximizes the time-integral of the quality of the conservation area x(t) with temporal discounting. Analyses based on dynamic programming and Pontryagin's maximum principle show that the optimal control consists of two phases: (1) in the first phase, the social concern level approaches to the final optimal value y(∗), (2) in the second phase, resources are allocated to both activities, and the social concern level is kept constant y(t) = y(∗). If the social concern starts from a low initial level, the optimal path includes a period in which the quality of the conservation area declines temporarily, because all the resources are invested to enhance the social concern. When the support rate increases with the quality of the conservation area itself x(t) as well as with the level of social concern y(t), both variables may increase simultaneously in the second phase. We discuss the implication of the results to good management of biodiversity conservation areas.