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International audience; Consumption satisfaction depends on other factors apart from the inherent characteristic ofcommodities. Leibenstein (1950) studies how the consumer's demand reacts to other factorsdifferent from the inherent characteristic of a specific commodity. In particular, he highlights thedesire of some consumers to be "in style", and the attempt by other for exclusiveness. The desireof some people to conform with the others, to be fashionable or stylish provokes a "bandwagoneffect": the demand for a commodity increases due to the fact that others are consuming this samecommodity. Conversely, the desire of some other people to be exclusive, or different from the"common hence" provokes the "snob" effect: the demand for a commodity decreases due to thefact that others are consuming it. This paper analyzes positional concerns and conformism in amodel of private contributions to public good. A positional consumer gets joy when his/her relativecontribution to the public good is higher than the average contribution by others. A conformistconsumers feels better if his behavior fits the average behavior in society, i.e., near the averagecontribution by others. The well-being of a conformist consumer decreases both when hiscontribution is above or below the average contribution by others. We analyze how positionalpreferences and conformism for voluntary contributions to a public good favor players'contributions and under which conditions can lead to social welfare improvements. A two-playerpublic good game between a positional and a conformist is analyzed, first in a one-shot game andlater in a simple dynamic game with inertia, placing particular attention to the transition path.Homogeneous and non-homogeneous individuals are considered regarding the players' valuationof the public good.

International audience; The nature of fishing activities is such that marine habitats can be deteriorated when employing destructive fishing gear. This makes even more complex the determination of sustainable fishing policies and has led some authors to propose dynamic models which take into account this habitat degradation. In this work, we analyze in detail one of these models, an extension of the single-species Gordon-Schaefer model to two state interrelated variables: stock of fish and habitat. The model assumes that stock and carrying capacity are positively linked, and that the fishing activity has a direct and negative impact on the carrying capacity. We extend and characterize Clark’s most rapid approach optimal solution to this case.

We study a problem of exploitation of a groundwater resource, mainly used for irrigation, in which a water agency is needed in order to manage an exceptional and priority extraction of water for an alternative/new use (e.g. domestic water). To this goal, we build a two-stage discrete Stackelberg game in which the leader (the water agency) just intervenes when the new use takes place (in the second stage) and the follower is a representative agent of the regular users of the aquifer, i.e. the agricultural users. We study two types of Stackelberg equilibrium, which can arise depending on the agents' commitment behavior, namely openloop commitment) equilibrium and feedback (non-commitment) equilibrium. We analyze and compare extraction behaviors of the different agents for the different equilibria and the consequences of these extraction behaviors for the final state of the resource and the agents'profits. For some hypotheses on the parameters, theoretical results show that commitment strategies lead to higher stock levels than non-commitment strategies when the leader's weight assigned to the profits from the agricultural use is lower or equal than the one assigned to the profits from the non-agricultural use. However, performing numerical simulations relaxing previous economic assumptions, we show that there are situations in which non-commitment strategies could be more favorable than commitment strategies not only in terms of final stock of the resource but also in terms of users' profits.

We introduce the family of Conjectural Learning procedures, in which agents form conjectures about what the opponent will play, as a function of their action or some state variable. We prove general properties of these procedures, comparing them to two dynamic systems generated by nearsighted agents solving repeatedly a static game, either cooperatively, or noncooperatively. We then specify three simple functional forms of conjectures and analyze the five resulting dynamic systems, in terms of steady states and convergence conditions. We next further specify these procedures to the case of a game of groundwater management, using a quadratic functional form for the profit function of agents. We obtain then explicit expressions for steady states and convergence conditions for the dynamic systems. Finally, we conduct numerical experiments in order to assess the “performance” of pairs of agents adopting each of the five behaviors.; Nous définissons une famille de procédures d’apprentissage conjectural, dans laquelle les agents formulent des conjectures au sujet de ce que l’adversaire va jouer, en fonction de leur propre action ou d’une variable d’état. Nous prouvons des propriétés générales de ces procédures, en les comparant aux deux systèmes dynamiques générés par des agents myopes qui résolvent à chaque étape un jeu statique, soit de façon coopérative, soit noncoopérative. Nous spécifions ensuite trois formes fonctionnelles simples pour les conjectures et nous analysons les cinq systèmes dynamiques ainsi définis, en termes d’états stationnaires et de conditions de convergence. Puis nous appliquons ces procédures pour un problème de gestion d’une nappe phréatique, en utilisant une forme fonctionnelle quadratique pour la fonction de profit des agents. Nous obtenons alors des formules explicites pour les états stationnaires et des conditions de convergence pour les systèmes dynamiques. Finalement, nous menons des expériences numériques afin d’évaluer les “performances” de paires d’agents qui adoptent chacun des cinq comportements.

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