Zugl.: Regensburg, Universiẗat, Diss., 2009.

La thèse porte sur des modèles économiques en présence d’externalités. En suivant Laffont (1988), nous donnons la définition suivante d’externalité.“Effet indirect” signifie que l’effet est créé par un agent économique différent de celui qui est affecté, et que l’effet n’est pas produit par l’intermédiaire du système de prix. Par conséquence, le système des prix ne joue que le rôle d’égaler à l’équilibre l’offre globale et la demande globale. La définition ci-dessus montre que la présence d’effets externes nécessite une nouvelle description des caractéristiques des agents, c’est-à-dire des préférences individuelles, des ensembles de consommation et des ensembles de production des producteurs. La thèse se compose de trois chapitres. Le premier chapitre étudie les restrictions de testabilité d’un modèle spécifique avec des externalités et des biens publics. Dans le deuxième chapitre et le troisième chapitre, nous considérons un modèle d’équilibre général avec des externalités au niveau des préférences individuelles et des ensembles de production des producteurs. Dans le deuxième chapitre nous traitons l’existence d’un équilibre concurrentiel en utilisant un approche différentiable, et dans le troisième chapitre nous donnons un résultat de régularité. Dans le Chapitre 2, nous considérons un modèle d’économie de propriété privée avec des externalités de consommation et de production. En utilisant une approche différentiable, nous prouvons que l’ensemble des équilibres concurrentiels avec des consommations et des prix strictement positifs est non vide et compact. Dans le Chapitre 3, nous considérons des économies de propriété privée avec externalités de consommation et de production. Nous étudions des conditions suffisantes pour la régularité générique de ces économies. / We study the testability implications of public versus private consumption in col-lective models of group consumption. The distinguishing feature of our approach is that we start from a revealed preference characterization of collectively rational behavior. Remarkably, we find that assumptions regarding the public or private nature of specific goods do have testability implications, even if one only observes the aggregate group consumption. In fact, these testability implications apply as soon as the analysis includes three goods and four observations. This stands in sharp contrast with existing results that start from a differential characterization of collectively rational behavior. In our opinion, our revealed preference approach obtains stronger testability conclusions because it focuses on a global characterization of collective rationality, whereas the differential approach starts from a local characterization.We consider a general model of private ownership economies with consumption and production externalities. Each firm is characterized by a technology described by a transformation function. Each household is characterized by a utility function, the shares on firms’ profit and an initial endowment of commodities. Describing equlib-ria in terms of first order conditions and market clearing conditions, and using a homotopy approach based on the seminal work by Smale (1974), under differentiability and boundary conditions, we prove the non-emptiness and the compactness of the set of competitive equilibria with consumptions and prices strictly positive.We consider a general equilibrium model of private ownership economy with con-sumption and production externalities. Each firm is owned by the households and it is characterized by a technology described by a transformation function. Each household is characterized by a utility function, the shares on the firms profits and an endowment of commodities. The choices of all agents (households and firms) affect utility functions and production technologies. Showing by an example that basic assumptions are not enough to guarantee a regularity result in the space of initial endowments, we provide sufficient conditions for the regularity in the space of endowments and perturbations of the transformation functions.

Thesis (MAgric (Agricultural Economics))—University of Stellenbosch, 2006. / The natural resources mainly land, forests, and grazing lands in the Highlands ago-ecological zone of Eritrea are in a severely degraded state. And much of these common pool resources comprise commons i.e. they are managed under the common property rights management regimes. “The tragedy of the commons”, model suggests that all commons will inexorably suffer overexploitation and degradation. Contrary to this deterministic proposition, however, common property theory argues that the ‘tragedy’ is not due to inherent flaws in the common property rights management regimes, but because of institutional failure to control access to resources, and to make and enforce internal decisions for collective use. If the commons dilemma situation exists- i.e. ‘tragedy’, then the underlying problem is the degeneration of the existing common property rights resource management regime into open-access-like regime—a condition that can potentially trigger “the tragedy of the commons”. The question of how to deal with the problem of the commons is, therefore, primarily an issue of the existence of efficient institutions. The prevailing severe degradation of the common-pool resources in the Highlands of the country thus calls into question the robustness of the common property rights regimes that are in place for the governance of these resources. This thesis attempts to address this important problem specifically in relation to forest and grazing land common pool resources. A case study based on a single-case qualitative and exploratory-explanatory research design was carried out in a village located in the Highlands of the country. Data were collected through various forms of interviews (semi-structured interviews, in-depth interviews, key informants interviews, group discussions, and informal conversational interviews), direct observation, and document review. The data, gathered largely through using these separate lines of enquiry, were crosschecked to provide a triangulation of methods and to strengthen the validity and reliability of the data. The empirical findings reveal that existing common property rights management regimes for the management of the local common pool resources of the case study area have weakened over time. These findings indicate that, there is a significant incongruence between appropriation and provision rules. And this is manifested in terms of appropriation externalities and demand side and supply side provision externalities. This situation implies that existing local institutional arrangements i.e. common property rights management regimes in the case study area are not sufficiently robust to solve common pool resource appropriation and provision externalities. Though generalisation cannot be made beyond the case that was studied, there are several lessons that may be drawn from this field analysis, which may have valid implications for the natural resources management challenges and opportunities of the entire Highlands agoecological zone of the country.

Microbes live in complex environments where competitive and cooperative interactions occur that dictate their success and the status of their environment. By furthering our understanding of the interactions between microbes, questions into the evolution of cooperation, disease virulence and biodiversity can be addressed. This will help develop strategies to overcome problems concerning disease, socioeconomics and conservation. We use an approach that combines evolutionary ecology theory with genetics and molecular biology to establish and develop model microbial ecological systems to examine feeding strategies, in what has been termed synthetic ecology. Using the model fungal plant pathogen system of rice blast disease, we generated less virulent gene deletion mutants to examine the sociality of feeding strategies during infection and test a nascent virulence reduction strategy based on competitive exclusion. We revealed that the success of the pathogen is unexpectedly enhanced in mixed strain infections containing the virulent wild-type strain with a less virulent gene deletion mutant of the metabolic enzyme invertase. Our finding is explained by interference between different social traits that occur during sucrose feeding. To test the generality of our result, gene deletion mutants of putative proteases were generated and characterised. We found that if virulence related genes acted ‘privately’, as predicted by social theory, the associated mutants would not make viable strains to use for this virulence reduction strategy by competitive exclusion. Our study then went on to study the fitness of digesting resources extracellularly, as many microbes do, given that this strategy is exposed to social exploitation by individuals who do not pay the metabolic costs. This was investigated by developing an experimental system with Saccharomyces cerevisiae. Though internalising digestion could suppress cheats, the relative fitness of opposing strategies was dependent upon the environmental and demographic conditions. Using this polymorphic system, the influence of competitors on the stability of cooperation, and the influence of cheats on the maintenance of diversity were assessed. To test the fitness of internal versus external digestion in a more natural setting, we generated an internally digesting strain of the rice blast fungus. In addition to suppressing cheats, the strain had enhanced fitness and virulence over the wild-type. We propose that this is caused by a shift in a trade-off between yield and rate. We show how a synthetic ecology approach can capture details of the biology underlying complex ecological processes, while having control over the factors that drive them, so that the underlying mechanisms can be teased apart.

The main of objective of this diploma thesis is to define health care as economic goods based on the theoretical definitions. The fact whether health care should be considered as private goods or public goods plays a vital role in this debate. The initial hypothesis presupposes that health care is (based on the basic economic criteria) private goods; however there is objective evidence demonstrating that health care should be understood in terms of public goods. The author defines the necessary terminology and theoretical concepts. According to several expert concepts the author concludes that based on the basic economic definitions health care could be understood as private goods, admitting that in the real world objective limitations exist, which prevent keeping health care exclusively in the economic sphere. The thesis also evaluates the role of individual health care sectors, including their drawbacks. The author demonstrates all concepts on the Czech health care system. In the analytic part of the thesis the author demonstrates discrepancies between theoretical concepts and practice on specific models, including the risks of exclusively private financing of health care. For this purpose three income groups has been defined. The author compares expenditures of these groups on selected medical services with different levels of their savings. The thesis also deals with methods of economical analysis and its limitations in health care system analysis.