Avec l'avènement du « big data », de nombreuses répercussions ont eu lieu dans tous les domaines de la technologie de l'information, préconisant des solutions innovantes remportant le meilleur compromis entre coûts et précision. En théorie des graphes, où les graphes constituent un support de modélisation puissant qui permet de formaliser des problèmes allant des plus simples aux plus complexes, la recherche pour des problèmes NP-complet ou NP-difficils se tourne plutôt vers des solutions approchées, mettant ainsi en avant les algorithmes d'approximations et les heuristiques alors que les solutions exactes deviennent extrêmement coûteuses et impossible d'utilisation.Nous abordons dans cette thèse deux problématiques principales: dans un premier temps, le problème du partitionnement des graphes est abordé d'une perspective « big data », où les graphes massifs sont partitionnés en streaming. Nous étudions et proposons plusieurs modèles de partitionnement en streaming et nous évaluons leurs performances autant sur le plan théorique qu'empirique. Dans un second temps, nous nous intéressons au requêtage des graphes distribués/partitionnés. Dans ce cadre, nous étudions la problématique de la « recherche agrégative dans les graphes » qui a pour but de répondre à des requêtes interrogeant plusieurs fragments de graphes et qui se charge de la reconstruction de la réponse finale tel que l'on obtient un « matching approché » avec la requête initiale / With the advent of the "big data", many repercussions have taken place in all fields of information technology, advocating innovative solutions with the best compromise between cost and accuracy. In graph theory, where graphs provide a powerful modeling support for formalizing problems ranging from the simplest to the most complex, the search for NP-complete or NP-difficult problems is rather directed towards approximate solutions, thus Forward approximation algorithms and heuristics while exact solutions become extremely expensive and impossible to use. In this thesis we discuss two main problems: first, the problem of partitioning graphs is approached from a perspective big data, where massive graphs are partitioned in streaming. We study and propose several models of streaming partitioning and we evaluate their performances both theoretically and empirically. In a second step, we are interested in querying distributed / partitioned graphs. In this context, we study the problem of aggregative search in graphs, which aims to answer queries that interrogate several fragments of graphs and which is responsible for reconstructing the final response such that a Matching approached with the initial query

O objetivo de estudo desta dissertação é o desenvolvimento de um modelo de planejamento agregado da produção que apóie as decisões de nível gerencial e de diretoria das usinas de açúcar e álcool no que tange às variedades de cana colhidas em cada semana, às compras de cana-de-açúcar de terceiros, ao tipo de transporte (próprio ou terceirizado) a se utilizar em cada semana, ao total de cana moída por semana para atendimento da demanda e aos processos (industrial e comercial) que se devem escolher para produzir e comercializar açúcar e álcool. As decisões devem ocorrer em função de preços nos mercados interno, externo e mercado futuro, do fluxo de caixa da empresa, da capacidade da usina para armazenar açúcar e álcool e da possibilidade de uso de estoque de terceiros. As decisões por compra de cana, escolha de processos e venda de produtos são tomadas semanalmente num horizonte móvel de planejamento de 52 semanas, que inclui o tempo de safra no centro-sul do Brasil (meados de março a meados de dezembro, aproximadamente 36 semanas) mais o período de entressafra (aproximadamente 16 semanas, de meados de dezembro a meados de março). A procura por melhores estratégias de comercialização de tal forma a auxiliar a tomada de decisões é uma necessidade constante dos empresários do setor, que muitas vezes são surpreendidos pelas variações de preços de açúcar e álcool no mercado interno, externo e mercado futuro. Na parte comercial, este trabalho utiliza o método Delphi de previsão de preços de açúcar e álcool que balizam as tomadas de decisão no planejamento e controle da produção das usinas de açúcar e álcool. Define-se Hedge como a operação financeira de proteger determinado ativo de uma empresa contra variações inesperadas de preços. Neste trabalho, utiliza-se um modelo de escolha de mix de produto para Hedge vinculado à lucratividade e minimização de risco denominado Modelo de Semi- Variância com análise de cenários de Markowitz. Nas decisões relacionadas com as partes agrícola, industrial e comercial, faz-se uso de um modelo de programação linear inteira mista e para resolvê-lo utiliza-se o software de programação matemática LINGO e suas interfaces com a planilha eletrônica Excel. Nas decisões vinculadas ao mix ótimo para o Hedge em cada semana, faz-se uso de um modelo de programação quadrática resolvido pelo LINGO e suas interfaces com a planilha eletrônica Excel. Um estudo de caso foi realizado numa usina de açúcar e álcool no município de Junqueirópolis (SP) para validar o modelo proposto. / The objective of study this dissertation is to develop a model of aggregate production planning to support the decisions of management and board level of sugar and alcohol plants in regard to varieties of cane harvested each week, purchasing cane of nonsugar, the type of transport (own or outsourced) to use each week, the total cane processed per week for taking care of the demand and processes (industrial and commercial) and that must be chosen to produce and sell sugar and alcohol. Decisions must occur in terms of domestic, foreign and future market prices, the company\'s cash flow and the capacity to store sugar and alcohol and the possibility of using stock to third parties. Decisions about buying cane, choice of processes and products for sale are made in a weekly mobile planning horizon of 52 weeks, which includes the time of harvest in central-southern Brazil (mid-March to mid-December, approximately 36 weeks) plus the off-season (approximately 16 weeks, from mid-December to mid March). The demand for better marketing strategies to help such decision making is a constant need for entrepreneurs in the sector, which are often surprised by the changes in prices of sugar and alcohol in the internal, external and future market. In the commercial part, this study uses the Delphi method of forecasting the price of sugar and alcohol that guides the decision-making in planning and controlling the production of sugar and alcohol plants. Hedging is defined as a financial transaction to protect certain assets of a business against unexpected changes in prices. In this work, it is used a model of choice of product mix for Hedge linked to profitability and minimizing risk named Model of Semi-Variance analysis with scenarios of Markowitz. In decisions related to the agricultural, industrial and commercial parts it is used a type of mixed integer linear programming and to solve it is used the mathematical programming software LINGO and its interface with Excel spreadsheets. In decisions related to the optimal mix for Hedge in each week, is used a quadratic programming model solved by LINGO and its interface with Excel spreadsheets. A case study was conducted in a sugar mill and alcohol in the city of Junqueirópolis (SP) to validate the proposed model.

Sommaire : Comprendre le fonctionnement des e??cosyste??mes est un enjeu crucial, en particulier dans un contexte de changements globaux. Afin de mieux pre??dire les processus e??cosyste??miques, j???ai teste?? la pre??cision et les limites des hypothe??ses du biomass-ratio de Grime (HBMR) et de l???annulation idiosyncratique (HAI), cette dernie??re e??tant une hypothe??se originale de cette the??se. Pour cela, j???ai applique?? le principe du biomass-ratio aux traits fonctionnels, en employant la me??thode des traits agre??ge??s en communaute??, pour estimer la re??ponse globale des espe??ces en me??lange. La de??composition des litie??res plurispe??cifiques constitue un bon mode??le biologique, pour lequel je me suis pose?? les questions suivantes : (1) est-ce que l???HBMR pre??dit bien les taux de de??composition en me??langes plurispe??cifiques ? ; (2) est-ce que le degre?? de variabilite?? de ces taux diminue pour des raisons biologiques avec l???augmentation de la richesse spe??cifique (RS) des me??langes (HAI) ? ; (3) est-ce que la variabilite?? des taux entre me??langes diminue quand les conditions abiotiques du site deviennent plus limitantes ? ; (4) conside??rant que les me??langes plus contraste??s fonctionnellement sont susceptibles de de??velopper plus d???interactions, est-ce que la de??viation a?? la pre??diction augmente avec la dispersion fonctionnelle des me??langes (?? FDis ??, Laliberte?? & Legendre 2010) ? Cette the??se inclut deux expe??riences de de??composition en sachets a?? litie??res : (1) a?? Sherbrooke (QC, Canada) avec des microcosmes, impliquant des litie??res de six espe??ces d???arbres, de??composant seules et en me??langes et (2) sur trois sites au climat contraste?? dans la re??gion de Clermont-Ferrand (France) avec des litie??res de quatre espe??ces d???herbace??es, de??composant seules et en me??langes. Les re??sultats montrent des de??viations positives et ne??gatives par rapport aux taux pre??dits, mais l???HBMR de??crit bien la re??ponse moyenne des litie??res plurispe??cifiques. Bien que l???HAI ait e??te?? rejete??e, les re??sultats montrent une convergence des taux observe??s vers les taux pre??dits quand (1) la RS des me??langes augmente, (2) l???e??chelle spatiale augmente et (3) le climat est plus limitant pour la de??composition. Enfin, malgre?? des corre??lations entre FDis et interactions entre espe??ces dans les litie??res, cette relation n???est pas ge??ne??ralisable et l???hypothe??se de corre??lation positive entre FDis et de??viation a?? l???HBMR a e??te?? rejete??e. // Abstract : Understanding ecosystem functioning is a key goal in ecology, especially in the context of global changes. To better predict ecosystem processes, I tested the accuracy and the limits of Grime???s biomass-ratio (BMRH) hypothesis and a novel idiosyncratic annulment (IAH) hypothesis. I applied the biomass-ratio to functional traits, using the community-weighted means (CWM) to estimate the global response of species in mixtures. I studied the decomposition of litter species mixtures as a biological model and asked the following questions : (1) does the BMRH predict well the decomposition rates of mixed species litters? ; (2) does the degree of variability of these rates decrease with increasing species richness (SR) beyond that expected from purely mathematical causes (IAH)? ; (3) does the variability of rates between mixtures decrease with less favourable abiotic conditions for decomposition? ; (4) as more functionally contrasted mixtures are expected to develop more interactions, does the deviation from prediction increase with increasing functional dispersion in mixtures (?? FDis ??, Lalibert?? & Legendre 2010)? This study involves two decomposition experiments using litterbags: (1) at Sherbrooke (QC, Canada), in microcosms, involving litters from six tree species, decomposed alone and in mixtures and (2) in three climatically contrasted sites in the region of Clermont-Ferrand (France) with litters from four herbaceous species, decomposed alone and in mixtures. Despite both positive and negative deviations from expectation occurring at all levels of SR, the BMRH well described the average response of mixed species litters. Although I rejected the IAH, the results showed a convergence to the predicted values based on CWM with (1) increasing the SR in mixtures, (2) increasing the spatial scale of the study and (3) a less favourable climate to decomposition. Finally, although there was a correlation between litter interactions and functional divergence, this relationship was not generalizable and I rejected the hypothesis of a positive correlation between FDis and the deviations from BMRH.

CHAPTER I: The present study has the objective to describe the life history of Aglaotenus lagotis since the youngest birth until adulthood, analysing the number of eggs in each cocoon, the birth rate, the instar number, sexual ratio and development time until adulthood, quantifying the size cephalothoraxes during all the stages of the development. The results indicate that the species is able to produce two egg sacs during the reproductive period with twelve instars after the outbreak. The youngest, during the development had the greatest a mortality rate on the three first instars, what characterizes a type III survival curve. During the adulthood the sexual ratio was turned to the female, and there is no significant differentiation between the cephalothoraxes width between males and females in laboratory environment, what makes it possible to, be considered a monomorphic species. The sexual dimorfism was observed on the coloration. Males show a light brown coloration and the female show a dark one. This study provides an opportunity to evaluate all the phases of life cycle of Lycosidae A. lagotis, what can help on the initial construction of studies about the post-embryonic development of the species, offering comparative parameters with other species from this family. CHAPTER II: The present study shows the description of the sexual behavior and the maternal care of the spider A. lagotis (Lycosidae), testing by experiments the hypothesis that the male of A. lagotis is attracted by chemical cues in the sheet web built by the female. A maternal care behavior is described, testing the hypothesis that youngest from the studied species that had maternal care have a greater fitness than youngest without the maternal care. The study made it clear that males are able to observe, note, identify realize chemical cues in the web, telling virgin females from females that were fertilized. It was possible to quantify e categorize the sexual behavior of the males into three different categories: court, pre-mate and mate. After the mate, the females built an cocoon that was transported adhered in the spinnerets and hold by the last pair of legs. After the outbreak of the eggs, the youngest migrated to a dorsal region of the mother s body for five days. It was observed during the maternal care that the mother eliminates a yellowish drop from its cheliceraes which is collected by the youngest. During the development of the youngest until the adulthood, the youngest that have the presence of their mother in the first stages of life have a greater survival, if compared with the ones that do not have the presence of their mother. So, for the A. lagotis species, by its abundance and wide distribution represent an interesting model of study for the hypothesis test in behavioral ecology, which makes possible new comparative analyses with other species of Lycosidae. CHAPTER III: The present study shows the ecological aspects of A. lagotis from two distinct populations, in a semi-deciduous dry forest in Araguari municipality, Minas Gerais. the study was developed in four distinct periods october 2008, january, april and july 2099, in two different sites. the results show that A. lagotis is a seasonal species, with an aggregated distribution and with a strong parental similarity component between the individuals from the same region. The life history of A. lagotis seems to be characterized by seasonal aspects, seen that some components of its life cycle show a well defined period of ocorrence. As long as they grow, both the area and the height of the web get bigger with the individual size, what suggests that webs progressively bigger and taller are necessary for the capture of prey enough for the maintenance of the individual biomass. Despite of happening little variation in the number of spider tenant individuals associated to the vertical interception web between the studied areas (except for April), a positive correlation was characterized between these variables in all the samples. It means that, the greater the volume of the vertical web, the greater the number of parasite spiders. So, the variations in the densities of spiders between the study sites and through time in each site, observed in this study, can be the result of the interaction between several factors, as the availability of food, climate factors and other parameters that must be investigated in future studies. / CAPÍTULO I: O presente estudo teve como objetivo de descrever a história de vida de Aglaoctenus lagotis desde o nascimento dos filhotes até a fase adulta, analisando o número de ovos em cada ovissaco, a taxa de nascimento, o número de instares, razão sexual e o tempo de desenvolvimento até a fase adulta, quantificando o tamanho do cefalotórax durante todas as etapas de desenvolvimento. Os resultados apresentados indicaram que a espécie estudada é capaz de produzir dois sacos de ovos durante o período reprodutivo e que após a eclosão o número de instares registrados foi de 12. Os filhotes, durante o desenvolvimento, tiveram uma taxa de mortalidade maior nos três primeiros instares, caracterizando uma curva de sobrevivência do tipo III. Na fase adulta a razão sexual foi voltada para a fêmea e não existindo diferenciação significativa entre a largura do cefalotórax entre macho e fêmeas em ambiente de laboratório, podendo, portanto ser considerada uma espécie monomórfica. O dimorfismo sexual encontrado foi na coloração da cutícula, machos apresentaram uma coloração marrom clara e a fêmea uma coloração marrom escura. Este estudo proporcionou uma oportunidade de avaliar todas as fases de vida do Lycosidae A. lagotis, podendo auxiliar na formação inicial de estudos sobre desenvolvimento pós-embrionário da espécie oferecendo parâmetros comparativos com outras espécies desta família. CAPÍTULO II: O presente estudo apresenta a descrição do comportamento sexual e do cuidado maternal da aranha Aglaoctenus lagotis (Lycosidae), testando experimentalmente a hipótese de que o macho é atraído por odores deixados na teia de lençol construída pela fêmea. Foi descrito o comportamento de cuidado maternal, testando a hipótese que filhotes da espécie estudada que tiveram cuidado maternal possuem o fitness maior do que filhotes sem o cuidado maternal. O estudo evidenciou que machos são capazes de perceber o odor presente na teia, diferenciando fêmeas virgens receptivas de fêmeas já fecundadas. Foi possível quantificar e categorizar o comportamento sexual dos machos em três categorias distintas: corte, pré-cópula e cópula. Depois da cópula as fêmeas construíram uma ooteca que foi transportada aderida nas fiandeiras e segurada pelo último par de pernas. Após a eclosão dos ovos os filhotes migraram para a região dorsal do corpo da mãe e permaneceram durante cinco dias. Foi observado durante o cuidado maternal a mãe eliminando uma gota amarelada de suas quelíceras,a qual é coletada pelos filhotes. Durante o desenvolvimento dos jovens até a fase adulta, os filhotes que tiveram a presença da mãe nos primeiros estágios de vida obtiveram uma sobrevivência maior, se comparado com os que não tiveram a presença da mãe. Portanto, devido à sua abundância e ampla distribuição a espécie Aglaoctenus lagotis representa um interessante modelo de estudo para teste de hipóteses em ecologia comportamental, possibilitando análises comparativas com outras espécies de Lycosidae. CAPÍTULO III: O presente estudo apresenta aspectos da ecologia da Aglaoctenus lagotis a partir de duas populações distintas, em floresta semi-decidual seca no Município de Araguari, Minas Gerais. O estudo foi desenvolvido em quatro períodos distintos - outubro de 2008, janeiro, abril e julho de 2009, em dois locais diferentes. Os resultados indicaram que A. lagotis é uma espécie sazonal, com distribuição agregada e com um forte componente de similaridade parental entre os indivíduos de uma mesma região. A história de vida de A. lagotis parece ser marcada por aspectos sazonais, sendo que alguns componentes de seu ciclo de vida apresentam um período bem definido de ocorrência. À medida que crescem, tanto a área da teia como a altura da teia aumentam com o tamanho do indivíduo, o que sugere que teias progressivamente maiores e mais altas são necessárias para a captura de presas suficientes para a manutenção da biomassa individual. Apesar de ocorrer pouca variação no número de indivíduos de aranhas inquilinas associadas à teia de interceptação vertical entre as áreas estudas (com exceção de abril) foi caracterizada uma correlação positiva entre estas variáveis em todas as amostras. Ou seja, quanto maior o volume da teia vertical maior número de aranhas parasitas. Portanto, as variações nas densidades de aranhas entre os locais de estudo e ao longo do tempo em cada local, observados neste estudo, podem ser resultado da interação entre diversos fatores, como disponibilidade de alimento, fatores climáticos e outros parâmetros que devem ser investigados em estudos posteriores. / Doutor em Ecologia e Conservação de Recursos Naturais

O objetivo de estudo desta dissertação é o desenvolvimento de um modelo de planejamento agregado da produção que apóie as decisões de nível gerencial e de diretoria das usinas de açúcar e álcool no que tange às variedades de cana colhidas em cada semana, às compras de cana-de-açúcar de terceiros, ao tipo de transporte (próprio ou terceirizado) a se utilizar em cada semana, ao total de cana moída por semana para atendimento da demanda e aos processos (industrial e comercial) que se devem escolher para produzir e comercializar açúcar e álcool. As decisões devem ocorrer em função de preços nos mercados interno, externo e mercado futuro, do fluxo de caixa da empresa, da capacidade da usina para armazenar açúcar e álcool e da possibilidade de uso de estoque de terceiros. As decisões por compra de cana, escolha de processos e venda de produtos são tomadas semanalmente num horizonte móvel de planejamento de 52 semanas, que inclui o tempo de safra no centro-sul do Brasil (meados de março a meados de dezembro, aproximadamente 36 semanas) mais o período de entressafra (aproximadamente 16 semanas, de meados de dezembro a meados de março). A procura por melhores estratégias de comercialização de tal forma a auxiliar a tomada de decisões é uma necessidade constante dos empresários do setor, que muitas vezes são surpreendidos pelas variações de preços de açúcar e álcool no mercado interno, externo e mercado futuro. Na parte comercial, este trabalho utiliza o método Delphi de previsão de preços de açúcar e álcool que balizam as tomadas de decisão no planejamento e controle da produção das usinas de açúcar e álcool. Define-se Hedge como a operação financeira de proteger determinado ativo de uma empresa contra variações inesperadas de preços. Neste trabalho, utiliza-se um modelo de escolha de mix de produto para Hedge vinculado à lucratividade e minimização de risco denominado Modelo de Semi- Variância com análise de cenários de Markowitz. Nas decisões relacionadas com as partes agrícola, industrial e comercial, faz-se uso de um modelo de programação linear inteira mista e para resolvê-lo utiliza-se o software de programação matemática LINGO e suas interfaces com a planilha eletrônica Excel. Nas decisões vinculadas ao mix ótimo para o Hedge em cada semana, faz-se uso de um modelo de programação quadrática resolvido pelo LINGO e suas interfaces com a planilha eletrônica Excel. Um estudo de caso foi realizado numa usina de açúcar e álcool no município de Junqueirópolis (SP) para validar o modelo proposto. / The objective of study this dissertation is to develop a model of aggregate production planning to support the decisions of management and board level of sugar and alcohol plants in regard to varieties of cane harvested each week, purchasing cane of nonsugar, the type of transport (own or outsourced) to use each week, the total cane processed per week for taking care of the demand and processes (industrial and commercial) and that must be chosen to produce and sell sugar and alcohol. Decisions must occur in terms of domestic, foreign and future market prices, the company\'s cash flow and the capacity to store sugar and alcohol and the possibility of using stock to third parties. Decisions about buying cane, choice of processes and products for sale are made in a weekly mobile planning horizon of 52 weeks, which includes the time of harvest in central-southern Brazil (mid-March to mid-December, approximately 36 weeks) plus the off-season (approximately 16 weeks, from mid-December to mid March). The demand for better marketing strategies to help such decision making is a constant need for entrepreneurs in the sector, which are often surprised by the changes in prices of sugar and alcohol in the internal, external and future market. In the commercial part, this study uses the Delphi method of forecasting the price of sugar and alcohol that guides the decision-making in planning and controlling the production of sugar and alcohol plants. Hedging is defined as a financial transaction to protect certain assets of a business against unexpected changes in prices. In this work, it is used a model of choice of product mix for Hedge linked to profitability and minimizing risk named Model of Semi-Variance analysis with scenarios of Markowitz. In decisions related to the agricultural, industrial and commercial parts it is used a type of mixed integer linear programming and to solve it is used the mathematical programming software LINGO and its interface with Excel spreadsheets. In decisions related to the optimal mix for Hedge in each week, is used a quadratic programming model solved by LINGO and its interface with Excel spreadsheets. A case study was conducted in a sugar mill and alcohol in the city of Junqueirópolis (SP) to validate the proposed model.

Premièrement, nous construisons de tels tests basés sur des approches par bootstrap ou par permutation, et étudions leurs propriétés asymptotiques dans un cadre de processus ponctuels, à travers l'étude du comportement asymptotique des lois conditionnelles des statistiques de test bootstrappée et permutée, sous l'hypothèse nulle ainsi que toute alternative. Nous les validons en pratique par simulation et les comparons à des méthodes classiques en neurosciences. Ensuite, nous nous concentrons sur les tests par permutation, connus pour contrôler non-asymptotiquement leur niveau. Les p-valeurs basées sur la notion de coïncidences avec délai, sont implémentées dans une procédure de tests multiples, appelée méthode Permutation Unitary Events, pour détecter les synchronisations entre deux neurones. Nous validons la méthode par simulation avant de l'appliquer à de vraies données. Deuxièmement, nous étudions les propriétés non-asymptotiques des tests par permutation en termes de vitesse de séparation uniforme. Nous construisons une procédure de tests agrégés, basée sur du seuillage par ondelettes dans un cadre de variables aléatoires à densité. Nous déduisons d'une inégalité fondamentale de Talagrand, une nouvelle inégalité de concentration de type Bernstein pour des sommes permutées aléatoirement qui nous permet de majorer la vitesse de séparation uniforme sur des espaces de Besov faibles et d'en déduire que cette procédure semble être optimale et adaptative au sens du minimax. / On the one hand, we construct such tests based on bootstrap and permutation approaches. Their asymptotic performance are studied in a point process framework through the analysis of the asymptotic behavior of the conditional distributions of both bootstrapped and permuted test statistics, under the null hypothesis as well as under any alternative. A simulation study is performed verifying the usability of these tests in practice, and comparing them to existing classical methods in Neuroscience. We then focus on the permutation tests, well known for their non-asymptotic level properties. Their p-values, based on the delayed coincidence count, are implemented in a multiple testing procedure, called Permutation Unitary Events method, to detect the synchronization occurrences between two neurons. The practical validity of the method is verified on a simulation study before being applied on real data. On the other hand, the non-asymptotic performances of the permutation tests are studied in terms of uniform separation rates. A new aggregated procedure based on a wavelet thresholding method is developed in the density framework. Based on Talagrand's fundamental inequalities, we provide a new Bernstein-type concentration inequality for randomly permuted sums. In particular, it allows us to upper bound the uniform separation rate of the aggregated procedure over weak Besov spaces and deduce that this procedure seems to be optimal and adaptive in the minimax sens.

For a simplified calculation of the price of work I propose methodology of creating aggregated items, so that to calculate the price of an object wouldn´t take not more than one hour, while the final price would be with the least deviation from the exercise price. The accuracy and performance will be assessed on two objects. Their price will be calculated and based on the proposed methodology.

Comprendre le fonctionnement des écosystèmes est un enjeu crucial, en particulier dans un contexte de changements globaux. Afin de mieux prédire les processus écosystémiques, j’ai testé la précision et les limites des hypothèses du biomass-ratio de Grime (HBMR) et de l’annulation idiosyncratique (HAI), cette dernière étant une hypothèse originale de cette thèse. Pour cela, j’ai appliqué le principe du biomass-ratio aux traits fonctionnels, en employant la méthode des traits agrégés en communauté, pour estimer la réponse globale des espèces en mélange. La décomposition des litières plurispécifiques constitue un bon modèle biologique, pour lequel je me suis posé les questions suivantes : (1) est-ce que l’HBMR prédit bien les taux de décomposition en mélanges plurispécifiques ? ; (2) est-ce que le degré de variabilité de ces taux diminue pour des raisons biologiques avec l’augmentation de la richesse spécifique (RS) des mélanges (HAI) ? ; (3) est-ce que la variabilité des taux entre mélanges diminue quand les conditions abiotiques du site deviennent plus limitantes ? ; (4)considérant que les mélanges plus contrastés fonctionnellement sont susceptibles de développer plus d’interactions, est-ce que la déviation à la prédiction augmente avec la dispersion fonctionnelle des mélanges(« FDis », La liberté & Legendre 2010) ? Cette thèse inclut deux expériences de décomposition en sachets à litières : (1) à Sherbrooke (QC, Canada) avec des microcosmes, impliquant des litières de six espèces d’arbres, décomposant seules et en mélanges et (2) sur trois sites au climat contrasté dans la région de Clermont-Ferrand (France) avec des litières de quatre espèces d’herbacées, décomposant seules et en mélanges. Les résultats montrent des déviations positives et négatives par rapport aux taux prédits, mais l’HBMR décrit bien la réponse moyenne des litières plurispécifiques. Bien que l’HAI ait été rejetée, les résultats montrent une convergence des taux observés vers les taux prédits quand (1) la RS des mélanges augmente, (2)l’échelle spatiale augmente et (3) le climat est plus limitant pour la décomposition. Enfin, malgré des corrélations entre FDis et interactions entre espèces dans les litières, cette relation n’est pas généralisable et l’hypothèse de corrélation positive entre FDis et déviation à l’HBMR a été rejetée. / Understanding ecosystem functioning is a key goal in ecology, especially in the context of global changes. To better predict ecosystem processes, I tested the accuracy and the limits of Grime’s biomass-ratio (BMRH) hypothesis and a novel idiosyncratic annulment (IAH) hypothesis. I applied the biomass-ratio to functional traits, using the community-weighted means (CWM) to estimate the global response of species in mixtures. I studied the decomposition of litter species mixtures as a biological model and asked the following questions : (1) does the BMRH predict well the decomposition rates of mixed species litters ? ; (2) does the degree of variability of these rates decrease with increasing species richness (SR) beyond that expected from purely mathematical causes (IAH) ? ; (3) does the variability of rates between mixtures decrease with less favourable abiotic conditions for decomposition ? ; (4) as more functionally contrasted mixtures are expected to develop more interactions, does the deviation from prediction increase with increasing functional dispersion in mixtures (« FDis », Laliberté & Legendre 2010) ? This study involves two decomposition experiments using litterbags : (1) at Sherbrooke (QC, Canada), in microcosms, involving litters from six tree species, decomposed alone and in mixtures and (2) in three climatically contrasted sites in the region of Clermont-Ferrand (France) with litters from four herbaceous species, decomposed alone and in mixtures. Despite both positive and negative deviations from expectation occurring at all levels of SR, the BMRH well described the average response of mixed species litters. Although I rejected the IAH, the results showed a convergence to the predicted values based on CWM with (1) increasing the SR in mixtures, (2) increasing the spatial scale of the study and (3) a less favourable climate to decomposition. Finally, although there was a correlation between litter interactions and functional divergence, this relationship was not generalizable and I rejected the hypothesis of a positive correlation between FDis and the deviations from BMRH.