Made available in DSpace on 2016-04-26T20:30:24Z (GMT). No. of bitstreams: 1 Vera Maria de Carvalho Pinto Rodrigues.pdf: 663787 bytes, checksum: 0ed00c284e05b5029793ab9a3aa0b98c (MD5) Previous issue date: 2010-06-01 / This essay intends to analyze the principle of mutualism in light of the eighteenth century contractual theory produced by Jean-Jacques Rousseau, as a form of free association that brings benefits for all of its members, which benefits are to be reached through the gathering of forces of those members aiming the common good. It will be explored the similarities between the contractual theory of Rousseau and the principle of mutualism, since in both cases the members of a collectivity contribute to get benefits from this association. Thus, these members assure protection against occasional misfortunes and related damages arising from its occurrence. Then, we start to view the social pact as a more specific kind of association, as in the insurance agreements, and not as a political organization. We will also study the relation between the risk inherent to the social contract and to the insurance agreement, which has the principle of mutualism as cornerstone. It will be discussed the philosophical fundaments of the principle of mutualism in the insurance agreements, since the insurance agreements are based on the concepts of the common good, presented in Rousseau's contractual theory; allowing that all the members of the insured collectivity benefit from the tranquility of having their personal or material assets protected against future or uncertain misfortunes, or against damages caused at the time of the loss, that could not be borne by them individually. At last, we will analyze the principle of mutualism and the insurance agreements in the Civil Code of 2002, and on recent decision of the Appellate Courts of the State of São Paulo / O presente trabalho tem por proposta a análise do princípio do mutualismo à luz da teoria contratualista do século XVIII elaborada por Jean-Jacques Rousseau, como forma de associação livre que traz benefícios para todos os que dela participam, alcançados pela soma de esforços para o bem comum. Serão exploradas as semelhanças a teoria contratualista de Rousseau entre o princípio do mutualismo, visto que em ambos os casos os membros de determinada coletividade contribuem para se beneficiar dessa associação, garantindo, assim, a proteção contra eventuais infortúnios e danos decorrentes de sua ocorrência. Passa-se, então a considerar o pacto social sob um prisma menor de associação, como nos contratos de seguro, e não sob o ponto de vista de organização política da sociedade; assim como será abordada a relação entre o risco inerente ao contrato social e ao contrato de seguro, cujo pilar de sustentação está no princípio do mutualismo. Serão feitas considerações sobre a fundamentação filosófica do princípio do mutualismo nos contratos de seguro, na medida em que este é fundado nas concepções de bem comum, tais como apresentadas no contratualismo de Rousseau; possibilitando que todos integrantes da massa segurada desfrutem da tranqüilidade de garantir seus bens pessoais ou materiais dos infortúnios futuros e incertos, ou dos danos efetivamente causados quando da ocorrência de sinistros, o que de forma isolada não teriam condições de assumir. Por fim, serão feitas reflexões sobre o princípio do mutualismo e os contratos de seguro no Código Civil de 2002, bem como sobre recentes decisões do E. Tribunal de Justiça do Estado de São Paulo

Le mutualisme entre les plantes et les champignons arbusculaires mycorhiziens est extrêmement répandu (~ 80% des plantes sont colonisées par ces organismes) et ancien (il ya plus de 450 millions d'années). Cette relation symbiotique est une composante essentielle du fonctionnement des écosystèmes et de leur productivité, et est fortement impliqué dans le cycle de deux éléments clés: le phosphore et le carbone. Le maintien de ce mutualisme est devenu particulièrement important dans le contexte actuel de perte de biodiversité. Un des objectifs de cette thèse était de comprendre la stabilité de ce mutualisme. L'accent a tout d'abord été mis sur les échanges de nutriments impliqués dans cette symbiose, en testant si la plante hôte et les symbiotes fongiques sont capables de discriminer leurs différents partenaires, et d'allouer davantage de ressources aux partenaires fournissant plus de nutriments. J'ai ensuite étudié la possibilité de l'implication de la plante hôte dans la protection des symbiotes mycorhiziens via un transfert de métabolites secondaires dans les hyphes. Nous avons alors pu emettre une nouvelle hypothèse suggérant que la protection en métabolites secondaires venant de la plante serait positivement corrélée avec le niveau de coopération (à savoir le transfert des nutriments) du champignon symbiotique. L'echelle d'étude est ensuite passée de l'individu à la communauté en étudiant les effets de la diminution de la diversité végétale sur la diversité des symbiotes racinaires. Pour ce faire, des analyses moléculaires et des outils novateurs ont été utilisés, tels que le séquençage à haut débit. Pour faciliter encore l'étude des séquences obtenues et d'autres séquences fongiques, j'ai collaboré avec des collègues afin de créer une base de données 'Phymyco-DB' rendue publique en 2012. Enfin, je discute de l'implication du mutualisme mycorhizien dans le contexte des systèmes agricoles actuels et propose de nouvelles trajectoires pour gérer ces systèmes. Ce projet de thèse apporte un nouvel éclairage sur la façon dont fonctionnent ces interactions entre les plantes et champignons MA et sur la manière dont ils façonnent les processus écologiques et les trajectoires évolutives dans les écosystèmes naturels et agricoles. Ces points sont d'une importance majeure pour développer une agriculture plus écologiquement intensive et durable. Le projet a fourni de nouvelles connaissances et perspectives sur la perte de la diversité végétale, et ses conséquences pour la stabilité de la symbiose AM. Comme les champignons mycorhiziens sont essentiels dans les processus des écosystèmes et l'entretien de la fertilité des sols, ce travail devrait avoir un large impact dans (i) la politique de protection des sols, (ii) la recherche sur l'amélioration des plantes et (iii) la conception de systèmes agricoles durables. / The mutualism between plants and arbuscular mycorrhizal fungi is extremely widespread (~ 80% of plants are colonized by these organisms) and ancient (over 450 million years ago). This symbiotic relationship is an essential component of healthy ecosystem functioning and productivity, and is strongly involved in the cycle of two key elements: phosphorus and carbon. Maintaining this mutualism has become especially important in the current context of a biodiversity loss. One goal of this thesis was to understand the stability of the mutualism. I first focused on nutrient exchange, testing whether plant host and fungal symbionts are able to discriminate among partners, and allocate more resources to those individuals providing more nutrients. I then explored the possibility of the host-plant involvement in the protection of mycorrhizal symbionts via a transfer of secondary metabolites into fungal hyphae. We introduced a new hypothesis suggesting that chemcial protection from the plant is positively correlated with the level of cooperation (i.e. nutrient transfer) of the fungal symbiont. I then moved from the individual to the community by studying the effects of decreasing plant diversity on the diversity of root symbionts. To this aim, I utilized molecular analyzes and innovative tools, such as high throughput sequencing. To further facilitate the study of the obtained sequences and other fungal sequences, I worked with colleagues to create a database ‘Phymyco-DB’ which was released to the public in 2012. Finally, I discuss the implication of the mycorrhizal mutualism in the context of current agricultural systems and propose new trajectories to manage these systems. This PhD project provides new insights on how plant and AM fungi interactions work and how they shape ecological processes and evolutionary trajectories in natural and agricultural ecosystems. These points are of major importance to develop a more ecologically intensive agriculture. The project has provided new knowledge and perspectives on the loss of plant diversity, and its consequences for AM symbiosis stability. As arbuscular mycorrhizal fungi are essential in ecosystem processes and soil fertility maintenance, this work should have a broad impact in (i) the soil protection policy, (ii) the research on plant breeding and (iii) the design of sustainable agricultural systems.

Abstract not available

1980年代以降，「產業群聚現象」為各國在發展高科技產業的歷程中，極重要的趨勢與特色，美國的矽谷模式可謂其濫觴並成為仿效的成功典範。透過在特定的地理區域中，結合產業界（私人部門）、學術機構、研究機構、中央與地方政府（公共部門），建構有利於高科技產業長期發展與繁榮地區經濟的「科學城」。 　　產業群聚的優勢在於群居成員可分攤基礎建設成本、共享所需的生存資源；更易因地理上的便利性，形成上下游或關聯性產業的合作網路，使產品、技術、資訊與情感的交流更密切，演化為利害與共、共存共榮的「命運共同體」。本研究以產業環境、研究環境與居住環境所組成的共生環境作為形成高科技產業群聚的中心假設，採用組織生態學、資源依賴與合作網路的觀點，以「環境資源共享」與「產業網路互補」為經緯，剖析不同群聚的共生型態與綜效利益，釐清不同的產業特性對群聚利益的呼應，與對整體產業與企業競爭力的影響。 　　本研究發現共生環境資源的多寡，決定高科技產業群聚的形成與長期發展。產業環境的優勢反映在生產效率與利益的增強，研究環境的優勢反映在技術與研發實力的提昇，居住環境的優勢有助吸引高科技人才加入。而高科技產業專業分工明顯、產品生命週期短、時效性要求高的產業特性，使得合作廠商需要頻繁的溝通與協調，而這些工作卻必須透過面對面的互動才能達成，這也是形成高科技產業群聚的主因。 　　產業群聚的利益在於地理上的接近性，使群聚成員共享生存環境資源，便於建構合作網路關係。「環境資源共享之經濟性」與「產業網路合作之互補性」兩構面，決定高科技產業群聚的共生綜效利益。共生綜效利益高低，會決定群聚的長期發展與演化。共生綜效利益越高，則產業群聚會趨於成長、擴張；反之，將逐漸萎縮、解散。而合作機制的建立，是提高群聚共生綜效的關鍵。合作網路體系中的核心廠商，則負有建立合作機制的責任，政府（公共部門）也可主導合作機制的建立。 　　不同的高科技產業特性，搭配「適合的」共生綜效利益，可提高產業與企業的競爭力。環境依賴程度高的產業特性，對環境資源共享之經濟性的需求就會較高；專業分工程度高的產業特性，對產業網路合作之互補性的需求就會較高。

Symbioses between microbes and multicellular eukaryotes are found in all biomes, and encompass a spectrum of symbiotic lifestyles that includes parasitism and disease, commensalism, and mutually beneficial interdependent host-microbe relationships. Regardless of outcome, these symbiotic lifestyles are governed by a complex molecular "courtship" between microbe and potential host. This courtship is the primary determinant of the host range of a given microsymbiont. Host immunity poses a formidable barrier to the establishment of host-microbe relationships, and the majority of microbial suitors will be thwarted by it. Only by successfully "wooing" the host cell's immune defenses with the appropriate molecular signals can a microsymbiont successfully colonize its host. A strategy common to microsymbionts across the spectrum of symbiotic lifestyles and host organisms is the delivery of microbial-encoded effector proteins into the cytoplasm of host cells to manipulate the host cell's molecular machinery for the purposes of subverting host immunity. Bacteria, in particular, have adapted a number of secretion systems for this purpose. The most well-characterized of these is the type III secretion system (T3SS), a molecular apparatus that specializes in injecting type III effector (T3Es) proteins directly into host cells. The work in this thesis focuses on T3Es of plant-associated bacteria, with particular emphasis on mutualistic bacteria. We present evidence that collections of T3Es from Sinorhizobium fredii and Bradyrhizobium japonicum are, in stark contrast to those of phytopathogenic bacteria, in a co-evolutionary equilibrium with their hosts. This equilibrium is characterized by highly conserved T3E collections consisting of many "core" T3Es with little variation in nucleotide sequence. The T3Es of Mesorhizobium loti MAFF303099 suggest a completely different picture of the evolution of T3Es. MAFF303099 recently acquired its T3SS locus, and the work in this thesis provides an evolutionary snapshot of a mutualist that is innovating a T3E collection primarily through horizontal gene transfer. Collectively, this work represents the first comprehensive catalog of T3Es of rhizobia and, in the case of Sinorhizobium and Bradyrhizobium, the first evidence of purifying selection for T3Es. / Graduation date: 2012

Bonobos (Pan paniscus) are threatened with extinction. They are the largest primates, and the only apes (except human), of the southern bank of the Congo Basin. Along with chimpanzees, they are our closest living relatives and are studied by anthropologists to include/understand our hominid origins; but what about their functional role in the forest? Would their disappearance have serious consequences for forest ecology? Answering this question is the aim of this new project, with several years of observations of a free-ranging habituated group of bonobos on the LuiKotale research station (DR Congo). In this tropical rainforest, the very great majority of plants need animals to reproduce and disperse their seeds. Bonobos are the largest frugivorous animals in this region, after elephants. During its life, each bonobo will ingest and disperse nine tons of seeds, from more than 91 species of lianas, grass, trees and shrubs. These seeds will travel 24 hours in the bonobo digestive tract, which will transfer them over several kilometers (mean 1.3 km; max: 4.5 km), far from their parents, where they will be deposited intact in their feces. These dispersed seeds remain viable, germinate better and more quickly than unpassed seeds. For those seeds, diplochory with dung-beetles (Scarabaeidae) imrpoves post-dispersal survival. Certain plants such as Dialium may even be dependent on bonobos to activate the germination of their seeds, characterized by tegumentary dormancy. The first parameters of the effectiveness of seed dispersal by bonobos are present. Behavior of the bonobo could affect the population structure of plants whose seeds they disperse. The majority of these zoochorous plants cannot recruit without dispersal and the homogeneous spatial structure of the trees suggests a direct link with their dispersal agent. Few species could replace bonobos in terms of seed dispersal services, just as bonobos could not replace elephants. There is little functional redundancy between frugivorous mammals of the Congo, which face severe human hunting pressures and local exctinction. The defaunation of the forests, leading to the empty forest syndrome, is critical in conservation biology, as will be illustrated here. The disappearance of the bonobos, which disperse seeds of 65% of the tree species in these forests, or 11.6 million individual seeds during the life of each bonobo, will have consequences for the conservation of the Congo rainforest

Orientador: Anselmo Nogueira / Resumo: Muitas características fenotípicas das plantas mudam drasticamente ao longo do desenvolvimento vegetal e podem influenciar as interações ecológicas. Dado que existe um custo energético associado a manutenção de diferentes mutualismos, investigamos a relação entre os estádios de desenvolvimento vegetal e o estabelecimento de três mutualismos, assim como a possível interferência do mutualismo raiz-rizóbio sobre os mutualismos nectário extrafloral-formiga e flor-abelha. No campo selecionamos 30 plantas da espécie de leguminosa de Cerrado, Chamaecrista desvauxii var. latistipula, com diferentes tamanhos, de indivíduos juvenis a maiores reprodutivos, para avaliar a ocorrência e intensidade das interações mutualistas raiz-rizóbio, nectário extrafloral-formiga e flor-abelha. Em casa de vegetação montamos um experimento manipulando as bactérias do tipo rizóbio e o tipo de solo em que as plantas foram cultivadas, no qual investigamos a interferência da interação raiz-rizóbio sobre os recursos vegetais disponíveis para outros mutualismos. As plantas amostradas em campo variaram entre 4 a 1300 unidade de tamanho. A interação raiz-rizóbio e nectário extrafloral-formiga ocorreu em plantas ainda muito pequenas, enquanto a interação flor-abelha se estabeleceu em plantas maiores. A intensidade da interação teve padrão exponencial para os nódulos radiculares e visitação das abelhas, e quadrático para as formigas. Esses padrões distintos na intensidade dos mutualismos sugeriram possível interf... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Plant phenotypic traits change drastically throughout plant development and can modify ecological interactions. Whereas there is an energy cost associated with maintenance of different mutualisms on the same plant, we investigated the relationship between plant development and the establishment of multiple mutualisms. Besides, we evaluated the possible interference of the root-rhizobia mutualism on extrafloral nectary-ant and flower-bee mutualisms. In the field, we selected 30 plants of Cerrado legume species, Chamaecrista desvauxii var. latistipula, with different sizes, from juvenile to reproductive individuals, to evaluate the occurrence and intensity of root-rhizobia, extrafloral nectary-ant and flower-bee interactions. In a greenhouse, we manipulate the rhizobia bacteria and soil type, investigating the interference of root-rhizobia on plant resources available for other mutualisms. Plants sampled in field ranged from 4 to 1300 plant size. Root-rhizobia and extrafloral nectary-ant interactions occurred on tiny plants, while flower-bee interaction was established on larger plants. The strength of interactions had an exponential pattern for root nodules and bee visitation, and quadratic for ant visitation. These distinct patterns suggested a possible interference between mutualisms since the number of root nodules and the flower-bee interaction increased and the extrafloral nectary-ant interaction decreased. Moreover, in the rhizobium exclusion experiment, plants with inoc... (Complete abstract click electronic access below) / Mestre

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Ants that collect nectar from plants bearing extrafloral nectaries (EFN) can defend them against the attacks of herbivores. Many cases of this food-for-protection mutualism have been described and the next step is to understand the mechanisms that structure these interactions. In this study, this issue was addressed through field observations and experiments on ant behaviour in studies compiled into five chapters. Specifically, we evaluated the plant\'s investment in attracting ants (nectar quality) and the competitive relationship between ants (resource dominance hierarchies) as structuring mechanisms of ant-plant interactions. The entire study took place in areas of the ecosystem known as Rupestrian Fields, located in Ouro Preto (Brazil), between June 2011 and March 2014. In Chapter 1, we observe that ant-plant interaction network in Rupestrian Fields is nested and generalized as expected for mutualisms, but differs from ant-hemipteran network, its ecological equivalent, despite both share ant species interactions. In Chapter 2, we delve into the study of the effect of resources in interaction frequency, and we showed that the quality more than quantity of nectar determines the pattern of interaction between plants (10 species) and ants (32 species), as well as the benefits of this interaction (conditional outcomes). In the Chapter 3, we focus on the ants to demonstrate, using paired encounters, that ants species are organized in dominance hierarchies based on aggressiveness. This hierarchies affects the numerical dominance based on territoriality and, more importantly, in the dominance of interactions and nectar. Keeping this line of thought, we demonstrated in Chapter 4 that not all ants that collect nectar really protect the plant against herbivores but only the ecological dominant and highly interacted species. Finally, we close the thesis demonstrating in Chapter 5 that the ant species interacted with plants during the day are not the same at night, but this diurnal-nocturnal turnover does not affect the structure of the interactions by only changing the dominant species. This study brings behavioural and empirical evidences on the importance of the identity of the ant species and its ecological dominance, as well the effect of the nectar quality, for the structure of ant-plant interactions and effectiveness of mutualisms. / As formigas que recolhem o néctar das plantas com nectários extraflorais (EFN) podem defendê-las contra ataques de herbívoros. Muitos casos desse tipo de mutualismo foram descritos mas ainda é preciso entender os mecanismos que estruturam essas interações. Neste estudo, esse problema foi abordado através de observações de campo e experimentos sobre o comportamento das formigas compilados em cinco capítulos. Especificamente, foi avaliado o investimento da planta em atrair formigas (qualidade do néctar) e a relação competitiva entre formigas pelo néctar (hierarquias de dominância) como mecanismos estruturadores das interações formiga-planta (partição das interações). Todo o estudo ocorreu em áreas do ecossistema Campo Rupestre, localizadas em Ouro Preto (Brasil), de junho de 2011 a março de 2014. No Capítulo 1, observamos que redes de interação formiga-planta em Campo rupestre é aninhada e generalizada como esperado para mutualismos, mas difere da rede formiga-hemíptero, seu equivalente ecológico, apesar de compartilharem as mesmas espécies de formigas interagentes. No Capítulo 2, nós aprofundamos no efeito dos recursos estruturando interações, e mostramos que a qualidade mais do que a quantidade de néctar determina o padrão de interação entre formigas (32 espécies) e plantas (10 espécies), bem como os benefícios desta interação (benefícios condicionais). No Capítulo 3, nós demonstramos através de encontros interespecíficos pareados que as formigas são organizadas em hierarquias de dominância comportamental baseadas em agressividade. Essa hierarquia afeta a dominância numérica por territorialidade e, mais importante, o domínio das interações e do néctar. Mantendo esta linha de pensamento, demonstramos no Capítulo 4 que nem todas as formigas que coletam néctar realmente protegem a planta contra herbívoros mas somente as espécies dominantes e altamente interagidas. Finalmente, fechamos a tese demonstrando no Capítulo 5 que as espécies de formiga que interagem com as plantas durante o dia não são o mesmo à noite, mas esta rotatividade diurno-noturno não afeta a estrutura das interações devido a troca específica da formiga dominante. Este estudo traz evidências comportamentais e empíricas sobre a importância da identidade de espécies de formiga e sua dominância ecológica, assim como da qualidade do recurso, para a estrutura de rede da formiga-planta e eficácia do mutualismo. / Doutor em Ecologia e Conservação de Recursos Naturais

Obligate nursery pollination mutualisms such as the fig–fig wasp system, with their central plant–pollinator mutualism associated with non-pollinating satellite wasp species, can function as closed system microcosms representative of tritrophic communities. In this system, enclosed inflorescences (syconia) function as sites of seed production, as well as brood-sites for the progeny of herbivorous mutualistic pollinators, non-pollinating gallers and parasitoids of the two. Plant reproductive traits such as inflorescence size (syconium volume) and within-plant phenology (within-tree asynchrony) as can affect inter-species relationships among the three trophic levels in such plant–herbivore–parasitoid systems. Induced or natural variations in such plant traits could influence various direct and indirect effects among the organisms in the community and could even lead to the formation of feedback cycles. Furthermore, changes in the abiotic environment could have major impacts on the biotic associations in the system either by affecting the community members directly, or through their effects on plant reproductive traits. Ficus racemosa with its fig wasp community comprised of a single herbivorous pollinator mutualist, three non-pollinating parasitic gallers and three non-pollinating parasitoids was used as a model to investigate: (1) the role of mutualistic and parasitic fig wasps in affecting within-tree phenology; (2) direct and indirect biotic associations between various groups of fig wasps (pollinators, gallers and parasitoids) and the influence of inflorescence size and within-tree phenology on them; and (3) variations in the reproduction of and the biotic associations between the organisms of the community under variable abiotic climatic conditions. Patterns of plant reproductive phenology are usually considered evolved responses directed at optimizing resource use, pollen receipt/donation schedules and seed dispersal for plant individuals. Within-plant reproductive synchrony or asynchrony can arise due to variation in floral initiation patterns, as well as from localised proximate mechanistic responses to interactants such as pollinators, parasites and herbivores which could affect floral longevity or fruit development time. The investigation was begun by exploring the role of a mutualistic pollinator, and for the first time in a brood-site mutualism, that of parasitic herbivores (gallers) and parasitoids in influencing within-plant reproductive phenology. Since a syconium functions as an inflorescence which develops into a fruit after pollination, investigations were carried out on the impact on syconium synchrony of fig wasps that began their development within the brood site syconium at pre-pollination, pollination, and post-pollination stages via their effects on the development time of individual syconia in Ficus racemosa. We found that syconium initiation patterns were not the only proximate mechanism for within-tree reproductive asynchrony, and that individual syconia (even within a tree) had highly plastic development times dependent on their sizes, pollination time and the species of wasp progeny developing within them. Syconium volume, pollination early in the pollen-receptive phase and presence of early-ovipositing galler progeny reduced syconium development time, whereas the presence of late-ovipositing parasitoid progeny or pollination late in the pollen-receptive phase increased syconium development time. These results suggest an ongoing tug-of-war between syconium inhabitants to modify syconium development times. Parasitic fig wasps pull in different directions to suit their own needs, such that final syconium development times are likely to be a compromise between conflicting demands from developing seeds and from different wasp species. Inter-species relationships among the three trophic levels in plant–herbivore–parasitoid systems can potentially include various direct and indirect effects possibly mediated by induced or natural variations in plant traits. Analysing the seed and fig wasp compositions of microcosm replicates, i.e. individual syconia, shows that besides direct competition for resources and predator–prey interactions, the F. racemosa community also displays exploitative or apparent competition and trait-mediated indirect interactions. Syconium volume and within-tree asynchrony were reproductive plant traits that not only affected plant–herbivore and plant–parasitoid associations, but also possibly modified herbivore–herbivore and herbivore–parasitoid interactions. Our results also indicated that the reciprocal effects of higher trophic level fauna on plant traits (and vice versa) within this system drive a positive feedback cycle between syconium inhabitants and within-tree reproductive asynchrony. In the F. racemosa system, abiotic environmental factors could affect the reproduction of mutualistic pollinators, non-mutualistic parasites and seed production via seasonal changes in plant reproductive traits such as syconium volume within-tree asynchrony. Temperature, relative humidity and rainfall defined four seasons: winter; hot days, cold nights; summer and wet seasons. Syconium volumes were highest in winter and lowest in summer, and affected syconium contents positively across all seasons. Greater transpiration from the nurseries was possibly responsible for smaller syconia in summer. The 3–5°C increase in mean temperatures between the cooler seasons and summer reduced fig wasp reproduction and increased seed production nearly two-fold. Yet, seed and pollinator progeny production were never negatively related in any season confirming the mutualistic fig–pollinator association across seasons. Parasites affected seed production negatively in some seasons, but had a surprisingly positive relationship with pollinators in most seasons. While within-tree reproductive phenology did not vary across seasons, its effect on syconium inhabitants varied with season. In all seasons, within-tree reproductive asynchrony affected parasite reproduction negatively, whereas it had a positive effect on pollinator reproduction in winter and a negative effect in summer. Seasonally variable syconium volumes probably caused the differential effect of within-tree reproductive phenology on pollinator reproduction. Within-tree reproductive asynchrony itself was positively affected by intra-tree variation in syconium contents and volume, creating a unique feedback loop which varied across seasons. Therefore, nursery size affected fig wasp reproduction, seed production and within-tree reproductive phenology via the feedback cycle in this system. Climatic factors affecting plant reproductive traits can cause biotic relationships between plants, mutualists and parasites to vary seasonally and must be accorded greater attention, especially in the context of climate change.

Cette thèse porte sur le rôle de l’espace dans l’organisation et dans la dynamique des communautés écologiques multi-espèces. Deux carences peuvent être identifiées dans les études théoriques actuelles portant sur la dimension spatiale des communautés écologiques : l’insuffisance de modèles multi-espèces représentant la dimension spatiale explicitement, et le manque d’attention portée aux interactions positives, tel le mutualisme, en dépit de la reconnaissance de leur ubiquité dans les systèmes écologiques. Cette thèse explore cette problématique propre à l’écologie des communautés, en utilisant une approche théorique s’inspirant de la théorie des systèmes complexes et de la mécanique statistique. Selon cette approche, les communautés d’espèces sont considérées comme des systèmes complexes dont les propriétés globales émergent des interactions locales entre les organismes qui les composent, et des interactions locales entre ces organismes et leur environnement. Le premier objectif de cette thèse est de développer un modèle de métacommunauté multi-espèces, explicitement spatial, orienté à l’échelle des individus et basé sur un réseau d’interactions interspécifiques générales comprenant à la fois des interactions d’exploitation, de compétition et de mutualisme. Dans ce modèle, les communautés locales sont formées par un processus d’assemblage des espèces à partir d’un réservoir régional. La croissance des populations est restreinte par une capacité limite et leur dynamique évolue suivant des mécanismes simples de reproduction et de dispersion des individus. Ces mécanismes sont dépendants des conditions biotiques et abiotiques des communautés locales et leur effet varie en fonction des espèces, du temps et de l’espace. Dans un deuxième temps, cette thèse a pour objectif de déterminer l’impact d’une connectivité spatiale croissante sur la dynamique spatiotemporelle et sur les propriétés structurelles et fonctionnelles de cette métacommunauté. Plus précisément, nous évaluons différentes propriétés des communautés en fonction du niveau de dispersion des espèces : i) la similarité dans la composition des communautés locales et ses patrons de corrélations spatiales; ii) la biodiversité locale et régionale, et la distribution locale de l’abondance des espèces; iii) la biomasse, la productivité et la stabilité dynamique aux échelles locale et régionale; et iv) la structure locale des interactions entre les espèces. Ces propriétés sont examinées selon deux schémas spatiaux. D’abord nous employons un environnement homogène et ensuite nous employons un environnement hétérogène où la capacité limite des communautés locales évoluent suivant un gradient. De façon générale, nos résultats révèlent que les communautés écologiques spatialement distribuées sont extrêmement sensibles aux modes et aux niveaux de dispersion des organismes. Leur dynamique spatiotemporelle et leurs propriétés structurelles et fonctionnelles peuvent subir des changements profonds sous forme de transitions significatives suivant une faible variation du niveau de dispersion. Ces changements apparaissent aussi par l’émergence de patrons spatiotemporels dans la distribution spatiale des populations qui sont typiques des transitions de phases observées généralement dans les systèmes physiques. La dynamique de la métacommunauté présente deux régimes. Dans le premier régime, correspondant aux niveaux faibles de dispersion des espèces, la dynamique d’assemblage favorise l’émergence de communautés stables, peu diverses et formées d’espèces abondantes et fortement mutualistes. La métacommunauté possède une forte diversité régionale puisque les communautés locales sont faiblement connectées et que leur composition demeure ainsi distincte. Par ailleurs dans le second régime, correspondant aux niveaux élevés de dispersion, la diversité régionale diminue au profit d’une augmentation de la diversité locale. Les communautés locales sont plus productives mais leur stabilité dynamique est réduite suite à la migration importante d’individus. Ce régime est aussi caractérisé par des assemblages incluant une plus grande diversité d’interactions interspécifiques. Ces résultats suggèrent qu’une augmentation du niveau de dispersion des organismes permet de coupler les communautés locales entre elles ce qui accroît la coexistence locale et favorise la formation de communautés écologiques plus riches et plus complexes. Finalement, notre étude suggère que le mutualisme est fondamentale à l’organisation et au maintient des communautés écologiques. Les espèces mutualistes dominent dans les habitats caractérisés par une capacité limite restreinte et servent d’ingénieurs écologiques en facilitant l’établissement de compétiteurs, prédateurs et opportunistes qui bénéficient de leur présence. / This thesis is a study of the role of space in the organization and dynamics of multi-species ecological communities. Two weaknesses can be identified from previous theoretical studies concerned with the spatial dimension of ecological communities: the scarcity of multi-species models based on a spatially explicit representation of space, and the lack of attention toward positive interspecific interactions, such as mutualism, despite the recognition of their ubiquity in ecological systems. This thesis explores this problematic by adopting a theoretical framework based on complex system theory and statistical mechanics. Following this approach, ecological communities can be viewed as complex systems whose global properties emerge from the local interactions between the organisms that composed them, and between the organisms and their environment. The first objective of this thesis is to develop a multi-species metacommunity model which is spatially explicit, individual-based, and centered on a general interspecific interaction web containing exploitation, competition as well as mutualism. In this model, local communities are created by an assembly process whereby species are drawn from a regional pool. Population growth is restricted by a carrying capacity and its dynamics is driven by simple reproduction and dispersal mechanisms acting at the level of single individual. These mechanisms depend on the biotic and abiotic conditions of the local communities and their effect varies with species, time and space. The second objective of this thesis is to determine the impact of an increasing spatial connectivity on the dynamics, and structural and functional properties of this metacommunity. More precisely, we set out to evaluate different community properties under changes in the level of species dispersal: i) the similarity in local community composition and its patterns of spatial correlations, ii) the local and regional diversity and the local species abundance, iii) the local and regional biomass, productivity and dynamical stability, and iv) the structure of the local interaction webs. These properties are examined under two spatial schemes. First, we employ a homogeneous environment, and second we employ a heterogeneous environment whereby the carrying capacity of local communities evolves along a gradient. In general, our results reveal that spatially distributed ecological communities are extremely sensitive to the modes and levels of species dispersal. Their spatiotemporal dynamics as well as their structural and functional properties can undergo profound changes in the form of significant transitions under slight changes of the level of dispersal. These changes are also highlighted by the emergence of spatiotemporal patterns in the spatial distribution of the populations, which are characteristics of phase transition generally observed in physical systems. The metacommunity presents two dynamical regimes. In the first regime, corresponding to weak levels of species dispersal, the assembly dynamics promotes the emergence of species-poor but stable communities made of abundant and strongly mutualistic species. The metacommunity has a high regional diversity since weakly connected communities conserve a distinct assemblage of species. On the other hand, in the second regime, corresponding to strong dispersal rates, regional diversity decreases at the benefit of an increase in local diversity. Local communities are more productive but their stability is reduced due to the important migration of individuals. This regime is also characterized by assemblages containing a richer diversity of interspecific interactions. These results suggest that an augmentation in the level of species dispersal permits organisms to couple local communities together which increases local coexistence and promotes the organization of richer and more complex ecological communities. Finally, our results suggest that mutualism is fundamental to the organization and persistence of ecological communities. Mutualistic species dominate in habitats characterized by a restricted carrying capacity and serve as ecological engineer by facilitating the establishment of competitors, predators and opportunists which benefit from their presence.