Dissertations / Theses: 'Interaction niche'

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Grégoire, Murielle. "Polynucléaires neutrophiles, cellules stromales, lymphocytes B : interaction tripartite dans la niche des lymphomes B." Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S156/document.

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Les polynucléaires neutrophiles ont longtemps été considérés comme des cellules n’intervenant que dans la réponse immune innée. Cependant, au cours de ces dernières années, de nombreuses publications suggèrent que ces cellules, retrouvées au sein du microenvironnement de nombreux cancers, pourraient également jouer un rôle dans la tumorigénèse et la progression tumorale. Ces études mettent en évidence leur fréquence comme marqueur pronostique dans différents cancers solides, mais peu de travaux se sont intéressés à la caractérisation fonctionnelle de ces cellules dans la progression tumorale. Dans de nombreux cancers dont les lymphomes B issus du centre germinatif, les cellules tumorales, qui sont incapables de proliférer et de survivre seules, sont dépendantes de leur microenvironnement de soutien. Dans cette étude, nous avons évalué la fonctionnalité des polynucléaires neutrophiles dans la croissance des lymphomes B. Ainsi, nous avons démontré pour la première fois que les polynucléaires neutrophiles soutiennent directement la croissance et la survie des cellules tumorales de lymphomes B. De plus, un dialogue bidirectionnel existe entre les polynucléaires neutrophiles et les cellules stromales. D’une part, les cellules stromales soutiennent la survie des polynucléaires neutrophiles, qui en retour induisent les caractéristiques d’un stroma lymphoïde. L’induction de ce phénotype permet aux cellules stromales d’acquérir de meilleures capacités de soutien envers les cellules tumorales. Cette étude confirme donc que les polynucléaires neutrophiles sont une composante importante du microenvironnement tumoral, et pourraient devenir une nouvelle cible thérapeutique pour le traitement des lymphomes B issus du centre germinatif For long time, neutrophils have only been considered as cells involved in the innate immune response. More recently, in descriptive publications, neutrophils were found in the microenvironment of many solid cancers, hypothesizing that they could also play a role in tumorigenesis and cancer progression. These studies highlighted the prognostic value of their frequency, but few of them focused on the functional characterization of these cells in tumor growth. In many cancers, including germinal centre-derived B-cell lymphomas, tumor cells are dependent on their microenvironment to proliferate and survive. In this study, we focused on the role of neutrophils in the progression of B-cell lymphomas, and for the first time we demonstrated that neutrophils directly support the growth and survival of tumor Bcells. In addition, we highlighted the existence of bidirectional cooperation between neutrophils and stromal cells. In one hand stromal cells support the survival of neutrophils. On the other hand, neutrophils induce a lymphoid stroma phenotype which is well known to enhance their supportive effect on tumor cells. This study demonstrates that neutrophils are a significant component of the tumor microenvironment and may be considered as a potential therapeutic target for the treatment of B-cell lymphomas

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Maby-El, Hajjami Hélène. "Microenvironnement et lymphomes B du centre germinatif : importance de la niche mésenchymateuse." Rennes 1, 2008. http://www.theses.fr/2008REN1S017.

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Le lymphome folliculaire (FL) est une pathologie tumorale se développant au dépens de lymphocytes B des centres germinatifs des ganglions. Il est caractérisé par une forte dépendance à un environnement ganglionnaire cellulaire et cytokinique complexe. La moelle osseuse fournit également une «niche» propice au développement du FL, puisqu’une infiltration tumorale est observée dans plus de 70% des cas au diagnostic, avec l'apparition ectopique d'un environnement de type ganglionnaire. L’originalité et le but de notre projet ont été d’étudier in vitro les cellules de FL dans le contexte de leur environnement de soutien, en nous intéressant plus particulièrement à deux compartiments mésenchymateux potentiellement impliqués dans la lymphomagenèse B: les cellules fibroblastiques réticulaires (FRC) et leur précurseur putatif, les cellules souches mésenchymateuses (CSM) présentes au niveau médullaire et ganglionnaire. Nous avons démontré que les CSM pouvaient acquérir l'ensemble des caractéristiques des FRC après stimulation par le tumor necrosis factor-α et la lymphotoxine-α1β2 ou après contact direct avec des cellules de FL, et devenaient ainsi capables de soutenir la migration, l'adhérence et la croissance des cellules de FL. Cependant, l’effet de soutien des CSM et FRC était inhibé suite à leur exposition à un environnement comportant de l’interféron-γ. En effet, ces cellules mésenchymateuses dans ce contexte développaient une activité indoléamine 2,3 dioxygénase, responsable d’effets antiprolifératif et pro-apoptotique sur les cellules tumorales. Ces résultats montrent l’importance et la complexité de l’environnement cellulaire et cytokinique au cours du FL Follicular lymphoma (FL) results from the malignant transformation of germinal center-derived B cells that accumulate within lymph nodes. This disease is characterized by an important crosstalk between non malignant cells and the tumoral compartment. Bone marrow also provides a preferential niche for FL malignant cells, since tumoral infiltration is found in up to 70% of FL cases at diagnosis, in association with the emergence of ectopic lymph node-like environment. The originality and the goal of our project were to study in vitro FL cells in respect of their supportive microenvironment. We focused our studies on mesenchymal cell compartments. Two cell populations seemed to be of great interest in B-cell lymphomagenesis: fibroblastic reticular cells (FRCs), and their postulated progenitors mesenchymal stem cells (MSCs). Indeed, cells with phenotypic and functional features of MSCs could be found not only in the medullar but also in the lymphoid compartments. We demonstrated that MSCs could acquire a complete phenotype of FRCs after stimulation with tumor necrosis factor-α and lymphotoxin-α1β2 or after a direct contact with FL cells, and were able to support migration, adhesion and growth of lymphoma B cells. However, the B cell-supportive properties of MSCs and FRCs were overruled following their pretreatment with interferon-γ. Indeed, IFN-γ-conditioned mesenchymal cells developed functional indoleamine 2, 3 dioxygenase activity, which was reponsible of both antiproliferative and proapoptotic effects on tumoral B cells. Our results underline the key role and the complexity of cellular and molecular environment in FL

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Sugimura, Ryohichi. "Non-canonical Wnt signaling maintains hematopoietic stem cell through Flamingo and Frizzled8 interaction in the niche." Thesis, Open University, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580673.

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Wnt signaling is involved in self-renewal and maintenance ofhematopoietic stem cells (HSCs); however, the particular role of non-canonical Wnt signaling in regulating HSCs in vivo is largely unknown. Here I show Flamingo and Frizzled8, members of non-canonical Wnt signaling, both express in and functionally maintain quiescent long-term HSCs. Flamingo regulates Frizzled8 distribution at the interface between HSCs and N-cadherin + osteoblasts (N-cad+OBs that enrich osteoprogenitors) in the niche. I further show that N-cad+OBs predominantly express non-canonical Wnt ligands and inhibitors of canonical Wnt signaling under homeostasis. This non-canonical Wnt signaling is attenuated prior to activation of HSCs. In the activated HSCs, however, canonical Wnt signaling is enhanced. Mechanistically, non-canonical Wnt signaling mediated by Frizzled8 suppresses the Ca2+-NF AT- IFNy pathway and antagonizes canonical Wnt signaling in HSCs. My findings demonstrate that non-canonical Wnt signaling maintains quiescent long- term HSCs through Flamingo and Frizzled8 interaction in the niche.

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Costa, Paula Lemos da. "Variação intrapopulacional no uso do recurso: modelos teóricos e evidência empírica." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/41/41134/tde-14102013-112513/.

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Tradicionalmente, nichos populacionais são descritos como a somatória de todos os recursos utilizados por uma população. Entretanto, diversos estudos mostram que indivíduos dentro de uma população podem usar recursos de forma distinta. Investigamos três maneiras pelas quais indivíduos podem variar quanto ao uso do recurso. Indivíduos podem apresentar a mesma preferência por presas, mas diferir na propensão à adição de novos itens alimentares em sua dieta (Preferências Compartilhadas); indivíduos podem apresentar a mesma presa preferida mas diferirem em suas presas alternativas (Refúgio Competitivo); ou indivíduos podem apresentar presas preferidas distintas (Preferências Distintas). Estudamos os padrões de interação que emergem sob os pressupostos de cada um dos modelos usando redes de interação entre indivíduos e os recursos que eles consomem. Dessa forma, para derivarmos as previsões de cada um dos modelos de uso de recurso, desenvolvemos modelos simples que geram redes de interação segundo regras que seguem os pressupostos dos modelos e confrontamos essas previsões com dados empíricos, comparando a estrutura dessa redes de interação. Encontramos que o modelo que menos se assemelha ao padrão de uso de recurso observado para as populações estudadas foi o modelo de Preferências Compartilhadas. Para as populações estudadas, a variação intrapopulacional na escolha de presas parece estar mais associada a diferenças nas sequências de preferências por presas entre indivíduos e não à propensão desses indivíduos em adicionarem novos recursos às suas dietas. Traditionally, a population\'s niche is described as the sum of all resources consumed by a population. However, several studies have highlighted that individuals within a population can use resources differently. We investigate three ways in which individuals can vary in their resource use. Individuals can show the same preference for prey, but differ in their likelihood of adding new prey to their diets (Shared Preferences); individuals can share the same top-ranked prey but differ in their alternative prey (Competitive Refuge); or individuals can have different top-ranked prey (Distinct Preferences). We studied the pattern of interaction that emerges under each model\'s assumption using interaction networks between individuals and the resources they consume. In this sense, to derive the predictions associated with each model of resource use, we developed simple models that generates interaction networks according to a set of rules that represent the assumptions of each model and then confronted these predictions with empirical data on interaction networks, by looking at the structure of these interaction networks. We found that the model that least resembles the pattern of resource use observed in the populations studied was the Shared Preferences model. For the studied populations, intrapopulation variation is not associated with individuals sharing the same rank sequence and differing in their willingness to add new resources to their diets. Instead, it seems that differences in the rank sequence of prey choice are more important in structuring the pattern of resource use in these populations.

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Escoriza, Daniel. "Factors regulating the invasion of two Mediterranean anurans. The role of niche conservatism, species interaction and habitat selection." Doctoral thesis, Universitat de Girona, 2015. http://hdl.handle.net/10803/300902.

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Amphibians are a group in worldwide decline. The factors that are causing this decline are not well known, but could be multifactorial, related to the recent expansion of pathogens and habitat disturbance. One of these factors related to the loss of habitat quality is the introduction of alien species. These species can compete with or prey on species of the recipient community, producing deep changes in the structure of these communities. For this reason it is a priority to know which factors act by facilitating the invasion process and which species could be more affected by the presence of this alien species. In Catalonia has become established an alien frog, the painted frog. Introduced in the extreme south of France in the early XXth century, this species has expanded gradually, reaching the Llobregat delta to the south and Llanguedoc to the north. This region is rich in native species of amphibians, some of them endemic, and therefore it is necessary to know how this newcomer species interacts with each of these species. We have used a novel approach when analyzing these interactions, applying the theory of morphospaces. The morphospace is the range of morphological variation observed within a community. This morphology is correlated with the use of a niche, and hence the morphological similarities between the invasive and native species serve as a proxy to assess the functional overlap. These analogies in morphospace were evaluated also in the area of native species and among other species of Discoglossus. The question asked is "Does the invasive species occupy a vacant niche, maintaining a similar morphological gap than that observed in the source assemblage and in the case of other species of the genus Discoglossus?”. Els amfibis són un grup en declivi a nivell mundial. Els factors que estan causant aquest declivi no són coneguts, però podria ser multifactorial, en relació amb l'expansió recent de certs patògens i les alteracions dels hàbitats. Un d'aquests factors que es relacionen amb la pèrdua de qualitat dels hàbitats és la introducció d'espècies exòtiques. Aquestes espècies poden competir o depredar sobre les espècies de la comunitat recipient, produint profundes alteracions en l'estructura d'aquestes comunitats. Per aquesta raó és prioritari conèixer que factors actuen facilitant el procés invasiu i quines espècies es poden veure més afectades per la presència d'una espècie exòtica. A Catalunya s'ha establert una espècie de anur d'origen africà, la granota pintada. Introduïda a l'extrem sud de França a inicis del segle XX, aquesta espècie s'ha anat expandint de forma progressiva, fins a arribar pel sud al delta del Llobregat i pel nord el Llenguadoc. Aquesta regió és rica en espècies natives d'amfibis, algunes d'elles endèmiques, i per tant cal conèixer com interacciona aquesta espècie recent arribada amb cadascuna d'aquestes espècies. Nosaltres hem utilitzat un enfocament nou en el moment d'analitzar aquestes interaccions, aplicant la teoria dels morfoespais. El morfoespai és el rang de variació morfològica que s'observa dins d'un acoblament. Aquesta morfologia es correlaciona amb l'ús d'un nínxol, i per tant les analogies morfològiques entre l'espècie invasora i les espècies natives poden servir com una aproximació per valorar el solapament funcional. Aquestes analogies en el morfoespai s'han avaluat també en l'area nativa de l'espècie i entre altres espècies de Discoglossus. La pregunta formulada és "ocupa l'espècie invasora un nínxol vacant, mantenint una distància morfològica similar que a l'acoblament d'origen i que altres espècies del gènere Discoglossus?".

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Nicvert, Lisa. "Méthodes statistiques et outils logiciels pour l'analyse et l'inférence de réseaux écologiques et le traitement de données multi-espèces." Electronic Thesis or Diss., Lyon 1, 2024. http://www.theses.fr/2024LYO10130.

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Les interactions entre espèces dans les communautés écologiques sont complexes : de nombreuses espèces peuvent interagir les unes avec les autres de façons variées et à différentes échelles spatiales et temporelles. De plus, ces réseaux d'interactions sont la résultante de multiples causes, engendrent de multiples processus et ont des conséquences parfois indirectes transmises au travers de la structure du réseau. Cette complexité nécessite une diversité d'approches pour comprendre les déterminants des interactions et prédire leurs effets dans les systèmes écologiques. Cette thèse étudie plusieurs aspects des réseaux d'interactions écologiques par une approche méthodologique qui se concentre sur la description, l'évaluation et le développement de méthodes statistiques et d'outils logiciels. Dans une première partie, j'étudie les causes de la structure des réseaux d'interactions en me concentrant sur les niches d'interactions et en utilisant la notion de concordance des traits entre espèces. Pour cela, j'utilise des méthodes de la famille de l'analyse des correspondances et j'applique et j'étends des méthodes de mise à l'échelle réciproque à l'analyse de réseaux bipartites. J'applique ces méthodes à l'analyse d'un réseau d'interactions plantes-frugivores d'une forêt de montagne péruvienne et je montre que les traits des espèces peuvent être reliés à leur largeur de niche. Dans une deuxième partie, j'étudie les conséquences des interactions au travers de leur influence sur la répartition spatio-temporelle des espèces. Pour cela, j'utilise des processus de Hawkes multivariés pour analyser des données de pièges photographiques. J'illustre ces modèles sur cinq mammifères de la savane sud-africaine et je montre des attractions et évitements entre plusieurs de ces espèces à courte échelle spatio-temporelle. Dans une troisième partie, je me penche sur l'analyse de données collectées par pièges photographiques. Je développe un package R pour nettoyer et standardiser ces données à l'usage du programme Snapshot Safari, ainsi qu'une application Shiny destinée à un usage plus général pour visualiser de données de façon interactive et reproductible. Cette thèse présente des méthodes statistiques et outils logiciels pour analyser des données écologiques complexes et améliorer la compréhension des réseaux d'interactions. Ces résultats ouvrent des perspectives nouvelles concernant l'analyse de données écologiques ainsi que les développement méthodologique en écologie Interactions between species in ecological communities are complex: many species can interact with each other in a variety of ways and at different spatial and temporal scales. Moreover, these interaction networks are the result of multiple causes, generate multiple processes and can have indirect effects transmitted through the structure of the network. This complexity calls for a variety of approaches to understand the determinants of interactions and predict their effects in ecological systems. This thesis studies several aspects of ecological interaction networks using a methodological approach that focuses on the description, evaluation and development of statistical methods and software tools. In a first part, I study causes of the structure of interaction networks, focusing on interaction niches and using the notion of trait matching between species. To this end, I use methods from the correspondence analysis family and apply and extend reciprocal scaling methods to the analysis of bipartite networks. I apply these methods to the analysis of a plant-frugivore interaction network in a Peruvian montane forest, and show that species traits can be related to their niche width. In a second part, I study the consequences of interactions through their influence on the spatio-temporal distribution of species. To this end, I use multivariate Hawkes processes to analyze camera trap data. I illustrate these models on five mammals from the South African savanna, showing attraction and avoidance between several of these species at a short spatio-temporal scale. In a third part, I consider camera trap data analysis. I develop a R package to clean and standardize camera trap data intended for the Snapshot Safari program, as well as a Shiny application intended for a more general use to visualize data in an interactive and reproducible way. This thesis presents statistical methods and software tools to analyze complex ecological data and improve our understanding of interaction networks. These results open new perspectives on ecological data analysis and methodological development in ecology

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Silva, Maria de Fátima de Oliveira Coutinho. "Concepções sobre desenvolvimento infantil de enfermeiros que atuam na Estratégia Saúde da Família." Universidade Federal da Paraíba, 2013. http://tede.biblioteca.ufpb.br:8080/handle/tede/6933.

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Made available in DSpace on 2015-05-14T13:16:17Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2464738 bytes, checksum: 75f49615b3f6ce2049d697a7992623c7 (MD5) Previous issue date: 2013-06-18 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES The aim of this research was to analyze the conceptions of child development for nurses working in the Family Health Strategy. This study is anchored in Social-Historical Theory of Vigotski, on the understanding that human development departs from the concept that all human organism is active and establishes successive interactions between the social and the biological basis of human behavior and the approach of the Niche Development of Harkness and Super, which provides insight on the quality of care and possible influences on child development in a given context. We conducted a field study, in the Family Health Units belonging to the Sanitary District III and it was used for data collection a questionnaire that captured the socio-demographic data, and a semi-structured interview, which was analyzed according to Bardin s Thematic Content Analysis. Participants were 38 nurses aged between 41-50 years, 30 were married, with children, and had an average of 20 years graduated. Regarding graduated studies, 35 participants were experts in Public Health and related areas and 32 underwent a Training Development Surveillance. Regarding time of service, 25 had around six years of activity in the Family Health Strategy. Applied and analyzed the interviews emerged a thematic class, ten categories, 27 sub-categories and 1.367 units of analysis. The results showed that the conceptions of nurses on child development are guided by the assumptions of the maturationist theory, transpiring in their speeches the actual theoretical construction of Health Ministry s guidelines for monitoring child development. Apprehends that nurses follow the protocols provided by Health Ministry found in the records or the Child Health Card for the children care and it sustains clearly that among the aspects of development evaluated by nurses predominating maintenance of a natural development conception, based on the existence of an intrinsic force from the child. This study finds these professionals as inconsistent and limited to the ideas of mothers on child development, reports that the process of child development is influenced by the family context, affective and environmental and guides mothers to stimulate child development, according to the contents of the Child Health Card or the age and developmental milestones. The study also reveals that majority of nurses do not realize the systematic care for children up to two years of age, judge their own performance in a fragmented way but realize the need to improve the children care. Apprehends, generally, that there are contradictions in the nurses conceptions, it concludes the need to create spaces for the reflection of these professionals, so that they rethink their conceptions from the context of their work place, and take into account the multiple variables in the understanding of the child, family and development. O objetivo desta pesquisa foi analisar as concepções sobre desenvolvimento infantil de enfermeiros que atuam na Estratégia Saúde da Família. O mesmo se ancorou na Teoria Sócio-Histórica de Vigotski, na compreensão de que o desenvolvimento humano parte da concepção que todo organismo humano é ativo e institui sucessivas interações entre as condições sociais e a base biológica do comportamento humano e na abordagem do Nicho do Desenvolvimento de Harkness e Super, na qual permite compreender sobre a qualidade do cuidado e possíveis influências no desenvolvimento infantil situado em um determinado contexto. Foi realizado um estudo de campo, nas Unidades de Saúde da Família pertencentes ao Distrito Sanitário III e utilizou-se para a coleta de dados um questionário que captava os dados sócio-demográficos e uma entrevista semi-estruturada, na qual foi analisada de acordo com Análise de Conteúdo Temática de Bardin. Participaram da pesquisa 38 enfermeiras com idades variando entre 41 a 50 anos, destas, 30 eram casadas, com filhos e apresentavam em média 20 anos de graduadas. Em relação à pós-graduação, 35 participantes eram especialistas em Saúde Coletiva e áreas a fins e 32 realizaram curso de Capacitação em Vigilância do Desenvolvimento. Quanto ao tempo de serviço, 25 apresentavam em torno de seis anos de atividades na Estratégia Saúde da Família. Das entrevistas aplicadas e analisadas, emergiram uma classe temática, dez categorias, 27 subcategorias e 1.367 unidades de análises. Os resultados apontaram que as concepções das enfermeiras sobre desenvolvimento infantil estão pautadas nos pressupostos da teoria maturacionista, transparecendo nos seus discursos a própria construção teórica das diretrizes de acompanhamento do desenvolvimento infantil do Ministério da Saúde. Apreende-se que as enfermeiras seguem os protocolos disponibilizados pelo Ministério da Saúde encontrados nos prontuários ou no Cartão de Saúde da Criança para o atendimento às crianças e percebe-se que dentre os aspectos do desenvolvimento avaliados pelas enfermeiras, predominam a manutenção de uma concepção de desenvolvimento natural, pautada na existência de uma força intrínseca à criança. Julgam ainda esses profissionais como inconsistentes e limitados às ideias das mães sobre desenvolvimento infantil, relatam que o processo de desenvolvimento infantil sofre influência do contexto familiar, afetivo e ambiental e orientam as mães para estimular o desenvolvimento infantil, de acordo com o conteúdo do Cartão de Saúde da Criança ou pela idade e marcos do desenvolvimento. Revela também o estudo, que a maioria das enfermeiras não realiza o atendimento sistemático à criança até aos dois anos de idade, julgam a sua própria atuação fragmentada, mas percebem a necessidade de melhorar o atendimento à criança. Apreende-se de um modo geral, que há contradições nas concepções dos enfermeiros, conclui-se a necessidade de criar espaços de reflexão para estes profissionais, a fim de que os mesmos repensem suas concepções a partir do contexto do seu lugar no trabalho, de modo que levem em consideração as múltiplas variáveis de entendimento sobre criança, família e desenvolvimento.

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Hornoy, Benjamin. "Processus évolutifs contribuant au succès envahissant de l'ajonc d'Europe, Ulex europaeus." Phd thesis, Université Rennes 1, 2012. http://tel.archives-ouvertes.fr/tel-00740154.

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Etudier les invasions biologiques est essentiel dans le cadre de la conservation de la biodiversité. De plus, elles représentent de véritables expérimentations grandeur nature pour appréhender les processus écologiques et évolutifs. La problématique de cette thèse est d‟étudier la contribution de processus évolutifs dans le succès envahissant de l‟ajonc d‟Europe, Ulex europaeus, à travers le monde, notamment en relation avec la perte de ses ennemis naturels (Enemy Release). La première partie s‟intéresse à l‟évolution de l‟ajonc dans sa zone d‟origine et au moment de l‟introduction dans de nouvelles régions, (i) en synthétisant les résultats concernant le polymorphisme de traits et la plasticité phénotypique, (ii) en couplant des données historiques et moléculaires pour inférer le mode d‟introduction de l‟ajonc dans le monde et ses conséquences sur la diversité génétique introduite. La deuxième partie s‟intéresse à l‟évolution post-introduction des populations d‟ajonc. Elle s‟appuie principalement sur des comparaisons en jardin expérimental d‟ajoncs issus de populations de régions d‟origine et envahies. L‟évolution des traits d‟histoire de vie et des stratégies de défense contre les ennemis a été étudiée en lien avec la perte d‟ennemis spécialistes en zone introduite. Nos résultats suggèrent que l‟histoire évolutive dans la zone d‟origine et le mode d‟introduction volontaire par l‟Homme ont conféré un fort potentiel évolutif aux populations d‟ajonc introduites. De plus, un relâchement des corrélations génétiques dans les régions d‟introduction a pu entraîner une évolution plus libre des traits d‟histoire de vie, facilitant l‟adaptation locale à une large gamme d‟environnements. Ces résultats suggèrent que l‟étude conjointe des niches écologiques et des matrices G pourrait permettre une meilleure compréhension des processus impliqués dans les invasions biologiques.

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Shimizu, Kaya. "Host plant use in the assemblage of herbivorous insects on Macaranga myrmecophytes." Kyoto University, 2014. http://hdl.handle.net/2433/188797.

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Kyoto University (京都大学) 0048 新制・課程博士 博士(人間・環境学) 甲第18359号 人博第672号 新制||人||162(附属図書館) 25||人博||672(吉田南総合図書館) 31217 京都大学大学院人間・環境学研究科相関環境学専攻 (主査)教授市岡孝朗, 教授加藤眞, 教授松井正文 学位規則第4条第1項該当

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Cloete, Andrea. "Exploring the uses and gratifications of Facebook : a psychological study." Diss., University of Pretoria, 2010. http://hdl.handle.net/2263/27560.

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Social networking sites such as Twitter, Facebook and My Space have experience rapid worldwide growth. It is crucial that this global phenomenon be investigated within the South African context. Social networking is a relatively new trend in South Africa and there is a paucity of academic literature on the topic. This quantitative study investigated one of the most popular social networking websites to date, namely Facebook. Facebook is a social networking website which was launched in early 2004. The primary research question focused on determining the usage patterns of South African Facebook users. In specific, the study investigated the purposes for which the site was used, the self-reported substitution of Facebook usage for face-to-face interaction and the relationship between Facebook affinity and Facebook use. A survey research design was used to collect data via an electronic questionnaire posted on Facebook. The theoretical point of departure was post-positivist. Media theories applied to the phenomenon under investigation include the uses and gratifications theory and the theory of the niche. The findings suggest that Facebook is primarily used for its intended purpose of communication. The respondents reported the gratification of versatile (multipurpose) communication. Furthermore, only half of the sample reported privacy concerns regarding Facebook. There was no significant indication that Facebook is a substitute for face-to-face interaction. Half of the sample claimed that their interpersonal contact has increased as a result of Facebook use. In addition, in accordance with expectations, the more affiliated a person is to Facebook, the more they will use Facebook. The findings of this study conform to other studies concerning social networking and provide a South African view of the global phenomenon of social networking websites. Dissertation (MA)--University of Pretoria, 2010. Psychology unrestricted

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Laviron, Marie. "Etude de la modulation des niches de macrophages au cours du développement tumoral et en réponse à la chimiothérapie." Electronic Thesis or Diss., Sorbonne université, 2021. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2021SORUS225.pdf.

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Les macrophages représentent la population la plus abondante dans la tumeur et leur accumulation est associée à un mauvais pronostic dans beaucoup de cancers. Ils forment un ensemble de sous-populations pouvant varier en termes d’origine, de localisation et de fonction. Ces caractéristiques, définissant l’interaction entre le macrophage et son environnement, forment la niche du macrophage. Les niches de macrophages ont été largement décrites dans les différents tissus à l’homéostasie mais leur évolution dans la tumeur est mal connue. Mon projet de thèse s’intéresse à caractériser les niches de macrophages et s’articule autour de deux projets ; l’évolution des niches de macrophages lors du développement tumoral ; et l’impact de la chimiothérapie sur les niches de macrophages, en particulier le rôle des Treg dans la polarisation de celles-ci. A travers ces projets, nous mettons en évidence que l’hétérogénéité des macrophages est directement associée à la diversité des niches spatiales définies dans la tumeur. La polarisation des macrophages est dictée par les signaux de ces niches. Nous suggérons également que la chimiothérapie favorise les interactions entre Treg et macrophages dans la tumeur, que la déplétion des Treg post-chimiothérapie conduit à une repolarisation des macrophages vers un phénotype pro-inflammatoire, associée à un contrôle de la croissance tumorale. Ce travail met en évidence l’importance de la relation du macrophage avec la tumeur dans l’induction de ses fonctions et pourrait permettre d’identifier les populations à cibler pour rétablir une réponse immunitaire anti-tumorale efficace Macrophages represent the most abundant population within the tumor and their accumulation is associated with bad prognosis in most cancers. They form a group of sub-populations that vary in terms of origin, localization and function. Those characteristics, defining the interaction between the macrophage and its environment, constitute the macrophage niche. Macrophage niches have been described in different tissues at homeostasis but their evolution during tumor development remains to be elucidated. My thesis project aims at characterizing macrophage niches and focuses on two parts; the evolution of macrophage niches during tumor development; and the impact of chemotherapy on macrophage niches, and specifically the role of Treg on their polarization in this setting. Through those projects, we highlight that the heterogeneity of macrophages is directly linked to the diversity of tumor spatial niches. Macrophage polarization is dictated by signals derived from the niche. We also suggest that chemotherapy favors Treg and macrophage interactions, and that Treg depletion post-chemotherapy leads to the repolarization of macrophages towards a pro-inflammatory phenotype, associated with better tumor control. This work sheds light on the importance of the relationship between the macrophage and the tumor for the induction of its functions, and could identify specific populations to target to restore an efficient anti-tumor immune response

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Carlucci, Marcos Bergmann. "Padrões funcionais de organização de árvores juvenis em manchas florestais na serra do sudeste do Rio Grande do Sul." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/30192.

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Uma das mais relevantes perspectivas que buscam explicar como as comunidades ecológicas se organizam é a teoria do nicho, que se divide em duas linhas de pesquisa com filosofias opostas. A primeira enfatiza que diferenças nas características funcionais de organismos permitem sua coexistência, enquanto que a segunda avalia até que ponto membros de uma mesma comunidade tendem a exibir similaridade em seus atributos funcionais. Uma variedade de métodos analíticos tem sido desenvolvida para avaliar mecanismos ligados a cada um dos processos. Explorando o padrão de distribuição de atributos de comunidades, a limitação de similaridade resulta em divergência de atributos, enquanto a ação local de filtros ambientais em geral produz convergência de atributos. Nesse sentido, o método para discriminação de padrões de organização por convergência ou por divergência de atributos no contexto de metacomunidades é de grande valor. Nesta dissertação, tal abordagem é utilizada para a avaliação de padrões de convergência e de divergência de atributos de plantas arbóreas juvenis em manchas florestais. Não incluímos informação filogenética ou de espécies a fim de avaliarmos até que ponto uma abordagem plenamente funcional pode explicar padrões de comunidades. O trabalho foi desenvolvido na Serra do Sudeste do RS, que consiste em um mosaico campo-floresta relativamente bem conservado. Algo instigante na Serra do Sudeste é a presença das coníferas Araucaria angustifolia (Bertol.) Kuntze e Podocarpus lambertii Klotzsch ex Endl. em várias manchas florestais, espécies reconhecidas como características da Floresta com Araucária do Planalto Sul-Brasileiro. Tal ocorrência vem sendo discutida há muitas décadas na literatura, mas nenhum estudo ecológico feito nessas áreas foi publicado ainda. Assim, nesta dissertação, tive como objetivos avançar na teoria relacionada à organização de comunidades e obter dados de qualidade para a avaliação continuada da dinâmica ecológica por trás dos mosaicos campo-floresta com presença de A. angustifolia na Serra do Sudeste. Os resultados encontrados revelaram padrões tanto de convergência quanto de divergência de atributos. A abordagem inteiramente funcional utilizada neste trabalho foi muito útil para a inferência de prováveis mecanismos de nicho envolvidos na organização das comunidades de árvores juvenis. Nós defendemos que a análise de dados de atributos referentes ao nível de indivíduos em um contexto de metacomunidades é a melhor maneira de explorar diretamente como a convergência e a divergência de atributos realmente se comporta ao longo de um dado gradiente. Com relação ao limite austral da distribuição de Araucaria angustifolia, caso as áreas da Serra do Sudeste sejam consideradas nativas, haveria uma ocorrência disjunta da espécie e, talvez, do tipo vegetacional Floresta com Araucária. Esse tema é especialmente importante no que concerne a uma possível migração da espécie ou mesmo da flora típica da formação rumo ao sul, ou alternativamente a uma possível evidência remanescente de que a espécie ou mesmo de que a formação tenham ocorrido continuamente até essas latitudes, talvez há centenas de milhares de anos atrás. A resolução desse mistério, entretanto, provavelmente só seja alcançada através de estudos paleopolínicos e genéticos. De qualquer forma, tais áreas devem ser protegidas, já que seu desconhecimento por grande parte da comunidade científica facilita a negligência de sua conservação. Ecologists have considered niche theory one of the most relevant perspectives attempting to explain ecological community assembly. It is divided in two research programs with opposed philosophies. The first emphasises that differences in functional attributes of organisms enable their coexistence, whereas the second evaluate to which extent members of a same community tend to exhibit similarity regarding their functional traits. A variety of analytical methods have been developed for assessing mechanisms related to each of these processes. By exploring the trait distribution pattern in communities, it is generally accepted that the local action of environmental filters generates a pattern of trait convergence, whereas limiting similarity leads to trait divergence. In this sense, the method for discriminating traitconvergence and trait-divergence assembly patterns in the metacommunity context is of great value. In this dissertation, such approach is used for evaluating convergence and divergence patterns of tree sapling traits in forest patches in the Serra do Sudeste region of Rio Grande do Sul state, southern Brazil. We did not include phylogenetic or species identity information in the analysis since we wanted to evaluate to which extent an entirely functional approach could explain community patterns. The study was carried out in Serra do Sudeste, which consists of a forest-grassland mosaic relatively well conserved. Something puzzling in Serra do Sudeste is the presence of conifers such as Araucaria angustifolia (Bertol.) Kuntze and Podocarpus lambertii Klotzsch ex Endl. in several forest patches. These species are characteristic of the Araucaria forest occurring in the South-Brazilian Plateau. Such occurrence has been matter of a long-lasting debate in the regional literature, but no ecological study done in these areas has been published yet. In this dissertation I aimed at advancing on the theoretical bases of community assembly and at gathering data for continuously evaluating the ecological dynamics of the forest-grassland mosaics with presence of A. angustifolia in Serra do Sudeste. The results revealed both trait convergence and divergence patterns, which indicated mechanisms for the assembly of tree sapling communities. The entirely functional approach applied here was very useful to infer probable mechanisms underlying community assembly. We argue that the use of individual-based trait information in a metacommunity context is the best way to directly explore how trait convergence and trait divergence behave along a given gradient. With regard to the austral boundary of Araucaria angustifolia distribution, if the patches of Serra do Sudeste are considered native, there would be a disjunct occurrence of the species and perhaps of the vegetational type Araucaria forest. This issue is especially important regarding a possible migration of the species or even of the typical associated flora southwards, or alternatively, regarding a possible relict evidence that the species had continuously occurred along such latitudes in a remote past. Nonetheless, the resolution of this puzzle probably only will be achieved through genetic and paleopollen studies. Anyway, such areas must be protected as their omission in important scientific studies facilitates the negligence of their conservation.

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Chintawar, Satyan. "Neural precursor cells: interaction with blood-brain barrier and neuroprotective effect in an animal model of cerebellar degeneration." Doctoral thesis, Universite Libre de Bruxelles, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210202.

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Adult neural precursor cells (NPCs) are a heterogeneous population of mitotically active, self-renewing multipotent cells of both adult and developing CNS. They can be expanded in vitro in the presence of mitogens. The B05 transgenic SCA1 mice, expressing human ataxin-1 with an expanded polyglutamine tract in cerebellar Purkinje cells (PCs), recapitulate many pathological and behavioral characteristics of the neurodegenerative disease spinocerebellar ataxia type 1 (SCA1), including progressive ataxia and PC loss. We transplanted neural precursor cells (NPCs) derived from the subventricular zone of GFP-expressing adult mice into the cerebellar white matter of SCA1 mice when they showed absent (5 weeks), initial (13 weeks) and significant PC loss (24 weeks). A stereological count demonstrates that mice with significant cell loss exhibit highest survival of grafted NPCs and migration to the vicinity of PCs as compared to wt and younger grafted animals. These animals showed improved motor skills as compared to sham animals. Confocal analysis and profiling shows that many of implanted cells present in the cerebellar cortex have formed gap junctions with host PCs and express connexin43. Grafted cells did not adopt characteristics of PCs, but stereological and morphometric analysis of the cerebellar cortex revealed that grafted animals had more surviving PCs and a better preserved morphology of these cells than the control groups. Perforated patch clamp recordings revealed a normalization of the PC basal membrane potential, which was abnormally depolarized in sham-treated animals. No significant increase in levels of several neurotrophic factors was observed, suggesting, along with morphological observation, that the neuroprotective effect of grafted NPCs was mediated by direct contact with the host PCs. In this study, evidence for a neuroprotective effect came, in addition to motor behavior improvement, from stereological and electrophysiological analyses and suggest that timing of stem cell delivery is important to determine its therapeutic effect.In a brain stem cell niche, NSCs reside in a complex cellular and extracellular microenvironment comprising their own progeny, ependymal cells, numerous blood vessels and various extracellular matrix molecules. Recently, it was reported that blood vessel ECs-NSCs crosstalk plays an important role in tissue homeostasis. Bloodstream offers a natural delivery vehicle especially in case of diffuse neurodegenerative diseases which require widespread distribution of exogenous cells. As NSCs are confronted with blood-brain barrier endothelial cells (BBB-ECs) before they can enter into brain parenchyma, we investigated their interaction using primary cultures in an in vitro BBB model. We isolated human fetal neural precursor cells (hfNPCs) from aborted fetal brain tissues and expanded in vitro. We showed that in an in vitro model, human BBB endothelium induces the rapid differentiation of hfNPCs and allows them to cross the endothelial monolayer, with the differentiated progeny remaining in close contact with endothelial cells. These results are not reproduced when using a non-BBB endothelium and are partly dependent on the cytokine MCP1. Our data suggest that, in the presence of attractive signals released by a damaged brain, intravascularly administered NPCs can move across an intact BBB endothelium and differentiate in its vicinity. Overall, our findings have implications for the development of cellular therapies for cerebellar degenerative diseases and understanding of the brain stem cell niche. Doctorat en Sciences biomédicales et pharmaceutiques info:eu-repo/semantics/nonPublished

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Mesquita, Neto José Neiva. "Interação planta-polinizador em espécies sincronopátricas de psychotria (rubiaceae)." Universidade Federal de Goiás, 2013. http://repositorio.bc.ufg.br/tede/handle/tede/3098.

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Submitted by Marlene Santos (marlene.bc.ufg@gmail.com) on 2014-09-17T21:01:01Z No. of bitstreams: 2 José Neiva Mesquita Neto.pdf: 2799737 bytes, checksum: 590e98d41066ac6babc47eeb04637796 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Rejected by Luciana Ferreira (lucgeral@gmail.com), reason: Marlene, olhe nas orientações a questão da citação, a qual deve ser de acordo com a NBR 6023: ALCÂNTARA, Guizelle Aparecida de. Caracterização farmacognostica e atividade antimicrobiana da folha e casca do caule da myrciarostratadc.(myrtaceae). 2012. 41 f. Dissertação (Mestrado em Ciências Farmacêuticas) - Universidade Federal de Goiás, Goiânia, 2012. on 2014-09-18T12:33:01Z (GMT) Submitted by Marlene Santos (marlene.bc.ufg@gmail.com) on 2014-09-18T19:01:02Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) José Neiva Mesquita Neto.pdf: 2799737 bytes, checksum: 590e98d41066ac6babc47eeb04637796 (MD5) Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2014-09-19T11:32:20Z (GMT) No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) José Neiva Mesquita Neto.pdf: 2799737 bytes, checksum: 590e98d41066ac6babc47eeb04637796 (MD5) Made available in DSpace on 2014-09-19T11:32:20Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) José Neiva Mesquita Neto.pdf: 2799737 bytes, checksum: 590e98d41066ac6babc47eeb04637796 (MD5) Previous issue date: 2013-09-19 Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES Plant-pollinator interactions in syncronopatric species of Psychotria (Rubiaceae). Psychotria species are commonly found in the understory of forested areas in tropical regions, and are important components for the functioning of these ecosystems. Many species of the genus are sympatric and bloom during the same period, being considered potentially syncronopatrics. For this reason, this genus has been considered as a good model to infer general patterns and mechanisms of speciation in the tropics. In the first paper of this dissertation, the interactions between potentially sympatric species of Psychotria and their pollinators were analyzed in order to verify the possible existence of sharing, specialization or generalization of pollinators and plants in the analyzed system. Then, data of secondary studies that contained identifying pollinators of Psychotria were analyzed From these data, we generated graphs and analyzes of interaction networks and niche overlap. Altogether, nine species of Psychotria and 25 species of pollinators of occurrence in the Atlantic Forest were included in the analyzes. The plant with the most generalist network is Psychotria tenuinervis and the pollinators with the highest proportion of links and consequently with more important role in the network belonged orders Lepidoptera and Hymenoptera. Psychotria species showed niche overlap in pollination and pollinator sharing. The period of greatest intensity of flowering coincided with the rainy season in the Atlantic Forest, with up to seven species coflowering. Because Psychotria species occur in sympatry and have flowering overlap and asymmetric interactions with flower visitors, it is possible that they are involved in a process of facilitation in pollination. The second paper aimed to investigate if four sympatric populations of Psychotria show pollinators sharing and pollination niche overlap . Another objective was to determine if their flowering season are synchronics. We found a dual synchrony in this system, the first in the intensity of flowering among the populations of Psychotria and the second in the increase of the abundance of flowers and pollinators. The species of Psychotria showed sharing fundamental niche of pollination and positive impact on reproductive success. However, we note that the sharing of pollinators can not be generalized to the entire system, but to the modules or pairs of species. Thus, each species of Psychotria has one or more species of preferential pollinator for sharing and that this relationship is not always reciprocal. This reinforces that the interactions among the plant species are asymmetric. Interação planta-polinizador em espécies sincronopátricas de Psychotria (Rubiaceae). Psychotria contribui de forma importante para a diversidade florística tropical e são comumente encontradas em sub-bosque de áreas florestadas em regiões tropicais, sendo importantes componentes para o funcionamento destes ecossistemas. Muitas espécies do gênero são simpátricas e florescem em um mesmo período do ano, sendo consideradas potencialmente sincronopátricas. Por esta razão, este gênero tem sido considerado como um bom modelo para inferir padrões e mecanismos gerais de especiação nos trópicos. No primeiro artigo, as interações entre espécies potencialmente simpátricas de Psychotria e seus polinizadores foram analisadas com o objetivo de verificar a possível existência de partilha, de especialização ou generalização de polinizadores e plantas no sistema analisado. Para isso, foram incluídas informações secundárias de estudos que continham a identificação em nível de espécie de polinizadores de Psychotria. A partir desses dados, foram gerados grafos e realizadas análises de redes de interação e sobreposição de nicho. Ao todo, foram incluídas nas análises nove espécies de Psychotria com registro de ocorrência para a Mata Atlântica, sendo que elas interagiram com 25 espécies de polinizadores. A planta mais generalista da rede foi Psychotria tenuinervis e os polinizadores que concentraram maior número de links e consequentemente com papel mais importante na rede pertenceram as ordens Lepidoptera e Hymenoptera. As espécies de Psychotria apresentaram sobreposição de nicho na polinização com partilha de polinizadores. O período de maior intensidade de floração coincidiu com o período chuvoso na Mata Atlântica, com até sete espécies apresentando coflorescimento. Assim, pode-se inferir que a polinização em Psychotria demanda polinizadores generalistas. Pelo fato das espécies de Psychotria ocorrerem em simpatria, possuírem floração sobreposta e interações assimétricas com visitantes florais, é possível que estejam envolvidas em um processo de facilitação na polinização. Já o segundo artigo objetivou averiguar se quatro populações simpátricas de Psychotria, em cofloração, apresentaram partilha de polinizadores e sobreposição de nicho na polinização. Além disso, objetivou verificar se existe sincronia entre as populações vegetais e destas com comunidade de polinizadores. Foi encontrada uma dupla sincronia nesse sistema, sendo a primeira na intensidade de floração entres as populações de Psychotria e a segunda no aumento da abundância de flores e de polinizadores. As espécies de Psychotria apresentaram partilha fundamental do nicho da polinização e com reflexo positivo no sucesso reprodutivo. No entanto, verificamos que a partilha de polinizadores não pode ser generalizada a todo o sistema, mas sim a módulos ou pares de espécies. Dessa forma, cada espécie de Psychotria possui uma ou mais espécies preferencias para partilha de polinizadores e que nem sempre essa relação é reciproca. Isso reforça que as interações entre as plantas são assimétricas.

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Galliger, Courtney C. "NAUGHTY OR NICE: SOCIAL INTERACTION ON THE SCHOOL BUS." Connect to this title online, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=bgsu1148236809.

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Yguel, Benjamin. "Sortir de sa niche ancestralele cas du chêne sessile et pédonculé : conséquences pour les interactions biotiques : le cas du chêne sessile et pédonculé." Rennes 1, 2012. http://www.theses.fr/2012REN1S142.

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Le conservatisme phylogénétique de niche se définit par la conservation, au cours du temps, de la niche écologique et des traits écologiques associés. Des espèces phylogénétiquement proches auront alors tendances à occuper des niches similaires, incluant des conditions abiotiques mais aussi des interactions biotiques similaires. Ainsi, un individu isolé phylogénétiquement de ses voisins, pourrait être considéré comme présent dans une nouvelle niche. Dans cette thèse, nous nous sommes intéressés aux interactions trophiques des individus de plantes hôtes colonisant une nouvelle niche, représentée par un voisinage phylogénétiquement éloigné, à la différence des individus hôtes restant dans leur niche ancestrale. Nous avons étudié plus particulièrement le cas du chêne et de ses phytophages, de leurs ennemis naturels, et enfin, des ectomycorhizes du chêne. Nos résultats indiquent que l'isolement phylogénétique des chênes hôtes (i) diminue l'abondance des phytophages et leurs pressions sur le chêne, (ii) diminue la pression des ennemis spécialistes sur ces phytophages, (iii) augmente l'abondance et l'activité des ectomycorhizes du chêne. Plus généralement, nos résultats permettent de discuter dans quelles situations une sortie de niche sera favorisée et dans quelles situations, une sortie de niche sera contrariée. Ces résultats suggèrent que les chênes phylogénétiquement isolés, mais aussi leurs phytophages et leurs mycorhizes, subissent des pressions de sélection particulières qui pourraient être à l'origine d'une différentiation évolutive à long terme Niche conservatism is defined as the conservation of the niche and its associated ecological traits over time. Thus, phylogenetically closely related species tend to occupy similar niches, including abiotic conditions but also biotic interactions. Hence, individuals surrounded by phylogenetically distantly related species could be considered as inhabitant of new niche. In this thesis we were interested in trophic interactions of host individuals inhabiting a new niche, represented by distantly related neighbours, as compared to hosts remaining in their ancestral niche. We studied oak hosts and their phytophages, the next trophic level, i. E. The oak phytophages and their natural enemies, and finally the ectomycorhizal fungi of oaks. Our results showed that phylogenetic isolation of oak hosts (i) decreases abundance and pressure of phytophages on oak hosts, (ii) decreases enemy pressure of specialized enemies on oak phytophages, (iii) increases ectomycorhizal fungi abundance and activity. Hence, our results indicate that phylogenetic isolation of oaks changes the intensity and the nature of biotic interactions all along the entire trophic chain based on oaks. Our results allow us to discuss the biotic forces that favor or impede the colonization of a new niche. Moreover, we suggest that phylogenetically isolated oaks, their phytophages and their ectomycorhizal mutualists undergo specific selective pressures that could trigger evolutionary differentiation in long term

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Chang, Chao-Hui. "Haematopoietic stem/progenitor cell interactions with the bone marrow vascular niche." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:452da334-bd4e-45c7-a7bd-fc8767d1239c.

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Umbilical cord blood (UCB) is used as a source of haematopoietic stem cells (HSCs) for transplantation but shows defective homing to the bone marrow niche and delayed haematological reconstitution. Following transplantation, HSCs will home to the bone marrow in response to the CXCL12 chemokine, adhere to the bone marrow sinusoidal endothelial cells and then migrate into and lodge in bone marrow niches. In addition to CXCR4, a variety of molecules have been described as being important in these processes. In this laboratory, junctional adhesion molecule-A (JAM-A) was shown to be expressed on human UCB CD133⁺/CD34⁺ cells and regulated by hypoxia. In this thesis, further phenotypic studies show that this molecule is most highly expressed on human CD41a⁺ megakaryocytes and CD14⁺ monocytes/macrophages in UCB. JAM-A was also found to be expressed on all human UCB CD133⁺ cells, which have been shown by others to encompass the HSCs and early myeloid-lymphoid precursors and on the majority of CD34⁺ haematopoietic progenitor cells (HPCs). While it is also present on bone marrow sinusoidal endothelium (BMEC), JAM-A is not detected on cultured bone marrow mesenchymal stromal cells (MSCs). JAM-A blockade, silencing and overexpression experiments showed that JAM-A contributes to, but is not solely responsible for, the adhesion of CD34⁺ haematopoietic progenitor cells to IL-1β activated BMEC-60 cells and fibronectin. Lack of significance in cell migration suggested that JAM-A is more likely to act as an adhesion molecule or a regulator of adhesion rather than as a migratory molecule in such cells. Further functional studies using the proximity ligation assay highlight a potential association of JAM-A with CXCR4 and the adhesion molecules, tetraspanin CD82 and integrin β1. Mechanistic studies were commenced to establish if JAMA could modulate CXCR4 signalling following CXCL12 stimulation, but time constraints prevented these from being completed. These preliminary experiments which were carried out first in the Jurkat cell line lacking JAM-A or transduced to express JAM-A, however, suggest that JAM-A may modulate CXCL12-induced Rap1 phosphorylation and ERK1/2 phosphorylation. The former pathway is important for integrin function and the latter pathway is important in cell adhesion. The results described here, although requiring finalisation, support the hypothesis that JAM-A acts as an adhesion molecule and also may fine tune CXCR4 and integrin mediated functions on human CD34⁺ cells, thereby potentially regulating engraftment of these cells to the bone marrow niche.

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Farquhar, Michael Robert. "Interspecific interactions of the sea urchin Parechinus angulosus and the effect of variations in microhabitat availability." Thesis, Rhodes University, 1995. http://hdl.handle.net/10962/d1005406.

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Intertidal populations of the sea urchin Parechinus angulosus were examined at seven sites along the south and east coasts of South Africa. At the five southerly sites, P. angulosus occurred in allopatry, while, at the two northerly sites, it occurred in sympatry with several species of Indopacific sea urchins. At the five southerly sites, there was a significant correlation of number of sea urchins per pool with the surface area of the overhang in that pool. This relationship broke down for P. angulosus at the two northerly sites, where there was a significant correlation between these two factors for Stomopneustes variolaris. The density of populations of P. angulosus at the two northerly sites, although not significantly different from all five southerly sites, were considerably lower. There was a significant difference between the mean size of populations at the seven sites. Although no direct evidence is available, a competitive interaction between these two species is proposed to explain the observed patterns of microhabitat utilization and densities. Two series of manipulative experiments were conducted at Kowie Point, where P. angulosus occurs in sympatry, The first, involved urchin removals from three experimental sites. The percentage cover of four functional algal groups was monitored in three experimental and three unaltered control sites over a three month period in spring (Sept. - Dec.) 1993. Two 100 point 0,25m² random point quadrats were thrown at each of the six sites at approximately monthly intervals over the experimental period. Since initial cover of algae varied at the six sites, ANOVA's of the change in percentage cover of four functional algal groups were used to determine treatment effects. No treatment effects were identified for any of the four functional algal groups. There was a strong negative correlation between the percentage cover of foliose algae and encrusting coralline algae, suggesting the possibility of a competitive relationship between them. The second, involved the experimental manipulation of microhabitat availability. The blocking of overhangs, by means of cement filled bags, resulted in an approximate 50% decrease in the total number of urchins in the two experimental pools, and the two control pools without overhangs. However, in the control pool with overhangs there was a slight increase in the number of urchins over the same period. Clearly, the presence of suitable shelters, is a prerequisite for the maintenance of dense intertidal population of P. angulosus. It is proposed that, due to the exposed nature of the South African coast, intertidal populations of P.angulosus are restricted to inhabiting suitable shelters from which they emerge to feed on passing drift algae. The implications of these findings are discussed in terms of current ecological literature.

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Jablonska, Marta. "Molecular interactions between gastric stem cells and their niche upon Helicobacter pylori infection." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21654.

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Infektionen mit H. pylori führen zu Veränderungen im Aufbau und der zellulären Zusammensetzung des Magenepithels. Aktuelle Studien haben gezeigt, dass Stromazellen, die sich in unmittelbarer Nähe der epithelialen Stammzelle befinden, die funktionelle Nische für dieses Kompartiment bilden und wichtige Faktoren für die Regulierung des Stammzellumsatzes und Differenzierung darstellen. Daher konzentriere ich mich bei dieser Arbeit auf die Rolle der Myh11+ Myofibroblasten, die sich sowohl unter als auch zwischen den Epitheldrüsenzellen befinden. Ich fand heraus, dass die Myofibroblasten in der Homöostase einen BMP-Gradienten entlang der Drüsenachse mit erhöhter Expression von Bmp2 im oberen Teil erzeugen, während die Drüsenbasis von Zellen umgeben ist, die Bmp-Inhibitoren produzieren. Basierend auf der Funktionsanalyse mit 3D-Organoidmodellen ist der Bmp-Signalweg ein zentraler Faktor für die rasche Differenzierung von Stammzellen in faveoläre mukusproduzierende Zellen. Darüber hinaus wurde ein auto-parakriner Signalweg gefunden, der zur Bildung von Bmp2 in Epithelzellen führt. Meine Untersuchungen Daten zeigten eine Verringerung des BMP-Signalwegs in H. pylori-infizierten Myofibroblasten. Darüber hinaus führte eine Infektion mit H. pylori nicht nur zum Verlust der stromalen, sondern auch der epithelialen Bmp2-Expression. Diese Beobachtung ging mit einer Zunahme von IFNγ einher, was auf eine Verbindung zwischen beiden Signalwegen hinwies. Tatsächlich zeigten anschließende Experimente mit Organoiden, dass IFNγ den Bmp-Signalweg hemmt und dadurch die terminale Differenzierung blockiert. Zusammenfassend zeigen meine Untersuchungen, dass das Schicksal einer Zelle, die zur Oberfläche der Magendrüse wandert, eine Induktion des BMP-Signalwegs erfährt. Die Reduktion dieses Signals durch IFNγ deutet auf einen Mechanismus hin, der Veränderungen in der zellulären Differenzierung und die Entwicklung von prämalignen epithelialen Läsionen im Verlauf einer H. pylori-Infektion bewirkt. Infection with Helicobacter pylori (H. pylori) leads to alterations of the topology and cellular composition of the gastric epithelium. Recent studies have shown that stromal cells located in close proximity to the epithelial stem cell are creating the niche for this compartment and provide crucial factors that regulate stem cell turnover and fate decisions. Therefore, this thesis focuses on of Myh11+ myofibroblasts that are located beneath and between the epithelial gland cells. I found that during homeostasis, the myofibroblasts generate a BMP gradient along the gland axis with strong expression of Bmp2 in the upper part, whereas the base is surrounded by cells producing BMP inhibitors. Based on functional analysis with 3D organoid models, the BMP gradient occurs to be a main factor responsible for rapid differentiation of stem cells into pit surface mucous cells. Moreover, experiments led me to identify an auto-paracrine feed-forward BMP2 loop in epithelial cells, which further stabilizes BMP signaling once it is activated and induces terminal differentiation. Data presented in this study demonstrated a reduction of BMP signaling in H. pylori-infected myofibroblasts. Furthermore, infection with H. pylori resulted in loss of not only stromal, but also epithelial Bmp2 expression. This observation was accompanied with increase of Interferon γ (IFNγ), which indicated a link between both pathways. Consistently, stimulation of organoids with IFNγ impairs BMP signaling and the BMP2 feed-forward loop, and thereby blocks terminal differentiation. Together, this study shows that the fate of a cell migrating into the surface of the gastric gland is determined by an induction of BMP signaling and stabilized by an auto-paracrine BMP signaling enhancement. Reduction of this signaling by IFNγ revealed a mechanism which contributes to altered cellular differentiation and development of premalignant epithelial alterations in the context of H. pylori infection.

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DeVries, Dennis R. "Complex interactions in aquatic communities : trophic-level interactions, ontogenetic niche shifts, and the role of an open-water planktivore /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487673114113769.

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21

Sigal, Michael [Verfasser]. "Fighting for the right niche: bacterial interactions with gastric epithelial stem cells / Michael Sigal." Berlin : Medizinische Fakultät Charité - Universitätsmedizin Berlin, 2020. http://d-nb.info/1209130823/34.

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22

Kong, Heng. "Variations spatio-temporelles de la structure taxonomique et la compétition alimentaire des poissons du lac Tonlé Sap, Cambodge." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30122/document.

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Le lac de Tonlé Sap (TSL), Cambodge, est un écosystème lac-rivière de forêt alluviale au régime d'écoulement alternatif. Le lac est un déversoir lors de l'inondation saisonnière du Mékong et sert de réservoir en période de basses eaux. La superficie du lac pendant la saison sèche (février à mai), est d'environ 2 700 km2 pour une profondeur d'environ 1 mètre. Cette superficie est pratiquement multipliée par six quand arrive la saison des pluies, pour atteindre près de 16 000 km2 et une profondeur de 9 mètres, noyant rizières et forêts. C'est le plus grand lac d'eau douce d'Asie du Sud-Est. C'est aussi l'une des zones de pêche d'eau douce les plus importantes et productives du monde avec près de 75% du volume annuel de pêche en eau douce du Cambodge, ce qui permet la survie de près de 2,5 millions de personnes. Les changements saisonniers du cycle hydrologique ont une influence sur la structuration des communautés de poissons à l'échelle temporelle et spatiale, mais aussi sur les comportements trophiques des principales espèces qui n'exploitent alors pas les mêmes habitats. Toutefois, le bassin versant du Mékong est en changement constant avec un développement important des infrastructures en lien avec l'eau : production d'hydro-électricité, besoins important en irrigation, maitrise des inondations, eau potable, ... Les changements climatiques accélèrent les modifications du cycle hydrologique annuel. Il est alors supposé que ces modifications ont des effets forts sur les habitats et les proies disponibles et finalement sur la biodiversité, notamment de l'ichtyofaune et sur l'abondance des poissons disponibles pour les pêcheries.Dans un premier temps, nous avons caractérisé les variations spatio-temporelles de la composition taxonomique des poissons et mis en lumière quels sont les déterminants de ces variations. À cette fin, nous avons estimé la diversité bêta comme la variance totale de la matrice site par communauté d'espèce et l'avons divisée en contribution locale à la diversité bêta (LCBD) et contribution des espèces à la diversité bêta (SCBD). Nous avons ensuite effectué plusieurs régressions linéaires pour déterminer si la richesse taxonomique, l'abondance des espèces et le niveau de l'eau expliquaient la variation temporelle de la contribution du site et de l'espèce à la diversité bêta. Nos résultats indiquent une forte variation temporelle de la diversité bêta due aux contributions différentielles des sites et des espèces à la variation spatiale de la composition taxonomique des poissons. Nous avons également constaté que la direction, la forme et l'effet relatif de la richesse spécifique, de l'abondance et du niveau de l'eau sur la variation temporelle des valeurs LCBD et SCBD varient grandement selon les sites. Ces résultats suggèrent ainsi une variation spatiale des processus conduisant à une variation temporelle de la composition de la communauté. Dans l'ensemble, nos résultats suggèrent que la composition taxonomique des poissons n'est pas distribuée de manière homogène dans l'espace et dans le temps et risque d'être affectée à l'avenir si la dynamique saisonnière d'écoulement du système est altérée par les activités humaines et/ou les changements climatiques. Dans un second temps, nous avons cherché à étudier le modèle d'évolution temporel des principales espèces en terme d'occurrence et d'abondance à travers le cycle saisonnier hydrologique The Tonle Sap Lake (TSL), Cambodia, is a flood-pulse system. It is the largest natural lake in South- East Asia and constitutes one of the largest fisheries over the world, supporting the livelihood 2.5 million peoples. Seasonal change in annual hydrological cycle appears to have influence on fish community structure, both spatial and temporal variation, particularly on feeding behavior of TSL's fishes. Nonetheless, the Mekong River Basin is changing rapidly due to accelerating water infrastructure development (hydropower, irrigation, flood control, and water supply) and climate change, bringing considerable modifications to the annual flood-pulse of the TSL. Such modifications are expected to have strong impacts on fish biodiversity, abundance, reduced habitat and food availability within the lake. To invest how TSL's fish community structure responds to the seasonal change, how they shift their diet across hydrological cycles and feeding competing for food resource: First, we aim to characterize the spatio-temporal variations of fish taxonomic composition and to highlights the underlying determinants of these variations. For this purpose, we estimated beta diversity as the total variance of the site-by-species community matrix and partitioned it into Local Contribution to Beta Diversity (LCBD) and Species Contribution to Beta Diversity (SCBD). We then performed multiple linear regressions to determine whether species richness, species abundances and water level explained the temporal variation in the contribution of site and species to beta diversity. Our results indicate strong temporal variation of beta diversity due to differential contributions of sites and species to the spatial variation of fish taxonomic composition. We further found that the direction, the shape and the relative effect of species richness, abundances and water level on temporal variation in LCBD and SCBD values greatly varied among sites, thus suggesting spatial variation in the processes leading to temporal variation in community composition. Overall, our results suggest that fish taxonomic composition is not homogeneously distributed over space and time and is likely to be impacted in the future if the flood-pulse dynamic of the system is altered by human activities. Second, we aim to investigate the temporal pattern of the most occurrence and abundance species and how their co-occurrence pattern across hydrological cycles. We found that occurrence and abundance patterns were temporally varied at all water level seasons. Strong temporal variation in species occurrence was occurred with visiting species such as Labiobarbus leptocheilus and Poropuntius deauratus while water level starts to fill into the TSL. We further observed that the abundance of 17 species was strongly varied while other 22 species (mainly TSL's residential species) were stable within the year. Positive species co-occurrence pattern was generally higher than negative species co-occurrence at all water level seasons. Highest positive co-occurrence patterns were found during the period of decrease and low water level seasons while fishes are migrating from flooded areas, competing for resource and habitats during low water season. Study on temporal distribution and species co-occurrence of fish and how community responds to the seasonal change in hydrological cycles provides critical information for fisheries management and conservation in the Tonle Sap Lake (TSL) as well as maintaining fish biodiversity in the Mekong system. Third, the implications of seasonality on food web structure have been notoriously understudied in empirical ecology, particularly in TSL's system. The current study, we focus on seasonal changes in one key attribute of a food web, vertical trophic position of consumers

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Jablonska, Marta [Verfasser]. "Molecular interactions between gastric stem cells and their niche upon Helicobacter pylori infection / Marta Jablonska." Berlin : Humboldt-Universität zu Berlin, 2020. http://d-nb.info/1216876916/34.

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24

Bazile, Vincent. "Diversité des stratégies de nutrition chez les plantes à urnes du genre Nepenthes : le rôle du fluide digestif, de ses propriétés physicochimiques et biotiques." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS290.

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Le genre Nepenthes regroupe environ 160 espèces de lianes carnivores, principalement situées en Asie du Sud-Est, sur des sols pauvres en nutriments assimilables. L’apex de leurs feuilles est modifié en une vrille portant une urne qui leur permet de capturer des proies et d’acquérir des nutriments, principalement de l’azote. Réputées toutes insectivores, avec des urnes équipées de cire glissante sur la paroi interne et un liquide enzymatique à rôle digestif, ces plantes ont en fait un régime alimentaire plus diversifié. Des espèces sont coprophages, détritivores ou encore spécialisées sur une guilde particulière d’insectes. Elles poussent dans des milieux variés, plus ou moins ouverts, sur sols sableux ou tourbeux. Les traits fonctionnels des pièges de Nepenthes varient selon les espèces, avec présence ou non d’une collerette attractive, d’une zone cireuse glissante, et un liquide, viscoélastique ou non, hébergeant une faune spécifique (inquilines). Ces traits peuvent représenter autant d’adaptations attestant d’une diversité de stratégies de séquestration de l’azote. Beaucoup d’études se sont intéressées au rôle des parois glissantes dans la capture des insectes, peu aux propriétés du fluide digestif. La quantité d’azote disponible du milieu et la forme sous laquelle il se présente influencent-elles la concentration en azote des feuilles de la plante, l’origine de ses ressources azotées et son degré de carnivorie ? Quel est le rôle du fluide dans la capture et la digestion des proies, dans la stratégie de séquestration de l’azote de la plante ? Quid des différences d’acidité, de viscoélasticité ou de pool enzymatique entre espèces ? Des différences d’abondance et de composition de la faune inquiline ? Quelles sont les conséquences de toutes ces différences en termes de recyclage d’azote pour la plante ?Cette thèse explore la contribution du fluide digestif, de ses propriétés physico-chimiques et biotiques à la capture et la digestion des proies de 7 espèces de Nepenthes du Brunei (Bornéo).Dans un premier volet, nous montrons que les espèces sont adaptées à des milieux de richesse variée en azote édaphique et biotique grâce à différentes stratégies d’acquisition de l’azote. Le contenu des urnes montre une variation du degré d’insectivorie. La diversité de leurs traits fonctionnels expliquerait les différences dans la nature des proies et l’efficacité de capture. Nectar extrafloral, fluide digestif acide et cire épicuticulaire glissante sont associés à la capture de fourmis, trichomes glandulaires, fourmi symbiotique et urnes cylindriques à la capture de termites et enfin, fluide acide et viscoélastique, mais surtout urne en entonnoir, à grande ouverture et production d’odeur florale expliquent l’abondance d’insectes volants. Les espèces varient aussi fortement dans leurs sécrétions enzymatiques et dans leurs cortèges d’inquilines. Dans un second volet, nous montrons in situ que les propriétés physicochimiques et biotiques du fluide expliquent en partie les différences de stratégies d’acquisition de l’azote chez les Nepenthes. Le pH et la viscoélasticité du fluide influencent la quantité et la nature des proies capturées. Ses propriétés physicochimiques conditionnent également la richesse de l’écosystème aquatique associé au fluide, avec une macrofaune aquatique plus abondante et diverse dans les urnes au liquide peu acide et au diamètre d’ouverture large. Cette macrofaune inquiline joue un rôle important dans la dégradation des proies, et la présence d’un top-prédateur s’avère essentielle dans le recyclage de l’azote. Nous discutons enfin du rôle majeur du fluide dans le régime alimentaire de la plante et dans la probable radiation adaptative du genre Nepenthes et concluons par une réflexion sur les différentes formes de carnivorie observées chez ces plantes et leurs systèmes de digestion, allant d’une stratégie agressive autonome à une stratégie mutualiste, redéfinissant par-là le concept de carnivorie dans le monde végétal The Nepenthes carnivorous plants genus encompasses about 160 species growing mostly in Southeast Asia in habitats characterised by their scarcity in absorbable nutrients. The leaf apex is modified into a tendril bearing a pitcher trap which allows the plant catching its prey and taking up the nutrients indispensable for its growth, mainly nitrogen. Reputed to be insectivorous, bearing traps equipped with a slippery wax covering the inner pitcher wall and with an enzymatic liquid involved in the digestion, Nepenthes species actually have a more diverse diet. Coprophagous, detritivorous, and insect-guild specialised species have been reported. These plants grow in more or less open environments, on sandy or peaty soils. Nepenthes traps show an inter-specific diversity of functional traits, bearing or not an attractive collar, a slippery waxy zone, and a viscoelastic liquid, which shelters a species-specific living infauna. Such different traits may reflect as many adaptations attesting to a diversity of nitrogen-sequestration. Many studies have focused on the role of slippery walls in insect capture but few of them have investigated the importance of the digestive fluid in both capture and digestion. Do the quantity of nitrogen available in the environment and the form of its availability influence the nitrogen foliar concentration of these plants, the source of their nitrogen supply and their carnivorous habit? How does the fluid influence prey capture and digestion? Can it contribute to the nitrogen-sequestration strategy of the plant? Do the fluids differ in their acidity, viscoelasticity, enzymatic pool, and in the abundance and species diversity of their infauna? What are the consequences of all these differences in terms of nitrogen recycling for the host plant?This PhD thesis explores the contribution of the digestive fluid and its physico-chemical and biotic properties on prey capture and digestion in 7 Nepenthes species in Brunei (Borneo).The first part shows that Nepenthes species have adapted to habitat differing in edaphic and biotic nitrogen available through distinct strategies of nitrogen acquisition. Pitcher contents’ analyses show that plants vary for their degree of insectivory. The variety of functional traits could explain the differences in their capture efficiency and prey diversity. While extrafloral nectar, slippery epicuticular wax and acidic fluid pH are associated with ants’ capture, cylinder-shaped traps, glandular trichomes and ant-association increase termites’ capture. Yellow colour, acidic pH and fluid viscoelasticity but above all, pitcher conicity, wide aperture diameter and magnitude of floral odour account for the abundance of flying insects. These Nepenthes species also strongly vary in their enzymatic secretions and inquilines spectra.In a second part, we show in situ how such differences in physico-chemical and biotic properties of the fluid partly account for the differences in nitrogen-sequestration strategy in these plants. Fluid pH and viscoelasticity influence the quantity and the nature of prey. Those physico-chemical properties also condition the richness of the aquatic ecosystem associated to the fluid, with an aquatic macrofauna more abundant and diverse in pitchers with lowly-acidic liquids and wide pitcher-openings. This inquiline macrofauna plays an essential role in prey degradation, and the presence of a top-predator is crucial for the nitrogen recycling to the plant.We finally discuss the major contribution of the fluid in the plant’s diet and its role in the probable adaptive radiation of the Nepenthes genus and conclude by a survey of the various forms of carnivory in these plants and their digestive systems, which range from an autonomous aggressive strategy to a mutualistic strategy, thus redefining the concept of carnivory in the plant’s world

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Guerra, Badell Joana 1986. "Cooperative interactions of stem and niche cells during skeletal muscle regeneration: role of IL-6 signaling." Doctoral thesis, Universitat Pompeu Fabra, 2016. http://hdl.handle.net/10803/482050.

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Adult skeletal muscle has a remarkable capacity of self-repairing after damage. The cellular communication processes and mediator molecules in the regenerative microenvironment that control muscle stem cell functions are poorly characterized. Muscle resident fibro/adipogenic progenitors (FAPs) are responsible of the fibrotic and adipose degeneration of muscle in pathological situations. In contrast with this function, here we demonstrate that blood-infiltrating neutrophils cooperate with FAPs to promote muscle regeneration after injury. By cell-type specific gene deletion and transplantation experiments, here we show the requirement of the soluble form of interleukin 6 (IL-6) receptor released by neutrophils and FAP-derived IL-6 to activate IL-6 trans-signaling for efficient muscle stem cell proliferative and regenerative functions. Exploitation of this physiological mechanism may be of therapeutic importance in pathologies coursing with poor regeneration of skeletal muscle. El múscul esquelètic adult té una notable capacitat d’autoregenerar-se després d’un dany. Els processos de comunicació cel·lular i les molècules mediadores que controlen les funcions de les cèl·lules mare musculars en el microambient regeneratiu, no han estat caracteritzats detalladament. Els progenitors fibro/adipogènics (FAPs) residents en el múscul esquelètic són responsables de la degeneració fibro/adiposa que pateix el teixit muscular en situacions patològiques. Contràriament a aquesta funció, aquest treball demostra que els FAPs cooperen amb els neutròfils provinents de la sang i que infiltren el teixit danyat, per expandir el nombre de cèl·lules mare musculars després d’una lesió. Mitjançant la supressió de l’expressió de gens específicament en diferents tipus cel·lulars i experiments de trasplantament, demostrem el requeriment de la interleucina 6 (IL-6), produïda de forma local i transitòria pels FAPs, que actua conjuntament amb la forma soluble del receptor de IL-6 (sIL-6Rα), alliberat pels neutròfils, per activar la trans-senyalització per IL-6 i així promoure la regeneració. L'explotació d'aquest mecanisme fisiològic pot tenir una importància terapèutica en patologies amb una deficient regeneració muscular.

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Sanhueza, Daniel. "Effets des conditions environnementales sur la croissance et l'expression génique de Mycobacterium ulcerans, agent causatif de l'ulcère de Buruli." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTT054.

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Mycobacterium ulcerans (MU), agent causatif de l'ulcère de Buruli (UB), une maladie infectieuse humaine émergente, est associé aux milieux aquatiques tropicaux, et en particulier ceux modifiés par les activités humaines. L’écologie de cette mycobactérie est encore peu informée, et des interrogations demeurent sur son cycle de transmission au sein des écosystèmes et à l’humain. La tendance observée aujourd’hui en recherche est de montrer l’existence d’une multitude de taxa porteurs du bacille au sein des écosystèmes aquatiques mais aussi terrestres, laissant donc imaginer qu’un ou quelques facteurs en commun puissent expliquer sa présence et son développement. Dans ce contexte, nous avons développé des approches expérimentales au laboratoire pour analyser les effets de paramètres environnementaux, sélectionnés comme être importants dans la définition de la niche écologique de MU, sur le maintien et le développement des populations bactériennes. En tenant compte de gammes de valeurs rencontrées dans des régions endémiques et non endémiques, où sévit, nous avons testé dans un premier temps l'effet de deux polysaccharides très largement présents dans les écosystèmes naturels (la chitine et l’amidon) ainsi que cinq composants chimiques (le fer, le calcium, le zinc, le phosphate et le sulfate), représentant des nutriments indispensables pour les bactéries, sur la croissance de MU. Notre travail montre que la chitine augmente de manière très significative la croissance de MU. A l’inverse, la présence d’amidon ne favorise pas son développement. Le calcium est le seul élément chimique à contribuer à l’augmentation de quantité de cellules de MU avec le temps, mais ce paramètre reste toutefois très marginal. L’absence d’effet joué par le fer, le zinc, le sulfate et le phosphate sur la croissance in vitro de MU tend à indiquer que les valeurs utilisées dans nos expériences correspondent à des valeurs limites pour expliquer la distribution géographique de MU dans les écosystèmes aquatiques tropicaux. Dans un deuxième temps, eu égard au peu d‘informations existant concernant le rôle joué par le pH sur la présence et le développement de MU, nous avons reproduit des environnements pour étudier la croissance de MU en fonction de différentes valeurs de pH rencontrées dans des régions du Cameroun et de Guyane française où la mycobactérie peut être présente ou absente. Nos résultats montrent que le pH présente un effet significatif sur la dynamique de croissance de MU avec un effet plus marqué pour des valeurs de pH proches de 6,0. De plus, il existe une forte interaction entre pH et chitine puisque pour des mêmes valeurs de pH, la croissance bactérienne est 10 fois plus importante en présence de milieu avec chitine. Ces résultats suggèrent aussi que des pH trop acides, inférieurs à 5,0, sont défavorables à la croissance de la mycobactérie.Finalement, nous nous sommes intéressés à l’expression génique de différents isolats de MU générés à partir de différents environnements expérimentaux. Pour ce faire, et en nous servant d’une nouvelle approche de séquençage des ARN, nous avons étudié l’expression de MU dans différents environnements ; Nous nous sommes notamment intéressés à l’expression des gènes impliqués dans les voies métaboliques de production de la mycolactone, le peptide responsable des ulcérations chez l’humain. Des contextes environnementaux spécifiques pourraient conduire à une sur-expression de toxine peptidique traduisant ainsi une écologie et une épidémiologie (micro-)contexte-dépendant ayant des incidences pathologiques et cliniques très particulières.Dans leur ensemble, nos résultats participent à une recherche permettant de mieux comprendre les paramètres clés de la niche écologique de M. ulcerans et au-delà contribue à l’identification des écosystèmes aquatiques favorables, ou non, au maintien et au développement de cette mycobactérie responsable de l’ulcère de Buruli Mycobacterium ulcerans (MU), the causative agent of Buruli ulcer (BU), an emerging human infectious disease, is associated with tropical aquatic environments, particularly those modified by human activities. The ecology of this mycobacterium is still poorly understood, and questions remain about its transmission cycle within ecosystems and from nature to humans. Nowadays the research orientation is to show the existence of a multitude of host taxa carrying the bacillus in both aquatic and riparian ecosystems. Thus, it is likely to think that one or a few common factors might contribute and explain the presence and development of this bacillus across distinct localities and regions.In this context, we have developed experimental approaches in the laboratory to analyze the effects of several environmental parameters, selected as being important in the definition of the MU ecological niche and in its growth and persistence in natural ecosystems. Considering ranges of values encountered in endemic and non-endemic regions where BU occurs, we first tested the effect on MU growth of two polysaccharides widely present in nature (chitin and starch) and five chemical components (iron, calcium, zinc, phosphate and sulfate) representing essential nutrients for bacteria. Our work shows that chitin increases significantly the growth of MU. Conversely, the presence of starch does not favor its development with time. Calcium is the only chemical element contributing to increase MU cell number over time, but this effect remains very marginal. The lack of effect exerted by iron, zinc, sulfate and phosphate on the in vitro growth of MU suggests that values used in our experiments correspond to the limit values to explain the geographical distribution of MU in tropical aquatic ecosystems.Secondly, given the few existing information about the role of pH on the presence and development of MU in natural settings, we have reproduced in the lab some environments to study the growth of MU depending on different pH values encountered in regions of Cameroon and French Guiana where the mycobacterium can be present or absent. Our results show that pH has a significant effect on MU growth with a greater effect at pH values close to 6.0. In addition, there is a strong interaction between pH and chitin as to the same pH bacterial growth is 10 times greater in the presence of medium with chitin. These results also suggest that pH too acidic, lower than 5.0 are unfavorable for MU growth.Finally, we looked at gene expression of different MU cultures from different experimental frameworks. Here, and by making use of a new RNA sequencing approach, we studied the genetic expression of MU in differents environments. We are especially interested in the expression of genes implicated in the metabolic pathways of mycolactone production, the peptide toxin responsible of ulcerations in human. Specific environmental contexts could lead to an over-expression of these genes by MU populations, thus pinpointing the fact that MU ecology and epidemiology could be (micro-) context-dependent having some pathological and clinical implications. Taken together, our results participate in a research allowing to better understand the key parameters of the ecological niche of MU, and beyond helping to identify the aquatic ecosystems favorable or not to the maintenance and development of this mycobacterium responsible for Buruli ulcer

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Yguel, Benjamin. "Sortir de sa niche ancestrale : conséquences pour les interactions trophiques, le cas du chêne pédonculé et sessile." Phd thesis, Université Rennes 1, 2012. http://tel.archives-ouvertes.fr/tel-00793651.

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Le conservatisme phylogénétique de niche se définit par la conservation, au cours du temps, de la niche écologique et des traits écologiques associés. Des espèces phylogénétiquement proches auront alors tendances à occuper des niches similaires, incluant des conditions abiotiques mais aussi des interactions biotiques similaires. Ainsi, un individu isolé phylogénétiquement de ses voisins, pourrait être considéré comme présent dans une nouvelle niche. Dans cette thèse, nous nous sommes intéressés aux interactions trophiques des individus de plantes hôtes colonisant une nouvelle niche, représentée par un voisinage phylogénétiquement éloigné, à la différence des individus hôtes restant dans leur niche ancestrale. Nous avons étudié plus particulièrement le cas du chêne et de ses phytophages, de leurs ennemis naturels, et enfin, des ectomycorhizes du chêne. Nos résultats indiquent que l'isolement phylogénétique des chênes hôtes (i) diminue l'abondance des phytophages et leurs pressions sur le chêne, (ii) diminue la pression des ennemis spécialistes sur ces phytophages, (iii) augmente l'abondance et l'activité des ectomycorhizes du chêne. Ainsi, l'isolement phylogénétique du chêne modifie l'intensité et la nature des interactions biotiques tout au long de la chaîne trophique à laquelle il appartient. Plus généralement, nos résultats permettent de discuter dans quelles situations une sortie de niche sera favorisée et dans quelles situations, une sortie de niche sera contrariée. Ces résultats suggèrent que les chênes phylogénétiquement isolés, mais aussi leurs phytophages et leurs mycorhizes, subissent des pressions de sélection particulières qui pourraient être à l'origine d'une différentiation évolutive à long terme.

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Dziasko, M. A. "Localisation of corneal epithelial progenitors and characterization of cell-cell interactions in the human limbal stem cell niche." Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1472700/.

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The cornea, the transparent tissue located at the front of the eye, is a highly specialized tissue that transmits and refracts light onto the retina. Maintenance of the corneal epithelium relies on a population of limbal epithelial stem cells (LESCs) that maintain transparency of the ocular surface that is essential for vision. Despite great advances in our understanding of ocular stem cell biology over the last decade, the exact location of the LESC niche remains unclear. After observing a high population of basal epithelial cells expressing stem cell markers within the previously identified limbal crypts (LC), the first aim of this study was to demonstrate by in vitro clonal analysis that these structures provide a niche for the resident LESCs. High-resolution transmission electron microscopy has been further used to image the basal epithelial layer at the limbus. Cells with morphology consistent with stem cells were present within the basal layer of the limbal crypts but not within the basal layer of non-crypt limbal biopsies. Moreover, LESCs appeared proximal to limbal stromal cell extensions that suggested a possible route for direct cell-to-cell interaction. These observations were further confirmed by serial block-face scanning electron microscopy that revealed, for the first time, direct epithelial-stromal interactions in the LESC niche whereas limbal melanocytes maintained the LESC apically. In order to assess the role of limbal melanocytes (hLM) as niche cells for the maintenance of LESC, a novel co-culture system was developed in which hLM were used as a feeder layer for the expansion of limbal epithelial cells in vitro. Interestingly, hLM had the ability to support the clonal growth of LECs that maintained stem cell-like characteristics in 2D and 3D tissue equivalents. Taken together, these observations suggest an important role for melanocytes as niche cells in the native human limbal crypts.

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Valdovinos, Fernanda S., Berry J. Brosi, Heather M. Briggs, de Espanés Pablo Moisset, Rodrigo Ramos-Jiliberto, and Neo D. Martinez. "Niche partitioning due to adaptive foraging reverses effects of nestedness and connectance on pollination network stability." WILEY-BLACKWELL, 2016. http://hdl.handle.net/10150/621210.

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Much research debates whether properties of ecological networks such as nestedness and connectance stabilise biological communities while ignoring key behavioural aspects of organisms within these networks. Here, we computationally assess how adaptive foraging (AF) behaviour interacts with network architecture to determine the stability of plant-pollinator networks. We find that AF reverses negative effects of nestedness and positive effects of connectance on the stability of the networks by partitioning the niches among species within guilds. This behaviour enables generalist pollinators to preferentially forage on the most specialised of their plant partners which increases the pollination services to specialist plants and cedes the resources of generalist plants to specialist pollinators. We corroborate these behavioural preferences with intensive field observations of bee foraging. Our results show that incorporating key organismal behaviours with well-known biological mechanisms such as consumer-resource interactions into the analysis of ecological networks may greatly improve our understanding of complex ecosystems.

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Psaila, Bethan. "Interactions between megakaryocytes and tumour cells in the bone marrow vascular stem cell niche promote tumour growth and metastasis." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/5945.

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Specialized bone marrow microenvironments (vascular and osteoblastic 'niches') regulate normal haematopoietic stem/progenitor cells. Recently, the vascular niche has also been implicated as an area for preferential engraftment of malignant cells. The cellular and molecular factors that regulate the vascular niche and, in particular, the role of megakaryocytes are poorly understood. The aim of my work was to investigate the role of megakaryocytes in homing and engraftment of malignant cells to the bone marrow vascular niche using mouse models. C57Bl/6 wild-type and megakaryocyte-deficient, thrombopoietin (TPO)-/- mice were injected with B16 melanoma or EL4 lymphoma cell lines and the megakaryocyte-vascular niche investigated by immunohistochemistry, confocal microscopy, in vitro culture, co-cultures and gene expression by RT-PCR. In wild-type mice injected with B16 melanoma, platelet size and megakaryocyte numbers significantly increased (P<0.02). B16 tumour cells were found to produce the thrombopoietic factors VEGF, SCF and IL11. Bone marrow sinusoids were almost universally surrounded by one of more megakaryocytes tightly abutting the vascular endothelium, forming the megakaryocyte-vascular niche. Metastatic B16 cells were observed in close association with megakaryocytes in the vascular niche, consistent with this being a port of entry to the bone marrow. In TPO-/- mice, tumour growth and metastasis was markedly retarded and no tumour cells were seen in the bone marrow, suggesting that megakaryocytes play a functional role in metastasis. In TPO-/- bone marrow, vessels were more tortuous and larger in diameter (P=0.01); and expression of PF4, TSP1, VEGF and TGFβ was 70%- 90% lower, suggesting that a major proportion of angiogenic regulatory factors is producted by megakaryocytes in the bone marrow in wild-type mice. Furthermore, in wild-type mice, expression of VEGF and TGFβ significantly increased during tumour growth and metastasis while PF4 expression decreased (P<0.05). Megakaryocyte-conditioned medium (MCM) enhanced the proliferation rate of B16 cells (P<0.001) and also was highly chemotactic for B16 cells (P<0.001), an effect mediated by pertussis toxin-sensitive Gi-protein receptors and reduced in the absence of TSP1. Co-culture with B16 cells increased megakaryocyte expression of VEGF, TGFβ and TSP1 and decreased PF4, consistent with the in vivo observations, while cocultured B16 cells displayed increased expression of VEGF and TGFβ and adhesion integrins. Moreover, pretreating B16 cells with MCM prior to tail vein injection enhanced metastatic engraftment. To investigate the role of megakaryocytes in human malignancy, trephine bone marrow biopsies from patients with metastatic carcinoma were examined. Increased megakaryocyte numbers and abnormal megakaryocyte clustering were observed in the majority of patients, suggesting that megakaryocyte-tumour interactions may also occur in the setting of human metastatic disease. In conclusion, my findings suggest that megakaryocytes contribute to the integrity and function of the bone marrow vascular niche and that cellular/molecular cross talk between megakaryocytes and tumour cells may promote metastasis. Targeting these interactions may be useful as adjunctive therapy in metastatic disease.

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Fugmann, Simon Martin. "Polymer chains with nonlinear interactions." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16254.

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Ziel dieser Arbeit ist es, den Einfluss der gekoppelten Dynamik in nichtlinearen Polymerketten auf Prozesse wie den thermischen Zerfall und den kraftinduzierten Abriss zu untersuchen. Dafür betrachten wir zunächst die Gleichgewichtsrelaxationseigenschaften von Ketten mit nichtlinearen Wechselwirkungspotentialen. Es kann gezeigt werden, dass die Relaxationseigenschaften des End-zu-End-Abstandes wie auch der Hauptkomponenten jene der harmonischen Kette sind. Die Korrelationszeiten weichen jedoch ab. Sogenannte weiche nichtlineare Potentiale erhöhen die Korrelationszeit. Doppelmuldenpotentiale können zum Anwachsen typischer Korrelationszeiten um mehrere Größenordnungen führen. Die Hauptkomponenten, deren Richtungen mit denen der Normalmoden der harmonischen Kette übereinstimmen, zeigen dabei unter Umständen eine subdiffusive Dynamik. In Bezug auf das thermisch aktivierte Bindungsversagen gehen wir auf zwei experimentell wichtige Problemstellungen ein. Zuerst untersuchen wir den thermisch aktivierten Zerfallsprozess einer homopolymeren Kette. Wir berechnen mittlere Aktivierungszeiten einzelner Bindungen für freie und befestigte Ketten. Wir können zeigen, dass diese Zeiten entscheidend von der Gesamtlänge der Kette sowie der Position der Bindung abhängen. An den freien Kettenenden weisen sie ein Minimum auf. Die zweite experimentell relevante Situation entspricht jener in Einzelmolekül-Zugexperimenten. Zusätzlich zum Einfluss nicht Markovscher Fluktuationen im gekoppelten System hat die verzögerte Kraftpropagation entlang der Kette einen weiteren Einfluss auf die Abrissdynamik. In langen Ketten brechbarer Bindungen verursacht das komplexe Zusammenspiel zwischen Kraftpropagation und der dem Abriss zugrundeliegenden Extremwertstatistik eine nicht monotone Abhängigkeit der wahrscheinlichsten Abrisskraft von der Kettenlänge. Abschließend analysieren wir experimentelle Abrissdaten von kovalenten Bindungen in zweisträngigen DNS Ringen. This work intends to show how the coupled dynamics of a nonlinear polymer chain alters processes such as thermal fragmentation and force-induced rupture. For that purpose we first examine the equilibrium relaxation properties of chains with nonlinear interaction potentials. We find that the relaxation properties of the end-to-end distance and the principal components are essentially those of the harmonic chain, though with shifted correlation times. Soft nonlinear potentials increase the correlation times. Double-well interaction potentials may lead to an increase of the relaxation times by orders of magnitude. The principal components, whose directions follow the normal modes of the harmonic chain, can exhibit vastly different subdiffusive kinetics. Concerning the thermally activated bond rupture in polymer chains we focus on two experimentally relevant situations. First, we consider the thermally activated fragmentation of a homopolymer chain. We calculate mean activation times of individual bonds for free and grafted chains. We show that these times crucially depend on the length of the chain and the location of the bond yielding a minimum at the free chain ends. Second, we study a set up corresponding to the one found in single molecule pulling experiments. In addition to the influence of non-Markovian fluctuations in the coupled system the delayed force propagation into the chain has a further impact on its overall rupture dynamics. In long chains of breakable bonds the complex interplay between the force propagation into the chain and the extreme value statistics underlying rupture causes a non-monotonic scaling of the most probable rupture force as a function of the chain length. Finally we analyze experimental data of the rupture of covalent bonds in ds-DNA loops.

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Priddis, Edmund R. "Niche Separation Along Environmental Gradients as a Mechanism to Promote the Coexistence of Native and Invasive Species." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2199.pdf.

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Grevet, Catherine. "Being nice on the internet: Designing for the coexistence of diverse opinions online." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55002.

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This thesis contributes to a better understanding of social media designs for more civil conversations online. I first demonstrated that people disengage from social media interactions when they encounter uncivil behavior from friends. To find alternative designs for social media that are more civil, I evaluated novel social interaction techniques. To do this, I designed a six-phase framework for prototyping social interactions called piggyback prototyping; and an algorithmic probe study methodology to include participants in the development of social curation algorithms. I built a piggyback prototype that modifies the civility on Facebook by highlighting positive posts in green and hiding impolite posts, and I deployed it as an algorithmic probe with 20 participants. I uncovered ways to improve the algorithm, and I found that participants responded most favorably to having civil posts highlighted. These findings open avenues for future research in designing pro-social platforms.

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Andrade, Thiago. "Évolution spatiotemporelle de la diversité et du fonctionnement d'une guilde de parasitoïdes." Thesis, Rennes 1, 2013. http://www.theses.fr/2013REN1S124/document.

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Cette thèse porte sur l’analyse des dimensions spatiale et temporelle du fonctionnement et de la diversité taxonomique et fonctionnelle d’une guilde. Au sein d’une guilde, les espèces exploitent un même type de ressources; pour cette raison, les niches écologiques fondamentales des membres d’une guilde sont similaires et une relation de compétition interspécifique se met en place si la ressource partagée est limitante. Quatre questions principales sur le fonctionnement d’une guilde ont été abordées : (1) à quelles échelles spatio-temporelles se structurent la guilde et les ressources exploitées, (2) quelles sont les influences respectives des filtres environnementaux et des interactions interspécifiques sur les traits fonctionnels des membres de la guilde, (3) quelle est la stratégie d’exploitation de ressources d’un membre de la guilde face à une faible disponibilité de ressources et (4) quel est l’impact du contexte climatique sur la structure d’une guilde et de son réseau trophique, et sur le degré de spécialisation écologique des espèces de la guilde sur la ressource. Le modèle biologique de cette étude a été une guilde de parasitoïdes de pucerons de céréales (Hymenoptera : Braconidae : Aphidiinae). Ces parasitoïdes s’attaquent aux pucerons (Homoptera : Aphididae) inféodés aux céréales dans les agroécosystèmes. Les variations d’abondance relative des parasitoïdes et de leurs hôtes ont été importantes aux échelles interrégionale et interannuelle, mais très faibles à l’échelle intra-régionale. La divergence des traits fonctionnels des parasitoïdes s’est maintenue sur trois régions et deux années, et le contexte local a influencé les traits de la guilde dans son ensemble. Pendant la saison hivernale, une période marquée par une faible densité de pucerons, le parasitoïde Aphidius rhopalosiphi a présenté des stratégies contrastées pour maximiser sa fitness en exploitant les hôtes Sitobion avenae et Rhopalosiphum padi, mais une forte spécialisation écologique sur le terrain a été observée en présence d’une espèce compétitrice : Aphidius avenae. Cette présence a pu être corrélée à une hausse des températures hivernales This thesis is an analysis of the spatial and temporal dimensions of the functioning and taxonomic and functional diversity of a guild. In a guild, species exploit the same type of resources; consequently, fundamental ecological niches of guild members are similar and an interspecific competitive relationship is established if shared resources are limiting. Four main questions on the functioning of a guild are addressed: (1) the spatiotemporal scales to which guilds the guild and its exploited resources are structures, (2) the respective weight of environmental filtering and interspecific interactions on the configuration of realized niches of guild members, (3) the strategy of resource exploitation in a guild member facing low resource availability and (4) the impact of climatic context on the structure of a guild and its food web, and the degree of specialisation on resources. The biological model chosen in this study was a cereal aphid parasitoid guild (Hymenoptera: Braconidae: Aphidiinae). Those parasitoids attack aphids (Homoptera: Aphididae) in agroecosystems, which are anthropised environments marked by high disturbance rates and in which host resources are variable in density and in quality. Relative abundance variations in parasitoids and in their hosts were considerable at interregional and interannual scales, but weak at the intra-regional scale. Functional trait divergence in parasitoids was maintained across three regions and two years, and regional and annual environmental contexts influenced guild traits as a whole. In winter, a period marked by low aphid density, the parasitoid Aphidius rhopalosiphi presented contrasted strategies to maximise fitness whilst exploiting Sitobion avenae and Rhopalosiphum padi hosts, but a high degree of ecological specialisation in the field was observed in the presence of a competitive species, Aphidius avenae. This presence was correlated to an increase in winter temperatures

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Gomes, Camilla Montes. "Interações entre aves e plantas: frugivoria, amplitude de nicho e relações morfológicas, em três diferentes ambientes." Universidade Federal de Uberlândia, 2013. https://repositorio.ufu.br/handle/123456789/13402.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico The interaction between frugivorous birds and plants is one of the most important mutualisms in tropical regions. However, the way these groups interact varies according to temporal availability of fruit. In seasonal sites, it is expected that a specialization in a particular type of fruit is not viable, because this feature is not available throughout the year, and species that occupy these sites have a broad trophic niche. With a more stable supply of resources, a greater level of specialization is expected, which would be reflected in a narrower niche width. A relationship between the morphology of birds and type of fruit consumed can also be associated with the specialization level of diet and niche width of the birds. This relationship might possibly be more evident in local with reduced seasonality. The goal of this paper is to investigate the relationships, both ecological as morphological, between frugivorous birds and plants consumed in sites with different levels of resource seasonality. Cerrado sensu stricto were considered the most seasonal, followed by seasonal deciduous and semi-deciduous forests, which were grouped as \"seasonal forests\". Atlantic forest was seen as a site less seasonal. We tested the hypothesis that species of the guild \"frugivorous\" will be more representative of the number of species and interactions in less seasonal area, and that species of more seasonal areas would have a more generalist diet and broader trophic niche than that observed for species less seasonal site. In Chapter 2 we investigated the existence of relationships between morphology of the birds beak and size of fruits eaten by them, testing the hypothesis that this combination was more evident in local whose species exhibit lower niche amplitude than in that have species with broader niche width. In this study the community structure of each site was described and was observed narrower trophic niche for species of seasonal forests and Atlantic forest (more specialized diet) than that found for species of cerrado ss (more generalist diet). However, morphological specialization was found only in species of seasonal forests, where we observed an association between the width and depth of the tip with the size of the fruit consumed. The variation observed for specialization in diet and morphology may be related to temporal availability of resources among different sites. Furthermore, other features in the selection of fruits, behavioral traits of birds and ecological interactions with other community members also seem to influence the consumption patterns of birds. A interação entre aves frugívoras e plantas é uma dos mutualismos mais importantes em ambientes tropicais. No entanto, a forma com que esses grupos se relacionam pode variar de acordo com a disponibilidade dos frutos ao longo do ano. Em ambientes sazonais, espera-se que uma especialização em determinado tipo de fruto seja inviável, uma vez que esse recurso não está disponível durante todo ano; e que as espécies que ocupam esses ambientes teriam uma maior amplitude de nicho trófico. Já em ambientes com uma oferta de recursos mais estável, um maior nível de especialização é esperado, o que refletiria em uma amplitude de nicho mais estreita. Associado ao nível de especialização da dieta, e consequentemente, à amplitude de nicho exibida pelas aves em cada ambiente, pode existir também uma relação entre a morfologia da avifauna e o tipo de fruto consumido, que possivelmente seria mais evidente em ambientes com sazonalidade reduzida. O objetivo central deste trabalho é investigar interações entre aves frugívoras e as plantas consumidas, e possíveis relações morfológicas, em ambientes com diferentes níveis de sazonalidade de recursos. Áreas de cerrado stricto sensu foram consideradas as mais sazonais, seguidas de matas estacionais decíduas e semidecíduas, que foram agrupadas como matas sazonais . Mata atlântica foi considerada como um ambiente menos sazonal. No capítulo 1, foram analisadas as interações entre as espécies vegetais e aves frugívora nos três ambientes citados acima. Nós testamos as hipóteses que espécies pertencentes à guilda frugívora serão mais representativas, quanto ao número de espécies e interações, em ambientes menos sazonais; e que espécies de áreas mais sazonais teriam uma dieta mais generalista e um nicho trófico mais amplo do que o observado para espécies de ambientes menos sazonais. No capítulo 2 foi investigada a existência de relações entre a morfológica do bico das aves e o tamanho dos frutos consumidos por elas, testando a hipótese que essa associação seria mais evidente em ambientes cujas espécies exibem menor amplitude de nicho, comparado a ambientes que possuem espécies com maior amplitude de nicho. No presente estudo, a estrutura das comunidades de cada ambiente foi descrita e foi observado um nicho trófico mais estreito para espécies de matas sazonais e mata atlântica (dieta mais especializada) do que o encontrado para espécies de cerrado ss (dieta mais generalista). No entanto, especialização na dieta somente foi refletida em uma especialização morfológica em espécies de matas sazonais. Nesse ambiente foi possível observar associação entre a largura e altura do bico com o tamanho do fruto consumido. Essa variação observada quanto à especialização na dieta e na morfologia pode estar relacionada à disponibilidade temporal de recursos distinta entre os ambientes. Além disso, outros critérios na seleção dos frutos, características comportamentais das aves e interações ecológicas com outros elementos da comunidade parecem influenciar também os padrões de consumo da avifauna. Mestre em Ecologia e Conservação de Recursos Naturais

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Serebryakova, Alexandra. "Acclimation and adaptation of invasive seaweeds - a case study with the brown alga sargassum muticum." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066475.

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Les algues non-indigènes ont des impacts sur les communautés naturelles à une échelle mondiale: elles affectent la biodiversité et le fonctionnement des écosystèmes ainsi que les services écosystémiques, avec des conséquences économiques et sociales. Parmi les conséquences de ces introductions sont le déplacement d'espèces indigènes, des compétitions avec des espèces en danger et des effets sur les trajectoires éco-évolutives des espèces des communautés envahies. Bien que crucial pour anticiper le devenir des espèces non-indigènes, comprendre les mécanismes d'acclimatation et d'adaptation agissant post-introduction reste un challenge chez les algues. Au cours de cette thèse, nous avons étudié certains processus d'acclimatation, en particulier le rôle des bactéries associées, et leurs effets, en utilisant comme modèle d'étude Sargassum muticum. Cette algue brune originaire d'Asie, est une espèce emblématique parmi les algues introduites avec une présence du Mexique à l'Alaska en Amérique et du Maroc à la Norvège en Europe. Nous avons effectué une analyse bibliographique des traits et caractéristiques écologiques qui pourraient expliquer son succès. Nous avons ensuite montré que l'acidification n'a pas d'effets significatifs sur les bacteries associées, bien que des changements saisonniers du microbiome aient été observés. Enfin, nous avons utilisé un modèle de niche écologique, intégrant la phénologie, pour prédire la distribution de S. muticum sous deux scénarios de changement climatique. Selon nos résultats, d'ici 2100, la distribution de S. muticum devrait se déplacer vers le nord dans l'hémisphère nord avec des régressions dans certaines zones actuellement occupées Non-indigenous seaweeds impact natural communities worldwide, affecting biodiversity, ecosystem functioning, and ecosystem services, resulting in significant economic and social consequences. Among major impacts are the displacement of native species, a threat to endangered species, and effects on ecological and evolutionary processes within the invaded communities. While critical to predict the fate of introduced species, understanding the mechanisms of acclimation and adaptation following introduction represents a great challenge in seaweeds. In this thesis, we investigated some acclimation processes, with an emphasis on the role of associated microbiota, and examined their effects with Sargassum muticum as a model species. This brown seaweed native to Asia, is an emblematic invader among seaweeds, with a distribution now ranging from Mexico to Alaska in America and from Morocco to Norway in Europe. We first reviewed the competitive advantages and traits that may contribute to its invasiveness. We then showed that acidification has no significant effects on associated bacteria, although seasonal changes in the microbiome have been observed. Finally, we applied ecological niche modelling, but innovatively accounting for phenology, to project the distribution of S. muticum under two future climate change scenarios. According to our projections, by 2100 the distribution of S. muticum is expected to shift northwards along its European, North American and Asian distributions with partial retreat from the currently occupied areas

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Reichstein, Birte. "Ontogenetic bottlenecks : effects on intraguild predation systems and ecosystem efficiency." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-105759.

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Size-dependent differences between individuals in size-structured organisms have fundamental effect on population and community dynamics. Intraguild predation (IGP) is one specifically interesting constellation that often arises when two size-structured populations interact. Ontogenetic bottlenecks that determine population size-structure are affected by both population intrinsic as well as population extrinsic factors, and are therefore context-dependent. Surprisingly, size-structured IGP systems have mainly been investigated theoretically and especially long-term empirical studies are widely lacking. In this thesis I investigate empirically how habitat complexity, interaction strength, and stage-specific resource availabilities affect population processes and their effects on the dynamics of a size-structured IGP system. I conducted multi-generation experiments in a size-structured IGP system, with the Least Killifish (Heterandria formosa) as IG prey and the Common Guppy (Poecilia reticulata) as IG predator. With no alternative resource next to the shared resource, IG predator and IG prey could not coexist. Weak interactions only increased IG prey and IG predator persistence times and observed exclusion patterns depended on habitat complexity. An alternative resource for either the juvenile IG predator or the juvenile IG prey on the other hand promoted coexistence. However, this coexistence was context-dependent. Ontogenetic bottlenecks played a central role in the dynamics of the size-structured IGP system in general. In the final study I show that an ontogenetic bottleneck can, through changes in stage-specific resource availabilities, be affected in a way that leads to increased trophic transfer efficiency with potential effects on higher trophic levels. Overall, the results emphasize importance of the broader context in which size-structured communities are embedded. Especially, when managing natural communities it is important to account for the combined effects of size-structure, stage-specific resource availabilities, and habitat structure. Specifically, when managing species that connect habitats or ecosystems all life-stages’ environmental conditions must be consider in order to ensure strong predictive power of tools used for ecosystem management planning.

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Laube, Irina [Verfasser], Catherine [Akademischer Betreuer] Graham, and Katrin [Akademischer Betreuer] Böhning-Gaese. "Avian range dynamics : traits, biotic interactions and niches in changing environments / Irina Laube. Gutachter: Catherine Graham ; Katrin Böhning-Gaese." Frankfurt am Main : Univ.-Bibliothek Frankfurt am Main, 2012. http://d-nb.info/1044275278/34.

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Mezher, Nader. "Modélisation numérique et quantification de l'effet sismique Site-Ville." Châtenay-Malabry, Ecole centrale de Paris, 2004. http://www.theses.fr/2004ECAP0947.

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L'interaction sol-structure à l'échelle individuelle a fait l'objet de nombreuses études alors que l'interaction globale entre les bâtiments d'une ville fortement urbanisée est largement ignorée sur le plan pratique. Ce sujet, d'actualité en Génie Parasismique, est apparu récemment sous le nom de l'effet Site-Ville. Quantifier les modifications apportées par une ville sur la sollicitation sismique mais aussi sur les comportements des bâtiments est primordial pour mieux contrôler le risque sismique en environnement urbain. L'originalité de ce travail réside dans l'étude de l'effet Site-Ville pour des configurations urbaines réelles (Nice, Mexico). Celle-ci est réalisée au moyen d'une modélisation numérique tridimensionnelle qui tient compte de la complexité du site. Avec la seule hypothèse de linéarité, le problème complet tridimensionnel d'interaction Site-Ville est traité à un coût raisonnable. En effet, l'approche par sous-structuration dynamique permet de coupler les domaines des bâtiments, modélisés par la méthode des éléments finis, avec celui du sol représenté à l'aide de la méthode des éléments finis de frontière. Les cas-tests réalisés montrent que la ville engendre des fluctuations incohérentes du champ sismique qui vont s'ajouter au champ libre. En particulier, ce travail montre que la durée des signaux est allongée et les paramètres de dimensionnement des structures modifiés.

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Matley, Jordan. "The ecology of Arctic cod (Boreogadus saida) and interactions with seabirds, seals, and whales in the Canadian Arctic." Springer, 2012. http://hdl.handle.net/1993/8868.

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This thesis investigates the foraging of Arctic cod (Boreogadus saida) and its predators during the summer in the Canadian Arctic. Findings included the identification of Arctic cod, ringed seal (Pusa hispida), beluga (Delphinapterus leucas), and narwhal (Monodon monoceros) diet shifts in response to seasonal prey availability; calculation of isotopic diet-tissue discrimination factors for Arctic cod, ringed seals, and whales based on local tissue and stomach content sampling; and determination of predatory cues to optimize foraging, such as the presence of schools. Additionally, I quantified seabird feeding and interspecific interactions such kleptoparasitism and found that black-legged kittiwakes (Rissa tridactyla) and northern fulmars (Fulmarus glacialis) captured cod directly but lost many to parasitic jaegers (Stercorarius parasiticus) and glaucous gulls (Larus hyperboreus). Finally, I determined that schools of cod were important prey sources for northern fulmars, glaucous gulls, and whales however non-schooling cod were a significant source for black-legged kittiwakes and ringed seals.

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Roy, Lise. "Ecologie évolutive d'un genre d'acarien hématophage : approche phylogénétique des délimitations interspécifiques et caractérisation comparative des populations de cinq espèces du genre Dermanyssus (Acari : Mesostigmata)." Phd thesis, AgroParisTech, 2009. http://pastel.archives-ouvertes.fr/pastel-00005531.

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Les acariens microprédateurs du genre Dermanyssus (espèces du groupe gallinae), inféodés aux oiseaux, représentent un modèle pour l'étude d'association lâche particulièrement intéressant : ces arthropodes aptères font partie intégrante du microécosystème du nid (repas de sang aussi rapide que celui du moustique) et leurs hôtes sont ailés. En outre, D. gallinae est une espèce d'importance économique, ce qui rend possible des comparaisons entre colonisation de milieux anthropisés et sauvages. Au début de l'étude, les espèces du groupe gallinae sont très mal délimitées. Les caractères morphologiques utilisés sont variables au sein de l'espèces, voire de la population, très chevauchants entre espèces. Afin de mieux comprendre les exigences écologiques du développement de D. gallinae et d'appréhender ses voies de dissémination, une investigation comparative basée sur des séquences d'ADN entre espèces du groupe gallinae a été adoptée. Un cheminement d'ordre taxinomique a permis de poser les bases nécessaires. Ensuite, l'exploration de certaines caractéristiques écologiques du groupe gallinae en relation avec sa phylogénie (spécificité d'hôte, flexibilité évolutive) a été menée à bien. Une espèce a été décrite, D. apodis, une lignée de D. gallinae constitue aussi une probable espèce inédite et D. longipes regroupe deux entités. Des différences écologiques marquées entre D. gallinae et les autres espèces semblent résulter non seulement de l'activité humaine, mais aussi de caractéristiques intrinsèques. Aujourd'hui, le rôle des flux commerciaux dans la dispersion de D. gallinae en élevage de pondeuses s'avère primordial, au moins en France, celui des oiseaux sauvages presque nul.

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Deraison, Hélène. "Effet de la diversité fonctionnelle de communautés d'insectes herbivores sur la diversité et le fonctionnement d'un écosystème prairial." Thesis, Poitiers, 2014. http://www.theses.fr/2014POIT2331.

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La biodiversité est un paramètre déterminant du fonctionnement des écosystèmes. Un effet généralement positif de la diversité en plantes a été observé dans plusieurs études pionnières. Cependant il y a un besoin urgent de mieux comprendre le rôle de la biodiversité au sein des écosystèmes notamment en intégrant différentes composantes importantes de la diversité telles que la diversité fonctionnelle entre et au sein de niveaux trophiques contrastés.Nous avons testé l’effet de la diversité spécifique et fonctionnelle de communautés d’herbivores généralistes (criquets, Acrididea) sur le fonctionnement d’un écosystème prairial. Nous avons créé des communautés expérimentales de criquets au sein desquelles les diversités spécifique et fonctionnelle ont été manipulées de manière indépendante.Cette expérimentation a permis d’identifier les traits fonctionnels d’effet déterminant l’intensité des interactions trophiques entre les communautés de plantes et de criquets. Nous montrons également que les mécanismes contrôlant l’impact des communautés de criquets sur la biomasse végétale dépendent de leur identité et de leur diversité fonctionnelles. Ainsi une plus forte diversité des traits mandibulaires au sein d’une communauté augmente la taille des niches alimentaires et l’impact total observé sur l’écosystème. Enfin, la réponse de l’écosystème face aux herbivores dépend directement de l’intensité de la pression d’herbivorie, de la diversité fonctionnelle en plantes et des changements de composition fonctionnelle au sein des communautés végétales.Cette étude contribue au développement des approches basées sur l’utilisation des traits au sein des interactions trophiques afin de relier l’effet de la biodiversité entre et au sein de multiples niveaux trophiques sur le fonctionnement des écosystèmes Biodiversity is a major determinant of ecosystem functioning. Pioneer biodiversity experiments have shown a general positive relationship between plant diversity and ecosystem functioning. However there is now a growing need to integrate the functional diversity within multi-trophic levels to improve our ability to scale biodiversity changes into future ecosystem functioning.We experimentally tested how the functional identity and diversity of generalist insect herbivore communities impact the functioning of a grassland ecosystem. We experimentally and independently manipulated the functional identity and diversity of grasshopper communities.We identified grasshopper functional effect traits determining the intensity of trophic interactions between plant and grasshopper communities. We demonstrated that the mechanisms driving grasshopper community impact on plant biomass depend on their functional identity and diversity. Thus a higher functional diversity of grasshopper mandibular traits increases the size of the feeding niche within communities and the total impact on ecosystem. Finally, ecosystem response to herbivores depends directly on the intensity of herbivory pressure, plant functional diversity and on the changes of plant functional structure within plant communities.Our study contributes to the development of the trait-based approach in the study of trophic interactions to link biodiversity between and within trophic levels on ecosystem functioning

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Marquitti, Flávia Maria Darcie. "Redes de interação entre morcegos frugívoros e plantas = variação geográfica e conservação de nicho." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/316163.

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Orientador: Paulo Roberto Guimarães Júnior Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia Made available in DSpace on 2018-08-18T07:48:51Z (GMT). No. of bitstreams: 1 Marquitti_FlaviaMariaDarcie_M.pdf: 1225354 bytes, checksum: 120811efd17809715c9eb6454a6b9c34 (MD5) Previous issue date: 2011 Resumo: Os mutualismos são interações importantes do ponto de vista ecológico e evolutivo, uma vez que influenciam a sobrevivência de diversos organismos, podendo determinar a organização da comunidade. Dada a importância ecológica e evolutiva das interações mutualísticas, é importante estudar quais fatores influenciam a sua organização. Como organismos aparentados compartilham características fenotípicas similares, é comum que espécies filogeneticamente próximas interajam com um conjunto de espécies similar, levando a um padrão conhecido por conservação filogenética do nicho. Apesar de este padrão ocorrer com frequencia, condições bióticas e abióticas locais podem levar à variação geográfica nas interações. A presença ou ausência de potenciais parceiros mutualísticos também podem alterar o padrão local de interações de uma espécie. Estudando interações entre morcegos frugívoros e plantas, investiguei como os padrões de interação de espécies em dez redes mutualísticas variavam conforme a distribuição geográfica. Nesse sentido, duas hipóteses principais guiaram este trabalho: a hipótese da conservação de nicho das interações e a hipótese da variação geográfica das interações. Caracterizei o padrão de interação das espécies de morcegos nas redes por meio de diferentes métricas usadas no estudo de redes ecológicas. Analisei a conservação de nicho das interações e a variação geográfica de espécies de morcego que ocorreram em um maior número de redes. Espécies filogeneticamente próximas não tenderam a apresentar padrões de interação mais parecidos entre si. Algumas das espécies mais frequentes apresentaram características dos padrões de interação em gradiente ou mosaico ao longo de sua distribuição geográfica. Estes resultados evidenciam que algumas características do padrão de interação de morcegos frugívoros, como grau de generalismo e o grau padronizado dentro do módulo são conservadas pela filogenia. No entanto algumas espécies apresentaram o grau de generalismo e o papel em relação aos módulos da rede variando ao longo da geografia, seguindo previsões da teoria do mosaico geográfico coevolutivo Abstract: Mutualisms are important interactions to ecology and evolution because they affect the survivorship of many organisms and may shape community organization. Therefore, it is important to study which factors affect their organization. As related organisms share similar phenotypic traits, it is common that close phylogenetic species interact with a similar set of species, resulting in a pattern known as phylogenetic niche conservatism. Although this pattern frequently occurs, biotic and abiotic local conditions may lead to geographic variation of the interactions. The presence or absence of potential mutualistic partners may also change local interactions of a species. I studied interactions between frugivorous bats and plants and I investigated how species interactions patterns varied geographically across ten mutualistic networks. Two main hypotheses guided this work: the interaction niche conservatism hypothesis and the geographical variation hypothesis. I delineated the interaction patterns of bat species in the networks through different metrics used in ecological network studies. I analyzed the niche conservatism and geographical variation of bat species which occurred frequently in the networks. Related species did not tend to have similar patterns of interaction. Within their geographical range, some species vary markedly in their patterns of interaction and this variation often occurs as mosaics or, less frequently, as gradients. These results point out that some patterns of interaction of frugivorous bats, as the specialization degree and the standardized within-module degree, are conserved by phylogeny. However, some species showed variations through geography both in the specialization degree and in their role regarding the network modules, leading to a geographic mosaic of coevolution with potential implications to ecology and coevolution Mestrado Ecologia Mestre em Ecologia

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Bertelsmeier, Cleo. "Biologie des invasions de fourmis dans un contexte de changement climatique." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112358/document.

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Le changement climatique et les invasions biologiques sont parmi les plus grandes menaces de la biodiversité et leurs impacts pourraient augmenter jusqu’à la fin du siècle. Parmi les espèces envahissantes, les fourmis sont un groupe particulièrement néfaste dû à leurs impacts sur les espèces natives, les processus écosystémique, la santé, l’agriculture et l’économie. L’objectif de cette thèse était de prédire les invasions de fourmis – en particulier avec le changement climatique qui pourrait favoriser les invasions en éliminant des barrières thermiques. J’ai utilisé trois approches complémentaires afin d’étudier le potentiel de différentes espèces à envahir : des modèles de distribution, des expériences comportementales et l’analyses d’une base de données de traits écologiques. J’ai modélisé l’aire favorable pour 15 espèces de fourmis parmi les pires, à la fois globalement, par continents, et dans les 34 hotspots de biodiversité. La distribution potentielle de seulement cinq espèce est prédite de diminuer (jusqu’à 35.8%) avec le changement climatique et l’aire potentielle diminue pour la plupart des espèces jusqu’à 63.2%. Les hotspots d’invasions de fourmis se situaient surtout dans des régions tropicales et subtropicales et ils correspondent particulièrement aux hotspots de biodiversité. Contrairement à ce qui est généralement admis, le changement climatique et les invasions biologiques n’agiront pas de manière synergique pour les fourmis. Par contre, les invasions de fourmis resteront probablement un problème global majeur, en particuliers dans les zones où les hotspots de biodiversité et les hotspots d’invasion se superposent. Les modèles de distribution ont identifié de larges zones de recouvrement entre aires favorables de plusieurs espèces de fourmis envahissantes. Dans le futur, ces espèces pourraient arriver simultanément dans les mêmes régions et entrer en compétition. Dans une série d’expériences, j’ai testé les différences comportementales entre 7 espèces de fourmis envahissantes (Anoplolepis gracilipes, Paratrechina longicornis, Myrmica rubra, Linepithema humile, Lasius neglectus, Wasmannia auropunctata et Pheidole megacephala). J’ai découvert deux stratégies comportementales différentes. Les interactions au niveau de la colonie ont suivi des processus démographiques plus complexes. De plus, j’ai mis au point deux expériences pour tester la capacité des fourmis envahissantes à explorer un nouvel espace et à exploiter des ressources. J’ai trouvé des différences significatives entre espèces et leur capacité à dominer par interférence comportementale était négativement corrélée à leurs capacités à découvrir et exploiter des ressources. Cette série d’expériences suggère que les ‘mécanismes’ d’invasion sont plus complexes que ce qui est généralement suggéré et que différentes espèces pourraient utiliser des stratégies comportementales différentes. Étant donné qu’il existe plus de 250 espèces de fourmis exotiques, il serait intéressant de pouvoir identifier à l’avance des futurs envahisseurs potentiels. Afin d’identifier des traits associés au caractère envahissant des fourmis, j’ai mis en place une base de données qui contient 2193 espèces de fourmis et 24 traits écologiques. J’ai effectué une analyse préliminaire de différences de traits entre fourmis natives et envahissantes qui a montré qu’il existe clairement des groupement distincts de natives et envahissantes, avec les espèces exotiques au milieu. Ces résultats pourraient servir de base pour construire un modèle prédictif des invasions de fourmis. Ces différentes approches (modèles, expériences, base de données) sont complémentaires car elles s’intéressent à des aspects différents du futur des invasions de fourmis qui sera vraisemblablement fortement influencé par le changement climatique. Le pires envahisseurs de demain ne seront probablement pas les même qu’aujourd’hui et les zones les plus à risque pourraient changer également Climate change and biological invasions are both among the greatest threats to biodiversity and their impacts might increase by the end of the century. Among invasive species, ants are a prominent group due to their negative impacts on native species, ecosystem processes, human and animal health, agro-ecosystems and the economy. The objective of this thesis was to forecast future ant invasions – especially in the light of on-going climate change, which is generally thought to favour invasive species by removing thermal barriers. I used three complementary approaches to study the potential of different ant species to invade in the future: species distribution modelling, behavioural experiments and the analysis of a database of ecological traits. I modelled suitable area for 15 of the worst invasive ant species, both currently and with predicted climate change, globally, regionally and within the world’s 34 biodiversity hotspots. Surprisingly, the potential distribution of only five species was predicted to increase (up to 35.8%) with climate change, with most declining by up to 63.3%. The ant invasion hotspots are predominantly in tropical and subtropical regions of South America, Africa, Asia and Oceanic islands, and particularly correspond with biodiversity hotspots. Contrary to general expectations, climate change and biological invasions will not systematically act synergistically for ants. In addition, I found that the impacts of climate change can change over time and even reverse the trend of the impact (i.e., an increase instead of a decrease or vice versa). However, ant invasions will likely remain as a major global problem, especially where invasion hotspots coincide with biodiversity hotspots. The species distribution models have identified large potentially overlapping distributions of several invasive ants. In the future, these species may arrive simultaneously in the same regions and compete with each other. In a series of experiments, I tested behavioural differences among 7 highly invasive ant species (Anoplolepis gracilipes, Paratrechina longicornis, Myrmica rubra, Linepithema humile, Lasius neglectus, Wasmannia auropunctata and Pheidole megacephala). I discovered two different behavioural strategies among invasive ants. Interactions at the colony level, exhibited more complex demographic processes and more variability. Further, I investigated resource competition and differences in resource exploitation. I found significant differences among species, with competitive abilities that were negatively correlated with behavioural dominance. This series of experiments suggests that the ‘mechanisms’ of invasiveness are more complex than previously thought and that different invasive ant species may use different behavioural strategies. Since there are more than 250 exotic species of ants, it would be interesting to identify potential future invaders. In order to identify traits associated with invasiveness in ants, I set up a database with 2193 ant species and 24 ecological characteristics. I performed a preliminary analysis of trait differences between native and invasive ants that shows clearly different clusters of invasive and native species, with exotic species in between. These results could be used as a basis to construct a predictive model of future ant invasions. The different methods used (models, experiments, database) are complementary in that they explore different aspects of the future ant invasions which are likely to be influenced by on-going climate change. The worst invaders of tomorrow may not be the same as today and similarly, areas most at risk are likely to change

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Lynch, Thomas John. "Adult stem cells in the trachea and tracheal submucosal glands." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/6464.

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Breathing is essential for human life, yet tens of millions of people in the U.S. alone suffer from lung diseases. With each breath, lungs are exposed to the external environment. Inhaled air first passes through the trachea, bronchi, and finally the bronchioles before it reaches the alveoli where gases are exchanged. A barrier of epithelial cells protects the airways. In addition, epithelial glands also secrete protein-rich fluids onto the airway surfaces to help maintain sterility. Injury, disease, or other factors can damage these cells, and regiospecific stem cells (SCs) can divide to replace them. However, many important details about lung SCs are still unknown. For example, what processes control SC division? How do region-specific SCs differ from one another? And how does disease or injury impact SC biology? We found that some processes that regulate lung development also control adult SC division following injury. We show that SCs from airway glands give rise to surface epithelial cell types and glandular cell types. In contrast, surface SCs only generated surface cell types. Finally, we identify a type of cell in the glands that can regenerate surface cell types after severe injury. These studies provide new insights into the neighborhoods in which SCs reside in the large airways and processes that control their contribution to airway repair following injury. Overall, this research provides important new insights into adult SC biology and conditions affecting lung health.

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Kubincová, Magdaléna, and Eveline Ingesson. "“They don't look real; they are not nice.” : Skeuomorphic vs. Flat Design Icons – Ease of use, Recognition and Preference of Children Aged 7-9." Thesis, Jönköping University, Tekniska Högskolan, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-53697.

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Icons are an important part of the user interface design. By representing objects and actions, they can quickly and efficiently convey information as well as make an interface more aesthetically pleasing for the user. Nowadays, the flat design is used as the industry standard while skeuomorphic icons fade away. In this study, we aimed to examine the value of both icon styles for a segment of users aged 7-9 years old. We tested the ease of use, recognition, and preference for skeuomorphic and flat design icons with twenty pupils from a Swedish primary school (N=20), using three experiments to measure these parameters. In the first experiment, participants completed simple tasks in an educational application prototype. The second experiment involved selecting icons with certain meaning from a grid. Lastly, the participants were presented with five pairs of icons and asked to choose which one they liked better. Although our results did not find a statistically significant difference in the ease of use or recognition for this age group, we found that the children had a strong preference towards the skeuomorphic design. Therefore, we suggest that skeuomorphic icons should be used in interfaces specifically designed for children, as they are more aesthetically pleasing for the users and do not affect the ease of use or recognition in a negative way.

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Valverde-Barrantes, Oscar Jesus. "A phylogenetic perspective on fine root ecology: assessing the role of root evolution on fine root functional traits and ecological interactions in woody angiosperms." Kent State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=kent1384641579.

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Crego, Ramiro Daniel. "Niche Expansion of an Invasive Predator (Neovison vison), Prey Response, and Facilitative Interactions with Other Invasive Mammals at the Southern End of the Americas: Conservation Challenges and Potential Solutions." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1062862/.

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The Cape Horn Biosphere Reserve is located at the southern tip of South America. This large archipelago is considered one of the last pristine areas left on the world. Despite it being an unpopulated area with most of the native forest cover intact, it has not been exempt from biological invasions, one of the major drivers of biodiversity loss. Three species that naturally interact in their native range in North America – American beavers (Castor canadensis), muskrats (Ondatra zibethicus), and American mink (Neovison vison) – were independently introduced in this remote region. In my dissertation, I investigated (i) the hypothesis of niche expansion in the invasive mink population on Navarino Island towards terrestrial habitats; (ii) potential mink impact on breeding success of forest-bird populations; (iii) habitat selection of small-rodent species and their perception on the mink's novel predation risk; and (iv) the dynamics of multiple-species invasions under the hypothesis of an invasional meltdown. Additionally, I worked within the framework of environmental philosophy. I provide an example of combining ecological and cultural dimensions within the International Long-Term Ecological Research network to disentangle the ethical dilemmas that surround the management of invasive species. I finally proposed a management plan based on the idea of multiple invasive species management, discussing potential solutions to overcome the challenges that the control of invasive species represent and to more effectively protect the biological integrity of the native ecosystems.

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Serebryakova, Alexandra. "Acclimation and adaptation of invasive seaweeds - a case study with the brown alga Sargassum muticum." Doctoral thesis, Paris 6, 2017. http://hdl.handle.net/10400.1/10824.

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Non-indigenous seaweeds impact natural communities worldwide, affecting biodiversity, ecosystem functioning, and ecosystem services, resulting in significant economic and social consequences. Among major impacts are the displacement of native species, a threat to endangered species, and effects on ecological and evolutionary processes within the invaded communities. While critical to predict the fate of introduced species, understanding the mechanisms of acclimation and adaptation following introduction represents a great challenge in seaweeds. In this thesis, we investigated some acclimation processes, with an emphasis on the role of associated microbiota, and examined their effects with Sargassum muticum as a model species. This brown seaweed native to Asia, is an emblematic invader among seaweeds, with a distribution now ranging from Mexico to Alaska in America and from Morocco to Norway in Europe. We first reviewed the competitive advantages and traits that may contribute to its invasiveness. In addition, we provided an overview of putative underlying mechanisms of acclimation and adaptation and highlighted their role in seaweed invasions. We then examined the effects of ocean acidification on the microbiome of S. muticum and revealed that it does not have significant effects on the seaweed-associated microbiota despite certain changes in the microbial community. We further investigated the seasonal changes in the seaweed-associated microbiota and revealed significant differences between seasons and geographic locations. Finally, we applied ecological niche modelling, but innovatively accounting for phenology, to project the distribution of S. muticum under two future climate change scenarios. According to our projections, by 2100 the distribution of S. muticum is expected to shift northwards along its European, North American and Asian distributions with a partial retreat from the currently occupied areas. As algas não indígenas afetam comunidades naturais em todo o mundo, afetando a biodiversidade, o funcionamento dos ecossistemas e os seus serviços, com consequências económicas e sociais significativas. Entre os principais impactos estão deslocamento de espécies nativas e espécies ameaçadas e efeitos sobre processos ecológicos e evolutivos nas comunidades invadidas. A compreensão dos mecanismos de aclimatação e adaptação após a introdução representa um grande desafio nas algas marinhas. Nesta tese investigamos alguns processos de aclimatação, com ênfase no papel dos microorganismos associados e examinamos os seus efeitos usando Sargassum muticum como espécie modelo. Esta alga marinha nativa da Ásia é uma importante invasora, com uma distribuição atual do México ao Alasca na América e de Marrocos à Noruega na Europa. Primeiro analisamos as vantagens e características competitivas que podem contribuir para sua invasibilidade. Além disso, fornecemos uma visão geral dos mecanismos de aclimatação e adaptação subjacentes e destacamos seu papel nas invasões de algas marinhas. Em seguida, examinamos os efeitos da acidificação dos oceanos no microbioma de S. muticum e revelamos que não tem efeitos significativos sobre a comunidade microbiana das algas marinhas apesar de causar algumas mudanças na comunidade. No estudo das mudanças sazonais na microbiota associada às algas marinhas revelamos diferenças significativas entre as estações e os locais geográficos. Finalmente, realizamos modelação de nicho ecológico de forma inovadora para a fenologia, para projetar a distribuição de S. muticum em dois cenários futuros de mudança climática. De acordo com nossas projeções, até 2100, a distribuição de S. muticum deverá expandir-se para norte ao longo das suas distribuições européia, norte-americana e asiática, com retração parcial das áreas atualmente ocupadas.

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Timmerman, Charles-André. "Variations saisonnières et ontogéniques des interactions trophiques : étude des poissons de Manche – mer du Nord à plusieurs niveaux d’organisation." Thesis, Lille 1, 2020. http://www.theses.fr/2020LIL1R042.

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Les interactions trophiques sont à la base de nombreux processus régissant la structure et le fonctionnement des écosystèmes. Cependant, de nombreuses sources de variations sont mal connues comme les variations saisonnières et ontogéniques. Ces variations ont été appréhendées à plusieurs niveaux d’organisation, l’assemblage, l’espèce et l’individu dans les écosystèmes de Manche orientale (MO) et de la baie sud de la mer du Nord (BSMDN). Ces variations ont été tout d’abord étudiées en analysant les isotopes stables du carbone (delta13C) et de l’azote (delta15N), qui fournissent des informations sur l’utilisation des ressources et de l’habitat dans un espace à deux dimensions. Ces analyses ont été réalisées sur plusieurs tissus en raison de leurs différents temps d’intégration reflétant l’assimilation selon différentes périodes de temps. Ces analyses ont été couplées aux analyses des contenus stomacaux. Si l’analyse des isotopes stables apporte une information intégrée de l’alimentation sur des périodes de temps variables selon le tissu étudié, l’analyse des contenus stomacaux apporte une information à court terme de l’alimentation. A l’échelle de l’assemblage, Le couplage entre les habitats benthique et pélagique est apparu comme une caractéristique importante de l’écosystème de Manche orientale, en raison de sa faible profondeur, ainsi qu’à la combinaison de deux processus écologiques. Premièrement, les interactions trophiques ont révélé une plasticité trophique pour la plupart des espèces de poisson de l’assemblage étudié ainsi qu’un partage des ressources. Deuxièmement, les changements de composition de l'assemblage de poissons n'ont pas eu d'impact sur le couplage bentho-pélagique car la plupart des espèces dominantes se sont généralisées au cours d'une période donnée, ce qui a permis une utilisation complète de toutes les ressources disponibles. Des analyses plus approfondies ont été réalisées sur le merlan qui est l’espèce dominante en Manche orientale et au sud de la mer du Nord en hiver, et ont révélé des changements saisonniers et ontogéniques d’alimentation pour cette espèce. Enfin, au niveau individuel, les espèces ont tendance à être généralistes mais composée d’individus spécialistes le long des axes du delta13C et du delta15N. Les espèces tendent à élargir leur niche principalement via une augmentation de la variation d’alimentation entre individus. Ce comportement peut être une stratégie pour limiter la compétition, stratégie peut-être favorisée par l’important couplage bentho-pélagique offrant une grande diversité de ressources pour les espèces. Cette étude a montré l’importance de considérer les changements ontogéniques et saisonniers des interactions trophiques. Renseigner ces changements dans les modèles écosystémiques augmenterait leur capacité à saisir la complexité des écosystèmes marins et à informer la gestion des pêches. Modéliser ces effets à plusieurs niveaux d’organisation est nécessaire afin de prédire les effets du changement global sur la structure et le fonctionnement des écosystèmes Identifying and quantifying trophic interactions between organisms is crucial to understand the structure and functioning of food webs. However, many sources of variation are poorly known, such as seasonal and ontogenetic variations. These variations have been studied at several levels of organization, assemblage, species and individual in the Eastern English Channel (EEC) and the Southern North Sea (SNS) ecosystems.These variations were studied by analyzing the stable isotopes of carbon (delta13C) and nitrogen (delta15N), which provides information on resource and habitat use in a two-dimensional space. These analyses were performed on several tissues because isotopic values of tissues reflect the diet over the period during which the tissue was synthesized providing dietary information over different temporal periods. These analyses were coupled with stomach contents analyses providing a short-term picture of feeding patterns. At the assemblage scale, coupling between benthic and pelagic habitats has emerged as an important feature of the EEC ecosystem, due to its shallow depth, as well as to the combination of two ecological processes. First, trophic interaction revealed trophic plasticity and resource partitioning. Second, changes in the composition of fish assemblage did not impact benthic-pelagic couplings as most dominant species were generalist within a period, allowing a complete use of all available resources. Further analyses were carried out on whiting, the dominant species in the EEC-SNS ecosystems in winter, and revealed seasonal and ontogenetic trophic changes for this species. Finally, at the individual scale, species tend to be generalist but composed of specialist individuals along the delta13C and delta15N axes. The species increase their niche mainly through an increase of the niche variation between individuals. This behavior may be a strategy to avoid competition and favored by the important benthic-pelagic coupling offering a wide diversity of resources for species. This study revealed the importance of considering ontogenetic and seasonal changes of trophic interactions. Informing these changes in ecosystem models would increase their ability to capture the complexity of marine ecosystems and inform fisheries management. Modeling these effects at several levels of organization is necessary to predict the effects of global change on ecosystem structure and functioning

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Dissertations / Theses on the topic 'Interaction niche'

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