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Dissertations / Theses on the topic 'Alpha and beta diversity'

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Published: 4 June 2021
Last updated: 16 June 2025

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1

Toussaint, Aurèle. "Diversité fonctionnelle des poissons d'eau douce à l'échelle mondiale : patrons, déterminants et impacts des activités humaines." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30403.

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Pendant longtemps, la biodiversité était caractérisée uniquement par sa diversité taxonomique, c'est-à-dire par le nombre et la composition en espèces des assemblages. Cependant, de récentes études montrent que la biodiversité ne peut être résumée uniquement à cette composante, car elle ne prend pas en compte les caractéristiques écologiques des espèces. Pour cela, la diversité fonctionnelle est un outil permettant de considérer les traits fonctionnels des espèces. Peu d'études à larges échelles ont décrit cette facette de la biodiversité et son lien avec la diversité taxonomique. L'objectif de cette thèse est donc de 1) décrire et comprendre la distribution de la diversité fonctionnelle des assemblages de poissons d'eau douce à l'échelle globale et de 2) quantifier les conséquences des activités humaines sur cette facette. Pour cela, nous avons construit une base de données de traits fonctionnels de plus de 9000 espèces de poissons d'eau douce. Nous avons mis en évidence que la diversité fonctionnelle mondiale est distribuée de façon très hétérogène. Elle est essentiellement concentrée dans les bassins Néotropicaux, contrastant avec des zones taxonomiquement riches mais fonctionnellement redondantes comme l'Afrique ou l'Asie. Ces patrons pouvaient être expliqués par une diversification fonctionnelle de certains ordres de poissons Néotropicaux. À l'échelle des bassins versants, nous avons montré une faible, mais significative, influence des variables environnementales en particulier des variables historiques pour expliquer l'hétérogénéité des patrons de diversité fonctionnel des bassins versants. Nous avons également montré que les activités humaines, sous l'effet des introductions d'espèces, ont contribué à modifier considérablement les patrons de diversité fonctionnelle par rapport aux changements de diversité taxonomique. Ces changements mettent en évidence la nécessité de prendre en compte les conséquences des espèces non-natives sur le fonctionnement des écosystèmes. Dans ce travail de thèse, nous avons ainsi démontré que la diversité fonctionnelle est une facette complémentaire à la diversité taxonomique chez des poissons d'eau douce. Ces résultats contribuent à enrichir les connaissances de la structure des assemblages et peuvent avoir des implications en termes de gestion de la biodiversité<br>For a long time, biodiversity was characterised solely by its taxonomic diversity, i.e. the number and species composition of assemblages. However, recent studies show that biodiversity cannot be summed up solely by this component as it does not take into account the ecological characteristics of species. For this, functional diversity is a tool for considering the functional traits of species. Few large-scale studies have described this facet of biodiversity and its link with taxonomic diversity. The aim of this thesis is therefore to 1) describe and understand the distribution of functional diversity of freshwater fish assemblages on a global scale and 2) quantify the consequences of human activities on this facet. For this purpose, we have built a database of functional traits of more than 9000 species of freshwater fish. We have shown that the world's functional diversity is very heterogeneously distributed. It is essentially concentrated in the Neotropical basins, contrasting with taxonomically rich but functionally redundant areas such as Africa or Asia. These patterns could be explained by a functional diversification of certain orders of Neotropical fish. At the watershed scale, we showed a weak, but significant, influence of environmental variables, in particular historical variables, to explain the heterogeneity of the functional diversity patterns of watersheds. We have also shown that human activities, under the effect of species introductions, have contributed to a significant change in functional diversity patterns compared to changes in taxonomic diversity. These changes highlight the need to take into account the consequences of non-native species on ecosystem functioning. In this thesis work, we have thus demonstrated that functional diversity is a complementary facet of taxonomic diversity in freshwater fish. These results contribute to knowledge of the structure of assemblages and may have implications in terms of biodiversity management
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2

Noble, Sidney Lake. "The Influence of Canopy Cover and Canopy Heterogeneity on Plant Diversity within Oak Savannas." Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1595843486558554.

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3

Mathon, Laëtitia. "L’ADN environnemental pour décrire les patrons de diversité des poissons à large échelle et informer la conservation." Electronic Thesis or Diss., Université de Montpellier (2022-....), 2023. http://www.theses.fr/2023UMONG005.

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L’accélération des changements globaux et les impacts humains menacent la survie des communautés de poissons à l’échelle mondiale. Or ces communautés sont indispensables au bon fonctionnement des écosystèmes marins et aux populations dépendantes de la pêche. Seul un suivi efficace et rapide des communautés de poissons à petite et grande échelle pour comprendre leurs distributions, les règles d’assemblage et les impacts des pressions humaines et environnementales peut permettre d’implémenter des mesures de conservation optimales. L’ADN environnemental (ADNe) est une méthode récente, dont l’efficacité a été démontrée à échelle locale et régionale pour étudier les communautés de poissons côtiers. Cette méthode permet de pallier certains biais induits par les méthodes de suivi conventionnelles (pêche, plongée, caméras). Le but de cette thèse est d’utiliser l’ADNe pour étudier les distributions des poissons à diverses échelles spatiales, en réponse à des facteurs environnementaux, géographiques et socio-économiques, puis de nourrir les approches de planification de conservation. J’ai d’abord comparé les outils bio-informatiques fréquemment utilisés pour l’analyse des données d’ADNe, identifié les meilleurs programmes et pipelines et construit un pipeline optimal pour identifier les espèces contenues dans un échantillon, dans le cas d’une base de référence complète. Cependant, à large échelle, les bases de références sont largement incomplètes pour le gène mitochondrial 12S que nous utilisons et ne permettent donc pas l’assignation taxonomique de tous les fragments d’ADNe. Les autres études de cette thèse reposent ainsi sur une méthode de regroupement des séquences en unités taxonomiques moléculaires (MOTUs). À partir d’un jeu de données échantillonné à large échelle dans trois océans (Indien, Pacifique, Atlantique), j’ai comparé les estimations de diversité de poissons de récifs coralliens obtenues avec l’ADNe et avec des données de recensements visuels en plongée, à l’échelle de plusieurs biorégions. J’ai démontré que l’ADNe estimait une plus grande diversité de familles et de MOTUs que les plongées, tout en retrouvant les grands patrons de distributions connus (gradient longitudinal, isolation de la faune des Caraïbes). Puis, à l’échelle globale, j’ai étudié l’influence de facteurs environnementaux, géographiques et socio-économiques sur plusieurs indices de diversité alpha et bêta, à partir de plus de 500 échantillons d’ADNe prélevés dans 11 régions du monde. Les résultats montrent un effet dominant de l’environnement (température et productivité) sur la diversité alpha et bêta, mais aussi une diminution de ces diversités dans les zones proches des populations humaines et notamment dans les pays dépendant des ressources marines. Enfin, à une échelle régionale en Nouvelle Calédonie, en combinant l’ADNe avec des méthodes plus conventionnelles (caméras appâtées et échosondeur acoustique), j’ai estimé et modélisé plusieurs métriques de diversité des poissons sur les pentes externes et monts sous-marins, jusqu’à 600m de profondeur, que j’ai ensuite intégrées dans une planification de conservation en trois dimensions. Ces résultats indiquent de fortes richesses, abondances et biomasses sur les monts sous-marins peu profonds et isolés, ainsi que sur les pentes externes des îles et atolls éloignés des zones urbanisées, qui sont donc à prioriser dans les plans de conservation. L’ensemble des travaux de cette thèse démontrent l’utilité du metabarcoding de l’ADNe pour étudier la distribution des poissons à fine et large échelles spatiales, étudier l’impact des conditions environnementales et socio-économique sur la diversité et la distribution des communautés de poissons et informer les gestionnaires sur les zones de priorité de conservation<br>Accelerating global changes and human impacts threaten the survival of fish communities worldwide, which are critical to the functioning of marine ecosystems and fisheries-dependent populations. Only an effective and rapid monitoring of fish communities at small and large scales to understand their distributions, assembly rules and impacts of human and environmental pressures can enable the implementation of optimal conservation measures. Environmental DNA (eDNA) is a recent method that has been demonstrated to be effective at local and regional scales for studying coastal fish communities. This method makes it possible to overcome some biases induced by conventional monitoring methods (fishing, diving, cameras). The goal of this thesis is to use eDNA to study fish distributions at various spatial scales in response to environmental, geographic, and socioeconomic factors, and then to feed conservation planning approaches. I first compared frequently used bioinformatics tools for eDNA data analysis, identified the best programs and pipelines, and constructed an optimal pipeline for identifying species contained in a sample, in the case of a complete reference database. However, at a large scale, the genetic reference databases are largely incomplete for the 12S mitochondrial gene we use, and thus do not allow for taxonomic assignment of all eDNA fragments. The other studies in this thesis therefore rely on a method of clustering sequences into molecular taxonomic units (MOTUs). From a large-scale dataset sampled in three oceans (Indian, Pacific, Atlantic), I compared estimates of coral reef fish diversity obtained with eDNA and with visual census data, at the scale of several bioregions. I demonstrated that eDNA estimated a higher diversity of families and MOTUs than visual census, while recovering the known major distribution patterns (longitudinal gradient, isolation of the Caribbean fauna). Then, on a global scale, I investigated the influence of environmental, geographical and socio-economic factors on several alpha and beta diversity indices, using more than 500 eDNA samples collected in 11 regions of the world. The results show a dominant effect of the environment (temperature and productivity) on alpha and beta diversity, but also a decrease of these diversities in areas close to human populations, and in particular in countries depending on marine resources. Finally, at a regional scale in New Caledonia, by combining eDNA with more conventional methods (baited cameras and acoustic echosounder), I estimated and modeled several metrics of fish diversity on deep outer slopes and seamounts, down to 600m depth, which I then integrated into three-dimensional conservation planning. These results indicate high richness, abundance and biomass on shallow and isolated seamounts, as well as on the deep slopes of islands and atolls far from urbanized areas, which should be prioritized in conservation plans. All this thesis work demonstrates the utility of eDNA metabarcoding to study fish distribution at fine and large spatial scales, to study the impact of environmental and socio-economic conditions on the diversity and distribution of fish communities, and to inform managers on priority areas for conservation
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4

Laurencio, David Edelman. "Environmental correlates to amphibian and reptile diversity in Costa Rica." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1675.

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5

TONELLI, MATTIA. "Effects of different pastures management on dung beetle communities in a sub-mountainous landscape of central Italy: a multicomponent biodiversity and ecological process analysis." Doctoral thesis, Urbino, 2017. http://hdl.handle.net/11576/2642392.

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6

Aguirre, Andrea Garafulic. "A diversidade da regeneração natural e fatores que podem influenciar o aumento da riqueza regenerante em áreas em processo de restauração com distintas idades /." Rio Claro, 2019. http://hdl.handle.net/11449/183187.

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Orientador: Massanori Takaki<br>Resumo: Grandes iniciativas mundiais no esforço de alavancar um aumento na restauração ecológica surgiram recentemente, como a Iniciativa 20 x 20 e a Bonn Challenge, que apresentam como meta conjunta restaurar 500 milhões de hectares até 2030. Assim, uma das metas da ecologia aplicada à restauração é buscar compreender as distintas maneiras pelas quais a vegetação varia durante o processo de restauração e quais fatores influenciam o aumento da riqueza de espécies regenerantes. Este trabalho teve como objetivos: (1) Compreender como variam a abundância relativa e riqueza rarefeita, quando se comparam a regeneração natural total e específica (espécies que ocorreram apenas na área de referência), nas áreas em restauração com diferentes idades. (2) Avaliar como variam a diversidade alfa e beta nas áreas em restauração com idades distintas. (3) Observar a variação na abertura do dossel nas áreas com idades distintas. (4) Analisar se as variáveis da abertura do dossel e a idade são fatores importantes no que tange à influência com o aumento da riqueza de espécies regenerantes. Nove áreas em processo de restauração, localizadas no município de Extrema (Minas Gerais), foram selecionadas com 4, 7 e 10 anos de idade e um fragmento de referência, onde ao todo, 360 parcelas foram instaladas. Em cada parcela foram mensurados todos os regenerantes entre 20 cm e 2 m de altura (ervas, trepadeiras, arbustos, arbóreas e pteridófitas). Resultados: Foram encontrados 6788 regenerantes. As herbáceas e arb... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: Major global initiatives in an effort to leverage an increase in the ecological restoration areas have recently emerged, such as the 20 x 20 Initiative and the Bonn Challenge, which aim to restore together 500 million hectares by 2030. Thus, one of the goals of ecology applied to restoration is to look at the different ways in which vegetation varies during the restoration process and what factors influence the increase of regenerating species richness. This work has as objectives: (1) To understand how the relative abundance and rarefied richness vary, when comparing the total and specific natural regeneration (species that occurred only in the reference area) in restoration areas having varying ages. (2) To evaluate how alpha and beta diversity varies in areas of restoration of different ages. (3) To observe the variation in canopy opening in areas of different ages. (4) To analyze whether the variable canopy opening and age are important factors in the influence or relation with the increase of the richness of regenerating species. Nine areas aged 4,7 and 10 under restoration process were selected and a reference fragment, in which a total of 360 parcels were installed. All the areas are located in the Municipality of Extrema, Minas Gerais. In each plot was measured all regenerants between 20 cm and 2 m in height (herbs, climbers, shrubs, trees and pteridophytes). Results: 6788 regenerants were found. Herbs and trees had the highest relative abundances, general and specifi... (Complete abstract click electronic access below)<br>Doutor
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7

Deheuvels, Olivier. "Compromis entre productivité et biodiversité sur un gradient d'intensité de gestion de systèmes agroforestiers à base de cacaoyers de Talamanca, Costa Rica." Thesis, Montpellier, SupAgro, 2011. http://www.theses.fr/2011NSAM0026/document.

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Le cacaoyer (Theobroma cacao, L.) est cultivé dans les tropiques humides d'Amérique latine, d'Afrique et d'Asie. Principale source de revenus d'une agriculture essentiellement familiale, les systèmes agroforestiers à base de cacaoyers fournissent de nombreux services écologiques et contribuent à la conservation de la biodiversité. Ces systèmes associent plantes ligneuses et cultures de manière simultanée, dans une gamme importante et peu décrite de richesses et de structures botaniques. Les connaissances actuelles sur leur productivité se limitent à des essais en milieu contrôlé associant un petit nombre d'espèces. Nos travaux testent l'hypothèse d'une relation de compromis entre le niveau de productivité des cacaoyers et le niveau de biodiversité hébergée par les agroforêts à base de cacaoyers. Nous caractérisons ces compromis sur un gradient de situations de production paysannes, reposant sur la structure verticale, l'intensité de gestion de la composante végétale et le contexte bio-physique des agro-systèmes étudiés. Sur un dispositif de 36 cacaoyères paysannes situées dans la région de Talamanca, Costa Rica, nous montrons que des variations significatives de la structure végétale reflètent les modes de gestion de la parcelle et affectent le rendement par cacaoyer (295 à 667g/arbre/an) mais pas le rendement en cacao (136 kg/ha/an), ni le volume végétal global (400 m3/ha). Ces variations de la structure végétale affectent peu la diversité α des peuplements de plantes associées, d'épiphytes, d'amphibiens, de reptiles, de mamifères, d'invertébrés du sol et de la litière, mais leur diversité β répond de manière contrastée à ces variations d'habitat. Les relations de compromis que nous mettons finalement en évidence entre la productivité en cacao marchand à l'hectare ou à l'arbre et les niveaux de biodiversité atteints sont de nature (linéaire, cubique, quadratique) et de tendances (négative, postive) contrastées selon le taxon considéré et remettent en cause les résultats de certains travaux récents. Nos travaux dévoilent également des situations de compromis optimales, offrant des perspectives positives pour l'intensification écologique des systèmes agroforestiers tropicaux<br>Cacao (Theobroma cacao, L.) is cultivated in the humid tropics of Latin America, Africa and Asia. Cocoa-based agroforestry systems are the main source of income for smallholders' families and provide numerous ecological services and contribute to biodiversity conservation. These systems associate trees with crops simultaneously, in a wide and poorly described range of botanical and structural plant diversity. The current knowledge about their productivity is restricted to controlled trials with a low numer of associated plant species. Our work tests the hypothesis of a trade-off relationship between the level of cocoa productivity and the level of biodiversity hosted in cocoa-based agroforests. We characterize these trade-offs on a gradient of production situations, based on the vertical structure, the management intensity of the vegetal component and the bio-physical context of cocoa-based agroforests. On the base of a 36 on farm cocoa plots network located in Talamanca, Costa Rica, we show that significant variations in the vegetation vertical structure reflect farmer's management strategies and affect the cocoa yield per tree (295 to 667g/tree/year) but neither the cocoa yield per plot (136 kg/ha/year), nor the global plant volume (400 m3/ha). The variations in vegetation structure poorly affected the α-diversity of 7 plant and animal taxa, but their β-diversity gave contrasted and significant responses to habitat variations. Finally, the trade-offs relationships we display between dry cocoa productivity per hectare or per tree and the observed biodiversity levels showed contrasted forms (cubic, quadratic, linear) and tendances (positive, negative) according to the taxa considered and question results from recent publications. Our work also revealed optimal trade-off situations which offer positive prospects for the ecological intensification of tropical agroforestry systems
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Labecca, Fábio Martins. "Menos complementares e redundantes, porém mais jovens: organização de assembleias de aves em monoculturas florestais." Universidade Federal de Goiás, 2015. http://repositorio.bc.ufg.br/tede/handle/tede/5068.

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Submitted by Erika Demachki (erikademachki@gmail.com) on 2016-01-07T15:35:40Z No. of bitstreams: 2 Dissertação - Fábio Martins Labecca - 2015.pdf: 2107333 bytes, checksum: cf5e7e0ac514e7f834e6ed7aab735b5d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5)<br>Approved for entry into archive by Erika Demachki (erikademachki@gmail.com) on 2016-01-07T15:37:02Z (GMT) No. of bitstreams: 2 Dissertação - Fábio Martins Labecca - 2015.pdf: 2107333 bytes, checksum: cf5e7e0ac514e7f834e6ed7aab735b5d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5)<br>Made available in DSpace on 2016-01-07T15:37:02Z (GMT). No. of bitstreams: 2 Dissertação - Fábio Martins Labecca - 2015.pdf: 2107333 bytes, checksum: cf5e7e0ac514e7f834e6ed7aab735b5d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-04-29<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES<br>The increasing demand for timber and pulpwood has triggered an increase in areas of tree monocultures. The effects of native vegetation conversion in such monocultures have been extensively debated, but the consequences of this land use change to functionality and evolutionary history conservation have been little studied. Here, we evaluated how the avifauna responds to nature ecosystem conversion in tree monocultures by quantifying changes in local diversity (alpha diversity) and in assemblage composition (beta diversity), in their functional and phylogenetic components. We compiled forty paired bird lists in native vegetation areas and in comparable tree monoculture areas. Changes in alpha diversity were quantified by paired tests of observed values in native vegetation and in tree monocultures, and changes in assemblages composition through additive partitioning of beta diversity in nestedness and turnover components. We observed that tree monocultures are impoverished in number of species, supporting lower functional richness and less functionally similar assemblages. This demonstrates that environmental filter selecting and limiting similarity processes concurrently modify functional structure of bird assemblages, resulting in loss of functional complementarity and redundancy. Species in tree monocultures are also evolutionary younger and less related to each other. We showed that bird assemblages in tree monoculture are composed largely by functionally and phylogenetic different species from that assemblages in native vegetation. Body size, diet and foraging traits were the major functional traits in predicting the absence of the species in tree monocultures. Alson, we show that annual average temperature, annual average pluviosity and stage of understory development in tree monocultures are important predictors of diversity loss in these type of monoculture.<br>A crescente demanda por madeira e celulose tem desencadeado um aumento das áreas de monocultura florestal. Os efeitos da conversão de áreas de vegetação nativa nesse tipo de monocultura, por sua vez, vêm sendo extensamente debatidos. As consequências dessa mudança no uso do solo para a funcionalidade e conservação da história evolutiva foram até agora pouco estudadas. Neste estudo, nós avaliamos como a avifauna responde a conversão de ecossistemas naturais em monoculturas florestais, quantificando mudanças na diversidade local (diversidade alfa) e na composição dessas assembleias (diversidade beta) em seus componentes funcional e filogenético. Para isto, compilamos quarenta listas pareadas de aves em áreas de vegetação nativa e em áreas comparáveis de monocultura florestal. As mudanças na diversidade alfa foram testadas por testes pareados dos valores observados em vegetação nativa e em monoculturas florestais, e as mudanças na composição das assembleias através da partição aditiva da diversidade beta nos componentes de aninhamento e substituição. Observamos que as áreas de monocultura florestal são empobrecidas no número de espécies, suportam menor riqueza funcional e são menos similares funcionalmente. Isto demonstra que os processos de filtro ambiental e de similaridade limitante modificam a estrutura funcional das assembleias de aves de forma concomitante, resultando em perda de complementaridade e também de redundância funcional. As espécies presentes em áreas de monocultura são também evolutivamente mais jovens e menos aparentadas entre si. Mostramos que as assembleias de monoculturas florestais são compostas em grande parte por espécies funcionalmente e filogeneticamente diferentes daquela avifauna em vegetação nativa. Tamanho corpóreo, dieta e estratégias de forrageamento se mostraram as características funcionais importantes na predição da ausência das espécies em monoculturas florestais. Ainda, mostramos que temperatura e pluviosidade média anual, e o estádio de desenvolvimento do sub-bosque são importantes preditores da perda de diversidade nesse tipo de monocultura.
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Rosset, Véronique, Albert Ruhi, Michael T. Bogan, and Thibault Datry. "Do lentic and lotic communities respond similarly to drying?" WILEY, 2017. http://hdl.handle.net/10150/625362.

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Disturbance is a central factor shaping composition, structure, and dynamics of local communities. Drying is a disturbance that occurs in aquatic ecosystems globally and can strongly influence their communities. Although the effects of drying may depend on ecosystem connectivity and the dispersal abilities of resident species, there have been no comparisons of community responses to drying between lentic and lotic ecosystems across different climates. Here, we predicted that drying would have stronger effects on aquatic communities in isolated lentic ecosystems than in dendritic lotic ecosystems, owing to the higher hydrological connectivity of the latter, and that drying would have stronger effects on passive than on active dispersers, because of the potentially higher recolonizing ability of the latter. We tested these predictions by comparing alpha diversity, phylogenetic relatedness, and beta diversity for active and passive dispersers, in both ecosystem types across five climatic regions. Drying caused greater declines in alpha diversity in lentic than in lotic ecosystems. Communities that experienced drying were more similar to one another than those of perennial sites, and this pattern was especially pronounced in lentic ecosystems. In contrast, drying did not influence the contributions of turnover and richness gradients to beta diversity. Additionally, dispersal mode did not influence community responses to drying. Relatively weaker effects of drying in lotic compared to lentic systems were likely due to the hydrological connectivity among perennial and temporary river sites, which may facilitate dispersal of organisms to escape drying and recolonize rewetted sites. Collectively, our results suggest that habitat connectivity may ameliorate (and fragmentation may worsen) the impacts of drying disturbance. This is an important finding in light of increasing drying and concomitant aquatic habitat fragmentation under global change.
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MARY, JEAN. "Etude de la diversite structurale de l'extremite carboxy-terminale des tubulines alpha et beta." Paris 7, 1996. http://www.theses.fr/1996PA077240.

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Le dimere de tubuline alpha/beta, unite structurale des microtubules, peut-etre tres heterogene. Cette heterogeneite a deux origines: genetique et post-traductionnelle. La region carboxy-terminale de la tubuline concentre la tres grande majorite de cette heterogeneite et serait impliquee dans les interactions entre le microtubule et les proteines qui lui sont associees. Nous avons etudie la tubuline de cerveaux de souris et d'axoneme de spermatozoides d'oursin. La methodologie mise en uvre a fait appel aux techniques de la chimie des proteines. Ce travail a permis de montrer que l'extremite carboxy-terminale de la tubuline alpha detyrosylee etait plus heterogene chez la souris adulte que chez le souriceau. Cette heterogeneite ne serait pas due a une diversification du mode de branchement entre les glutamates ajoutes post-traductionnellement, mais a un accroissement de la proportion de tubuline alpha non tyrosylable. La polyglutamylation a ete caracterisee sur les isotypes de tubuline beta un et quatre a, sur les residus glutamyls en position quatre cent quarante et un et quatre cent trente quatre, respectivement. L'ensemble des isotypes de tubuline beta exprimes dans le cerveau de mammiferes peut donc etre glutamyle. Les differentes modifications post-traductionnelles localisees dans la region carboxy-terminale de la tubuline axonemale de spermatozoides d'oursin et leur importance relative determinee. Dans ce systeme, la majorite des tubulines ne sont pas modifiees dans leur region carboxy-terminale. La tubuline beta peut etre polyglycylee et la tubuline alpha peut etre a la fois polyglutamylee et polyglycylee
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Santos, Anita Stival dos. "Efeitos de filtros ambientais nos padrões de diversidade de árvores na floresta atlântica do sul do Brasil sob uma perspectiva de metacomunidades." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/106403.

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Entender padrões de diversidade e composição de espécies ao longo de múltiplas escalas espaciais constitui um dos principais objetivos em ecologia e biogeografia. A relativa importância dos mecanismos responsáveis por estruturar as comunidades de plantas e como eles interagem para influenciar estes padrões têm sido foco de intensos debates. No presente estudo, foram utilizados dados do Inventário Florístico Florestal de Santa Catarina a fim de investigar os padrões de diversidade de espécies de árvores e suas relações com a heterogeneidade ambiental sob uma das perspectivas oriundas da teoria de metacomunidades, conhecida como “sorteio de espécies”. A predição chave deste ponto de vista é a de que a composição de espécies varia em resposta a diferenças nas condições ambientais entre manchas de hábitat. O presente estudo é focado nessa predição e objetivou entender como processos relacionados a filtros ambientais interagem direta e indiretamente sobre os padrões de diversidade em uma área de 95000 km 2 (dados de 432 unidades amostrais). Foi utilizada modelagem de equações estruturais (PLS Path Modeling), a fim de investigar os efeitos interativos da topografia, clima, balanço de água e energia e geometria das manchas de floresta sobre os padrões de alfa (α) e beta (β) diversidade de uma metacomunidade de floresta atlântica no sul do Brasil. Fatores relacionados a filtros ambientais mostraram substanciais efeitos sobre a diversidade alfa e beta. A quantidade total da variação na beta diversidade explicada pela filtragem de hábitat foi alta (64%), corroborando a predição testada no nível de metacomunidades. Os fatores mais importantes para explicar a diversidade beta foram: extremos climáticos, balanço de água e energia e alfa diversidade, enquanto tamanho da mancha e balanço de água e energia foram os fatores chaves para a alfa diversidade. O teste de Mantel parcial mostrou que os efeitos ambientais ocorrem amplamente independente de efeitos espaciais, reforçando a predição testada. O estudo provê forte suporte empírico para a predição de que a beta diversidade reflete primariamente processos determinísticos associados com o nicho das espécies e suas respostas às condições ambientais na escala espacial considerada.<br>Understanding patterns of species diversity and composition across multiple scales is one of the main purpose in ecology and biogeography. The relative importance of the mechanisms that structure plant communities and how they interact to influence these patterns remains a topic of hot debate. In the present study, we use data from the Forest Inventory of Santa Catarina to investigate the patterns of species diversity of subtropical Atlantic forests and its relationships with environmental heterogeneity on a metacommunity perspective (species-sorting). The key prediction of this viewpoint is that community composition varies in response to differences in environmental conditions among habitat patches. Our study focused on this perspective, aiming to understand how environmental filtering processes interact directly and indirectly on diversity patterns in an area of 95000 km 2 (data from 432 forest plots). We employed structural equation modeling (PLS Path Modeling) to disentangle the interactive effects of topography, climate, water-energy balance, and geometry of forest patches upon the alpha and beta diversity of a subtropical forest metacommunity in southern Brazil. Factors related to environmental filtering showed substantial effects upon tree alpha and beta diversity. The total amount of variation in beta diversity explained by environmental filtering was high (64%) and was even more when together with alpha diversity (73%), corroborating the prediction of species-sorting model at the metacommunity level. Climatic extremes, water-energy balance and alpha diversity were the key determinants of beta diversity and patch size and water- energy balance the key determinants of alpha diversity in the South Brazilian Atlantic forests. Partial mantel test showed that environmental effects occurred largely independent of spatial effects, reinforcing the tested prediction. Our study provides strong empirical support for the prediction that beta diversity primarily reflects deterministic factors associated with species niches and their responses to environmental conditions in the studied spatial scale.
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12

Lee, Jonathan Eric. "Partitioning β-diversity in species-area relationships: implications for biodiversity and conservation". Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1273172956.

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13

Casanova, Jean-Laurent, and Pierre-André Cazenave. "Selection des lymphocytes t cytotoxiques par l'antigene : etude de la diversite des recepteurs t alpha-beta." Paris 6, 1992. http://www.theses.fr/1992PA066433.

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Les lymphocytes t cytotoxiques (ctl) reconnaissent l'antigene sous forme de peptide presente par une molecule du complexe majeur d'histocompatibilite (cmh) de classe i. La reconnaissance d'un tel ligand est assuree par le recepteur lymphocytaire t (tcr). Nous avons etudie et compare la diversite des tcr selectionnes par trois peptides antigeniques presentes aux ctl murins par la molecule du cmh de classe i h-2k#d. Les ctl selectionnes par un premier peptide, issu de la proteine circumsporozoite de plasmodium berghei (pbcs), expriment des tcr extremement divers, malgre l'emploi preferentiel d'un segment v. Les segments v, j et j utilises sont nombreux et les regions de jonction v-j et sont tres heterogenes dans leur sequence. Parmi les clones ctl analyses, aucun n'exprime de chaine ou identique a un autre. En revanche, les ctl selectionnes par un second peptide, issu de la molecule d'histocompatibilite humaine hla-cw3, expriment des tcr tres limites dans l'ensemble de leur structure. Peu de segments v, v, j et j sont utilises, et les regions de jonction v-j et sont tres homogenes dans leur sequence. De plus, de nombreux clones ctl expriment une chaine et/ou identique. Ces deux etudes demontrent qu'il existe une grande variation, d'un antigene a l'autre, dans l'etendue de la diversite des tcr au cours de la selection des ctl. De plus, l'antigene hla-cw3 etant homologue au soi, au contraire de l'antigene pbcs, cette variation suggere que la tolerance naturelle aux peptides du soi presentes par les molecules du cmh de classe i peut reduire l'etendue de la diversite des tcr selectionnes par un peptide antigenique homologue au soi. En accord avec cette hypothese, les ctl selectionnes par un troisieme peptide, issu d'une autre molecule d'histocompatibilite humaine, hla-a24, expriment aussi des tcr limites dans leur structure. Les deux sites antigeniques de hla-a24 et de hla-cw3 ne different qu'en une seule position, situee dans la partie amino terminale du peptide, et les tcr selectionnes par chacun des peptides presentent des traits structuraux communs. Parmi les ctl selectionnes par hla-a24, certains reconnaissent aussi hla-cw3 et les tcr exprimes par ceux-ci ressemblent en tous points a ceux exprimes par les ctl directement selectionnes par hla-cw3. En revanche, d'autres ctl selectionnes par hla-a24 ne reconnaissent pas hla-cw3 et expriment des tcr qui different au niveau de la jonction v-j de la chaine de ceux exprimes par les ctl directement selectionnes par hla-cw3. Ces resultats demontrent que la region de jonction v-j de la chaine du tcr interagit avec la partie amino terminale des peptides hla-cw3 et a24. De plus, la selection dans la jonction v-j de la chaine des tcr exprimes par les ctl selectionnes par hla-cw3 ou par hla-a24 de residus charges complementaires de ceux situes dans la partie carboxy terminale des deux peptides, suggere que la jonction v-j de la chaine du tcr interagit avec la partie carboxy terminale des peptides hla-cw3 et a24. Ces resultats suggerent donc que les jonctions v-j des tcr exprimes par les ctl interagissent avec le peptide antigenique de telle sorte que la jonction v-j de la chaine reconnait la partie amino terminale et la jonction v-j de la chaine la partie carboxy terminale du peptide. De plus, ces resultats suggerent que la variation dans l'etendue de la diversite des tcr exprimes par les ctl selectionnes par l'antigene depend en partie de l'homologie du peptide antigenique avec le soi
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14

Tripathi, Hemant Gangaprasad. "Biodiversity of the African savanna woodlands : how does it change with land use?" Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/28965.

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The savanna woodlands of Southern Africa, colloquially termed the miombo, are poorly described in terms of biodiversity compared to other biomes. They have therefore been underrepresented in the wider understanding of how land use intensification is shaping global biodiversity. Land use change is known to reduce biodiversity and disrupt intactness of ecological communities with consequences for ecosystem functioning, resilience, and services. Miombo woodlands are described as biodiversity hotspots due to a high endemism of species and the presence of megafauna. At the same time, they are also considered dynamic socio-ecological systems shaped by disturbances and the land use activities of people. The patterns of biodiversity change in these tropical ecosystems may, therefore, have their own unique contexts, understanding of which will be essential for biodiversity and land use management in these ecosystems. In this thesis, I identified the patterns of biodiversity change in response to the two major land use practices in the two dominant woodland types in southern African woodlands: the selective logging due to charcoal production in the mopane woodlands, and agricultural expansion in the miombo. I also examined the impact of two main disturbance agents, humans and elephants, on habitat structure and biodiversity in mopane woodlands. Across all chapters in this thesis, I investigated the effects of land use change and habitat modification on biodiversity empirically using chronosequences. To understand biodiversity change, I employed a hierarchical multilevel modelling approach making inferences at the three levels of ecological communities: species, community, and meta-community (set of ecological communities at different sites). I selected six villages in the charcoal production hotspot of southern Mozambique and carried out field surveys for three taxonomic groups: trees, mammals and ground beetles. I modelled the counts of trees and beetles and incidence of mammals using meta-community occurrence models in a Bayesian framework with the intensity class of the villages, above-ground biomass and land cover type as predictors. The results suggested that the species richness of trees and mammals declined by 12 and 8.5 % respectively while that of beetles increased by 3.5%, albeit non-significantly. In addition, the beta diversity of trees decreased while that of mammals increased. The results show that while both trees and mammals reduced in richness, they responded differently to charcoal production in terms of community organisation. The trees underwent subtractive homogenisation (decrease in alpha and beta diversities) primarily because of deterministic processes induced by selective harvesting of tree stems for charcoal. Mammal communities, on the other hand, showed subtractive heterogenization (decrease in alpha, but increase in beta diversity) mainly due to random extinctions. In the agriculture frontier of miombo-dominated northern Mozambique, I investigated the effects of fragmentation and habitat loss caused by agricultural expansion on diversity and composition of trees and mammals. I modelled the occurrences of trees and mammals using occupancy models with the fragmentation and quantity of woodland cover as predictors. The model showed that most tree species (n=10), mainly the timber and firewood species, linearly declined in population size as fragmentation increased. Mammals, on the other hand, showed a nonlinear response. Seven mammal species increased at the lower levels of fragmentation. However, at the higher levels, none of the mammal species increased while two declined. Similarly, the species richness of trees linearly declined, while that of mammals increased up to a fragmentation level of 55-65% and declined above this limit. The beta diversity of trees increased with fragmentation while that of mammals decreased. The results suggest that, although fragmentation reduces species richness of both trees and mammals, it affects their species compositions in different ways. Trees undergo subtractive heterogenization due to random species losses while mammals experience subtractive homogenisation mainly due to the combined effects of fragmentation-led habitat loss and intensified hunting. Finally, this study concludes that, above 75% fragmentation or below 26% habitat quantity, both taxonomic groups endure biodiversity loss. The threshold results here corroborate similar habitat quantity thresholds (20-30%) observed elsewhere in different ecosystems. However, they differ with the widespread notion that above 30% habitat quantity, the effect of fragmentation is non-existent. The results here emphasize that taxonomic groups respond differently, the diversity and population size of mammals reduced only after the habitat threshold, whereas, those of trees showed linear decrease with fragmentation most likely due to fragmentation-led habitat loss. Lastly, I examined the effects of disturbance by humans and elephants on habitat structure and bird diversity by conducting a space for time substitution comparison in the mopane woodlands of Zambia. To examine the woodland structure, I modelled the structural attributes of habitat (stem diameter, stand density, and basal area) using mixed models with the proportion of affected stems by humans and elephants as explanatory variables. I found that elephant disturbance was associated with higher stem diameters, low stand densities, but no change in basal area. Human disturbance, on the other hand, was related to reductions in stand density and basal area, but no change in the stem diameter. Further, I tested species and functional diversity of birds against the covariates of habitat structure and disturbance. I found that bird communities reduced in species richness in both, human as well as elephant disturbed areas. However, the functional diversity did not change with elephant disturbance. I concluded that human disturbance reduces woody biomass (basal area is correlated with woody biomass) of mopane woodlands and functional diversity of birds whilst elephants do not. In this thesis, I conclude that human driven land use change in the miombo woodlands erodes alpha diversity of all taxonomic groups. However, increases in beta diversity of mammals with charcoal land use and trees in agricultural land use may maintain their diversities at the meta-community level.
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15

Costa, Tha?s Ribeiro. "An?lise flor?stico-estrutural, rela??o vegeta??o-ambiente e transi??o floresta-campo das matas de galeria do Parque Nacional das Sempre-Vivas (PNSV), MG." UFVJM, 2017. http://acervo.ufvjm.edu.br/jspui/handle/1/1744.

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Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2018-07-06T13:25:22Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) thais_ribeiro_costa.pdf: 3235496 bytes, checksum: 6f8cdc08809043df5efea75372782e92 (MD5)<br>Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2018-07-18T13:13:10Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) thais_ribeiro_costa.pdf: 3235496 bytes, checksum: 6f8cdc08809043df5efea75372782e92 (MD5)<br>Made available in DSpace on 2018-07-18T13:13:10Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) thais_ribeiro_costa.pdf: 3235496 bytes, checksum: 6f8cdc08809043df5efea75372782e92 (MD5) Previous issue date: 2017<br>Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM)<br>Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)<br>Este estudo teve como objetivo conhecer a composi??o flor?stica da comunidade arb?rea e sua rela??o com o ambiente, bem como avaliar a diversidade, estrutura e as fun??es ecol?gicas das esp?cies de dezoito fragmentos de mata de galeria inund?vel. Al?m disso, se prop?s a caracterizar a vegeta??o da matriz de entorno de nove fragmentos de mata e galeria, bem como verificar se vari?veis ambientais atuam na transi??o entre as duas fitofisionomias, com ?nfase nas propriedades qu?micas do solo. O estudo foi conduzido no Parque Nacional das Sempre-Vivas, na Serra do Espinha?o, Minas Gerais. Foram inventariadas 5% da ?rea total de cada fragmento, instalando-se parcelas permanentes de 100 m? (totalizando 0,72 ha de amostragem), onde foram amostrados todos os indiv?duos arb?reos com di?metro ? altura do peito igual ou superior a 5 cm (DAP ? 5 cm). Para amostragem da cobertura vegetacional da matriz de entorno, foi utilizado o m?todo dos pontos, totalizando 12 pontos por fragmento, distribu?dos nas dist?ncias de 10, 20 e 30 m no sentido borda-campo. Em cada parcela e em cada ponto, foi mensurada a umidade do solo e coletadas amostras de solo, para posteriores an?lises qu?micas. Para os fragmentos foram mensurados qualitivamente a cobertura do dossel, altura de crestamento e impactos ambientais. Foram amostrados 1265 indiv?duos arb?reos, distribu?dos em 76 esp?cies, 55 g?neros e 32 fam?lias. A comunidade em geral, apresentou valores de diversidade e equabilidade compativeis com outras matas de galeria inund?veis do pa?s. As esp?cies amostradas foram agrupadas em seis grupos funcionais distintos. A maioria dos fragmentos apresentou uma tend?ncia de est?gio seral mais avan?ado, com esp?cies predominantemente secund?rias iniciais e tardias, zooc?ricas, zoo?filas, densidade m?dia da madeira, sementes recalcitrantes e pl?ntulas do tipo faneroep?geo-foli?ceo. A distribui??o por classes diam?tricas dos indiv?duos da comunidade arb?rea e para as principais popula??es obteve uma tend?ncia de J-invertido, indicando bom potencial regenerativo. As vari?veis ambientais que se correlacionaram com a varia??o da composi??o de esp?cies foram ? disponibilidade de ?gua e condi??es de acidez. O baixo percentual de explica??o das vari?veis ambientais e espaciais ressaltam que as esp?cies nos fragmentos de mata de galeria distribuem-se de maneira estoc?stica. O fogo constituiu o impacto mais frequente no interior dos fragmentos, o que ressalta a necessidade de t?cnicas de manejo nessas ?reas. Os campos ?midos ao entorno dos fragmentos apresentaram-se com elevada cobertura de herb?ceas, mesmo ap?s o manejo do fogo. Para as caracter?sticas ed?ficas avaliadas observaram-se os maiores valores de umidade, pot?ssio, soma de bases, capacidade de troca cati?nica total e mat?ria org?nica nos solos sob floresta. Portanto, a defini??o dos limites entre as duas fitocenoses estudadas parece ser primariamente relacionada com o gradiente de fertilidade e umidade do solo. Permite-se aqui chamar a aten??o para a import?ncia de estudos de pequenos fragmentos vegetacionais para a amplia??o do conhecimento sobre a diversidade ambiental local e regional, e seus principais determinantes, e poss?veis consequ?ncias para a din?mica da vegeta??o dos ecossistemas.<br>Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Ci?ncia Florestal, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017.<br>This study aimed to know the floristic composition of the tree community and its relationship with the environment, as well as to evaluate the diversity, structure and ecological functions of the species of eighteen fragments of forest of flooded gallery. In addition, it was proposed to characterize the vegetation of the surrounding matrix of nine forest fragments and gallery, as well as to verify if environmental variables act in the transition between the two phytophysiognomies, with emphasis on the chemical properties of the soil. The study was conducted in the Sempre-Vivas National Park, in the Serra do Espinha?o, Minas Gerais. 5% of the total area of each fragment were inventoried, and permanent plots of 100 m? (totaling 0.72 ha of sampling) were sampled, where all arboreal individuals with a breast height diameter equal to or greater than 5 cm were sampled (DAP ? 5 cm). In order to sample the vegetative cover of the environment matrix, the points method was used, totaling 12 points per fragment, distributed at distances of 10, 20 and 30 m in the edge-field direction. In each plot and at each point, soil moisture was measured and soil samples were collected for further chemical analysis. For the fragments, the canopy cover, height of crust and environmental impacts were measured. A total of 1265 arboreal individuals were sampled, distributed in 76 species, 55 genera and 32 families. The community in general presented values of diversity and equability compatible with other floodplain gallery forests in the country. The species sampled were grouped into six distinct functional groups. Most of the fragments presented a trend of more advanced seral stage, with predominantly early and late secondary species, zoocoric, zoo-philological, mean wood density, recalcitrant seeds, and phaneroege-foliaceous-type seedlings. The distribution by diameter classes of the individuals of the tree community and for the main populations obtained a tendency of J-inverted, indicating good regenerative potential. The environmental variables that correlated with the variation of the species composition were the availability of water and acidity conditions. The low percentage of explanation of the environmental and spatial variables emphasize that the species in the fragments of gallery forest distribute stochastic way. Fire was the most frequent impact within the fragments, which highlights the need for management techniques in these areas. The wetlands surrounding the fragments presented high herbaceous cover, even after fire management. The highest values of moisture, potassium, sum of bases, total cation exchange capacity and organic matter in soils under forest were observed for edaphic characteristics evaluated. Therefore, the definition of the boundaries between the two phytochenoses studied seems to be primarily related to the fertility and soil moisture gradients. It is worth noting here the importance of studies of small vegetation fragments to increase knowledge about local and regional environmental diversity and their main determinants and possible consequences for the dynamics of ecosystem vegetation.
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16

Karns, Rachael Cassandra. "Microbial Community Richness Distinguishes Shark Species Microbiomes in South Florida." NSUWorks, 2017. http://nsuworks.nova.edu/occ_stuetd/453.

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The microbiome (microbial community) of individuals is crucial when characterizing and understanding processes that are required for organism function and survival. Microbial organisms, which make up an individual’s microbiome, can be linked to disease or function of the host organism. In humans, individuals differ substantially in their microbiome compositions in various areas of the body. The cause of much of the composition diversity is yet unexplained, however, it is speculated that habitat, diet, and early exposure to microbes could be altering the microbiomes of individuals (Human Microbiome Project Consortium, 2012b, 2012a). To date, only one study has reported on microbiome characterization in a shark (Doane et al., 2017; skin microbiome of the common thresher shark). A comparative characterization of microbiomes sampled from different shark species and anatomical locations will allow an understanding of the differences in microbiomes that may be explained by variance in shark habitat and diet. Florida leads as shark bite capitol of the world, with 778 unprovoked bites recorded since 1837, or 4-5 average bites per year. With only a few bites a year, there is not a lot of opportunities to study these bites. What can be studied, however, is how the microbial environment in shark’s teeth is composed. To understand overall microbiome composition, and if microbiomes are distinct from the environment, or specific by species or anatomical location (henceforth location), we characterized microbiomes from the teeth, gill, skin, and cloacal microbiomes of 8 shark species in south Florida (nurse, lemon, sandbar, Caribbean reef, Atlantic sharpnose, blacktip, bull, and tiger) using high throughput DNA sequencing of the 16S rRNA gene V4 region. There was a significant difference in microbial community richness among species, sample location, but not the interaction between species and location. Microbial diversity by location was significantly different for both the Shannon index and Inverse Simpson index. Samples examined by species had no significant difference in microbial community diversity overall for both Shannon and Inverse Simpson indexes. Microbial community diversity of samples by location and species combined significantly differed when submitted to an analysis of variance with the Shannon index, but not the Inverse Simpson index. Teeth microbial communities showed the most diversity based on both Shannon and Inverse Simpson indices. Teeth microbiomes are distinct but also share taxa with the water they inhabit, including potentially pathogenic genera such as Streptococcus (8.0% ± 9.0%) and Haemophilus (2.9% ± 3.3%) in the Caribbean reef shark. The lemon shark teeth hosted Vibrio (10.8% ± 26.0%) and the Corynebacterium genus (1.6%±5.1%). The Vibrio genus (2.8% ± 6.34%), Salmonella enterica (2.6% ± 6.4%), and the genus Kordia (3.1% ± 6.0%) are found in the nurse shark teeth microbial community. Strikingly, the Vibrio genus was represented in the sandbar shark (54.0% ± 46.0%) and tiger shark (5.8% ±12.3%) teeth microbiomes. One OTU related to traditionally non-pathogenic family Phyllobacteriaceae appear to be driving up to 32% of variance in teeth microbiome diversity. We conclude that south Florida sharks host distinct microbiomes from the surrounding environment and vary among species due to differences in microbial community richness. Future work should focus on bacteria found in shark teeth to determine if those present are pathogenic and could provide insights to bite treatment.
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17

Delsinne, Thibaut. "Structure des assemblages de fourmis le long d'un gradient d'aridité situé dans le Chaco sec paraguayen." Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210665.

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Contexte: L’importance écologique des fourmis dans les écosystèmes terrestres justifie qu’elles soient considérées comme groupe cible pour des actions de conservation. De plus, de par leur abondance, leur facilité de récolte et leur réponse à des perturbations, elles présentent un potentiel intéressant comme groupe indicateur précoce de l’état de santé des écosystèmes. Par contre, pour le choix d’aires à protéger, leur utilité comme intégrateur des conditions de milieu par rapport à des indicateurs classiques tels que les assemblages de plantes n’est pas clairement établie. En d’autres termes, répondent-elles plus finement que les plantes à différentes conditions de milieu et dans ce cas doit-on s’attendre à trouver au sein de formations végétales comparables plusieurs types d’assemblages de foumis? Si tel est le cas, la méthode utilisant les assemblages de végétaux pour sélectionner les sites à protéger peut ne pas permettre une conservation efficace de la diversité des fourmis. Ce type de problématique s’aborde bien le long de gradients environnementaux. Pour faciliter l’interprétation des résultats en terme de réponse aux facteurs abiotiques il est préférable de limiter le nombre de facteurs qui varient en même temps. Dans ce sens, le Chaco sec paraguayen représente un système très favorable: faible déclivité, faibles variations de températures moyennes mais gamme très étendue de conditions de pluviométrie (350mm à 1000mm de précipitations moyennes annuelles) et des sols variables (texture limoneuse à sableuse). L’aridité est l’un des principaux facteurs pouvant limiter la diversité des fourmis soit directement en exerçant un stress physiologique sur les espèces, soit indirectement en limitant la productivité primaire de l’habitat. Les conditions édaphiques peuvent également avoir une influence en affectant par exemple la survie des colonies qui nidifient dans le sol. <p>Objectifs: Les principaux buts de la thèse sont (1) de déterminer l’influence de l’aridité et des conditions édaphiques sur la distribution et la structure des assemblages de fourmis terricoles du sol en forêts tropicales sèches, (2) mettre en évidence les mécanismes qui facilitent la coexistence des espèces de fourmis à l’échelle locale, (3) déterminer si à l’échelle régionale les fourmis et les plantes répondent de façon similaire aux conditions du milieu. <p>Méthode: Onze localités ont été échantillonnées le long d’un transect régional long de 400km. Au niveau de chaque localité, trois transects élémentaires longs de 200m et séparés les uns des autres par 200m ont été effectués. La myrmécofaune a été échantillonnée à l’aide de 20 pièges à fosse et de 20 Winkler par transect élémentaire. La végétation de chaque site a été caractérisée sur base de l’abondance de 45 espèces d’arbres ou d’arbustes caractéristiques de la flore chaquéenne. Les propriétés physico-chimiques du sol ont également été mesurées. A fine échelle, l’organisation spatio-temporelle d’un assemblage a été étudié dans une localité de référence.<p>Résultats: Au total, plus de 50.000 spécimens correspondant à 206 espèces de fourmis ont été collectés avec en moyenne (± SD) 62 ± 10 espèces par localité. Pour un même effort d’échantillonnage, le nombre d’espèces de fourmis récoltées à l’aide des pièges à fosse augmente avec l’aridité et une tendance inverse est observée pour les Winkler. Puisque les Winkler peuvent entraîner une sévère sous-estimation de la diversité des fourmis d’un habitat, seules les données des pièges à fosse sont utilisées pour la suite des analyses. La diversité locale &<br>Doctorat en Sciences<br>info:eu-repo/semantics/nonPublished
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Rollin, Orianne. "Etude multi-échelle du patron de diversité des abeilles et utilisation des ressources fleuries dans un agrosystème intensif." Phd thesis, Université d'Avignon, 2013. http://tel.archives-ouvertes.fr/tel-00993034.

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Les abeilles sont des pollinisateurs essentiels pour les cultures et les plantes sauvages, mais l'intensification des pratiques agricoles a engendré une baisse importante de leur abondance et diversité. Afin de protéger efficacement les abeilles dans les paysages agricoles, il est nécessaire d'avoir une meilleure connaissance de leurs patrons de diversité. L'objectif général de cette thèse était de déterminer les patrons spatio-temporels de la diversité des abeilles et l'utilisation des ressource fleuries dans un système agricole intensif. L'échantillonnage spatialement extensif de l'activité de butinage des abeilles sauvages et domestiques nous a permis de recenser 45040 individus (29314 abeilles domestiques et 15726 sauvages), appartenant à 192 espèces recensées à l'échelle territoriale. Cette diversité représente près de 20% de la richesse des espèces apiformes connues à l'échelle nationale. Cette communauté est caractérisée par une forte proportion d'espèces rares (28,8%) et de fortes variations temporelles et spatiales, en particulier de l'échelle locale jusqu'à 10-20 km2. L'importance des habitats semi-naturels pour soutenir les populations d'abeilles sauvages a été confirmée dans cette étude. Durant les périodes de floraison des cultures oléagineuses, les abeilles sauvages étaient étroitement associées aux habitats semi-naturels alors que les abeilles domestiques ont montré une nette préférence pour les cultures à floraison massive. La diversité des abeilles sauvages dans les habitats semi- naturels était 3-4 fois supérieure à celle observée dans le colza ou le tournesol. L'importance de certains facteurs écologiques clefs pour la diversité des abeilles, comme la richesse floristique locale et la quantité d'habitats semi-naturels dans le paysage, a été confirmée et quantifiée. Il a également été démontré que ces effets varient en fonction de la saison et de l'échelle spatiale. Ces résultats mettent en évidence les processus écologiques responsables des partons de diversité des abeilles à différentes échelles spatiales, et peuvent contribuer à optimiser la conception des mesures de conservation visant à promouvoir la diversité des abeilles dans les agrosystèmes intensifs.
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Horton, Dean J. "Using molecular techniques to investigate soil invertebrate communities in temperate forests." Kent State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1448799316.

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20

PARTULA, SYLVIE. "Structure primaire et diversite des chaines alpha et beta du recepteur specifique des lymphocytes t et des chaines legeres (l2) des immunoglobulines chez la truite arc-en-ciel (oncorhynchus mykiss)." Paris 6, 1996. http://www.theses.fr/1996PA066317.

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La structure des chaines alpha et beta du tcr de la truite arc-en-ciel a ete analysee. Quatre segments v beta appartenant a des familles differentes ont ete identifies. L'un d'entre eux (v beta1) presente une similarite significative avec la famille v beta20 humaine. Les dix segments j beta sont tres proches de ceux des autres vertebres. La comparaison de 66 jonctions v(d)j montre que la moitie d'entre-elles partage un element d beta. Une diversite considerable est observee au niveau des jonctions v-d-j (n-nucleotides). Un fort pourcentage de rearrangements hors phase est observe, suggerant que des modalites particulieres de selection du repertoire des lymphocytes t. Le domaine extracellulaire de la region constante est plus court que celui des mammiferes et la region charniere ne comporte pas le residu cysteine. Le domaine transmembranaire est bien conserve et contient le motif cart et un residu lysine. Six familles v alpha ont ete caracterisees, ayant des similarites significatives avec les segments v alpha/delta des mammiferes. Parmi 32 jonctions v(d)j, on trouve 29 segments j alpha differents, suggerant que les poissons possedent un grand nombre d'elements genomiques j alpha. Les jonctions v-j des chaines alpha montrent une grande diversite et possedent des residus glycine. La region constante c alpha est courte. Toutefois la structure minimale des feuillets beta est retrouvee. La taille, la composition en acides amines, le motif cart-alpha et les residus charges sont tres bien conserves dans la region transmembranaire. Nous avons egalement mis en evidence un nouvel isotype (l2) de chaine legere des ig de truite qui sur le plan evolutif, ne peut etre classe parmi les isotypes ou des mammiferes. Comme chez les autres teleosteens, l'analyse genomique du locus l2 de truite revele un grand nombre de segments cl2 et vl2, suggerant une organisation en cassettes du locus igl2
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COUEDEL, CHRYSTELLE. "Contribution a l'etude du recepteur a l'antigene des lymphocytes t humains : mecanismes de regulation des rearrangements des genes du recepteur t ; diversite du repertoire de reconnaissance des lymphocytes t alpha/beta." Paris 6, 2001. http://www.theses.fr/2001PA066061.

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En caracterisant les rearrangements du tcr, et de nombreux clones t humains v1+ ou v2+, nous avons confirme la sequence d'initiation des rearrangements sur les differents loci (, puis ) et montre une cinetique ordonnee des rearrangements. De plus, nous montrons l'existence d'une exclusion allelique sur le locus. Nous confirmons l'absence d'exclusion allelique sur le locus mais de nombreux clones v1 portent deux rearrangements fonctionnels, suggerant des contraintes d'appariement entre chaines et. Les deux populations se distinguent aussi par les rearrangements et nos resultats suggerent une competition entre lignages t / pour les cellules v2. D'autre part, l'eventualite de rearrangements multiples a ete evaluee par l'etude des positions des v et j utilises sur les deux alleles de nombreuses cellules t murines et humaines, qui montre que les j sont colocalises contrairement aux v. Les regions v s'ouvriraient selon deux fenetres distinctes ou les rearrangements ont lieu de facon stochastique. Cette etude suggere un nombre limite de rearrangements sur chaque allele. En second lieu, nous montrons que les tcr de clones specifiques d'un meme epitope ebv sont tres divers. La selection de ces cellules serait basee sur leur avidite similaire, une contribution variable du cd8 contrebalancant les differences d'affinite des tcr. L'etude chez plusieurs individus des tcr de cellules specifiques d'un autre epitope ebv montre une diversite elevee des chaines qui varie d'un individu a l'autre. Neanmoins, plusieurs sous-populations expriment des chaines portant des v particuliers associees a des chaines portant le meme v, suggerant une implication importante des clonotypes publiques dans les reponses immunodominantes. Enfin, nous montrons que les cellules t nk humaines portant la chaine v24j18 invariante reconnaissent des -glycosylceramides synthetiques presentes par le cd1d, et cela quand elles expriment une chaine v11.
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Buckley, Elan. "Change in the Structure of Soil Microbial Communities in Response to Waste Amendments." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/101499.

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Soil microbial communities are affected extensively by addition of amendments to their environment. Of particular concern is the addition of poultry litter, which contains a substantial C, energy, and nutrient supply, but also antibiotic resistance genes (ARG), antimicrobials, and a multitude of microbial species. This project seeks to primarily assess if there is a change in bacterial community structure in response to poultry litter amendments to pasture land across geographically independent land across northern Georgia. It may be that changes in the relative abundance of bacterial communities also result in alteration in ARGs, and the community resistance to antibiotics (“resistome”) which in turn increases the potential threat of antibiotic resistance genes. While another part of this study will determine changes in integrons and specific ARGs, this project will focus on changes in bacterial communities and the potential functional changes in the community, which in turn have consequences for ARG levels and its horizontal transfer to various members of the soil community. Addition of waste from livestock is a historical method for increasing nutrients needed in the soil for the cultivation of crops, and in turn causes pronounced shifts in soil microbial communities due to the addition of large amounts of carbon, nutrients, foreign microbes, and other material. This study is unique because it utilizes a novel and relatively large landscape-scale to determine if there are discernable and repeatable patterns of bacterial community structure change in response to amendment regardless of exact soil type or source of chicken litter amendment. In the future, these data can also provide insight into the changes in the relative abundance antibiotic related genes associated with community change.<br>M.S.<br>Soil is complicated, both in terms of its physical makeup and the organisms that live inside of it. Predicting changes in soil based on the addition of foreign material such as chemicals or biological waste is not an easy process, and whether or not it is even possible to reliably predict those changes is a matter of some dispute. This study is designed to illustrate that such changes can in fact be reliably and consistently predicted even with regard to the addition of complicated materials to the soil. In this study, specifically, the material in question is chicken litter. A mix of the bedding and waste produced by chickens, litter is commonly handled by composting and is added to soil in farms as a fertilizer rich in organic matter. It is possible to point at specific elements of the soil such as the chemistry and bacteria and see how it is changed with the addition of chicken litter, which allows us to determine the nature and extent of the change that chicken litter has on soil. This study is conducted on a larger scale than similar experiments conducted in the past, making it apparent that these relationships exist on a repeated basis. It is the object of this study to pave the way and make it easier for scientists in the future to determine these relationships in other unique contexts.
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Argudo, Fernández Maria. "Microbial communities responses in fluvial biofilms under metal stressed scenarios." Doctoral thesis, Universitat de Girona, 2021. http://hdl.handle.net/10803/671673.

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This thesis shows how the metals of natural and anthropic origin change significantly the composition of the prokaryotic communities (mainly the composition of bacteria). The β-diversity is the most sensitive variable to the effects of metals, unlike α-diversity, which is hardly affected or even benefited. In scenarios with high and chronic metal pollution, the resident community (DNA fraction) suffers changes in its composition that can be detected at phylum or class taxonomic level. However, in fluvial ecosystems, subjected to lower levels of metal pollution, only the RNA fraction is affected by selecting more active OTUs/ASVs. In addition, the knowledge about the bacterial composition of communities and, consequently, the selection of specific taxa is useful to find some potential prokaryotes functions important in stress response caused by metals<br>Esta tesis muestra cómo los metales de origen natural y antrópico cambian la composición de las comunidades de procariotas, sobre todo de las bacterias. La β-diversidad es la variable más sensible a los efectos de los metales, a diferencia de la α-diversidad, que no se muestra casi afectada o incluso es beneficiada. En escenarios con contaminación alta y crónica de metales, la comunidad residente (fracción de ADN) sufre cambios en su composición que pueden ser detectados a nivel de filo o clase. Sin embargo, en ecosistemas fluviales sometidos a niveles más bajos de contaminación de metales sólo la fracción de ARN se ve afectada selecionando los OTUs/ASVs más activos. El conocimiento de la composición de la comunidad bacteriana y por consiguiente la elección de algunos taxones como bioindicadores, ayuda a encontrar funciones potenciales de las bacterias que podrían ser importantes en las respuestas al estrés causado por metales
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Walls, Philip Andrew. "#alpha#-#beta# sialons." Thesis, University of Newcastle Upon Tyne, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235618.

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Lindgren, Jessica. "Small remnant habitats : Important structures in fragmented landscapes." Doctoral thesis, Stockholms universitet, Institutionen för naturgeografi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-148653.

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The world-wide intensification of agriculture has led to a decline in species richness due to land use change, isolation, and fragmentation of natural and semi-natural habitats in agricultural and forestry landscapes. As a consequence, there is a current landscape management focus on the importance of green infrastructure to mitigate biodiversity decline and preserve ecosystem functions e.g. pollination services and pest control. Even though intensification in agriculture has been ongoing for several hundreds of years, remnant habitats from earlier management practices may still be remaining with a surprisingly high plant richness. Preserving these habitats could help conserving plant species richness in agricultural landscapes, as well as other organisms that are dependent on plants for food and shelter. In this thesis I focus on two small remnant habitats; midfield islets and borders between managed forest and crop field in southeastern Sweden. In the past, both habitats were included in the grazing system and therefore often still have remnant population of grassland specialist species left today. I have used these two remnant habitats as model habitats to investigate the effect of landscape factors and local factors on species richness of plants, flower morphologies and plants with fleshy fruits. Additively, I analysed the effect of surrounding landscape and local openness on the functions; pollination success, biological pest control of aphids and seed predation on midfield islets. One of my studies showed that spatial distribution and size of the habitat affected plant species richness. Larger habitat size and higher connectivity between habitats increased species richness of plants in the habitats. Openness of the habitats was shown to be an important factor to increase species richness and richness of flower morphologies, both on midfield islets and in forest borders. Even though midfield islets had the highest species and morphology richness, both habitat types are needed for habitat complementary as forest borders have more plants with fleshy fruits and a higher richness of plant species that flowers in spring/early summer. It was also shown that a more complex forest border, not just with gaps in the canopy, but also with high variation in tree stem sizes increases plant species richness in the field layer. The conclusion is that by managing small remnant habitats to remain or become more semi-open and complex in their structure, would increase species richness of plants, grassland specialist species, and flower morphologies. It would also increase some ecosystem functions as seed predation and biologic pest control of aphids are more effective close to trees. If both midfield islets and forest borders would be managed to be semi-open, the area and connectivity of semi-open habitat would increase in the agricultural landscape, which may also improve pollination success as the connectivity between populations has a possibility to increase. Grassland specialist species are clearly abundant in the small remnant habitats. As the decline of semi-natural grasslands is causing a decline in grassland specialists’ species, not only plants, I recommend that small remnant habitats are included in conservation and management plans and strategies to improve habitat availability and connectivity for grassland species in agricultural landscapes.<br><p>Research funder Ekoklim. Project:4339602.</p><p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>
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Palau, Lluch Gerard. "alpha,beta-difunctionalization of alpha,beta-unsaturated carbonyl compounds through borylation reaction." Doctoral thesis, Universitat Rovira i Virgili, 2015. http://hdl.handle.net/10803/311620.

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Aquesta tesi presenta resultats referits a noves metodologies aplicades cap a la obtenció de productes alfa-funcionalitzats i beta-borilats, que no tenen precedents en la bibliografia, a partir de cetones alfa,beta-insaturatdes. Les funcionalitzacions estudiades han sigut utilitzant fluor, per obtenir alfa-fluoro beta-boryl cetones; halogens, per obtenir alfa-halo beta-boryl cetones (sent els halogens clor i brom); i finalment difuncionalitzar cetones alfa,beta-insaturades per obtenir alfa-aryl beta-boryl cetones, que tal i com es reporta a la tesi, han sigut els intermedis cap a la sintesi de 2-aryl-1,3-diones, que són productes de sintesis molt valorats en la industria per les seves propietats com a pesticides. En tots tres casos, s'ha aconseguit la obtenció dels productes difuncionalitzats, dels quals cap havia sigut previament presentat a la bibligrafia existent, concluent per tant que aquest ha sigut un treball pioner cap a la sintesi i obtenció d'aquests compostos difuncionalitzats.<br>Esta tesis presenta los resultados pertenecientes a nuevas metodologias aplicadas hacia la obtención de productos alfa-funcionalizados y beta-borilados que no tienen precedente en la bibliografia, a partir de cetonas alfa,beta-insaturadas. Las funcionalizaciones estudiadas han sido utilizando fluor, para obtener alfa-fluoro beta-boryl cetonas; halogenos, para obtener alfa-halo beta-boril cetonas (siendo los halogenos cloro y bromo); y finalmente la difuncionalización de cetonas alfa,beta-insaturadas para obtener alfa-aryl beta-boryl cetonas, que tal y como se presenta en la tesis, han sido los productos intermedios hacia la sintesi de 2-aryl-1,3-dionas, que són productos de sintesis muy valorados en la indústria por sus propiedades como pesticidas. En todos los tres casos, se consiguió la obtención de los productos difuncionalizados, de los cuales ninguno habia sido previamente presentado en la bibliografia existente, concluyendo que éste ha sido un trabajo pionero hacia la sintesi y obtención de estos compuestos difuncionalizados.<br>This thesis presents the results concerning new methodologies towards the obtantion of alpha-functionalized beta-borylated compounds from alpha,beta-unsaturated carbonyl compounds, with no precedent in the litherature. The functionalizations studied focused on fluorine, to obtain alpha-fluoro beta-boryl ketones; halogens, to obtain alpha-halo beta-boryl ketones (being the halogens chlorine and bromine); and finally, the difunctionalization of alpha,beta-unsaturated ketones to obtain the corresponding alpha-aryl beta-boryl ketones, which as presented in this thesis, they have been the intermadiates towards the synthesis of 2-aryl-1,3-diones. 2-aryl-1,3-diones are highly valued products in industry for their properties as pesticides. In the three cases studied, we obtained the desired difunctionalized products, which any of them has been previously presented in the existing literature, concluding that this has been a pioneering work towards the synthesis and obtantion of such difunctionalized compounds.
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Szeki, Andrea. "Stereoselective synthesis of #alpha#-hydroxy-#beta#-amino and #alpha#,#beta#-diamino acid derivatives." Thesis, University of Newcastle Upon Tyne, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285938.

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28

Grudzinska, Joanna. "Charakterisierung der Ligandenbindung am [alpha]1-homo- [alpha-1-homo-] und [alpha]1[beta]-heterooligomeren [alpha-1-beta-heterooligomeren] Glycinrezeptor." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976836025.

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29

Shakya, Sagar Raj. "Studies on alpha,alpha-disubstituted bicyclic beta-lactams." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/7571.

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General Organization. This thesis contains a brief introduction to the area of $\beta$-lactam antibiotics and four other Chapters dealing with the syntheses of various 6-methoxy $\beta$-lactams. Due to the tremendous level of activity in this area the introductory literature material is presented in an illustrative approach rather than a comprehensive approach. Literature surveys were carried out using Chemical Abstracts from 1982 to February 1992. Experimental details are given at the end of each Chapter. Compounds in the schemes which did not lead to desired conclusion were not completely characterized; $\sp1$H NMR and other spectral data whenever available are given in the Experimental section. IR was not recorded in most of these cases. Elemental analyses were not performed at all, since the data from such experiments do not always represent the purity of product. Chapter 1. This section describes the development of various $\beta$-lactam antibiotics, major representative structures, mode of action and overall objectives of the research undertaken. Chapter 2. 7-Methoxy-7-ethyl and 7-methoxy-7-hydroxyethylisocephem analogs were prepared from 4-cinnamyl-3-methoxyazetidinone which was prepared in a multigram scale. This precursor can be purified simply by trituration with ether. The transformation of this monocyclic starting material to the cyclization precursor involved introduction of an additional side-chain at C-3 via. generation of anion using lithium diisopropylamide and quenching of the anion with either ethyl iodide or acetaldehyde. In the case of the hydroxyethyl side-chain oxidation with pyridinium chlorochromate, reduction with L-Selectride and silylation with tert-butyldimethylsilyl triflate was required before carrying out further manipulations. The cinnamyl group was converted to a methylene bearing a leaving group and the p-methoxyphenyl moiety on nitrogen was cleaved and a suitable acetate side-chain was introduced. The anionic annulation with CS$\sb2$ gave the desired bicyclic compounds. An optically active isocephem having a thienamycin type side-chain at C-7 and and a racemic isocephem having a methoxy group at C-7 were prepared by similar method. Chapter 3. 7-Ethyl-7-methoxycarbacephem was prepared using a rhodium carbenoid reaction starting from 4-cinnamyl-3-methoxyazetidinone. A similar method was applied to prepare an advanced intermediate for 7-hydroxyethyl-7-methoxycarbacephem. Chapter 4. 6-Methoxy-PS 5 synthesis was attempted which was found to be unstable. The cyclization was carried out applying the rhodium carbenoid methodology. The cyclization precursor was obtained using nitroaldol condensation starting from an aldehyde which was prepared from 4-cinnamyl-3-methoxyazetidinone. Chapter 5. Syntheses of 6-methoxy-1-methyl-PS 5 analogs were attempted starting from 3-ethyl-3-methoxy-4-methylcinnamylazetidinone. The introduction of 1-methyl group involved the reduction of a suitable $\alpha,\beta$-unsaturated ester obtained via. palladium catalyzed carbonylation reaction.
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30

Lider, Mustafa Cem. "Alpha-beta Transition In Quartz." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613650/index.pdf.

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Alpha-Beta transition in quartz is studied using the Raman scattering. The Raman frequencies of some lattice modes are analyzed at various temperatures close to the alpha beta transition in quartz. For this analysis, the experimental data from the literature is used and the soft mode behavior of those Raman phonons is investigated . On the basis of the predictions of some models, the temperature dependencies for the Raman frequencies of the lattice modes which move towards zero (soft mode) and their bandwidths close to the transition temperature Tc are explained for the alpha-beta transition in quartz. In addition, by using the experimental volume data from literature, calculation of the temperature dependence of the Raman frequencies through the Gr&uuml<br>neisen parameter have been studied near the phase transition.
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Arndt, Torsten. "Niedermolekulare [alpha]4[beta]7-Integrinantagonisten [Alpha-4-Beta-7-Integrinantagonisten] und Synthese transmembraner Peptide." [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=970264259.

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32

Leppert, Jan. "Identifizierung und Charakterisierung von Interaktionspartnern des Integrins [alpha]6[beta]4 [alpha-6-beta-4]." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=974508780.

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33

Gangadharan, Denise Michelle. "Thymic development of CS8[alpha][alpha]⁺ TCR[alpha][beta]⁺ agonist selected IEL." Diss., Connected to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2005. http://wwwlib.umi.com/cr/ucsd/fullcit?p3189998.

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Thesis (Ph. D.)--University of California, San Diego, 2005.<br>Title from first page of PDF file (viewed Marc 6, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 100-116).
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Gaertner, Christoph. "Prognostische Relevanz von [alpha]-, [beta]- und [gamma]-Cateninen [Alpha-, Beta- und Gamma-Cateninen] bei oralen Plattenepithelkarzinomen." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971234655.

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35

Xu, Xiao. "Human alpha defensin CNV haplotype diversity." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/51262/.

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Humans have highly variable number of alpha defensin genes, with between 3-16 diploid copies. Alpha-defensin genes have important roles in human innate immunity and diseases. Recently, GWAS studies reported this locus associated with IgA nephropathy and periodontitis. However, the underlying mechanism of association is not clear. In this Ph.D. thesis, human alpha defensin CNV flanking haplotype diversity in global populations was studied and the association between diseases and haplotype classes was discussed. Then a novo method to detect variants from inside the DEFA1A3 CNV was developed and a list of potential disease-related mutations for further functional studies was generated. The association between CNV internal variants and flanking haplotype classes was studied. Non-allelic homologous recombination was found to be the major mechanism of CNV formation of alpha defensin CNV. Analysis results were verified by PCR and Sanger sequencing-based methods. Additional to that, the haplotype diversity analysis highlighted an unusual haplotype 5T/7C which is only found in European populations but highly diverged from other human haplotypes. Further evidence was provided to suggest that this is an introgressed haplotype from Neanderthals. Furthermore, we used Oxford Nanopore to reconstruct haplotype structure in DEFA1A3 CNV and discussed its advantages and limitations by our analysis results. In brief, this Ph.D. research greatly improved our understanding of DEFA1A3 global diversity, evolutionary history, diseases and haplotype association.
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36

Beresford, Kenneth James Mcrae. "Additions to chiral #alpha#, #beta#-epoxyimines." Thesis, University of Salford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304594.

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37

Linden, Sven. "[Alpha]-Tocopherol [Alpha-Tocopherol], [beta]-Carotin [Beta-Carotin] und L-Ascorbinsäure in der Rindermast Einfluss auf Qualitätsparameter /." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968806600.

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38

Chakraborty, Arup R. "Differential expression of integrin [alpha]₃[beta]₁ and [alpha]₆[beta]₄ molecules on a panel of rat esophageal cell lines." Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=bgsu1131345357.

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39

Claren, Jörg. "Design stabiler und katalytisch aktiver (beta, alpha)8-Barrel-Enzyme durch Rekombination von (beta, alpha)4-Halbbarrel-Domänen." kostenfrei, 2008. http://www.opus-bayern.de/uni-regensburg/volltexte/2009/1094/.

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40

Zimmermann, Dunja. "Der Einfluss cyclischer RGD-Peptide auf die Wechselwirkung Fibronectin-Integrin [alpha]5[beta]1[alpha 5 beta 1]." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=970414277.

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41

Rajagopal, Thivisa. "Synthesis of Single Isomer Trisubstituted Olefins from beta-chloro-alpha-iodo-alpha, beta-Unsaturated Esters and Alkynyl Esters." Thesis, University of Ottawa (Canada), 2010. http://hdl.handle.net/10393/28552.

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A convenient method to synthesize regiospecific and stereoselective trisubstituted olefins bearing three substitutents with various functionalities is disclosed. A unique olefin template such as (E)-beta-chloro-alpha-iodo-alpha,beta-unsaturated esters cross-couple with 9-alkyl-9-BBN to produce single isomer trisubstituted olefins using palladium-catalyzed Suzuki-Miyaura cross-coupling reaction. This methodology can be further expanded to introduce various alkyl groups at the beta-position. The mechanism is somewhat unusual as it involves two catalytic cycles with an allenoate intermediate to explain the observed stereochemistry and protonolysis of that intermediate produces the key product, (E)-beta-chloro-alpha,beta-unsaturated ester. The protonolysis is mediated by the presence of H2O in the inorganic base, K3PO4&middot;H2O.* Similarly, another method has been developed to synthesize trisubstituted olefins using the alkynyl ester and 9-alkyl-9-BBN. This process also has a broad scope to introduce various alkyl groups at the beta-position. The mechanism currently proposed involves an oxidation of palladium to form H-[Pd]-OH species. This was confirmed based on the importance of water in the catalytic system and the isotopic experiments also confirmed the olefinic hydrogen at the alpha-position arises from the water itself. Following the formation of H-[Pd]-OH, syn carbopalladation to the alkynyl ester creates the hydroxyl palladium vinyl intermediate. However, this mechanism does not explain the observed stereochemistry. A more detailed study is required regarding this mechanism.* *Please refer to dissertation for diagrams.
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42

Howe, G. P. "Stereoselective additions to #alpha#,#beta#-epoxy-aldehydes." Thesis, University of Salford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381818.

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Turp, Edward Robert. "Stereoselective additions to #alpha#,#beta#-epoxy-aldehydes." Thesis, University of Salford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245017.

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44

Shah, Aalok K. "Geometry Of Alpha And Beta Protein Structures." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/578419.

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Proteins have a wide array of essential functions: from serving as enzymatic catalysts to protecting the immune system as antibodies. Proteins spontaneously self-organize into specific, folded structures determined by their amino acid sequences and the interaction between molecular forces. Since the 3-dimensional structure into which they fold often relates to the specific function of the protein, much effort has been directed towards methods to predict the folded structure from a given sequence, with the hope of being able to understand protein functions from sequence information. The protein folding problem can be summarized as the attempt to understand the relationship between a protein sequence and a protein's geometric shape, or fold. Thus, there are two principal problems: given a sequence, what 3-dimensional form will the protein take (forward problem), and given a particular fold, what sequence or sequences code for that form (the inverse problem). In this work, models that represent folds as continuous structures are explored. Models of the two prevalent motifs in protein folds, α helices and β barrels, are developed using axially deformed tubes and surfaces of revolution. These models are then analyzed and used to develop coordinate models of known and unknown structures.
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Henn-Sax, Martina. "Evolution und katalytischer Mechanismus eines thermostabilen ([beta]/[alpha]8-Barrel-Enzyms [(Beta/Alpha)-8-Barrel-Enzyms] aus der Histidinbiosynthese." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=964922649.

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46

Baskakova, Alevtina. "Synthesis of branched [alpha]-[alpha-] and [beta]-amino[beta-amino] acids using C-nucleophile additions to imines and nitrones." Berlin Logos-Verl, 2009. http://d-nb.info/99789301X/04.

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47

McCandless, John Richard 1954. "Alpha-6 beta-1 and alpha-6 beta-4 integrin expression and the vascularization of human prostate tumor xenografts." Thesis, The University of Arizona, 1997. http://hdl.handle.net/10150/278603.

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Growth and metastasis of tumors appear to be dependent on the ability of tumor cells to recruit blood vessels. Integrins are a class of cell adhesion molecules that may have a role in angiogenesis. In this study the effect of the expression of two integrins, α6β1 and α6β4, on microvessel density in human prostate tumor xenografts in SCID mice was evaluated. Five methods (one-person count, two-person count, digital analysis of immunostained tissues, and digital analysis of vascular corrosion casts) were used to measure microvessel density. Results indicate that alpha6 integrin expression correlates negatively with tumor vessel density. and with tumor cell proliferation but not the extent of the tumor burden. β4 integrin expression does not appear to affect tumor vessel density, tumor cell proliferation, nor tumor burden. Comparison of methods of quantitation suggest that computer-assisted vessel counting may offer advantages over optical counting or computer-assisted area measurement.
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48

Ali, Mayssam H. (Mayssam Hani) 1976. "The design and structural characterization of oligomeric beta beta alpha mini-proteins." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/17737.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004.<br>Vita.<br>Includes bibliographical references.<br>Oligomeric mini-proteins, short peptides with protein-like features, constitute valuable minimal models for the study of oligomeric proteins. Oligomerization is a common feature of cellular proteins that may confer structural and functional advantages. Oligomerization is proposed to have arisen by several evolutionary pathways. The structural characterization of peptide 1, a stable oligomeric mini-protein previously developed in the Imperiali group, was undertaken by X-ray crystallography, as knowledge of the structure would enable the rational design of subsequent generations of BBA oligomers varying in packing and stoichiometry. The structure of peptide 1 could not be solved by direct methods, by molecular replacement with search models derived from the monomeric precursor, or by the introduction of heavy atoms. Two selenomethionine mutants having solution-phase properties comparable to the native were identified. The structures of these two peptides were independently solved via MAD phasing experiments, and the refined structures employed as search models for a molecular replacement solution of 1. The structures of the three peptides are homologous, and constitute the first reported structures of a mixed act/ oligomeric mini-protein. The X-ray crystal structures reveal that the oligomeric BBA motif has a domain-swapped architecture that supports a protein-like and water-exclusive core. The structures elucidate the unique role of unnatural amino acids in conferring native secondary structure in a short peptide sequence (21 residues per monomer).<br>(cont.) Furthermore, the crystal structures reveal that the stoichiometry of the oligomer is tetrameric, rather than trimeric, as originally proposed. A tetrameric solution-phase stoichiometry for this mini-protein family was confirmed by rigorous analytical ultracentrifugation experiments. Heterooligomeric BBA peptides have been designed and characterized in collaboration with Christina M. Taylor and Professor Amy E. Keating of the MIT Biology Department. Acidic and basic residues were substituted along the inter-monomer interface and specific steric interactions were designed in order to disfavor homoassociation and favor heteroassociation. Heterotetramers comparable to peptide 1 in terms of structure and stoichiometry, and approaching the native homotetramer in terms of stability, have been characterized by a variety of biophysical techniques.<br>by Mayssam H. Ali.<br>Ph.D.
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Weiken, Claudia. "Kollagenrezeptor [alpha]2[beta]1-Integrin [Alpha-2-Beta-1-Integrin] auf humanen und tierischen Thrombozyten Heterogenität und ihre Bedeutung /." [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=976077981.

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50

Broich, Kerstin. "Importance of [alpha]v[beta]3 [alpha-v-beta-3] integrin in arteriogenesis in the peripheral circulation of the rabbit." Giessen : DVG-Service-GmbH, 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972754466.

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