The variation in community composition among sites is often used to gain insight into the processes of plant community assembly. In this study, we looked for evidence of environmentally and spatially mediated community assembly mechanisms in a temperate forest in eastern North America. To test this, we measured, identified and mapped all woody stems ≥1 cm in diameter at breast height (DBH) in 12 ha of a 20 ha forest plot. We used principal coordinates of neighbor matrices (PCNM) to obtain variables that modelled spatial processes (eg. dispersal, drift) at the community level. Topographic variables (slope, elevation, convexity, aspect) were used to model environmental conditions. Variation partitioning was used to isolate the unique and shared effects of topographic and spatial variables on community composition. We were also interested in studying how associations with the environment change with tree size. For this we assessed the abundance of a subset of focal species in response to topography as well as human disturbance. Species abundance were divided into three stem size classes: small (< 5 cm), medium (≥5 cm and < 15), and big (≥15 cm). We found that topography and space jointly explained 63% of the variation in community composition. This variation was almost entirely spatially structured with the component of pure topography only contributing 1% to the total explained variation. A redundancy analysis showed that slope and elevation were the most important topographic variables structuring the distribution of trees. The focal species had largely independent distributions across the environmental gradients and three of the five species showed within-species differences associated with size class effects on the relationship with topography and human disturbance. The implications of these results are relevant to conservation efforts and suggest that large contiguous areas of heterogeneous environments are essential in maintaining biodiversity. / Thesis / Master of Science (MSc)

Résumé: Deux facteurs principaux, une fois combinés, permettent de comprendre l’assemblage des communautés, soient i) l’environnement (abiotique et biotique), qui agit comme un filtre sélectionnant les espèces les mieux adaptées aux conditions données, et ii) les traits fonctionnels, sur lesquels s’effectue ce filtrage environnemental puisqu’ils représentent les adaptations des espèces aux conditions données. Il est donc essentiel d’établir des relations fiables entre les conditions environnementales et la structure fonctionnelle des communautés afin de pouvoir identifier et comprendre les mécanismes régissant l’assemblage des communautés. Cependant, plusieurs facteurs tels que les interactions entre variables environnementales à différentes échelles spatiales (par exemple le climat et la fertilité des sols) peuvent complexifier la situation et c’est pourquoi, malgré une quantité grandissante d’études sur le sujet, les processus d’assemblage des communautés restent difficiles à définir et à généraliser. Cette thèse vise donc à i) mieux définir et quantifier les relations trait-environnement des systèmes d’herbacées au travers de différentes échelles spatiales et ii) déterminer l’influence de ces relations sur l’assemblage des communautés et le fonctionnement des écosystèmes. Pour réaliser ces objectifs, j’ai travaillé avec les données de programmes ayant collecté des données taxonomiques et fonctionnelles sur les communautés d’herbacées à travers la France (DivHerbe et DivGrass) et, à moindre mesure, l’Europe (VISTA). Ces bases de données couvrent donc de larges gradients climatiques régionaux ainsi que des gradients environnementaux plus locaux relatifs à la qualité des sols et aux perturbations. J’ai d’abord testé l’importance de considérer à la fois des variables environnementales locales et régionales ainsi que leurs interactions pour déterminer la structure fonctionnelle et taxonomique des communautés. J’ai ensuite étudié comment l’importance relative des processus menant soit à la convergence ou à la divergence fonctionnelle peut changer le long d’une succession, puis comment ces deux types de processus influencent notre capacité à prédire l’assemblage des communautés à partir des traits fonctionnels. Finalement, j’ai présenté comment les résultats au niveau des communautés peuvent être utiles pour étudier le niveau des écosystèmes. Les résultats de cette thèse démontrent que les variables climatiques régionales interagissent fortement avec les variables environnementales locales pour influencer les processus locaux déterminant l’assemblage des communautés. Évaluer le contexte régional semble donc nécessaire afin d’éviter des interprétations erronées des patrons d’assemblage observés. Travaillant avec ces deux niveaux de variation environnementale, une dissociation important entre la variation taxonomique et fonctionnelle des communautés a été mise à jour, reflétant l’importance de considérer plusieurs facettes de biodiversité pour comprendre la dynamique des communautés. Les résultats ont aussi démontré que les processus d’assemblage menant à la convergence et à la divergence ont un impact très différent et prédictible sur les relations liant les traits et les abondances des espèces, c’est-à-dire notre capacité à prédire l’assemblage des communautés à partir des traits. Finalement, toutes ces notions, relatives aux relations trait-environnement et à l’assemblage des communautés basé sur les traits, ont été utilisées dans un contexte de biogéographie fonctionnelle. Il a été démontré qu’il était possible de construire des cartes de valeurs de traits fonctionnels dans les prairies permanentes à l’échelle de la France, à partir de variables environnementales. Certaines propriétés écosystémiques ont ensuite pu être prédites à partir de ces cartes. Ces travaux ont donc permis d’illustrer les défis à surmonter pour utiliser nos connaissances de l’écologie fonctionnelle en vue d’une conservation et d’une exploitation viables de nos écosystèmes. / Abstract: There are two main factors which, combined together, allow understanding community assembly : i) the environment (both abiotic and biotic), which acts as a filter selecting species according to how well-adapted they are to given conditions, and ii) functional traits, on which this environmental filtering occurs since they represent species adaptations to particular conditions. It is thus essential to establish reliable relationships between environmental conditions and the functional structure of communities in order to identify and understand the mechanisms driving community assembly. However, several factors such as cross-scale interactions between environmental variables (e.g. between climate and soil fertility) complicate the situation. This is why, despite a growing body of studies on the subject, processes of community assembly are still poorly understood and are difficult to generalize. The purpose of this thesis is to i) better define and quantify the trait-environment relationships in herbaceous systems across different spatial scales and ii) determine the influence of those relationships on community assembly and on ecosystem functioning. To realize these objectives, I worked with data from programs which assembled taxonomic and functional data on herbaceous communities across France (DivHerbe and DivGrass) and, to a lesser extent, Europe (VISTA). These databases thus cover large regional climatic gradients, as well as more local environmental gradients related to soil quality and disturbances. I first tested the importance of simultaneously considering local and regional environmental variables as well as their interactions to determine the taxonomic and functional structure of communities. Then, I studied how the relative importance of processes leading to either functional convergence or divergence can change along a successional gradient, and how these two types of processes influence our ability to predict community assembly from functional traits. Finally, I presented how the results at the community-level can be used to study the ecosystem-level. The results of this thesis demonstrate that regional climatic variables strongly interact with local environmental variables in driving the local processes responsible for community assembly. Assessing the regional context is thus necessary in order to avoid erroneous interpretations of observed assembly patterns. Working with those two levels of environmental variation, important discrepancies were found between taxonomic and functional variations across communities, reflecting the importance of considering several aspects of biodiversity in order to understand community dynamics. The results also demonstrated that the assembly processes leading to functional convergence and divergence have a very different and predictable impact on the relationships between traits and species relative abundances, i.e. on our ability to predict community assembly from traits. Finally, these notions related to trait-environment relationships and to trait-based community assembly were used in a functional biogeography framework: It was possible to build maps of functional traits values in permanent grasslands across France using environmental variables. These maps then allowed predicting particular ecosystem properties. Thus, this work allowed illustrating some challenges that we are facing in using our knowledge in functional ecology to build sustainable conservation and exploitation plans for our ecosystems.

Understanding how temperature affects biological systems is a central question in ecology and evolutionary biology. Anthropogenic climate change adds urgency to this topic, as the demise or success of species under climate change is expected to depend on how temperature affects important aspects of organismal performance, such as growth, development, survival and reproduction. Rates of biological processes generally increase with increasing temperature up to some maximal temperature. Variation in the slope of the initial, rising phase has attracted considerable interest and forms the focus of this thesis. I explore variation in growth rate-temperature relationships over several levels of biological organization, both between and within species, over individuals’ lifetime, depending on the ecological context and in relation to important life history characteristics such as generation length and winter dormancy.       Specifically, I examine how a clade of temperate damselflies have adapted to their thermal environment along a 3,600 km long latitudinal transect spanning from Southern Spain to Northern Sweden. For each of six species, I sampled populations from close to the northern and southern range margin, as well from the center of the latitudinal range. I reared larvae in the laboratory at several temperatures in order to measure indiviudal growth rates. Very few studies of thermal adaptation have employed such an extensive sampling approach, and my finding reveal variation in temperature responses at several levels of organization.       My main finding was that temperature responses became steeper with increasing latitude, both between species but also between latitudinal populations of the same species. Additional genetic studies revealed that this trend was maintained despite strong gene flow. I highlight the need to use more refined characterizations of latitudinal temperature clines in order to explain these findings. I also show that species differ in their ability to acclimate to novel conditions during ontogeny, and propose that this may reflect a cost-benefit trade-off driven by whether seasonal transitions occur rapidly or gradually during ontogeny.       I also carried out a microcosm experiment, where two of the six species were reared either separately or together, to determine the interacting effects of temperature and competition on larval growth rates and population size structure. The results revealed that the effects of competition can be strong enough to completely overcome the rate-depressing effects of low temperatures. I also found that competition had stronger effects on the amount of variation in growth rates than on the average value.       In summary, my thesis offers several novel insights into how temperature affects biological systems, from individuals to populations and across species’ ranges. I also show how it is possible to refine our hypotheses about thermal adaptation by considering the interacting effects of ecology, life history and environmental variation.

The original aim of my diploma thesis was examination of fixed samples of cladocerans from the Daphnia longispina species complex from reservoirs Vír and Vranov for the presence of 4 groups of microparasites: microsporidia, oomycetes, the protozoan Caullerya mesnili, and the yeast Metschnikowia bicuspidata. The next aim was to determine the effect of parasites on Daphnia fecundity, and determination of their spatial and temporal distribution within reservoirs. From the total number 4452 of examined Daphnia females, however, only 56 individuals were infected. This number was not sufficient for the planned analyses. As I recorded for all examined individuals the clutch size, I thus dealt to a large extent with an alternative issue: the temporal and spatial variation of, and the influence of environmental factors on Daphnia fecundity. Both studied reservoirs are characteristic by canyon-shaped profile that allows formation of environmental gradients on the horizontal as well as vertical axis. The results confirm that reservoir identity, season, and location within the reservoir (or gradient of food supply) have all significant effects on fecundity. During my work I have encountered difficulties associated with determining microparazites from fixed zooplankton samples. The appendix section of my thesis...

Vulcões ativos na Antártica contrastam com a paisagem predominantemente gelada do continente. Eles fornecem condições únicas capazes de selecionar uma grande variedade de adaptações microbianas. A Ilha Deception localiza-se na região da Península Antártica e difere de outros vulcões antárticos especialmente pela influência marinha e temperaturas mais elevadas. Foram coletadas amostras de sedimentos associados a fumarolas e geleiras em dois sítios geotermais de Deception, com temperaturas variando entre 0°C a 98°C. Diferentes técnicas independentes de cultivo foram empregadas com o intuito de entender como as comunidades microbianas respondem as variações ambientais extremas produzidas pela atividade vulcânica. Os resultados indicaram que a co-ocorrência de arqueias hipertermófilas e suas adaptações com micro-organismos metabolicamente diversos adaptados a regiões geladas representa uma estrutura de comunidades única para ecossistemas antárticos. Este trabalho forneceu dados ineditos sobre questoes centrais de diversidade e adaptacao microbiana a ambientes geotermais polares. / Active volcanoes in Antarctica contrast with the predominately icy landscape. They harbor unique conditions capable to select an extreme range of microbial adaptations. Deception Island is located in the Antarctic Peninsula region and differs from other Antarctic volcanoes specially by its higher temperatures and marine influence. We collected sediment samples associated to active fumaroles and glaciers on two geothermal sites of Deception Island, with temperatures ranging from 0°C to 98°C. Different cultivation-indepedent techniques were used to understand how microbial communities respond to extreme environmental variations produced by volcanic activity. The results indicate that co-occurrence of hyperthermophiles and their specific adaptations with metabolically diverse cold-adapted micro-organisms represents a unique community structure for antarctic ecosystems. This study provided primordial data on central questions about microbial diversity and adaptation to polar geothermal environments.

Submitted by Erika Demachki (erikademachki@gmail.com) on 2014-09-23T21:19:16Z No. of bitstreams: 2 Peixoto, Franciele Parreira-Dissertação-2013.pdf: 995120 bytes, checksum: 365969ffce47a58af2a011eb0370ed04 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Jaqueline Silva (jtas29@gmail.com) on 2014-09-23T21:58:54Z (GMT) No. of bitstreams: 2 Peixoto, Franciele Parreira-Dissertação-2013.pdf: 995120 bytes, checksum: 365969ffce47a58af2a011eb0370ed04 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-09-23T21:58:54Z (GMT). No. of bitstreams: 2 Peixoto, Franciele Parreira-Dissertação-2013.pdf: 995120 bytes, checksum: 365969ffce47a58af2a011eb0370ed04 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2013-03-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Aim: To investigate global patterns of phylobetadiversity (PBD) in bats, with the purpose to better understand the mechanisms underlying current biodiversity patterns. We also aimed to use a metric that allows partitioning PBD into two components to distinguish the relative roles of local (e.g. lineage filtering) and regional processes (e.g. speciation) in shaping broad-scale patterns of PBD. Furthermore, we analyzed the distance-decay relationship of phylogenetic beta diversity to provide more information about factors that act in the PBD patterns. Location: global, delimited by biogeographic regions. Methods: Using the global distribution of bats and a supertree available for most species, we calculated PBD using the complement of phylosor index. We used a null model to test if two assemblages were more or less phylogenetically dissimilar than expected by chance. In addition, we decoupled PBD into turnover and nestednessresultant components, providing information about two factors that produce differences in assemblage phylogenetic composition. We also performed a Mantel analysis to analyze the distance-decay patterns of PBD and its two components. Results: The most striking difference in PBD was found between the Old and New World “phylogenetic composition”. We found the lowest values of PBD between adjacent regions (i.e., Neotropical/Neartic; Indo-Malay/Paleartic), revealing a strong geographical structure in PBD. These values were even lower when the turnover component was analyzed, demonstrating the differences in the role of regional processes in shaping regional diversity. On the other hand, we found out that for some adjacent regions (e.g., Afrotropical/Paleartic), the observed PBD was higher than expected by chance and comparatively different from expected by the distance decay relationship. This value remained high, even when we analyzed just the PBD turnover component. This demonstrates that although these regions are relatively close in space, there are other factors driving phylogenetic differences between them (e.g. an environmental barrier). Main conclusions: Our analyses revealed differences in the expected patterns of bat PBD among regions, suggesting that at broad scales, besides the effects of distance and geographic barriers, we also have to consider the importance of environmental gradients when studying the phylogenetic origin of bat assemblages. / A abordagem mais comum no uso de PD (diversidade filogenética) para conservação é selecionar locais com maior diversidade evolutiva. Essa estratégia parte do pressuposto de que locais com maior quantidade de PD indicam maior potencial para respostas evolutivas a mudanças ambientais futuras. No entanto, há um crescente debate sobre se as prioridades de conservação deveriam também ser voltadas para locais com baixo valor de PD, que podem representar centros de diversificação de espécies ou “berçários de diversidade”. Alguns trabalhos têm testado se os hotspots globais de biodiversidade, baseados em riqueza, também representam locais de desproporcional concentração de história evolutiva. Nós testamos aqui se os hotspots contêm mais, menos ou igual diversidade filogenética (PD) que o esperado por uma amostragem ao acaso de espécies em qualquer posição na filogenia, para a ordem Chiroptera. Buscamos responder qual a real contribuição de cada hotspot para a conservação de padrões e processos relacionados à diversidade filogenética. Nós utilizamos uma supertree disponível para a maioria das espécies da ordem, e dados de distribuição das espécies. Nós calculamos o PD para cada hotspot separadamente e utilizamos um modelo nulo para obter os valores esperados dado a riqueza. De 34 hotspots, apenas um apresentou maior PD do que o esperado, treze apresentaram valores menores e o restante valores iguais ao esperado. Nós demonstramos que a relação entre PD e riqueza varia entre regiões biogeográficas, de modo que não há como fazer generalizações acerca da contribuição dos hotspots para a conservação de diversidade evolutiva. De modo geral nossos resultados demonstram que devido ao fato da história evolutiva variar regionalmente, também devem ser estabelecidas as prioridades de conservação nessa escala.

Submitted by CARLA MARIA GOULART DE MORAES (carlagm) on 2015-05-07T14:18:15Z No. of bitstreams: 1 EriveltonTomazzoniGoncalves.pdf: 514129 bytes, checksum: 16d68cb85838c6e25971df9dbe3e7cf1 (MD5) / Made available in DSpace on 2015-05-07T14:18:15Z (GMT). No. of bitstreams: 1 EriveltonTomazzoniGoncalves.pdf: 514129 bytes, checksum: 16d68cb85838c6e25971df9dbe3e7cf1 (MD5) Previous issue date: 2011 / Nenhuma / A variação espacial da abundância das espécies pode ser determinada por uma série de causas históricas e ambientais. Visando a identificação de grupos florísticos e a sua relação com um conjunto de variáveis edáficas e climáticas (ambientais), do espaço geográfico (histórico) na estruturação da composição arbórea ao longo de formações ombrófilas e estacionais do extremo sul do bioma Mata Atlântica-Brasil, extraiu-se da literatura dados de composição e abundância da flora arbórea (Dap >9.5 cm), de 52 unidades amostrais com cerca de 1 ha de extensão. As comunidades foram caracterizadas através de sete variáveis climáticas, nove variáveis edáficas, três estruturais, além da diversidade Jost, altitude e suas coordenadas geográficas. Análises de ordenação foram empregadas para síntese dos descritores edafo-climáticos e características estruturais (PCA), na estruturação florística entre as parcelas (NMDS) e posterior correlação com os fatores ambientais. Através de análise de agrupamento hierárquico identificou-se grupos florísticos com utilização de espécies indicadoras, as quais foram classificadas quanto aos seus corredores migratórios. Com o uso do teste G, avaliou-se a independência das rotas históricas de dispersão com a composição das espécies indicadoras dos grupos florísticos. Fatores relacionados ao nicho das espécies, como a temperatura, precipitação total e secundariamente a drenagem, fertilidade e profundidade do solo são consistentes com a distribuição da composição arbórea. Do mesmo modo a longitude configurou-se um forte preditor desta variação florística formando um gradiente ao longo dos corredores de dispersão tropicais, bem como os grupos florísticos obtidos apresentaram espécies indicadoras dependentes dos seus contingentes de origem. Identificou-se um gradiente estrutural de variação de área basal, altura média e densidade entre Florestas Ombrófilas Mistas e Florestas Estacionais, ao contrário da diversidade. Os grupos florestais exibem diferentes graus de separação entre si. As Florestas Estacionais e a Floresta Ombrófila Densa formam um gradiente florístico contínuo ao longo de dois corredores migratórios de modo a consistir um bloco único. A Floresta Ombrófila Mista constitui um grupo dissimilar a estas formações com uma subdivisão marcada por espécies indicadoras exclusivas. Fatores ambientais e históricos são responsáveis tanto pela divisão entre grupos, que podem ser de forma abrupta ou gradativa, quanto pela diferenciação interna destas formações. / The spatial variation of species abundance can be determined by a series of historical and environmental causes. In order to identify floristic groups and their relationship to a set of soil and climatic variables (environmental), the geographic area (historical) in structuring the composition of trees along formations and seasonal rainforests from southern Atlantic forest, Brazil drew from the literature data on the composition and abundance of tree flora (DBH> 9.5 cm) of 52 sample units with about 1 ha in extension. The communities were characterized using seven climate, nine soil and three structural variables, as well as the Jost diversity, altitude and geographic coordinates. Ordination analysis were employed for the synthesis of soil, climatic and structural descriptors (PCA), the floristic structure between plots (NMDS) and subsequent correlation with environmental factors. Through hierarchical cluster analysis identified himself with floristic groups using indicator species, which were classified according to their migratory corridors. By using the G test, we evaluate the independence between the historic routes of dispersion and the composition of indicator species groups. Factors related to the niche of the species, such as temperature, total precipitation, and secondarily drainage, fertility and soil depth, are consistent with the distribution of the composition tree. Likewise the longitude is a strong predictor of floristic variation forming a gradient along the corridors of dispersal tropical flora, and the groups obtained were dependent indicator species of origin of their contingents Unlike the diversity, it was identified a structural gradient of basal area variation, average height and density between Araucaria forest and seasonal forests,. The forestry groups exhibit different degrees of separation between themselves. Seasonal forests and form a dense rain forest floristic gradient along two continuous migration corridors in order to consist a single block. The Araucaria forest is a group dissimilar to these formations with a subdivision marked by unique indicator species. Environmental and historical factors are responsible for both, the division between groups that may be abrupt or gradual, as well as the internal differentiation of these formations.

The influence of small gradients of altitude (0-500 meters) and order (1st to 4th) in the spatial distribution of mollusk communities was studied, based on 40 samples collected in a watershed of a temperate climate region, in Brazil. Richness was higher in lower ranges of altitude (0-100), and increased with the increase of orders, independently of altitude. However, composition and proportional abundance of species of the communities were not structured by the environmental gradients. The small influence of landscape factors on the spatiality of many abiotic factors, and the tolerance of many species to variations in the environmental factors analyzed determined these results. The proximity of the lower of altitudes with a transitional relief area, and the large width of the 4th order streams, which favored a higher number of ecological niches, provided higher complexity to the sites localized in these areas, allowing the occurrence of higher richness. The existence of patchy spatial structured pattern in good environmental conditions determined the absence of the proportional abundance of species. However, few landscape heterogeneity and possibly, interference of vertebrate vectors in the dispersion of the freshwater mollusks hinder to find clear patterns of spatial distribution. / A influência de pequenos gradientes de altitude (0-500 m) e ordem (1ª a 4ª) na distribuição espacial das comunidades de moluscos foi estudada, com base em 40 amostras coletadas em uma bacia hidrográfica, localizada em região de clima temperado, no Brasil. A riqueza foi maior nas faixas mais baixas de altitude (0-100), e aumentou com o aumento das ordens, independentemente da altitude. No entanto, a composição e abundância proporcional de espécies das comunidades não foram estruturadas pelos gradientes ambientais. A pequena influência dos fatores de paisagem analisados sobre a espacialidade de muitos fatores abióticos, e a tolerância de muitas espécies às variações dos fatores ambientais analisados, determinaram esses resultados. A localização das áreas de altitude mais baixas em uma região de transição de relevo e a maior largura dos rios de 4ª ordem, a qual favorece a existência de um maior número de nichos ecológicos, determinaram maior heterogenidade ambiental, permitindo a ocorrência de maior riqueza. A existência de locais com condições ambientais favoráveis a cada espécie em particular sem estruturação espacial refletiu-se na falta de estruturação das comunidades, quanto a abundância proporcional de espécies. No entanto, a poucas heterogeneidade espacial e, possivelmente, a interferência de vetores vertebrados na dispersão dos moluscos de água doce, impediram encontrar padrões mais claros de distribuição espacial.

Les formes de croissance végétales ont fait l'objet de nombreuses études mais elles constituent encore aujourd'hui un ensemble mal défini et sans cesse remis en question en raison de l'incohérence et de l'hétérogénéité des méthodes employées pour les analyser. Cette imprécision a des répercussions négatives lorsque les formes de croissance sont utilisées dans l'étude des communautés végétales et de leur dynamique. Nous avons tenté de remédier partiellement à cette situation en appliquant à certaines d'entre elles la méthode d'analyse architecturale initiée par Hallé et Oldeman dont l'efficacité s'est avérée remarquable pour la compréhension des formes arborescentes.L'étude était destinée 1) à interpréter ces formes de croissance et leur variabilité à l'aide des concepts architecturaux, 2) à suivre les changements des traits architecturaux au sein d'une communauté végétale se développant sur des talus, lors d'une chronoséquence et en fonction de différents gradients environnementaux. Nos observations montrent que 1) les concepts et les traits architecturaux sont applicables aux formes de croissance herbacées, suffrutescentes, et buissonnantes, 2) l'expression de la réitération est la source principale de variation structurale des formes de croissance aussi bien à l'échelle spécifique qu'infra-spécifique, 3) la valeur des traits architecturaux change au cours de la succession au sein de la communauté : les plantes vivant sur des talus jeunes ont une unité architecturale simple et réitèrent à la base alors que celles croissant sur des talus plus anciens ont des unités architecturales complexes et réitèrent de manière acrotone.Ces résultats nous conduisent à discuter de la valeur holistique de la méthode d'analyse architecturale pour la caractérisation des formes de croissance, des processus biologiques permettant de passer d'une forme de croissance à une autre et de l'intérêt pratique de l'utilisation des traits architecturaux dans l'étude des communautés végétales. / The growth forms of plant have been studied many times but they still represent nowadays a fuzzy set, often modified because of the inconsistency and the heterogeneity of the methods used in their analysis. This lack of precision often leads to an inconsistency of the use of the growth forms as a trait in the studies of plants communities and their dynamics. We tried to remedy this situation by applying to some of them the architectural analysis initiated by Hallé and Oldeman, which has been relevant for the understanding of the tree growth form.This study aimed to 1) interpret these growth forms and their variability by means of architectural concepts, 2) study architectural traits variation within roadsides plants communities during succession and in a mowing context. Our resultats show that 1) the architectural concepts and traits are applicable to herbaceous, treelet and bush grosth forms, 2) the expression of the reiteration is the main source of structural variation of growth forms at specific and intraspecific levels and 3) that traits values are changing during succession within the communities : Plants living at early successionnal stages got a simple architectural unit and reiterate at the base of the individual while plants living at late successional stages got complex architectural unit and acrotonic reiteration.These resultats lead us to discuss the holistic value of the architectural analysis for growth forms charaterisation, of biological processes allowing for growth form variation and the interest of the use of architectural traits in plant communities studies.

Vulcões ativos na Antártica contrastam com a paisagem predominantemente gelada do continente. Eles fornecem condições únicas capazes de selecionar uma grande variedade de adaptações microbianas. A Ilha Deception localiza-se na região da Península Antártica e difere de outros vulcões antárticos especialmente pela influência marinha e temperaturas mais elevadas. Foram coletadas amostras de sedimentos associados a fumarolas e geleiras em dois sítios geotermais de Deception, com temperaturas variando entre 0°C a 98°C. Diferentes técnicas independentes de cultivo foram empregadas com o intuito de entender como as comunidades microbianas respondem as variações ambientais extremas produzidas pela atividade vulcânica. Os resultados indicaram que a co-ocorrência de arqueias hipertermófilas e suas adaptações com micro-organismos metabolicamente diversos adaptados a regiões geladas representa uma estrutura de comunidades única para ecossistemas antárticos. Este trabalho forneceu dados ineditos sobre questoes centrais de diversidade e adaptacao microbiana a ambientes geotermais polares. / Active volcanoes in Antarctica contrast with the predominately icy landscape. They harbor unique conditions capable to select an extreme range of microbial adaptations. Deception Island is located in the Antarctic Peninsula region and differs from other Antarctic volcanoes specially by its higher temperatures and marine influence. We collected sediment samples associated to active fumaroles and glaciers on two geothermal sites of Deception Island, with temperatures ranging from 0°C to 98°C. Different cultivation-indepedent techniques were used to understand how microbial communities respond to extreme environmental variations produced by volcanic activity. The results indicate that co-occurrence of hyperthermophiles and their specific adaptations with metabolically diverse cold-adapted micro-organisms represents a unique community structure for antarctic ecosystems. This study provided primordial data on central questions about microbial diversity and adaptation to polar geothermal environments.