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[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples [Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiples; International audience; Resilience in river ecosystems requires that organisms must persist in the face of highly dynamic hydrological and geomorphological variations. Disturbance events such as floods and droughts are postulated to shape life history traits that support resilience, but river management and conservation would benefit from greater understanding of the emergent effects in communities of river organisms. We unify current knowledge of taxonomic‐, phylogenetic‐, and trait‐based aspects of river communities that might aid the identification and quantification of resilience mechanisms. Temporal variations in river productivity, physical connectivity, and environmental heterogeneity resulting from floods and droughts are highlighted as key characteristics that promote resilience in these dynamic ecosystems. Three community‐wide mechanisms that underlie resilience are (a) partitioning (competition/facilitation) of dynamically varying resources, (b) dispersal, recolonization, and recruitment promoted by connectivity, and (c) functional redundancy in communities promoted by resource heterogeneity and refugia. Along with taxonomic and phylogenetic identity, biological traits related to feeding specialization, dispersal ability, and habitat specialization mediate organism responses to disturbance. Measures of these factors might also enable assessment of the relative contributions of different mechanisms to community resilience. Interactions between abiotic drivers and biotic aspects of resource use, dispersal, and persistence have clear implications for river conservation and management. To support these management needs, we propose a set of taxonomic, phylogenetic, and life‐history trait metrics that might be used to measure resilience mechanisms. By identifying such indicators, our proposed framework can enable targeted management strategies to adapt river ecosystems to global change.

International audience; To quantify the relative contributions of local community assembly processes versus γ‐diversity to β‐diversity, and to assess how spatial scale and anthropogenic disturbance (i.e. nutrient enrichment) interact to dictate which driver dominates. Location: France and the United States. Time period: 1993 - 2011. Major taxa studied: Freshwater stream diatoms. Methods: β‐ diversity along a nutrient enrichment gradient was examined across multiple spatial scales. β‐ diversity was estimated using multi‐site Sørensen dissimilarity. We assessed the relative importance of specialists versus generalists using Friedley coefficient, and the contribution of local community assembly versus γ‐ diversity to β‐ diversity across spatial scales, with a null model. Finally, we estimated the response of β‐ diversity to environmental and spatial factors by testing the correlations between community, environmental and geographical distance matrices with partial Mantel tests. Results: β‐ diversity generally increased with spatial scale but the rate of increase depended on nutrient enrichment level. β‐diversity decreased significantly with increasing nutrient enrichment level due to the loss of specialist species. Local assembly was an important driver of β‐ diversity especially under low nutrient enrichment. Significant partial Mantel correlations were observed between diatom β‐ diversity and pure environmental distances under these conditions, highlighting the role of species sorting in local assembly processes. Conversely, in heavily enriched sites, only spatial distances were significantly correlated with β‐ diversity, which indicated a substantial role of dispersal processes. Main conclusions: Nutrient concentration mediated the expected increase in β‐diversity with spatial scales. Across spatial scales, β‐ diversity was more influenced by local assembly processes rather than by γ‐diversity. Nutrient enrichment was associated with an overall decline in diatom β‐ diversity and a shift in assembly processes from species sorting to dispersal, notably due to the elimination of some specialists and their subsequent replacement by generalists.

International audience; The interaction of land use with local versus regional processes driving biological homogenization (β-diversity loss) is poorly understood. We explored: (a) stream β‐diversity responses to land cover (forest versus agriculture) in terms of physico‐chemistry and physicochemical heterogeneity; (b) whether these responses were constrained by the regional species pool, i.e. γ diversity, or local assembly processes through local (α) diversity; (c) whether local assembly operated through the regional species abundance distribution (SAD) or intraspecific spatial aggregation; and (d) the dependence on body size, dispersal capacity and trophic level (producer versus consumer).

In the era of the Anthropocene, environmental change is accelerating biodiversity loss across ecosystems on Earth, among which freshwaters are likely the most threatened. Different biodiversity facets in the freshwater realm suffer from various environmental changes that jeopardize the ecosystem functions and services important for humankind. In this work we examine how environmental changes (e.g., climate change, eutrophication, or invasive species) affect trait-based, functional, and phylogenetic diversity of biological communities. We first developed a simple conceptual model of the possible relationships between environmental change and these three diversity facets in freshwaters and, secondly, systematically reviewed articles where these relationships had been investigated in different freshwater ecosystems. Finally, we highlighted research gaps from the perspectives of organisms, ecosystems, stressors, and geographical locations. Our conceptual model suggested that both natural factors and global change operating at various spatial scales influence freshwater community structure and ecosystem functioning. The relationships between biodiversity and environmental change depend on geographical region, organism group, spatial scale, and environmental change gradient length. The systematic review revealed that environmental change impacts biodiversity patterns in freshwaters, but there is no single type of biodiversity response to the observed global changes. Natural stressors had different, even contradictory, effects (i.e., multiple, negative, and positive) on biodiversity compared with anthropogenic stressors. Anthropogenic stressors more often decreased biodiversity, although eutrophication and climate change affected freshwater ecosystems in a complex, more multi-dimensional way. The research gaps we identified were related, for example, to the low number of community-based biodiversity studies, the lack of information on true phylogenies for all freshwater organism groups, the missing evaluations whether species traits are phylogenetically conserved, and the geographical biases in research (i.e., absence of studies from Africa, Southern Asia, and Russia). We hope that our review will stimulate more research on the less well-known facets and topics of biodiversity loss in highly vulnerable freshwater ecosystems.

International audience; Niche conservatism, whereby species niche characteristics are conserved over space and time, is an important cause for large-scale species distributions and diversity gradients on Earth. Dispersal mechanisms are expected to have a strong effect on niche conservatism, considering that high dispersal rate may prevent local adaptation and favor niche conservatism. In freshwater ecosystems, diatoms are usually recognized as cosmopolitan species, due to low dispersal limitation and high reproductive rates. However, the extent to which niche characteristics of diatoms are conserved across space has rarely been tested and should give interesting insights for the understanding of their biogeographic distribution. To address this question, we implemented species distribution modeling and analyses of species niche breadths and optima. Species distribution models (SDMs) along environmental and climatic gradients were developed with data from the US and then tested with datasets from France, Finland, New Zealand, Antilles and La R ́eunion islands. Given that the US SDMs poorly predicted the species distributions in other regions, we concluded that diatoms do not appear to exhibit niche conservatism. Weak correspondence of niche optima and niche breadths in one region with the respective species properties in another region further indicated a general lack of niche conservatism. Analyses of species differing in occupancy (i.e., core vs. satellite species) and traits (i.e., diatom ecological guilds) further confirmed that niche conservatism was also weak across functional groups. Although diatoms species are considered to be generally dispersal-unlimited, our results indicate that their dispersal rate may be more moderate than previously thought. Finally, the capacity to adapt locally to environmental and climatic conditions may allow diatoms to better cope with global environmental changes

International audience; This is the first inter-continental comparative assessment of diatom richness and species abundance distribution (SAD) along spatial, climatic, and water chemistry gradients using stream data from the US and Finland. We tested a number of hypotheses about the causes of variability in richness and by extension, the SAD, including the metabolic theory, the species-energy, the more individuals, the climatic variability, and the climatic tolerance hypotheses. We found no support for any of these concepts, given that the relationships of richness with explanatory variables were non-existent, weak or unexpected. Diatom richness and the SAD responded more strongly to climatic variability, climatic extremes, and water chemistry, especially nutrient levels, than to mean temperature. A consequence of the weak energy dependence was a non-linear latitudinal gradient of richness in both countries, and a non-linear latitudinal gradient of the SAD in the US. The SAD was not entirely driven by richness but displayed distinct responses to spatial, climatic, and water chemistry factors, indicating that the environment had complementary effects on richness and the SAD. This emphasizes the utility of the SAD for ecological research.

International audience; Understanding the mechanisms that drive beta diversity, an important aspect of regional biodiversity, remains a key ecological question. Beta diversity and its components can provide an insight into the processes generating regional biodiversity patterns. We tested whether environmental filtering or dispersal related processes predominated along the stream watercourse by analysing the responses of taxonomic and functional diatom beta diversity to environmental and spatial factors. We examined the variation of total beta diversity and its components (turnover and nestedness) in benthic diatom species and ecological guilds (motile, planktonic, low- and high profile) with respect to watercourse position (up-, mid-, and downstream) in 2182 sites throughout France. We tested the effects of pure environmental and pure spatial factors on beta diversity with partial Mantel tests. Environmental factors included eight physico-chemical variables, while geographical distances between sites were used as spatial factors. We also correlated alpha and gamma diversity, and the degree of nestedness (NODF metric) with environmental variables. Total beta diversity and its turnover component displayed higher values upstream than mid- and downstream. The nestedness component exhibited low values, even when NODF values increased from up- to downstream. Pure environmental factors were highly significant for explaining total beta diversity and turnover regardless of watercourse position, but pure spatial factors were mostly significant mid- and downstream, with geographical distance being positively correlated with beta diversity. Across sites, nutrient enrichment decreased turnover but increased the degree of nestedness. Motile and low profile diatoms comprised the most abundant guilds, but their beta diversity patterns varied in an opposite way. The lowest guild beta diversity was observed upstream for low profile species, and downstream for motile species. In conclusion, environmental filtering seemed to play a major role in structuring metacommunities irrespective of site watercourse position. Filtering promoted strong turnover patterns, especially in disconnected upstream sites. The greater role of spatial factors mid- and downstream was consistent with mass effects rather than neutral processes because these sites had lower total beta diversity than upstream sites. Motile species were most strongly affected by mass effects processes, whereas low profile species were primarily influenced by environmental conditions. Collectively, these findings suggest that partitioning of total beta diversity into its components and the use of diatom ecological guilds provide a useful framework for assessing the mechanisms underlying the metacommunity patterns along the stream watercourse.

Aim: Understanding variation in biodiversity typically requires consideration of factors operating at different spatial scales. Recently, ecologists and biogeographers have recognized the need of analysing ecological communities in the light of multiple facets including not only species‐level information but also functional and phylogenetic approaches to improve our understanding of the relative contribution of processes shaping biodiversity. Here, our aim was to disentangle the relative importance of environmental variables measured at multiple levels (i.e., local, catchment, climate, and spatial variables) influencing variation in macroinvertebrate beta diversity facets (i.e., species, traits, and phylogeny) and their components (i.e., replacement and abundance difference) in boreal streams. Taxon: Aquatic macroinvertebrates Location: Western Finland Methods: A total of 105 streams were sampled in western Finland, encompassing a geographical extent over 500 km. We analysed variation in the different beta diversity facets and components using distance‐based redundancy analysis and associated variation partitioning procedures. We modelled spatial structures using distance‐based Moran eigenvector maps. Results: We found that the relative influence of explanatory variables on each diversity facet and component revealed relatively similar patterns. Our main finding was that local environmental and spatial variables generally contributed most to the total explained variability in all facets and components of beta diversity, whereas catchment and climate variables explained less variation in the beta diversity facets at the spatial scale considered in this study. Main conclusions: Different facets of beta diversity were mainly influenced by local environmental variables and spatial structuring, likely acting through deterministic and stochastic pathways respectively. Identifying the ecological variables and mechanisms that drive variation in beta diversity may be used to guide the conservation and restoration efforts for biodiversity under global change.

International audience; The taxonomic composition of a community results from an interplay of regional (dispersal and species pool) and local (species sorting) processes and a key question in community ecology is to understand the relative influence of these processes along gradients. β-diversity might represent a potential key to contribute to this question. Diatoms play a central role in aquatic ecosystems and more and more researchers focused their attention on finely understanding the mechanisms that govern their community assembly. It is now accepted that the biogeographical distribution of stream diatoms depends mainly on environmental heterogeneity, anthropogenic impacts and dispersal-related processes. Today we only have a limited understanding of how species sorting and dispersal-related processes interact to affect diatom species distribution, and of how these potential interactions are modulated by the geographic scale (environmental heterogeneity) and by anthropogenic stressors. In this study, we explored the β-diversity evolution of stream diatom communities from local to global scales, across different levels of nutrient enrichment, with a dataset encompassing 3000 samples from France and the US. According to the arguments developed before, we tested four main hypotheses: (1) β-diversity in diatom communities increases from local to larger scales, as environmental heterogeneity increases. (2) β-diversity in natural conditions is always higher than β-diversity in communities under high nutrient levels, regardless of scale. (3) In unimpacted conditions, β-diversity is mainly controlled by species-sorting and the relative contribution of this process is expected to increase from local to larger scales. (4) In impacted conditions, species-sorting influence should be tenuous and constant across spatial scales, allowing to detect the signal of dispersal-related processes. Our results highlight that beta-diversity increases from local to global scales and is always higher in unimpacted conditions than in impacted ones. After extracting the effect of gamma diversity with null models, we detected significant changes in the relative impact of local community assembly processes vs. regional processes according to the scale of observation. The relative importance of species-sorting increases simultaneously with the scale and this phenomenon is particularly pronounced for unimpacted environments. In impacted conditions, species-sorting influence is weakened and we detected the signal of dispersal-related processes. Our results generate novel insights into the main mechanisms driving beta-diversity patterns.

International audience; The taxonomic composition of a community results from an interplay of regional (dispersal and species pool) and local (species sorting) processes and a key question in community ecology is to understand the relative influence of these processes along gradients. β-diversity might represent a potential key to contribute to this question. Diatoms play a central role in aquatic ecosystems and more and more researchers focused their attention on finely understanding the mechanisms that govern their community assembly. It is now accepted that the biogeographical distribution of stream diatoms depends mainly on environmental heterogeneity, anthropogenic impacts and dispersal-related processes. Today we only have a limited understanding of how species sorting and dispersal-related processes interact to affect diatom species distribution, and of how these potential interactions are modulated by the geographic scale (environmental heterogeneity) and by anthropogenic stressors. In this study, we explored the β-diversity evolution of stream diatom communities from local to global scales, across different levels of nutrient enrichment, with a dataset encompassing 3000 samples from France and the US. According to the arguments developed before, we tested four main hypotheses: (1) β-diversity in diatom communities increases from local to larger scales, as environmental heterogeneity increases. (2) β-diversity in natural conditions is always higher than β-diversity in communities under high nutrient levels, regardless of scale. (3) In unimpacted conditions, β-diversity is mainly controlled by species-sorting and the relative contribution of this process is expected to increase from local to larger scales. (4) In impacted conditions, species-sorting influence should be tenuous and constant across spatial scales, allowing to detect the signal of dispersal-related processes. Our results highlight that beta-diversity increases from local to global scales and is always higher in unimpacted conditions than in impacted ones. After extracting the effect of gamma diversity with null models, we detected significant changes in the relative impact of local community assembly processes vs. regional processes according to the scale of observation. The relative importance of species-sorting increases simultaneously with the scale and this phenomenon is particularly pronounced for unimpacted environments. In impacted conditions, species-sorting influence is weakened and we detected the signal of dispersal-related processes. Our results generate novel insights into the main mechanisms driving beta-diversity patterns.

International audience; Le mécanisme de dispersion est un des mécanismes clés à avoir un effet sur la répartition des individus, des populations et des communautés dans la nature. Malgré des progrès au niveau de l'étude des espèces uniques, il a été notoirement difficile de représenter le mécanisme de dispersion quant aux métacommununautés multispécifiques, où ce mécanisme a potentiellement des répercussions marquées sur la structure communautaire au-delà de celles des conditions environnementales locales. La dispersion devrait ainsi être directement intégrée tant au niveau de la recherche fondamentale qu'appliquée, et ce, au moyen de variables substitutives. Ici, nous passons en revue l'utilisation de variables substitutives dans la recherche actuelle des métacommunautés, suggérons de nouvelles variables substitutives et discutons comment les variables substitutives pourraient être utilisées au niveau de la modélisation de communautés, particulièrement concernant les systèmes d'eau douce. Nous suggérons que tandis que des variables substitutives traditionnelles peuvent toujours être utiles, les variables substitutives autrefois utilisées dans la géographie du transport peuvent fournir de nouveaux renseignements utiles en ce qui concerne la structure de communautés de systèmes d'eau douce. Nous suggérons aussi que comprendre l'utilité de telles variables substitutives au niveau de la dispersion dans les métacommunautés soit de la plus haute importance dans beaucoup de domaines appliqués, comme l'évaluation biologique d'eau douce, la planification de conservation et la recherche en matière de reconstitution du milieu naturel. Ces domaines de recherche n'ont souvent pas tenu compte de la dynamique spatiale et se sont concentrés surtout sur des conditions environnementales locales et des changements afférents. Pourtant, les conclusions de ces études appliquées peuvent changer considérablement si le mécanisme de dispersion est pris en compte.

International audience; A central question for ecologists is to understand processes structuring species assemblages. Environmental and dispersal-related processes interplay, leading to potential species replacement (turnover) or species loss (nestedness) patterns. However, the relative contribution of these processes is still unclear, especially in freshwater ecosystems. Here, we examined the relative influence of environmental filtering, mass effects and dispersal limitations along the watercourse on diatom taxonomic and functional beta diversity. We used a random sample selection to examine the variation of nestedness and turnover components according to watercourse position of 2194 sites throughout France. We tested the variation of taxonomic and functional beta-diversity explained by pure environmental and spatial factors and correlated beta diversity values to environmental variables indicative of anthropogenic effects. The turnover component of beta diversity was largely predominant, while decreasing from up- to downstream following the total beta diversity dynamic. Environmental conditions seemed to exert a major influence on beta-diversity patterns, in particular anthropogenic factors tended to homogenize communities whatever the position along the watercourse. The influence of spatial factors increased along the longitudinal gradient. The functional beta diversity significantly changed along the watercourse and its relation with pure environment and spatial factors appeared to be guild dependent. We concluded that environmental filtering has a major influence in structuring diatoms metacommunities regardless of the watercourse position of the sites. The increasing influence of spatial factors mid- and downstream associated with results of taxonomic and functional compositions also suggest an important role of mass-effect processes at the end of the longitudinal gradient.

Metacommunity patterns and underlying processes in aquatic organisms have typically been studied within a drainage basin. We examined variation in the composition of six freshwater organismal groups across various drainage basins in Finland. We first modelled spatial structures within each drainage basin using Moran eigenvector maps. Second, we partitioned variation in community structure among three groups of predictors using constrained ordination: (1) local environmental variables, (2) spatial variables, and (3) dummy variable drainage basin identity. Third, we examined turnover and nestedness components of multiple-site beta diversity, and tested the best fit patterns of our datasets using the “elements of metacommunity structure” analysis. Our results showed that basin identity and local environmental variables were significant predictors of community structure, whereas within-basin spatial effects were typically negligible. In half of the organismal groups (diatoms, bryophytes, zooplankton), basin identity was a slightly better predictor of community structure than local environmental variables, whereas the opposite was true for the remaining three organismal groups (insects, macrophytes, fish). Both pure basin and local environmental fractions were, however, significant after accounting for the effects of the other predictor variable sets. All organismal groups exhibited high levels of beta diversity, which was mostly attributable to the turnover component. Our results showed consistent Clementsian-type metacommunity structures, suggesting that subgroups of species responded similarly to environmental factors or drainage basin limits. We conclude that aquatic communities across large scales are mostly determined by environmental and basin effects, which leads to high beta diversity and prevalence of Clementsian community types.

International audience; A central question for ecologists is to understand processes patterning species assemblages, considering the relative importance of environmental gradients, biotic interactions or species dispersal abilities. Although it has been suggested that micro-organisms are everywhere and that only environmental variables selects, numerous studies have since showed that diatoms species could also be dispersal limited. Here we propose a (not exhaustive) overview of the main processes patterning diatom metacommunities, with illustrations from results we recently obtained. In particular, we tried to highlight processes related to species dispersal abilities, from an intercontinental dataset (US, Finland, France including tropical islands). In a second time, as particular beta-diversity patterns arise from such mechanisms, we tried to discriminate turnover and nestedness components from the total community dissimilarity and their relationships with environmental conditions.

International audience; Species co-occurrence patterns give significant insights into the processes shaping communities. While biotic interactions have been widely studied using co-occurrence analyses in animals and larger plants, studies about co-occurrences among micro-organisms are quite rare. We examined stream diatom co-occurrences and nestedness in France, and tested the significance of the patterns with a set of random and environmentally constrained null models. Real communities showed a higher segregation than the most conservative random null models, but a general aggregation of co-occurrences when compared to environmentally constrained null models. We did not find any evidence of limiting similarity between co-occurring species. Aggregations of species co-occurrences were associated with the high levels of nestedness. Altogether, these results suggested that biotic interactions were not structuring co-occurrences of diatom species at our study scale. Instead, the patterns were more likely to be related with colonization patterns, mass-effect, and local dynamics of diatom biofilms. We further highlight that the association of random and environmentally constrained null models may give realistic insights into the co-occurrence patterns of microbial communities data.

International audience; Different processes explain community biodiversity, considering the relative importance of environmental gradients, biotic interactions or species dispersal capacities. From those mechanisms arise particular beta-diversity patterns, such as turnover and nestedness. If river benthic diatoms are deeply studied, and in particular their relationships with environmental parameters, little is known about their pure spatial distribution patterns. Research still needs to focus on two points: the extent to which those patterns are i) related to the observational scale, and ii) influenced by natural or anthropogenic stress. Here, we propose to tackle these key questions from a large French dataset, gathering 2748 diatom samples collected from 1992 to 2009. In particular, we try to discriminate turnover (Sorensen index) and nestedness (NODF index) patterns from the total community dissimilarity and their relative predominance according to the river Stralher ranks, at different scales (hydroecoregion, biotype, whole hydrosystem). Results are systematically compared to the one obtained with random communities from null models. The potential role of different environmental parameters in the determination of the prevailing pattern is tested with mixed models. Main results show that at each scale of observation, turnover is predominant at low Stralher ranks (in particular in mountainous regions), while nestedness becomes higher downsteam. Natural stressors (mainly related to the altitudinal context) are clearly correlated with turnover. At higher ranks, a loss of specialist taxa is observed, leading to typical nestedness patterns. Anthropogenic parameters, in particular higher orthohosphates concentrations, are significantly related to this pattern. In conclusion, our results tend to support the hypothesis of Gutiérrez-Canova et al. (2013), stating that natural and anthropogenic parameters generate different spatial patterns in community beta-diversity. This may have implications for conservation strategies, which should for example focus on different natural locations when turnover prevails.

Contingency planning is a significant challenge when dealing with rarely occurring cases. First of all, the situation related threats can be difficult to identify. Moreover, it is difficult to conclude what happens when multiple threats occur simultaneously. In this paper we introduce the idea of an application which allows seamless cooperation between many experts. In this paper we describe a computer based simulation application which is designed to support contingency planning - having resources available - in extreme winter condition. First we introduce the background of the simulation - sparsely populated areas in Northern Finland where long distances and extremely cold weather can make disturbance situations even more difficult to be normalized by authorities. Secondly we present the tools that are used to build up the application. Finally, we discuss what benefits the application offers for the authorities, preparedness planning and society.

International audience; Les diatomées benthiques ont, jusqu'à très récemment, été considérées comme des micro-organismes très ubiquistes en raison de leur petite taille et de leur forte densité de population. Selon cette théorie de «tout est partout, et l’environnement sélectionne», les conditions locales du milieu sont supposées jouer un rôle prépondérant dans l'assemblage local de ces espèces. Cependant, de récentes études tendent à montrer que des phénomènes plus stochastiques, liés aux processus régionaux et historiques, jouent également un rôle important dans la structure de ces communautés. Nous proposons ici d'étudier les patrons globaux d'assemblage des espèces de diatomées benthiques d'un point de vue taxonomique et fonctionnel à une échelle mondiale. Nous avons pour ceci utilisé des relevés taxonomiques effectués dans les rivières de France, de Finlande, des Etats-Unis, de Nouvelle-Zélande, des Antilles et de l'île de la Réunion, associés à un ensemble de variables environnementales locales, climatiques et spatiales. La composition taxonomique et fonctionnelle a été étudiée par des NMS («Non-metric multidimensional scaling») et des analyses canoniques de redondance (RDA) couplées à une partition de variance. Les richesses spécifiques et fonctionnelles ont également été traitées par des modèles linéaires à effets mixtes utilisant les variables environnementales climatiques et spatiales comme variables explicatives. La composition taxonomique est significativement différente entre les régions mais la composition fonctionnelle est beaucoup plus homogène, à l'exception des sites de Finlande qui montrent une communauté davantage composée d’espèces acidiphiles. Toutes les variables locales, climatiques et spatiales sont significativement associées à la composition taxonomique et fonctionnelle, mais le pH est la variable ressortant comme étant la plus importante. La partition de variance montre néanmoins que bien que les variables locales expliquent principalement la composition spécifique et fonctionnelle, les variables climatiques et spatiales jouent également un rôle important. Toutes les variables environnementales, climatiques et spatiales permettent également d'expliquer les richesses spécifiques et fonctionnelles. Ces résultats indiquent un rôle non négligeable des processus régionaux et historiques dans l'assemblage local des espèces. La composition fonctionnelle plus uniforme entre les régions suggère une forte réponse individuelle des espèces et l'influence de processus micro-évolutifs responsables d'une certaine redondance fonctionnelle des communautés.

National audience; Visant à restaurer la continuité écologique à l'échelle nationale, les trames vertes et bleues sont une mesure phare du grenelle de l'environnement et une composante essentielle de la politique environnementale française. Cette notion de trame verte et bleue est le résultat d'études basées sur des macro-organismes (visibles à l'oeil nu) qui ont démontré la sensibilité des populations de plantes ou d'animaux isolées dans un contexte de régression des habitats naturels. Certaines théories de biogéographie considèrent que, du fait de fortes capacités de dispersion et de gigantesques tailles de populations, les espèces de micro-organismes sont présentes sans restriction dans tous les environnements permettant leur développement. Or nos études à l'échelle de la France sur les communautés de diatomées benthiques montrent que celles-ci présentent une forte structure spatiale, liée aux dynamiques de dispersion et de colonisation des différentes espèces (Thèse de Marius Bottin, 2012). Les biofilms diatomiques sont donc affectés eux-aussi par ces notions de continuité écologique et de dynamiques de colonisation. En plus de la connaissance nécessaire pour comprendre l'impact de la restauration d'une continuité écologique sur le maintien de la biodiversité dans les biofilms, les diatomées apparaissent aussi comme un modèle biologique intéressant pour l'étude de ces phénomènes. En effet, ces organismes présentent de très rapides cycles de vie permettant l'élaboration de tests expérimentaux à l'échelle de plusieurs générations, et de très larges bases de données existent, utilisables pour la description de l'effet de la connectivité dans les milieux naturels. Des études à Irstea ont déjà eu lieu qui pourrait permettre d'alimenter les réflexions sur la trame bleue. Une de ces études a montré que la dynamique de récupération structurelle et fonctionnelle (potentiel photosynthétique) de communautés après une contamination toxique était facilitée par la migration d'espèces (Lambert et al, 2012 ; Morin et al, 2012). Une autre étude a montré que les dynamiques de colonisation à l'échelle de la France semblaient se structurer grâce à des communautés sources, alimentant et influençant fortement les communautés environnantes (Thèse de Marius Bottin, 2012). Nous discuterons de l'implication de ces résultats dans le cadre de la trame verte et bleue, ainsi que des éventuelles études complémentaires à conduire sur les biofilms diatomiques.

In this article, a cognitive management framework is proposed for ensuring exploitation of the Future Internet of Things (FIoT). Cognitive systems offer self-x and learning. A cognitive system has the ability to dynamically select its behavior through self-management/awareness functionality, taking into account information and knowledge on the context of the operations as well as policies and including the generation of the context itself. The framework is based on the principle that any real world object and any digital object that is available, accessible, observable or controllable can have a virtual representation in the Future Internet, which is called Virtual Object (VO). Basic VOs can be composed in a more sophisticated way by forming Composite VOs (CVOs), which provide services to high-level applications and end-users. The described paradigm is applied to various applications scenarios: smart home, smart office, smart city and smart business. This paper presents some background in IoT, identifies the requirements and challenges, and sets the directions that should be followed. © 2012 SCPE.

International audience; Depuis une quinzaine d’années, les diatomées sont utilisées en routine afin d'évaluer l'état écologique des hydrosystèmes. Toutefois les indices diatomiques classiques ne permettent pas de diagnostiquer finement les différents types de pollution, et intègrent mal les variations naturelles, temporelles ou spatiales des communautés. Le but de travail est d'utiliser les traits biologiques (résistance, résilience) et écologiques (affinités pour l’habitat) des diatomées afin de tester leur pertinence dans un diagnostic de qualité écologique.