Stream diatom biodiversity in islands and continents—A global perspective on effects of area, isolation and environment

Aim The species-area relationship (SAR) is one of the most distinctive biogeographic patterns, but global comparisons of the SARs between island and mainland are lacking for microbial taxa. Here, we explore whether the form of the SAR and the drivers of species richness, including area, environmental heterogeneity, climate and physico-chemistry, differ between islands and similarly sized areas on mainland, referred to as continental area equivalents (CAEs). Location Global. Taxon Stream benthic diatoms. Methods We generated CAEs on six continental datasets and examined the SARs of CAEs and islands (ISAR). Then, we compared CAEs and islands in terms of total richness and richness of different ecological guilds. We tested the factors contributing to richness in islands and CAEs with regressions. We used structural equation models to determine the effects of area versus environmental heterogeneity, climate and local conditions on species richness. Results We found a non-significant ISAR, but a significant positive SAR in CAEs. Richness in islands was related to productivity. Richness in CAEs was mainly dependent on area and climate, but not directly on environmental heterogeneity. Species richness within guilds exhibited inconsistent relationships with island isolation and area. Main conclusions Ecological and evolutionary processes shaping diatom island biogeography do not depend on area at the worldwide scale probably due to the presence of distinct species pool across islands. Conversely, area was an important driver of diatom richness in continents, and this effect could be attributed to dispersal. Continents had greater richness than islands, but this was a consequence of differences in environmental conditions such as specific island climatic conditions. We stress the need for more island data on benthic diatoms, particularly from archipelagos, to better understand the biogeography of this most speciose group of algae

Dissolving the digital divide : Creating coherence in young people's social ecologies of learning and identity building

This chapter discusses current research on educational efforts to connect school learning with young people’s digital practices in- and out-of-school. Instead of focusing on divides between in-school and out-of-school learning or between the “digital generation” and other age groups, in this chapter we discuss what recent research says about the ways in which school can become a space in which young people’s digital practices can transformatively converge with schooling, and how this convergence is related to their learning and identity building. We begin our narrative reflection of current research by focusing on the myth of digital natives. Next, we will conceptualize recent efforts to researching and understanding young people’s engagement, learning and identity building across sites and contexts. We will then turn to illuminating some key rationales of current educational research on creating convergence in young people’s social ecologies via the use of digital technologies and media. We conclude our reflections by pointing out that although there are some promising findings on how digital technologies and media can create convergence in young people’s engagement and learning across sites and contexts, less research attention is given to young people’s personal sense-making and self-making mediated by their digital practices, and how formal education could build on those practices for academic, vocational and/or civic ends.Peer reviewe

The three Rs of river ecosystem resilience : Resources, recruitment, and refugia

This review article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived VersionResilience 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

Field-study science classrooms as positive and enjoyable learning environments

We investigated differences between field-study classrooms and traditional science classrooms in terms of the learning environment and students’ attitudes to science, as well as the differential effectiveness of field-study classrooms for students differing in sex and English proficiency. A modified version of selected scales from the What Is Happening In this Class? questionnaire was used to assess the learning environment, whereas students’ attitudes were assessed with a shortened version of a scale from the Test of Science Related Attitudes. A sample of 765 grade 5 students from 17 schools responded to the learning environment and attitude scales in terms of both their traditional science classrooms and classrooms at a field-study centre in Florida. Large effect sizes supported the effectiveness of the field-studies classroom in terms of both the learning environment and student attitudes. Relative to the home school science class, the field-study class was considerably more effective for students with limited English proficiency than for native English speakers

Variable Stars in Galactic Globular Clusters

Based on a search of the literature up to May 2001, the number of known variable stars in Galactic globular clusters is approximately 3000. Of these, more than 2200 have known periods and the majority (approximately 1800) are of the RR Lyrae type. In addition to the RR Lyrae population, there are approximately 100 eclipsing binaries, 120 SX Phe variables, 60 Cepheids (including population II Cepheids, anomalous Cepheids and RV Tauri) and 120 SR/red variables. The mean period of the fundamental mode RR Lyrae variables is 0.585, for the overtone variables it is 0.342 (0.349 for the first-overtone pulsators and 0.296 for the second-overtone pulsators) and approximately 30% are overtone pulsators. These numbers indicate that about 65% of RR Lyrae variables in Galactic globular clusters belong to Oosterhoff type I systems. The mean period of the RR Lyrae variables in the Oosterhoff type I clusters seems to be correlated with metal abundance in the sense that the periods are longer in the more metal poor clusters. Such a correlation does not exist for the Oosterhoff type II clusters. Most of the Cepheids are in clusters with blue horizontal branches.Comment: 45 pages, 10 figures, to be published in AJ November 200

Patrons globaux structurant la composition des communautés de diatomées benthiques

International audienceTo examine species and trait composition in stream diatoms along environmental, climatic and spatial radients and to ascertain if the use of different levels of biological organization is beneficial for investigating global environmental changes and the role of history in structuring communities. Global cover with datasets from the Antilles, France, Finland, New Zealand, La Reunion and the United States. We related diatom species composition, guild composition, total richness and richness across guilds to environmental, climatic and spatial variables. We used non-metric multidimensional scaling (NMDS) with environmental variable fitting, redundancy analysis (RDA) with variation partitioning, analysis of similarities and linear mixed models as statistical tools. Results Species composition differed significantly among the study regions, while the differences in guild composition were less pronounced. US and French streams shared a large number of species, whereas islands shared only a few species with continents. For species composition, all predictors showed significant relationships with diatoms but pH, longitude, annual temperature and precipitation had the strongest impact. Variation partitioning revealed that the local environment outperformed climatic and spatial variables. For guild composition, there was a substantial overlap across regions in NMDS. The results from RDA demonstrated, however, that guild composition was better explained than species composition, especially by environmental variables. Both species and guild richness were significantly correlated with most predictors. Notably, species richness scaled positively with latitude. Main conclusions Diatom species and guild composition varied substantially in response to local environment and climatic and spatial variables indicating both environmental and historical effects. Species composition discriminated the geographical regions better, while guild composition detected the environmental gradients better. This emphasizes the need to examine different levels of organization to gain a deeper understanding of the roles of environment versus history in structuring communities. These findings suggest that diatom species distributions are under strong microevolutionary constraints. Conversely, factors and are driven primarily by the environment, which makes them better suited for research on global environmental change

Les patrons de répartition spatiale des communautés de diatomées varient-ils selon les régions et les années ?

International audienceAuthors of several studies of the spatial distributions of microorganisms have shown strong geographical patterns and stressed the importance of considering the spatial component explicitly when studying assemblage–environment relationships. The processes underlying the patterns are still under debate because it is difficult to separate the unique roles of dispersal limitation and mass effects from spatially structured variation in environment. We analyzed correlations between assemblage dissimilarity and geographical and environmental distances in a large French diatom database, subdivided into regions, years, and different water-quality levels, with multiple regression on distance matrices (MRM) and partial Mantel correlograms. Before we applied MRM, we identified the strongest environmental predictors with the BIO-ENV procedure, which selects the best predictors after testing correlations between distance matrices including every possible set of variables. Environmental control of assemblages was stronger than spatial factors in explaining assemblage patterns, but purely spatial patterns also were significant at the national scale and within some regions. When we averaged environmental and biological data over 3 y, environmental variables accounted for more variability in assemblage structure than relationships estimated with data from a single year. Assemblages in mountainous regions showed particularly strong spatial patterns, perhaps because dispersal barriers hinder the exchange of colonists across sites. The strong spatial structure in the diatom data leads us to encourage researchers to divide ecoregions into smaller areas, especially in mountainous landscapes, when studying assemblage–environment relationships. We also recommend the use of averaged biological and environmental assessment and conservation

Et si tout n’était pas partout ? Assemblages spécifiques et fonctionnels des communautés de diatomées à une échelle globale

International audienceLes 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