Beta diversity of diatom species and ecological guilds : Response to environmental and spatial mechanisms along the stream watercourse

1. Understanding the mechanisms that drive beta diversity (i.e. beta-diversity), an important aspect of regional biodiversity, remains a priority for ecological research. beta-diversity and its components can provide insights 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. 2. We examined the variation in 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 2,182 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 physicochemical variables, while geographical distances between sites were used as spatial factors. We also correlated a and c-diversity, and the degree of nestedness (NODF metric) with environmental variables. 3. 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. 4. 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 metacommunity patterns along the stream watercourse.Peer reviewe

Les cartes auto-organisatrices de Kohonen appliquées à l'étude des communautés de micro-algues des cours d'eau

Les cartes auto-organisatrices de Kohonen appliquées à l'étude des communautés de micro-algues des cours d'ea

Diatom beta-diversity in streams increases with spatial scale and decreases with nutrient enrichment across regional to sub-continental scales

Aim To quantify the relative contributions of local community assembly processes versus gamma-diversity to beta-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 beta-diversity along a nutrient enrichment gradient was examined across multiple spatial scales. beta-diversity was estimated using multi-site Sorensen dissimilarity. We assessed the relative importance of specialists versus generalists using Friedley coefficient, and the contribution of local community assembly versus gamma-diversity to beta-diversity across spatial scales, with a null model. Finally, we estimated the response of beta-diversity to environmental and spatial factors by testing the correlations between community, environmental and geographical distance matrices with partial Mantel tests. Results beta-diversity generally increased with spatial scale but the rate of increase depended on nutrient enrichment level. beta-diversity decreased significantly with increasing nutrient enrichment level due to the loss of specialist species. Local assembly was an important driver of beta-diversity especially under low nutrient enrichment. Significant partial Mantel correlations were observed between diatom beta-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 beta-diversity, which indicated a substantial role of dispersal processes. Main conclusions Nutrient concentration mediated the expected increase in beta-diversity with spatial scales. Across spatial scales, beta-diversity was more influenced by local assembly processes rather than by gamma-diversity. Nutrient enrichment was associated with an overall decline in diatom beta-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.Peer reviewe

Biogeographical Patterns of Species Richness and Abundance Distribution in Stream Diatoms Are Driven by Climate and Water Chemistry

In this intercontinental study of stream diatoms, we asked three important but still unresolved ecological questions: (1) What factors drive the biogeography of species richness and species abundance distribution (SAD)? (2) Are climate-related hypotheses, which have dominated the research on the latitudinal and altitudinal diversity gradients, adequate in explaining spatial biotic variability? and (3) Is the SAD response to the environment independent of richness? We tested a number of climatic theories and hypotheses (i.e., the species-energy theory, the metabolic theory, the energy variability hypothesis, and the climatic tolerance hypothesis) but found no support for any of these concepts, as the relationships of richness with explanatory variables were nonexistent, weak, or unexpected. Instead, we demonstrated that diatom richness and SAD evenness generally increased with temperature seasonality and at mid- to high total phosphorus concentrations. The spatial patterns of diatom richness and the SADmainly longitudinal in the United States but latitudinal in Finlandwere defined primarily by the covariance of climate and water chemistry with space. The SAD was not entirely controlled by richness, emphasizing its utility for ecological research. Thus, we found support for the operation of both climate and water chemistry mechanisms in structuring diatom communities, which underscores their complex response to the environment and the necessity for novel predictive frameworks.Peer reviewe

Front. Plant Sci.

International audienc

Dispersal-niche continuum index : a new quantitative metric for assessing the relative importance of dispersal versus niche processes in community assembly

Patterns in community composition are scale-dependent and generally difficult to distinguish. Therefore, quantifying the main assembly processes in various systems and across different datasets has remained challenging. Building on the PER-SIMPER method, we propose a new metric, the dispersal-niche continuum index (DNCI), which estimates whether dispersal or niche processes dominate community assembly and facilitates the comparisons of processes among datasets. The DNCI was tested for robustness using simulations and applied to observational datasets comprising organismal groups with different trophic level and dispersal potential. Based on the robustness tests, the DNCI discriminated the respective contribution of niche and dispersal processes in pairwise comparisons of site groups with less than 40% and 30% differences in their taxa and site numbers, respectively. In the observational datasets, the DNCI suggested that dispersal rather than niche assembly was the dominant assembly process which, however, varied in intensity among organismal groups and study contexts, including spatial scale and ecosystem types. The proposed DNCI measures the relative strength of community assembly processes in a way that is simple, easily quantifiable and comparable across datasets. We discuss the strengths and weaknesses of the DNCI and provide perspectives for future research.Peer reviewe

Invasive Aquatic Plants as Ecosystem Engineers in an Oligo-Mesotrophic Shallow Lake

Exotic hydrophytes are often considered as aquatic weeds, especially when forming dense mats on an originally poorly colonized environment. While management efforts and research are focused on the control and on the impacts of aquatic weeds on biodiversity, their influence on shallow lakes’ biogeochemical cycles is still unwell explored. The aim of the present study is to understand whether invasive aquatic plants may affect the biogeochemistry of shallow lakes and act as ecosystem engineers. We performed a multi-year investigation (2013–2015) of dissolved biogeochemical parameters in an oligo-mesotrophic shallow lake of south-west of France (Lacanau Lake), where wind-sheltered bays are colonized by dense mats of exotic Egeria densa Planch. and Lagarosiphon major (Ridl.) Moss. We collected seasonal samples at densely vegetated and plant-free areas, in order to extrapolate and quantify the role of the presence of invasive plants on the biogeochemistry, at the macrophyte stand scale and at the lake scale. Results revealed that elevated plant biomass triggers oxygen (O2), dissolved inorganic carbon (DIC) and nitrogen (DIN) stratification, with hypoxia events frequently occurring at the bottom of the water column. Within plants bed, elevated respiration rates generated important amounts of carbon dioxide (CO2), methane (CH4) and ammonium (NH4+). The balance between benthic nutrients regeneration and fixation into biomass results strictly connected to the seasonal lifecycle of the plants. Indeed, during summer, DIC and DIN regenerated from the sediment are quickly fixed into plant biomass and sustain elevated growth rates. On the opposite, in spring and autumn, bacterial and plant respiration overcome nutrients fixation, resulting in an excess of nutrients in the water and in the increase of carbon emission toward the atmosphere. Our study suggests that aquatic weeds may perform as ecosystem engineers, by negatively affecting local oxygenation and by stimulating nutrients regeneration

Biodiversité et vulnérabilité des communautés de diatomées benthiques en milieu lotique

Biodiversité et vulnérabilité des communautés de diatomées benthiques en milieu lotique

Guide iconographique pour la mise en oeuvre de l'Indice Biologique Diatomée 2007

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCA [Relecteur_IRSTEA]Dreal ; Bart van de VijverSince its revision in 2007, the Biological Diatom Index is calculated on the basis of a list of 1478 taxa (including 476 synonyms and 190 abnormal forms), which ecological profiles have been previously determined. A new iconographic guide has then been achieved, accompanying the implementation of the index. This guide illustrates more than 900 taxa taken into account for the calculations, and which names correspond to those cited in the AFNOR standard. When appropriate, a most recently name is proposed in synonymy. Some additional taxa are illustrated.Depuis sa révision en 2007, l'Indice Biologique Diatomée se calcule sur la base d'une liste de 1478 taxons (dont 476 synonymes anciens et 190 formes anormales), dont les profils écologiques ont été au préalable déterminés. Un guide iconographique a donc été réalisé, accompagnant la mise en oeuvre de l'indice. Ce guide illustre plus de 900 taxons répartis en 188 planches et retenus pour le calcul de l'IBD. Les dénominations utilisées correspondent à celles figurant dans la norme AFNOR. Le cas échéant, une dénomination secondaire plus récente est proposée en synonymie. Certains taxons non retenus dans la norme ont tout de même été illustrés, lorsque cela paraissait utile du point de vue taxinomique. Il faut noter que plus de 200 combinaisons nouvelles (sur 812 taxons IBD) sont apparues depuis 2007 ce qui devrait justifier une nouvelle révision de la norme. 768 taxons représentés dans le guide sont retenus dans la norme et 213 supplémentaires (non retenus par la norme) sont illustrés. Ils représentent des combinaisons nouvelles ou des taxons proches susceptibles de donner lieu à des confusions ou encore des formes halophiles ou tropicales dont l'intégration dans les futurs indices en cours d'élaboration est envisagée