Dans le cadre du plan de gestion de la Réserve naturelle (RN) nationale des Hauts de Chartreuse (Savoie – Isère, France), deux campagnes de mesure de la faune des syrphes (Diptera) sont réalisées, l’une en 2008, l’autre en 2019-2020. Ces échantillonnages sont effectués avec quatre pièges à interception de type Malaise dans deux sites remarquables composés d’habitats d’altitude (pelouses/landes subalpines et pinèdes). Une réduction significative de la richesse spécifique et de la diversité des espèces est observée au Mont Granier durant la décennie, contrairement à la Dent de Crolles où ces deux paramètres sont plus stables. En revanche, un changement clair dans la composition des espèces pour les deux sites, entre les deux périodes, est mis en évidence. Ces modifications suivent la même trajectoire dans les deux sites, conséquence probable d’un facteur commun d’évolution. L’étude des guildes souligne des contraintes naturelles fortes, illustrées de l’absence de la quasi-totalité des espèces détritivores associées à l’accumulation de la litière et de l’humus. Les caractéristiques naturelles du Massif de la Chartreuse (savane karstique) dans un contexte climatique subalpin imposent des contraintes stationnelles particulières. Cette spécificité explique la présence inattendue de plusieurs espèces liées à des variantes acides (décalcifiées) des pelouses et landes subalpines. Ces espèces ont cependant disparu en 2019-2020. Sur les deux sites, tous les groupes phytophages (–18 %) et zoophages (–23 %) ont connu un fort déclin entre 2008 et 2019-20. Ces déclins sont particulièrement marqués sur le Mont Granier. L’analyse des assemblages d’espèces, avec la base de données Syrph the Net, permet de quantifier une dégradation fonctionnelle (ratio des espèces au rendez-vous sur celles prédites) sur les deux sites d’étude, entre 2008 et 2019-20. À la Dent-de-Crolles, la diminution est de –8 % et au Mont Granier de –27 %. Depuis 2008, on observe également une augmentation marquée des espèces inattendues provenant de la forêt de basse altitude de la zone montagnarde, associées à des peuplements forestiers (hêtraie, sapinière-pessière) qui ne sont pas représentées aux altitudes échantillonnées. Un autre changement concerne la proportion d’espèces provenant d’habitats frais et humides, que l’on trouve également à la périphérie des sites étudiés. Il s’agit d’espèces dont la présence n’est pas prévue sur les sites échantillonnés, car leurs habitats y sont absents. La proportion de cette communauté décroît fortement durant la décennie, passant de 37 à 24 % à la Dent de Crolles et de 34 à 15 % au Mont Granier. Ces diminutions inquiétantes de la syrphidofaune subalpine entre 2008 et 2020 sont certainement plus induites par les perturbations climatiques que ces habitats subalpins subissent de plein fouet depuis un demi-siècle, que par l’impact des pratiques humaines inexistantes ou abandonnées depuis plusieurs décennies. Les interprétations n’ont malheureusement pu être croisées avec d’autres études standardisées locales. Il est préconisé de mettre en place dans la RN des Hauts de Chartreuse plusieurs dispositifs de suivis et de poursuivre l’étude des communautés syrphidiennes sur le long terme.

Socio-ecological research enlists inter- and transdisciplinarity to address complex environmental issues. Yet the "socio-ecological system" concept can be interpreted in many different ways. A characterization of the diverse practices in socio-ecological research could facilitate dialogue between researchers about the possible conceptual and ethical approaches. In this study, we investigated if a detailed analysis of scientific articles would reveal the nature and course of a socio-ecological research network, and the research angle of its members. The example we used was the Rhône River Long-Term Socio-Ecological Research (LTSER) platform in France. We combined a multivariate analysis of a reading grid of publications by Rhône River LTSER researchers and a textual analysis of the scientific narratives. The publications were from a 10-year period and corresponded to those used in a recent international comparative analysis of LTSER platforms. The analysis revealed that the research was dominated by a biophysical approach, with a progressive increase in social aspects. The emergence of a transdisciplinary approach, co-constructed with operational partners, was also shown. The research conducted by the Rhône River LTSER was grounded in the context of managing a river with strong anthropic influences and interests, and the scientific approach aimed to provide knowledge for guiding decisions. Little referencfte was made in the publications to socio-ecological conceptual frameworks. Beyond the example of this LTSER platform, we identified indicators for describing the degree of inter- and transdisciplinarity and the different perceptions of socio-ecological systems. The narrative analysis revealed the angle of the research approach; this method could be used in future studies for a comparison of the diverse approaches of multiple research groups.

Alpine river biodiversity around the world is under threat from glacier retreat driven by rapid warming, yet our ability to predict the future distributions of specialist cold-water species is currently limited. Here we link future glacier projections, hydrological routing methods and species distribution models to quantify the changing influence of glaciers on population distributions of 15 alpine river invertebrate species across the entire European Alps, from 2020 to 2100. Glacial influence on rivers is projected to decrease steadily, with river networks expanding into higher elevations at a rate of 1% per decade. Species are projected to undergo upstream distribution shifts where glaciers persist but become functionally extinct where glaciers disappear completely. Several alpine catchments are predicted to offer climate refugia for cold-water specialists. However, present-day protected area networks provide relatively poor coverage of these future refugia, suggesting that alpine conservation strategies must change to accommodate the future effects of global warming.

In large river floodplains, the availability of trophic resources to the fish fauna is highly variable as a consequence of seasonal environmental change and habitat diversity. Young--of--the--year fishes ( YOY) must find suitable habitats to settle, feed and survive. However, very few in--depth studies are available about the food preferences of the young fishes during their first growing season. Here, we investigated the composition of planktonic assemblages and the YOY diet of three generalist fish species Alburnus alburnus (Linnaeus, 1758), Squalius cephalus (Linnaeus, 1758) and Pseudorasbora parva (Temminck & Schlegel, 1846) from four floodplain sites of the French Upper Rhone River. More specifically, we studied their temporal and spatial variations in relation to five environmental variables: hydrology, dissolved oxygen, primary production, water temperature and conductivity. Stable flow conditions and the associated temperature and conductivity strongly structured the phytoplankton community in the floodplain channels, whereas water movements within channels and dissolved oxygen concentrations were significantly correlated to the zooplankton composition. A zooplankton density above approximate to 100 ind L-1 allowed the initiation of a YOY diet mainly based upon zooplankton for the three fish species. When zooplankton densities were insufficient, all three species used phytoplankton as their main food resource. Finally, the diet overlaps between species, differed significantly between sites. The study highlights the need to examine the diet of juvenile fishes and environmental variables in the floodplains.

River floodplain channels can serve as reproduction, nursery or refuge areas for fish. Although the complementary use of floodplain and main channels is known, few studies attempted to quantify this use and even fewer analysed its controlling factors. The objectives of this study are (1) to describe the spatio-temporal use of floodplain habitats and to identify their roles as complementary habitats for fish and (2) to analyse how abiotic variations and their modifications under restoration impact habitat use by fish. To meet these objectives, we analysed (Principal Components Analysis and Coinertia Analysis) multi-site data collected over 20 years in eight main channels and 23 floodplain channels of eight restored sectors of the French Rhône River. Results show that habitat use by fish is mainly related to spatial effects, with 37 % of within-sector variance in taxonomic assemblages explained by the stations. As expected, rheophilic species were more abundant in lotic stations and limnophilic species in lentic ones. In addition, we identified an euryecious guild, grouping young of the year taxa (roach, gudgeon, chub, bleak) that used all types of habitats and particularly lentic floodplain channels with short life-span. Temporal effects (with ~10 % of the variance explained by years) combine (1) the effect of restoration, that increased the diversity of fish assemblages across the floodplain, with stronger changes in floodplain channels whose connectivity regime was modified, (2) the effect of high flows on fish habitat use, that reinforces the nursery and refuge functions of floodplain channels. Our results demonstrate the importance of restoring the diversity of habitats and connectivity because floodplain habitats have complementary functions for fish. Furthermore, our results also suggest to account for temporal variations in order to better estimate the potential effects of restoration on river and their floodplains.

Large river floodplains are dynamic environments, where alternating low and high flows are key ecological processes shaping aquatic biota. As a result of fluctuations in flow in floodplain channels, the diversity of benthic assemblages is assumed to result from the balance between surface flow connections, which are dominant during high flows, and groundwater inputs, which are dominant during low flows. However, the relative importance of these inputs in explaining aquatic invertebrate diversity has never been tested. The response of aquatic invertebrates to hydrological changes of a river floodplain was investigated in seven braided and six braided-anastomosed floodplain channels of the French upper Rhone River that are fed by three different processes: groundwater supply (which controls the thermal inertia of the water bodies), surface slow flow connections (i.e. diffuse overbank flows; passive overflow), and surface shear stress-related connections (i.e. condensed flows; active overflow) during high flows. Generalised dissimilarity models indicated that floodplain invertebrate composition had complex relationships with the three processes considered. The relative importance of the latter appeared dependent upon the morphology of the floodplain channels. In the braided channels, the effects of shear stress-related connections were more prominent than in the anastomosed ones, for which the effects of the three processes were more similar. Overall, the diversity of flow connections, that is, lateral surface water connections (both shear stress-related and slow, as defined above) and vertical connection with groundwater (inferred through thermal inertia) enhanced the species turnover at the reach scale. Thermal inertia influenced invertebrate composition when, during low flow periods, surface flow connections had limited effect. Our results highlighted that the role of hydrologic connectivity upon floodplain diversity cannot be reduced to a single process. They also indicate the importance of vertical connectivity for maintaining biodiversity in floodplain habitats where surface flow connectivity is neither frequent nor constant.

Description du sujet. Dans le contexte actuel de réduction des risques liés à l’utilisation de produits phytosanitaires et de promotion de la biodiversité dans les milieux agricoles, il apparaît primordial d'améliorer nos connaissances sur les insectes auxiliaires qui fréquentent et se développent dans ces écosystèmes. Objectifs. Cet article vise à dresser un état des connaissances sur les auxiliaires et à mettre en lumière les principaux apports faunistiques, écologiques et fonctionnels tirés de récentes études réalisées en contexte agricole à Genève. Méthode. Les données ont été acquises de 2014 à 2019 sur plusieurs familles d'auxiliaires prédateurs et pollinisateurs dans des contextes agricoles variés (prairies extensives, vignes, vergers, cultures de colza, maraîchage) à l’aide de pièges Barber, Malaise et à émergence. Résultats. Ces travaux ont permis de récolter 48 921 données et d'inventorier 477 espèces appartenant aux grandes familles d’auxiliaires ; parmi elles, quatre espèces sont observées pour la première fois en Suisse et une cinquantaine dans le canton de Genève. Au total, 357 (± 75 %) des espèces inventoriées possèdent un stade prédateur et 103 (± 22 %) sont considérées comme de bons auxiliaires des cultures. L'utilisation de pièges à émergence a permis d'attester qu'un tiers au moins des espèces inventoriées, dont certaines rares ou menacées, peuvent compléter leur cycle de vie dans les milieux agricoles ou les utiliser comme site d'hivernation. Conclusions. Cette synthèse contribue à améliorer notre compréhension de la composition de la biodiversité des milieux agricoles qui constitue une composante non négligeable de la biodiversité en Suisse et dans les pays voisins. Elle met également en lumière le rôle des habitats semi-naturels, tels que les prairies extensives ou les interlignes des vignes, comme support pour le développement de nombreuses espèces rares et parfois menacées.

Description of the subject. In the context of biodiversity maintenance in agricultural environments and of risk reduction related to the use of phytosanitary products, it seems essential to improve our knowledge of the beneficial insects that develop in these ecosystems. Objectives. This article reviews the state of knowledge regarding insect auxiliaries and highlights the main faunal, ecological and functional contributions from recent studies carried out in an agricultural context in Geneva. Method. Data were collected from 2014 to 2019 on several families of predatory and pollinating auxiliaries in various agricultural contexts (extensive grasslands, vineyards, orchards, rapeseed crops, vegetable crops) using Barber, Malaise and emergence traps. Results. 48,921 individual records were collected belonging to 477 species of the main families of auxiliaries. Of these, four species were observed for the first time in Switzerland and 50 in the canton of Geneva. 357 (+/- 75%) of the species had a predatory stage and 103 (+/- 22%) could be regarded as valuable crop auxiliaries. The use of emergence traps made it possible to attest that at least a third of the species, including some rare or threatened species, are able to successfully carry out their life cycles within agricultural environments or to use them as overwintering sites. Conclusions. This review increases our understanding of the composition of the biodiversity of agricultural environments, which constitutes a significant component of biodiversity in Switzerland and in neighboring countries. It also highlights the role of semi-natural habitats as extensive grasslands or inter-rows of vineyards in supporting the development of many rare and sometimes threatened species.

Abstract β‐Diversity, commonly defined as the compositional variation among localities that links local diversity (α‐diversity) and regional diversity (γ‐diversity), can arise from two different ecological phenomena, namely the spatial species turnover (i.e., species replacement) and the nestedness of assemblages (i.e., species loss). However, any assessment that does not account for stochasticity in community assembly could be biased and misinform conservation management. In this study, we aimed to provide a better understanding of the overall ecological phenomena underlying stream β‐diversity along elevation gradients and to contribute to the rich debate on null model approaches to identify nonrandom patterns in the distribution of taxa. Based on presence‐absence data of 78 stream invertebrate families from 309 sites located in the Swiss Alpine region, we analyzed the effect size of nonrandom spatial distribution of stream invertebrates on the β‐diversity and its two components (i.e., turnover and nestedness). We used a modeling framework that allows exploring the complete range of existing algorithms used in null model analysis and assessing how distribution patterns vary according to an array of possible ecological assumptions. Overall, the turnover of stream invertebrates and the nestedness of assemblages were significantly lower and higher, respectively, than the ones expected by chance. This pattern increased with elevation, and the consistent trend observed along the altitudinal gradient, even in the most conservative analysis, strengthened our findings. Our study suggests that deterministic distribution of stream invertebrates in the Swiss Alpine region is significantly driven by differential dispersal capacity and environmental stress gradients. As long as the ecological assumptions for constructing the null models and their implications are acknowledged, we believe that they still represent useful tools to measure the effect size of nonrandom spatial distribution of taxa on β‐diversity.

Body size is perhaps the most fundamental property of an organism and its relationship with abundance is one of the most studied relationships in ecology. Although numerous studies have examined these relationships in local communities, few have investigated how they vary at different temporal and spatial scales. We investigated the relationship between body size and abundance of local macroinvertebrate communities in two floodplain channels of the French upper Rhone River. The two channels differ in their vegetation coverage (high vs. low vegetation) and hydrological regimes. The shapes of the size–abundance relationship were similar between channels on a yearly basis but differed when compared between months. The variation in local size–abundance relationships between months was related to variation in the functional diversity across time. Our findings suggest that local size–abundance relationships are able to quantitatively describe temporal changes in community structure, showing the importance of relating diversity with ecosystem function in a more realistic context.

We present a novel meta-community approach to explore the influence of species traits, such as adult body size, larval feeding type and microhabitat, as well as larval macrohabitat (main river channel vs. floodplain water bodies) on the concentration of total Hg accumulated ([THg]) in assemblages of adult caddisflies. We analyzed [THg] in 157 light-trapped adult caddisflies in a floodplain sector of the French upper Rhône River and used a linear mixed effect model to decipher the role of species traits and habitats in Hg accumulation. Variation of [THg] between species was best explained by the larval feeding type, whereas the contributions of adult size and larval micro and macro-habitat were minor. Results showed that [THg] in species associated with floodplain macrohabitats in the larval stage was lower than in those associated with the main river channel. This difference could depend on complexation of Hg by DOM (in the floodplain) and MES (in the main channel). This research provides a first evidence of the potential of an entire caddisfly assemblage for the assessment of contamination in large alluvial rivers. The implications of the results are discussed in view of the possible role of caddisflies as vectors of Hg to riparian predators.

Aquatic ecologists face challenges in identifying the general rules of the functioning of ecosystems. A common framework, including freshwater, marine, benthic, and pelagic ecologists, is needed to bridge communication gaps and foster knowledge sharing. This framework should transcend local specificities and taxonomy in order to provide a common ground and shareable tools to address common scientific challenges. Here, we advocate the use of functional trait-based approaches (FTBAs) for aquatic ecologists and propose concrete paths to go forward. Firstly, we propose to unify existing definitions in FTBAs to adopt a common language. Secondly, we list the numerous databases referencing functional traits for aquatic organisms. Thirdly, we present a synthesis on traditional as well as recent promising methods for the study of aquatic functional traits, including imaging and genomics. Finally, we conclude with a highlight on scientific challenges and promising venues for which FTBAs should foster opportunities for future research. By offering practical tools, our framework provides a clear path forward to the adoption of trait-based approaches in aquatic ecology.

The high biotic diversity supported by floodplains is ruled by the interplay of geomorphic and hydrological processes at various time scales, from daily fluctuations to decennial successions. Because understanding such processes is a key question in river restoration, we attempted to model changes in taxonomic richness in an assemblage of 58 macroinvertebrate taxa (21 gastropoda and 37 ephemeroptera, plecoptera and trichoptera, EPT) along two successional sequences typical for former braided channels. Individual models relating the occurrence of taxa to overflow and backflow durations were developed from field measurements in 19 floodplain channels of the Rhône floodplain (France) monitored over 10 years. The models were combined to simulate diversity changes along a progressive alluviation and disconnection sequence after the reconnection with the main river of a previously isolated channel. Two scenarios were considered: (i) an upstream + downstream reconnection creating a lotic channel, (ii) a downstream reconnection creating a semi-lotic channel. Reconnection led to a direct increase in invertebrate richness (on average x2.5). However, taxonomical richness showed a constant decrease as isolation progressed and reached an average of 2 for EPT and 7 for gastropods at the end of the scenarios. With more than 80% of the taxonomic models with an AUC equal or higher than 0.7 and slopes of linear relations between observed and predicted richness of 0.75 (gastropods) and 1 (EPT), the Boosted Regression Trees (BRT) provided a good basis for prediction of species assemblages. These models can be used to quantify a priori the sustainability and ecological efficiency of restoration actions and help floodplain restoration planning and management.

Freshwater biodiversity loss is a major concern, and global warming is already playing a significant role in species extinctions. Our main goal was to predict climate change impacts on aquatic insect species distribution and richness in Swiss running waters according to two climate change scenarios (RCP2.6 and RCP8.5), using different modeling approaches, that is, species distribution models (SDMs), stacked‐SDMs (S‐SDMs) and a macroecological model (MEM). We analyzed 10,808 reaches, used as spatial units for model predictions, for a total river network length of 20,610 km. Results were assessed at both the countrywide and the biogeographic regional scales. We used incidence data of 41 species of Ephemeroptera, Plecoptera and Trichoptera (EPT) from 259 sites distributed across Switzerland. We integrated a coupled model for hydrology and glacier retreat to simulate monthly time‐step discharge from which we derived hydrological variables. These, along with thermal, land‐cover, topographic and spatially explicit data, served as predictors for our ecological models. Predictions of occurrence probabilities and EPT richness were compared among the different regions, periods and scenarios. A Shiny web application was developed to interactively explore all the models’ details, to ensure transparency and promote the sharing of information. MEM and S‐SDMs approaches consistently showed that overall, climate change is likely to reduce EPT richness. Decrease could be around 10% in the least conservative scenario, depending on the region. Global warming was shown to represent a threat to species from high elevation, but in terms of species richness, running waters from lowlands and medium elevation seemed more vulnerable. Finally, our results suggested that the effects of anthropogenic activities could overweight natural factors in shaping the future of river biodiversity.