The synthesis of long-term ecological research in the context of concurrently developed ecological theory: design of a research strategy for the Upper Rhône River and its floodplain

• 1 Using sites from the Upper Rhône River, France, as an example, the objective of this paper is to identify the essential elements needed to test current ecological theories with previously collected data. Procedures developed may enable other groups to design comparable research strategies for syntheses of long-term studies of ecological systems.
• 2 Because of the high number (more than 200) and turnover of researchers, the long study period (about 17 years), the evolution of research methods and interests, and the diverse systematic groups that were considered (from micro-organisms to birds), the data available for a synthesis were quite heterogeneous. The application of a ‘fuzzy coding’ technique allowed such disparate information to be structured for analysis.
• 3 The habitat templet concept and the patch dynamics concept were selected for analysis with existing data on the Upper Rhône because theories, such as these, that link ecological responses to habitat templets are a focus of current ecological debate and potentially may serve as a general tool for ecologically orientated river management.
• 4 A preliminary trial to structure the existing knowledge, to identify (and manage) gaps in it, and to create and apply the analytical tools in a way that predictions from theory could be tested was an essential element in the design of this project.
• 5 Predictions derived from the theoretical concepts had to match the format of the available information on the Upper Rhône; potential bias was avoided by having a priori predictions developed by previously uninvolved colleagues.
• 6 Synthesis of the long-term study of the Upper Rhône in the context of concurrently developed ecological theory required, at times, an unconventional research strategy. Hence, the generation of hypotheses and methods, the presentation of results, and consequently the discussions in papers of this special issue of Freshwater Biology (Statzner, Resh & Dolédec, 1994) represent an innovative approach to testing ecological theory.

     

Plant response strategies to stress and disturbance: the case of aquatic plants

The environmental factors controlling the establishment and development of plants in different ecosystems are of two types, stress and disturbance. The effects of stress or disturbance on aquatic systems are discussed in relation to the following questions:Can we predict the state and rate of recolonization after a disturbance? What are the strategies of recolonization developed by plants? How high is the resilience of a disturbed system? Two theories, the intermediate disturbance hypothesis, and the patch dynamics concept proposed to predict the composition, structure and dynamics of plants due to physical-chemical factors, were tested on two scales, that of communities and that of species, within two alluvial floodplains (the Rhine and the Rhône systems in France).With regard to the change of community on a larger scale (i.e. the whole network of the cut-off channels in the floodplain), large gradients of connection and disturbance induce high diversities within communities. Moreover, the highest flood disturbance induces a higher species richness and the occurrence of a particular species. The change in species is analysed using biological traits (morphological, reproductive or physiological). In the floodplain of the river Rhône, the response of plants corresponds well to theory, i.e. that habitats with an intermediate disturbance are richer than more or less disturbed habitats. So we can predict, through the biological traits, the functioning of a habitat. The last remaining question is that of the resilience of the system, which can be discussed in terms of species competition and the risk of biological invasion after an opening of habitat.     

Relationships between Solutes,Nutrients, and the Biofilm in Sediments of Floodplain Karstic and Alluvial Springs

Two pairs of springs were surveyed in the floodplain of the Upper Rhône River. Each pair included a karstic (upstream) and an alluvial (downstream) spring in the same catchment. Various physical, chemical, and biological factors were measured in the water and the sediment. The study showed karstic and alluvial spring typology. In each pair, the karstic springs were characterized by higher alkalinity, whereas alluvial springs were fed both by karstic groundwater and Rhône River water with higher sulphate content. Organic matter dynamics and retention processes were different in each spring. The distribution and abundance of fine sediment played a prominent role in the storage of particulate organic carbon and the development of microbial biomass and activity. The hydrological cycle governed organic and inorganic nutrient fluxes, and was, with temperature, the main factor influencing microbial and macroinvertebrate dynamics. The high amount of organic matter in one alluvial spring was correlated with high microbial biomass and activity.     

Theoretical habitat templets, species traits, and species richness: floodplain vegetation in the Upper Rhône River

• 1 The floodplain vegetation at approximately 100 sites located in nine different habitat types of the Upper Rhône River, France, was surveyed three times over the past 27 years. Information on species traits of the higher plants comprising the Rhône floodplain vegetation was based on studies conducted between Geneva, Switzerland, and Lyon, France.
• 2 These data were structured using a ‘fuzzy coding’ technique and then examined using ordination analyses to investigate: (i) relationships among species traits; (ii) habitat utilization; (iii) the relationship between species traits and habitat utilization; and (iv) trends of species traits and species richness in the framework of spatial–temporal habitat variability to test predictions of the river habitat templet and the patch dynamics concept.
• 3 Size, number of descendants per reproductive cycle, number of reproductive cycles per individual, and the regeneration potential of an individual were positively related with each other, whereas the degree of attachment to the soil decreased, and the reproductive period shifted from autumn/late summer towards early summer/spring, as size increased.
• 4 The habitat utilization by the higher plants of the floodplain revealed a double lateral gradient: the first was from the banks of the temporary waters to terrestrial flats; the second from aggrading pebble to aggrading silt habitats. These gradients were related to gradients in water saturation, oxygen conditions, nutrient loading, and nutrient retention of the soils.
• 5 A significant relationship between species traits and habitat utilization was observed for the floodplain vegetation, i.e. plant communities used particular habitat types with a particular set of species trait modalities (= categories).
• 6 Patterns of species trait modalities were significantly related to temporal and spatial habitat variability but only modalities of the trait ‘parental care’ conformed to trends predicted from theory.
• 7 No trends were observed when species richness of different habitat types was considered in the framework of spatial–temporal habitat variability.
• 8 Although the habitats of the Upper Rhône clearly act as a templet for the species traits of the floodplain vegetation, the lack of agreement between observations and predictions on trends in species traits and richness in terms of habitat variability suggest that important elements of theory should be rejected. However, human-induced changes in these habitats are too recent when compared with the longer time periods required for floodplain vegetation to respond to such changes.

     

Impact of mosquito control operations on waterbirds in a Camargue nature reserve

Wetlands Ecology and Management - The Domaine de la Palissade is a 700-ha nature reserve located at the mouth of the Rhône river in southern France. Since 2006, the tidal wetlands have been...     

Theoretical habitat templets, species traits, and species richness: 548 plant and animal species in the Upper Rhône River and its floodplain

• 1 For practical reasons, conceptual developments in community ecology are usually based on studies of a restricted systematic group. The cooperation of thirty or so specialists in the synthesis of long-term ecological research on the Upper Rhône River, France, provided a unique occasion to investigate relationships among species traits, the habitat utilization by species, the relationship between species traits and habitat utilization, and trends of species traits and species richness in the framework of spatial-temporal habitat variability for 548 species of plants (Hyphomycetes, aquatic macrophytes, floodplain vegetation) and animals (Tricladida, Oligochaeta, several groups of Crustacea, Insecta and Vertebrata).
• 2 Using correspondence analysis, 100 modalities of eighteen species traits were examined; the resulting typology demonstrates that systematic groups are the most important elements for separating species traits such as size, fecundity of individuals, parental care, mobility, body form, and food type. Small species have an intermediate number of descendants per reproductive cycle and few reproductive cycles both per year and per individual; in contrast, large species have a high number of descendants per reproductive cycle and few reproductive cycles per year but many potential reproductive cycles per individual.
• 3 The analysis of habitat utilization in the Upper Rhône River and its floodplain by the 548 species demonstrated a vertical gradient separating interstitial from superficial habitats; a transverse gradient for superficial habitats from the main channel towards more terrestrial ones is also evident.
• 4 Because of a significant (P < 0.01) relationship between species traits and habitat utilization, traits such as size, fecundity of individuals, parental care, tolerance to variation in humidity, and respiration are arranged along the vertical and transverse habitat gradient. Size, the number of reproductive cycles per individual, and the tolerance to variation of humidity increases from permanent waters to temporary waters, aggrading habitats, and terrestrial habitats.
• 5 Species traits showed significant (P < 0.01) trends in the framework of spatial-temporal habitat variability and were compared with predictions based on the river habitat templet. Although each habitat showed a mixture of species traits at low temporal and spatial variability, and at high variability sites, trends corresponded to predictions for three traits (number of descendants per reproductive cycle, number of reproductive cycles per individual, attachment to soil or substrate) along a gradient of increasing temporal habitat variability.
• 6 The species richness of each habitat within the Upper Rhône River and its floodplain significantly (P = 0.03) increased as the spatial variability of habitats increased but there is no statistical correlation between spedes richness and temporal variability. An altemative hypothesis predicting that fewer spedes per resource occur in temporally stable habitats is also not supported.

     

Temporal and spatial environmental variability in the Upper Rhône River and its floodplain

• 1 This paper develops a framework of spatial and temporal variability for a habitat typology of the Upper Rhône River (France) and its alluvial floodplain that is based on about 17 years of data collection and analysis. The aim was to provide a scale of spatial-temporal variability for river habitat templet predictions on trends in species traits and species richness.
• 2 In developing this framework, eight physical-chemical variables were available and could be considered for twenty-two habitat types: seventeen superficial (surface) and five interstitial (0.5 m below the substrate surface). These habitat types were selected in two areas (Jons and Brégnier-Cordon) after geomorphological considerations and because of differences in their biological characteristics.
• 3 The data sets used were processed by a ‘fuzzy coding’ method using, for each variable, the frequency distribution (by modalities = categories) of all measurements and monthly means over an annual scale. Two tables were produced; the first corresponded to an expression of the total variability, and the second represented an evaluation of the temporal variability.
• 4 Each of these tables was analysed by correspondence analysis, which provided factorial scores that were used to calculate, by habitat type and by variable, a total variability and a temporal variability in terms of cumulated variability of factorial scores for the eight physical–chemical variables. The rationale in describing variability from these two tables is that total variability equals temporal variability plus spatial variability. The spatial variability was then determined by the difference between total and temporal variability. From this procedure, a positioning of the twenty-two habitat types on the spatial and temporal variability axes was obtained.
• 5 The estimate of spatial variability did not consider any error term that may have occurred in the above model; it was then tested by an independent assessment of the spatial variability using thirteen variables in nine major habitat types. A high correlation between the two ways of assessing spatial variability (r = 0.85, P < 0.004) underscored the reliability of the spatial variability that was calculated previously.
• 6 The river habitat templet obtained for the Upper Rhône and its alluvial floodplain appears to be appropriate to test the predictions on patterns of species traits and species richness in the framework of spatial and temporal variability.

     

Ecology of fish spawning and nursery zones in the flood plain,using a new sampling approach

Horizontal zonation of fish reproduction, a lotic-to-lentic succession similar to that seen with increasing stream order, was evident from the relative abundance of larval and 0 + juvenile fishes in three floodplain spawning and nursery areas (lotic, semi-lotic, lentic) of the Upper Rhône River, France. Although the lotic and lentic ecosystems provided similar estimates of standing crop (0 + juveniles), differences were apparent in the reproductive and trophic guild structure of the YOY taxocoenoses at the three sites. A new sampling approach (Random Point-Abundance Sampling and modified electrofishing) is described for early-life fish ecology. The electrofishing method employed is mobile, effective for all sizes of larvae and 0 + juveniles of most species, quantitative, and applicable to a number of freshwater situations; and the punctual data resulting from this sampling approach are comparable both spatially and temporally.     

Theoretical habitat templets, species traits, and species richness: fish in the Upper Rhône River and its floodplain

• 1 Recent developments in ecological theory concerned with habitat templets, species assemblages, and life history traits were examined for the riverine fish communities of the Upper Rhône River, France, in the context of spatial–temporal habitat variability. Relationships among species traits, habitat utilization of species, the relationship between species traits and habitat utilization, and trends of species traits and species richness in the spatial–temporal variability of the habitat types were analysed.
• 2 Relationships among twelve species traits, and utilization of eight habitats were examined for twenty-five fish species using correspondence analysis; the relationship between species traits and habitat utilization was investigated by co-inertia analysis.
• 3 Positive relationships among species traits were observed for size, fecundity, and the number of reproductive cycles per individual. However, species were not well differentiated according to the habitat utilization, except for habitats rarely connected with the main channel (i.e. two types of oxbow lakes).
• 4 No significant relationship was found between species traits and habitat utilization, nor for either species traits or species richness when examined in the framework of spatial–temporal habitat variability. Only two species traits corresponded (with slight trends) to predictions in a river habitat templet: (i) the number of descendants per reproductive cycle increased along with temporal variability; and (ii) the number of reproductive cycles per individual was either low or high at low temporal variability and intermediate at elevated temporal variability.
• 5 The discrepancy between the predictions of the river habitat templet as well as of the patch dynamics concept and the results observed for the fish in the Upper Rhône was explained in terms of scale problems, the evolutionary ecology of the European fish fauna, and the history of the Rhône River.

     

Theoretical habitat templets, species traits, and species richness: Plecoptera and Ephemeroptera in the Upper Rhône River and its floodplain

• 1 Ephemeroptera and Plecoptera in two sites of the Upper Rhône River (France) were examined using multivariate analyses to determine: (i) relationships among seventeen species traits; (ii) habitat utilization of the fifty-five species present; (iii) the relationship between species traits and habitat utilization; (iv) trends of species traits and species richness in a framework of spatial and temporal habitat variability.
• 2 The species traits having the highest correlation ratios correspond to reproduction or life cycle, behavioural, and morphological characteristics. According to their traits, species of Baetidae, Caenidae, and Leptophlebiidae (Ephemeroptera) are opposite species of Perlidae and Perlodidae (Plecoptera).
• 3 The distribution of species in thirteen habitat types of the Upper Rhône River floodplain demonstrates a transverse gradient from the main channel to the oxbow lakes. Plecoptera are restricted to the different main channel habitats; in contrast, Ephemeroptera families have a broader distribution with Baetidae and Leptophlebiidae occurring in most floodplain habitats.
• 4 Plecoptera exhibit a significant relationship between species traits and habitat utilization but no relationship is evident for Ephemeroptera. Baetidae use many habitat types and have diverse species traits; in contrast, Leptophlebiidae, Heptageniidae, and Caenidae use many habitat types but each family has a rather uniform set of traits.
• 5 Trends in species traits were significantly related to both the spatial and temporal variability of habitats. Considering only temporal variability, the distribution of species trait modalities (= categories) corresponded well to predictions on trends in the river habitat templet for ‘minimum age at reproduction’ and ‘potential longevity’, and in general for ‘descendants per reproductive cycle’, ‘reproductive cycles per year’, ‘potential size’, and ‘body flexibility’ trends in six other traits did not match predictions.
• 6 No trends in species richness were evident in spatial–temporal framework of habitat variability.

     

Theoretical habitat templets, species traits, and species richness: aquatic insects in the Upper Rhône River and its floodplain

• 1 For five orders of Insecta (Plecoptera, Ephemeroptera, Odonata, Trichoptera, and Coleoptera) in two sites of the Upper Rhône River (France), the following are examined: (i) relationships among nineteen species traits; (ii) habitat utilization of species; (iii) the relationship between species traits and habitat utilization; and (iv) trends of species traits and species richness in a templet of spatial-temporal habitat variability.
• 2 The species traits having the highest correlations correspond to reproduction, life cycle, nutritional, and morphological features. Species trait characteristics of Coleoptera are distinctly contrasted with those of Plecoptera and Ephemeroptera; Odonata and Trichoptera are intermediate to these orders.
• 3 The distribution of species in fourteen habitat types of the Upper Rhône River floodplain demonstrates a transverse gradient from the main channel to the oxbow lakes and the temporary water habitats, and a vertical gradient from interstitial to superficial habitats.
• 4 Despite a significant relationship between species traits and habitat utilization, superposition between species traits and habitat utilization is limited. At the order level, species form usually one (Ephemeroptera, Trichoptera, Odonata) or several (Coleoptera) groups of relatively homogeneous species traits; however, the species of each of these groups utilize rather different habitat types.
• 5 Only for some life history traits, e.g. the minimum age of reproduction or the number of reproductive cycles per year, do the trends observed in the framework of spatial—temporal variability of habitat types agree with the predictions from the river habitat templet. This mismatch mainly results from the unique phylogenetic history of the Coleoptera compared with that of the other four orders.
• 6 Species richness peaks at an intermediate level of temporal variability; however, it does not gradually increase with increasing spatial variability, nor increase from low to intermediate temporal variability.

     

Microhabitat diversity and associated macroinvertebrates in aquatic banks of a large European river

Microhabitats and associated macroinvertebrate communities in aquatic banks of the Upper Rhône River (upstream from Lyon, France) were studied during the autumn of 1985, under low flow conditions. Based on a regular sampling design (one site every 500 m) along 70 km of riverbank, 18 microhabitat types were identified. Mineral microhabitats (from boulders to clay) accounted for 70%; the remainder corresponded chiefly to the microhabitats of aerial or semi-aerial submerged vegetation (27%) and aquatic vegetation (less than 2%). Using various methods, 239 faunistic samples of microhabitat types resulted in the collection of nearly 64 000 organisms representing 133 taxa. A correspondence analysis showed that most of the 18 microhabitat types were on average well characterized by a specific macrofauna. Microhabitats of aquatic vegetation (hydrophytes and algae) contained the richest fauna in terms of both mean specific richness (15.0 and 13.2 per sample, respectively) and mean density (73 125 and 59 475 ind. m^?2, respectively). By contrast, mineral microhabitats were faunistically poorer (mean specific richness per sample <6.0, except cobbles; and mean density ≤10405 ind. m^?2). The fewest species and lowest density occurred in clay, silt and sand. Estimated mean density of macroinvertebrates in the aquatic banks of the Upper Rhône River was approximately 16 000 ind. m^?2. This was four times higher than in deeper sections of the channel at the same season. The aquatic banks of this large European river, with its great diversity of microhabitats, must be taken into account in all macroinvertebrate studies of fluvial systems.     

Genetic analysis of potential postglacial watershed crossings in Central Europe by the bullhead (Cottus gobio L.)

Natural colonizations across watersheds have been frequently proposed to explain the present distributions of many freshwater fish species. However, detailed studies of such potential watershed crossings are still missing. Here, we investigated potential postglacial watershed crossings of the widely distributed European bullhead (Cottus gobio L.) in two different areas along the Rhine–Rhône watershed using detailed genetic analysis. The main advantage of studying bullheads vs. other freshwater fish species is that their distribution has been lightly influenced by human activities and as such, interpretations of colonization history are not confounded by artificial transplantations. The genetic analyses of eight microsatellite loci revealed strong genetic similarities between populations of both sides of the Rhine–Rhône watershed in the Lake Geneva area, giving strong evidence for a natural watershed crossing of bullheads from the upper Rhine drainage into the Rhône drainage in the Lake Geneva area likely facilitated by the retreat of the glaciers after the last glacial maximum some 20 000 years ago. Populations from the Lake Geneva basin were genetically more similar to populations from across the watershed in the upper Rhine drainage than to populations further downstream in the lower Rhône. In contrast, populations from Belfort, an area, which was not covered by ice during the last glacial maximum, showed strong genetic differentiation between populations of the upper Rhine and Rhône drainages. Based on our results on the bullhead, we propose that glacial retreat may have eased the dispersal of numerous European freshwater fish species across several geological boundaries.     

Reappraisal and range extension of non-indigenous Mysidae (Crustacea, Mysida) in continental and coastal waters of eastern France

A survey of species belonging to the family Mysidae, conducted in June 2007 in fresh- to brackish waters of eastern France, revealed a recent range extension of the invasive Ponto-Caspian species Hemimysis anomala to the Moselle, Saône, and Rhône rivers. In the estuary of the Grand Rhône it reached for the first time the Mediterranean coast. The network of navigation canals in NE France was likely a key element of its north to south pathway starting from the Rhine River. Important range extensions were also noted for Limnomysis benedeni in this network and in the Moselle River. The euryhaline species Neomysis integer, endemic in coastal waters of the NE Atlantic, was found in the Rhône delta, thus confirming previous very rare records in the 1930–1950s from the Mediterranean coast of France. Invasion mechanisms and pathways, expansion potential, and establishment conditions of the species are discussed.     

Alien aquatic macroinvertebrates along the lateral dimension of a large floodplain

Floodplains are simultaneously among the most species-rich and the most threatened ecosystems. Alien aquatic macroinvertebrates contribute to this threat but remain scarcely studied in the lateral dimension of floodplains. We modelled the realized ecological niches of the alien species occurring in 24 floodplain channels of the Rhône River. Environmental variables depicting the ecological niches were associated to the lateral hydrological connectivity and light availability, both being modified during floodplain restoration works. Eight alien species were observed and they demonstrated either ubiquity or a restricted niche, with no link to the date of introduction. For most of them, the main river channel appeared as an important dispersal route in the lateral dimension of the floodplain. An increase of both lateral connectivity and light availability favoured most of the modelled species. Consequently, we recommend that sector-scale restoration programmes preserve varying levels of lateral connectivity for floodplain channels to prevent the expansion of alien aquatic macroinvertebrates.     

Phylogeographical structure, postglacial recolonization and barriers to gene flow in the distinctive Valais chromosome race of the common shrew (Sorex araneus)

Using one male‐inherited and eight biparentally inherited microsatellite markers, we investigate the population genetic structure of the Valais chromosome race of the common shrew (Sorex araneus) in the Central Alps of Europe. Unexpectedly, the Y‐chromosome microsatellite suggests nearly complete absence of male gene flow among populations from the St‐Bernard and Simplon regions (Switzerland). Autosomal markers also show significant genetic structuring among these two geographical areas. Isolation by distance is significant and possible barriers to gene flow exist in the study area. Two different approaches are used to better understand the geographical patterns and the causes of this structuring. Using a principal component analysis for which testing procedure exists, and partial Mantel tests, we show that the St‐Bernard pass does not represent a significant barrier to gene flow although it culminates at 2469 m, close to the highest altitudinal record for this species. Similar results are found for the Simplon pass, indicating that both passes represented potential postglacial recolonization routes into Switzerland from Italian refugia after the last Pleistocene glaciations. In contrast with the weak effect of these mountain passes, the Rhône valley lowlands significantly reduce gene flow in this species. Natural obstacles (the large Rhône river) and unsuitable habitats (dry slopes) are both present in the valley. Moreover, anthropogenic changes to landscape structures are likely to have strongly reduced available habitats for this shrew in the lowlands, thereby promoting genetic differentiation of populations found on opposite sides of the Rhône valley.     

Sur un nouveau gisement fossilifere du Miocene superieur (Tortonien-Turolien moyen) de Cucuron (Vaucluse)

The fossiliferous layer is located in tortonian fresh water marls with “Helix” christoli within Durance basin.Micromammals, molluscs and ostracodes are yielded. The fauna analysis get to place it in Middle turolian (MN 12 zone) and to give an Upper Turolian age (MN 13) to the Luberon red limes and gravels formation. It appears clearly that the lacustrine biotop with Paralimnocythere bouleigensis spread more and more late southward in the Rhône valley. At the Tortonian, the sea stopped longuer in the Durance basin than in the Valréas one.     

Phylogeography and recolonization of the Swiss Alps by the Valais shrew (Sorex antinorii), inferred with autosomal and sex‐specific markers

Using one male‐inherited, one female‐inherited and eight biparentally inherited markers, we investigate the population genetic structure of the Valais shrew (Sorex antinorii) in the Swiss Alps. Bayesian analysis on autosomal microsatellites suggests a clear genetic differentiation between two groups of populations. This geographically based structure is consistent with two separate postglacial recolonization routes of the species into Switzerland from Italian refugia after the last Pleistocene glaciations. Sex‐specific markers also confirm genetic structuring among western and eastern areas, since very few haplotypes for either Y chromosome or mtDNA genome are shared between the two regions. Overall, these results suggest that two already well‐differentiated genetic lineages colonized the Swiss Alps and came into secondary contact in the Rhône Valley. Low level of admixture between the two lineages is likely explained by the mountainous landscape structure of lateral valleys orthogonal to the main Rhône valley.     

Impacts of global changes and extreme hydroclimatic events on macroinvertebrate community structures in the French Rhône River

We assessed the temporal changes in and the relationships between the structures of the macroinvertebrate communities and the environmental conditions of the French Rhône River (the river from Lake Geneva to the Mediterranean Sea) over the last 20 years (1985–2004). Multisite environmental and biological datasets were analysed using multiple CO-inertia analysis (MCOA) and Procrustean analysis. Changes in environmental conditions were mainly marked by an improvement in water quality between 1985 and 1991 and by an increase in water temperature from 1985 onwards due to climate change. Improvement in water quality seemed to delay changes in community structures under global warming. We then observed trends in community structures coupled with high temperatures and a decrease in oxygen content. Interestingly, we observed both gradual changes and rapid switches in community states. These shifts seemed coupled to extreme hydroclimatic events (i.e. pulse disturbances). Floods and the 2003 heatwave enhanced the development of eurytolerant and invasive taxa which were probably able to take advantage of gradual warming environmental conditions. Despite various site-specific “press” constraints (e.g. hydropower schemes, nuclear power plants), similar changes in community structures were observed along the French Rhône River. Such consistency in temporal processes at large geographical scales underlined the strength of hydroclimatic constraints on community dynamics compared to specific local disturbances. Finally, community structures did not show any sign of recovery, and their relative sensitivities to extreme hydroclimatic events seemed to increase with time. Thus, our results suggest that global changes may reduce the resilience of current community states.     

Historical presence of the sturgeon Acipenser sturio in the Rhône basin determined by the analysis of ancient DNA cytochrome b sequences

Sturgeon disappeared from the Rhône River in the mid 70’s without certitude about which species it was and about the existence of a sympatry between European sturgeon, Acipenser sturio, and Adriatic sturgeon, A. naccarii, in this watershed. In order to reach a reliable specific determination of this extinct sturgeon population, archaeozoological remains of the Jardin d’Hiver in Arles city, on the Rhône river banks, were genetically analysed, following strict criteria of authentication for the ancient DNA work. The rich collection of Arles sturgeon bone remains stems from human activities between the 6th and the 2nd Century BC. Sequences of 86 bp of the cytochrome b gene were obtained on four bones, from different anatomical parts of the fish and from different archaeological layers. All gave A. sturio diagnostic sequences. This preliminary analysis is an essential first step in the project of sturgeon reintroduction in the Rhône River. Thus, further analyses on a larger sample are necessary to comfort this result and to solve the question of sympatry with A. naccarii.