Spatial synchrony in stream fish populations: influence of species traits

Spatial synchrony in population dynamics has been identified in most taxonomic groups. Numerous studies have reported varying levels of spatial synchrony among closely-related species, suggesting that species' characteristics may play a role in determining the level of synchrony. However, few studies have attempted to relate this synchrony to the ecological characteristics and/or life-history traits of species. Yet, as to some extent the extinction risk may be related to synchrony patterns, identifying a link between species' characteristics and spatial synchrony is crucial, and would help us to define effective conservation planning. Here, we investigated whether species attributes and temperature synchrony (i.e. a proxy of the Moran effect) account for the differences in spatial population synchrony observed in 27 stream fish species in France. After measuring and testing the level of synchrony for each species, we performed a comparative analysis to detect the phylogenetic signal of these levels, and to construct various multi-predictor models with species traits and temperature synchrony as covariates, while taking phylogenetic relatedness into account. We then performed model averaging on selected models to take model uncertainty into account in our parameter estimates. Fifteen of the 27 species displayed a significant level of synchrony. Synchrony was weak, but highly variable between species, and was not conserved across the phylogeny. We found that some species' characteristics significantly influenced synchrony levels. Indeed, the average model indicated that species associated with greater dispersal abilities, lower thermal tolerance, and opportunistic strategy displayed a higher degree of synchrony. These findings indicate that phylogeny and spatial temperature synchrony do not provide information pertinent for explaining the variations in species' synchrony levels, whereas the dispersal abilities, the life-history strategies and the upper thermal tolerance limits of species do appear to be quite reliable predictors of synchrony levels

Systematic conservation planning for intraspecific genetic diversity

Intraspecific diversity informs the demographic and evolutionary histories of populations, and should be a main conservation target. Although approaches exist for identifying relevant biological conservation units, attempts to identify priority conservation areas for intraspecific diversity are scarce, especially within a multi-specific framework. We used neutral molecular data on six European freshwater fish species (Squalius cephalus, Phoxinus phoxinus, Barbatula barbatula, Gobio occitaniae, Leuciscus burdigalensis and Parachondrostoma toxostoma) sampled at the riverscape scale (i.e. the Garonne-Dordogne river basin, France) to determine hot-and coldspots of genetic diversity, and to identify priority conservation areas using a systematic conservation planning approach. We demonstrate that systematic conservation planning is efficient for identifying priority areas representing a predefined part of the total genetic diversity of a whole landscape. With the exception of private allelic richness (PA), classical genetic diversity indices (allelic richness, genetic uniqueness) were poor predictors for identifying priority areas. Moreover, we identified weak surrogacies among conservation solutions found for each species, implying that conservation solutions are highly species-specific. Nonetheless, we showed that priority areas identified using intraspecific genetic data from multiple species provide more effective conservation solutions than areas identified for single species or on the basis of traditional taxonomic criteria

Age, growth, mortality and recruitment of thin sharpbelly Toxabramis swinhonis Günther, 1873 in three shallow lakes along the middle and lower reaches of the Yangtze River basin, China

Despite being the most dominant and widespread small fish species in the lakes along the middle and lower reaches of the Yangtze River basin, Toxabramis swinhonis has been paid little attention by fisheries scientists and little is known about its population characteristics. For this reason, we estimated age, growth, mortality and recruitment of this species based on three shallow lakes, Biandantang Lake, Shengjin Lake and Kuilei Lake (BDT, SJH and KLH, respectively) in this region. A total of 13,585 (8,818 in BDT, 2,207 in SJH and 2,560 in KLH) individuals were collected during monthly sampling from July 2016 to September 2017. The results revealed that the age structures of T. swinhonis consisted of four age groups (0+–3+), with 0+–1+ year old fish comprising more than 98% of the samples. Allometric growth patterns were displayed by fish from all sampling sites and the von Bertalanffy growth functions estimated were Lt = 173.25 (1 – e−1.20 (t + 1.09)): BDT; Lt = 162.75 (1 – e−1.20 (t + 1.08)): SJH and Lt = 215.25 (1 – e−1.20 (t + 1.12)): KLH, respectively. The rates of total mortality (Z), natural mortality (M) and fishing mortality (F) at BDT, SJH and KLH were computed as 5.82, 5.50 and 4.55 year−1; 1.89, 1.87 and 1.75 year−1; 3.93, 3.63 and 2.80 year−1, respectively. Meanwhile, growth performance indices (φ′) were 0.68 (in BDT), 0.66 (in SJH) and 0.62 (in KLH), which indicated that T. swinhonis were overfished slightly in all study areas. Area-specific recruitment patterns were similar to each other, displaying evidence of batch spawning, with major peaks in April and August, accounting for 92.21% (BDT), 88.21% (SJH) and 88.73% (KLH) of total recruitment, respectively. These results showed that brief generation-time, fast growth rate, relatively high natural mortality rate and strong reproductive capacity (r-strategies) are reasons why this species became the most dominant species in many lakes of China

Déterminants de la variabilité temporelle et spatiale du recrutement piscicole en milieu fluvial (facteurs climatiques et interactions biotiques)

En eaux courantes, l'étude des communautés a longtemps focalisé sur l'influence des facteurs physiques (hydrauliques en particulier), mais peu de travaux concernent les parties aval des cours d'eaux où des conditions hydrauliques plus homogènes peuvent faciliter la mise en évidence d'autres facteurs. Dans ce contexte, cette thèse se propose d'étudier, à différentes échelles d'observation, les déterminants de la variabilité temporelle et spatiale des juvéniles de poissons. Ce travail aborde (1) l'importance de facteurs climatiques et densité-dépendants sur les fluctuations d'abondance à large échelle (inter-annuelle et inter-site), et (2) le rôle des ressources trophiques et des structures végétales à une échelle plus fine. Au cours de ce travail, j'ai pu montrer l'effet majeur de la thermique par rapport à l'hydrologie sur les fluctuations d'abondance de la première classe d'âge d'une espèce (induisant un fort synchronisme entre populations), alors qu'une survie densité-dépendante régule les classes plus âgées. Mes résultats démontrent l'importance du zooplancton (abondance et taille) pour la distribution des juvéniles. La végétation est un facteur majeur de l'habitat fluvial des poissons et l'hypothèse d'une préférence des habitats de complexité intermédiaire est confirmée. La morphologie des macrophytes est discutée en terme d'efficacité de l'alimentation et du risque de prédation. Pour des cours d'eaux de grande taille, j'ai ainsi démontré l'importance de la thermique à large échelle, ainsi que des ressources et de la végétation à petite échelle. Les relations entre fluctuations d'abondance et préférences d'habitat trouvent des implications en terme de développement de modèles prédictifs. La prise en compte des traits biologiques des espèces (stades de développement, stratégies de reproduction) et le couplage des approches spatiales et temporelles de la distribution des populations offrent des perspectives pour l'étude d'espèces ayant des cycles de vie complexes.LYON1-BU.Sciences (692662101) / SudocPARIS-Museum-Bib. d'ichtyologie (751052306) / SudocSudocFranceF

Disentangling the Drivers of the Sampling Bias of Freshwater Fish across Europe

The Wallacean shortfall refers to the knowledge gap in biodiversity distributions. There is still limited knowledge for freshwater fish species despite the importance of focusing conservation efforts towards this group due to their alarming extinction risk and the increasing human pressure on freshwater ecosystems. Here, we addressed the Wallacean shortfall for freshwater fish faunas across Europe by using the completeness indicator derived from species accumulation curves to quantify the fish sampling efforts. The multiple potential drivers of completeness that were previously related to the sampling efforts for other species (i.e., population density, nature reserves, or distance to cities) were tested using a 10 × 10 km2 grid resolution, as well as environmental (e.g., climatic) factors. Our results suggested that although there was an overall spatial pattern at the European level, the completeness was highly country-dependent. Accessibility parameters explained the sampling efforts, as for other taxa. Likewise, climate factors were related to survey completeness, possibly pointing to the river conditions required for fish sampling. The survey effort map we provide can be used to optimize future sampling, aiming at filling the data gaps in undersampled regions like the eastern European countries, as well as to account for the current bias in any ecological modeling using such data, with important implications for conservation and management

Data from: Climate interacts with anthropogenic drivers to determine extirpation dynamics

Theoretical studies suggest that the dynamics of a species’ range during a period of climate change depends upon the existence and interplay of various ecological and evolutionary processes. Here we tested how anthropogenic pressures contribute to climate-mediated extirpation patterns of 32 freshwater fish species over the last 20 yr. We contrasted two extreme cases to determine whether extirpations were governed by patterns of climate exposure, assuming full adaptation of species to local climate, or instead by the interplay between climate exposure and the distance from the centroid of species’ climatic niches, assuming a fixed niche, and asked whether anthropogenic disturbances interact with these climatic drivers. We found strong support for the fixed niche hypothesis, but showed that species-specific local adaptation to climate may also be important in determining extirpation dynamics. We also demonstrated that anthropogenic disturbance acted in concert with climate, ultimately determining population changes. Our results add novel evidence that unravelling the direct links between range dynamics and climate requires a multifaceted treatment, and that accounting for the cumulative effects of anthropogenic pressures deserves special attention in the context of climate change

Poissons des rivières françaises et changement climatique (impacts sur la distribution des espèces et incertitudes des projections)

Les changements climatiques et leurs impacts sur la biodiversité font aujourd'hui l'objet d'une attention croissante de la part de la communauté scientifique et des gestionnaires des écosystèmes naturels. En effet, le climat influence la biologie et l'écologie des espèces animales et végétales, depuis leur physiologie jusqu'à leur répartition. Les modifications climatiques pourraient donc avoir des répercussions importantes sur les espèces et les assemblages. Au sein des écosystèmes aquatiques continentaux, les poissons de rivière sont des organismes incapables de réguler leur température corporelle et soumis à une variabilité hydrologique importante ainsi qu'à de fortes pressions anthropiques. Leur réponse aux modifications du climat actuelles et à venir a pourtant été encore peu abordée. L'objectif de ce travail de thèse est donc d'évaluer les impacts potentiels du changement climatique sur les poissons des rivières françaises, et plus particulièrement sur la distribution des espèces et la structure des assemblages. Des données fournies par l'Office National de l'Eau et des Milieux Aquatiques ainsi qu'une approche de modélisation basée sur les niches écologiques des espèces (i.e., modèles de distribution) ont été utilisées. Différentes sources d'incertitude ont également été testées dans une approche d'ensembles afin de prendre en compte la variabilité entre les impacts projetés et fournir ainsi une évaluation robuste de ces impacts. La première partie de ce travail a consisté en l'identification des principaux déterminants environnementaux qui structurent la répartition spatiale des espèces de poisson au sein des réseaux hydrographiques. Globalement, il apparaît qu'une combinaison de facteurs climatiques et de variables décrivant l'habitat local et la position des habitats au sein des réseaux hydrographiques est importante pour expliquer la distribution actuelle des espèces. De plus, les espèces ont toutes des réponses différentes aux facteurs de l'environnement. Dans un second temps, nous avons mis en évidence que le choix de la méthode statistique de modélisation de la niche écologique est crucial, les patrons actuels et futurs de distribution prédits étant fortement contrastés selon la méthode de modélisation considérée. Cette dernière s'avère même être la principale source d'incertitude dans les projections futures, bien plus encore que les modèles climatiques de circulation générale et les scénarios d'émission de gaz à effet de serre. La variabilité entre les prédictions issues de plusieurs techniques de modélisation peut être prise en compte par une approche de consensus. Un modèle consensuel basé sur la valeur moyenne de l'ensemble de prédictions est capable de prédire correctement la distribution actuelle des espèces et la composition des assemblages. Nous avons donc choisi de retenir cette approche pour évaluer au mieux les impacts potentiels du changement climatique sur les poissons des rivières françaises à la fin du 21ème siècle. Nous avons montré que la majorité des espèces de poisson pourrait être affectée par les futures modifications du climat. Seules quelques espèces d'eau froide (e.g. truite fario, chabot) pourraient restreindre leur distribution aux parties les plus apicales des réseaux hydrographiques. Au contraire, les espèces tolérant des températures plus élevées pourraient coloniser de nouveaux habitats et étendre ainsi leur répartition. Ces modifications de la distribution des espèces pourraient conduire à un réarrangement des assemblages au niveau taxonomique et fonctionnel. Une augmentation de la diversité locale et de la similarité régionale (i.e., homogénéisation) sont ainsi prédites simultanément. L'ensemble de ces résultats apporte donc des éléments sur la compréhension de la distribution des poissons d'eau douce et sur les conséquences du changement climatique qui peuvent être envisagées. Ce travail fournit ainsi une base aux acteurs de la gestion de la biodiversité afin d'initier des mesures de conservation concrètes. De plus, les considérations méthodologiques développées dans cette thèse sont une contribution importante à l'amélioration des projections issues de modèles statistiques de distribution et à la quantification de leur incertitude.Climate change and its impact on biodiversity are receiving increasing attention from scientists and people managing natural ecosystems. Indeed, climate has a major influence on the biology and ecology of fauna and flora, from physiology to distribution. Climate change may thus have major consequences on species and assemblages. Among freshwater ecosystems, stream fish have no physiological ability to regulate their body temperature and they have to cope with streams' hydrological variability and strong anthropogenic pressures. Yet their response to current and future climate change has been poorly studied. The aim of this PhD thesis is to assess the potential impact of climate change on fish in French streams, mainly on species distribution and assemblages' structure. Data provided by the Office National de l'Eau et des Milieux Aquatiques combined with a modelling approach based on species' ecological niche (i.e., distribution models) have been used. Several sources of uncertainty have also been considered in an ensemble modeling framework in order to account for the variability between projected impacts and to provide reliable estimates of such impact. First, we have identified the main environmental factors that determine the spatial distribution of fish species within river networks. Overall, it appears that a combination of both climatic variables and variables describing the local habitat and its position within the river network is important to explain the current species distribution. Moreover, each fish species responded differently to the environmental factors. Second, we have highlighted that the choice of the statistical method used to model the fish ecological niche is crucial given that the current and future patterns of distribution predicted by different statistical methods vary significantly. The statistical method appears to be the main source of uncertainty, resulting in more variability in projections than the global circulation models and greenhouse gas emission scenarios. The variability between predictions from several statistical methods can be taken into account by a consensus approach. Consensual predictions based on the computation of the average of the whole predictions ensemble have achieved accurate predictions of the current species distribution and assemblages' composition. We have therefore selected this approach to assess the potential impacts of climate change on fish in French streams at the end of the 21st century with the highest degree of confidence. We have found that most fish species could be sensitive to the future climate modifications. Only a few cold-water species (i.e., brown trout, bullhead) could restrict their distribution to the most upstream parts of river networks. On the contrary, cool- and warm-water fish species could colonize many newly suitable habitats and expand strongly their distribution. These changes of species distribution could lead to a rearrangement of fish assemblages both at the taxonomic and functional levels. An increase in local diversity together with an increase in regional similarity (i.e., homogenization) are therefore expected. All these results bring new insights for the understanding of stream fish species distribution and expected consequences of climate change. This work thus provides biodiversity managers and conservationists with a basis to take efficient preservation measures. In addition, methodological developments considered in this PhD thesis are an important contribution to the improvements of projections by statistical models of species distribution and to the quantification of their uncertainty.TOULOUSE-INP (315552154) / SudocSudocFranceF

Evidence of Water Quality Degradation in Lower Mekong Basin Revealed by Self-Organizing Map.

To reach a better understanding of the spatial variability of water quality in the Lower Mekong Basin (LMB), the Self-Organizing Map (SOM) was used to classify 117 monitoring sites and hotspots of pollution within the basin identified according to water quality indicators and US-EPA guidelines. Four different clusters were identified based on their similar physicochemical characteristics. The majority of sites in upper (Laos and Thailand) and middle part (Cambodia) of the basin were grouped in two clusters, considered as good quality water with high DO and low nutrient levels. The other two clusters were mostly composed of sites in Mekong delta (Vietnam) and few sites in upstream tributaries (i.e., northwestern Thailand, Tonle Sap Lake, and swamps close to Vientiane), known for moderate to poor quality of water and characterized by high nutrient and dissolved solid levels. Overall, we found that the water in the mainstream was less polluted than its tributaries; eutrophication and salinity could be key factors affecting water quality in LMB. Moreover, the seasonal variation of water quality seemed to be less marked than spatial variation occurring along the longitudinal gradient of Mekong River. Significant degradations were mainly associated with human disturbance and particularly apparent in sites distributed along the man-made canals in Vietnam delta where population growth and agricultural development are intensive

Temporal dynamics for the 32 species

Temporal dynamics for the 32 species between 8 consecutives time periods at 794 sites across the French hydrographic network

Fish size spectrum as a complementary biomonitoring approach of freshwater ecosystems

Freshwater bioindicators have been developed to assess ecosystem health and responses to human-induced stressors. To date, most bioindicators primarily rely on the species identity of plant and animal communities and do not account for interactions among organisms and fluxes of energy between trophic levels. Body size is one of the most important ecological traits in aquatic ecosystems because it governs interactions among organisms and is affected by environmental conditions but, surprisingly, many of assessment approaches do not use individual body size. The community size spectrum is defined as the linear relationship between the abundance and the body size of organisms and reflects several important ecological features including ecosystem carrying capacity, predation-prey interactions, and trophic energy fluxes. In this study, we explored the potential of using the size spectrum parameters (slope, elevation and linearity) of fish community as a complementary bioindicator in 51 natural lakes and 102 reservoirs distributed across France. We determined how the fish size spectrum and other common bioindicators based on fish, macrophyte and phytoplankton communities responded to the water quality degradation, littoral habitat alterations and fish invasions. Results demonstrated that: (i) the size spectrum was driven by water quality degradation both in lakes and reservoirs, while size spectrum was affected by habitat loss in natural lakes and by fish invasion in reservoirs and (ii) the size spectrum was more sensitive to habitat loss than common bioindicators in natural lakes. This study highlights that the use of fish community size spectrum could provide additional insights into our understanding of the responses of freshwater ecosystems to global changes and could serve to improve the efficiency of management programs. This can be done at very limited additional cost because fish body size is commonly measured in biomonitoring protocols