The recovery of European freshwater biodiversity has come to a halt.

Owing to a long history of anthropogenic pressures, freshwater ecosystems are among the most vulnerable to biodiversity loss1. Mitigation measures, including wastewater treatment and hydromorphological restoration, have aimed to improve environmental quality and foster the recovery of freshwater biodiversity2. Here, using 1,816 time series of freshwater invertebrate communities collected across 22 European countries between 1968 and 2020, we quantified temporal trends in taxonomic and functional diversity and their responses to environmental pressures and gradients. We observed overall increases in taxon richness (0.73% per year), functional richness (2.4% per year) and abundance (1.17% per year). However, these increases primarily occurred before the 2010s, and have since plateaued. Freshwater communities downstream of dams, urban areas and cropland were less likely to experience recovery. Communities at sites with faster rates of warming had fewer gains in taxon richness, functional richness and abundance. Although biodiversity gains in the 1990s and 2000s probably reflect the effectiveness of water-quality improvements and restoration projects, the decelerating trajectory in the 2010s suggests that the current measures offer diminishing returns. Given new and persistent pressures on freshwater ecosystems, including emerging pollutants, climate change and the spread of invasive species, we call for additional mitigation to revive the recovery of freshwater biodiversity.

Quantitative measurement of geodiversity uniqueness: research implications and conservation applications.

Quantitative approaches are needed to complement qualitative explorations to identify sites with unique geodiversity and thereby guide geoconservation and geoheritage programmes. Here, we introduce the concept and associated index of 'geodiversity uniqueness'. This index is based on a numerical analysis of geofeatures and allows the identification of sites with unique geodiversity in a study area. We applied this approach to geofeature data from three areas in Finland. Our results showed that patterns of geodiversity uniqueness varied profoundly among the three study areas and across sites within each area. This was due to different sets of geofeatures and distinct characteristics of each study area. More importantly, the approach presented here was robust across the datasets and selection criteria for sets of sites, showing potential for geoconservation in each study area. The geodiversity uniqueness approach is a promising starting point to identify and map sites with unique geodiversity that can be further verified using field observations. To improve our knowledge of geodiversity variation, complementary approaches providing objective information on contributions to total beta geodiversity are needed to advance geoconservation programmes across areas and different spatial scales. This article is part of the Theo Murphy meeting issue 'Geodiversity for science and society'.

Spatial and temporal variation in lake macroinvertebrate communities is decreased by eutrophication.

Eutrophication impacts freshwater ecosystems and biodiversity across the world. While temporal monitoring has shown changes in the nutrient inputs in many areas, how spatial and temporal beta diversity change along the eutrophication gradient under a changing context remains unclear. In this regard, analyses based on time series spanning multiple years are particularly scarce. We sampled benthic macroinvertebrates in 32 sites across three lake habitat types (MACROPHYTE, OPEN WATER, PHYTOPLANKTON) along the eutrophication gradient of Lake Taihu in four seasons from 2007 to 2019. Our purpose was to identify the relative contributions of spatial and temporal dissimilarity (i.e., inter-annual dissimilarity and seasonal dissimilarity) to overall benthic biodiversity. We also examined spatio-temporal patterns in community assembly mechanisms and how associated variation in benthic macroinvertebrate communities responded to nutrient indicators. Results showed that eutrophication caused macroinvertebrate community homogenization both along spatial and temporal gradients. Though spatial variability dominated the variation of species richness, abundance and community dissimilarity, seasons within years dissimilarity, inter-annual dissimilarity and seasonal dissimilarity were much more sensitive to eutrophication. Moreover, eutrophication inhibited a strong environmental control in benthic macroinvertebrate community assembly, including a dominant role of deterministic process in the spatial variation of macroinvertebrate communities and transition from stochastic to deterministic process in the temporal assembly of macroinvertebrate communities along the eutrophication gradient. In addition, some sites in PHYTOPLANKTON habitats showed similar spatial dissimilarity and spatial SES as sites in MACROPHYTE habitats, and the decreased spatial dissimilarity of three habitats implying that lake ecosystem recovery projects have achieved their goal at least to a certain degree.

Historical and dispersal processes drive community assembly of multiple aquatic taxa in glacierized catchments in the Qinghai-Tibet plateau.

Understanding the relative role of dispersal dynamics and niche constraints is not only a core task in community ecology, but also becomes an important prerequisite for bioassessment. Despite the recent progress in our knowledge of community assembly in space and time, patterns and processes underlying biotic communities in alpine glacierized catchments remain mostly ignored. To fill this knowledge gap, we combined the recently proposed dispersal-niche continuum index (DNCI) with traditional constrained ordinations and idealized patterns of species distributions to unravel community assembly mechanisms of different key groups of primary producers and consumers (i.e., phytoplankton, epiphytic algae, zooplankton, macroinvertebrates, and fishes) in rivers in the Qinghai-Tibet Plateau, the World's Third Pole. We tested whether organismal groups with contrasting body sizes differed in their assembly processes, and discussed their applicability in bioassessment in alpine zones. We found that community structure of alpine river biotas was always predominantly explained in terms of dispersal dynamics and historical biogeography. These patterns are most likely the result of differences in species-specific functional attributes, the stochastic colonization-extinction dynamics driven by multi-year glacier disturbances and the repeated hydrodynamic separation among alpine catchments after the rising of the Qilian mountains. Additionally, we found that the strength of dispersal dynamics and niche constraints was partially mediated by organismal body sizes, with dispersal processes being more influential for microscopic primary producers. Finding that zooplankton and macroinvertebrate communities followed clumped species replacement structures (i.e., Clementsian gradients) supports the notion that environmental filtering also contributes to the structure of high-altitude animal communities in glacierized catchments. In terms of the applied fields, we argue that freshwater bioassessment in glacierized catchments can benefit from incorporating the metacommunity perspective and applying novel approaches to (i) detect the optimal spatial scale for species sorting and (ii) identify and eliminate the species that are sensitive to dispersal-related processes.

Disentangling the effects of geographic distance, environment and history on beta diversity of freshwater fish at a biogeographical crossroads.

Examining assemblage turnover and variation along geographic and environmental distances is a useful approach to evaluate beta diversity patterns and associated driving mechanisms. However, such studies are relatively limited in freshwater systems. Here, we compared the relationships between freshwater fish beta diversity and geographic distances among 165 hydrological units (HUs) in four zoogeographical regions (PA, Palearctic Region; CA, High Central Asia; EA, East Asia, SA, South Asia) across China and adjacent areas. This area can be considered a biogeographical crossroads, where faunal composition shares elements with different biogeographic and evolutionary origins. We found a considerably high level of between-HU overall dissimilarity (ßsor, range from ca. 0.60 to 0.85) in all four regions, mainly due to the turnover component (the relative contribution of ßsim to ßsor ranged from 60% to 90%). In general, ßsor and ßsim both significantly increased with geographic distance (except in PA), whereas the nestedness-resultant component (ßsne) decreased with geographic distance. The intercepts and slopes of the relationships between dissimilarities and distance (RDDs) both varied significantly among the four regions. The intercepts of ßsor and ßsim were both highest in SA, followed by CA, PA and EA, implying different levels of fish faunal heterogeneity at short distances. In contrast, the slopes of these two dissimilarities followed the decreasing trend from EA > CA > SA > PA, suggesting different environmental suitability and dispersal ability of fish species among regions. Variation partitioning in distance-based redundancy analysis showed that the spatial and historical factors were more important than area-heterogeneity and energy factors across all HUs and within three individual ecoregions (EA, SA and CA), but spatial factors were non-significant in PA. Our study highlighted the usefulness of RDDs in understanding biogeographical patterns and enhancing the biodiversity conservation of freshwater fishes.

Human land-uses homogenize stream assemblages and reduce animal biomass production.

Human land-use change is a major threat to natural ecosystems worldwide. Nonetheless, the effects of human land-uses on the structure of plant and animal assemblages and their functional characteristics need to be better understood. Furthermore, the pathways by which human land uses affect ecosystem functions, such as biomass production, still need to be clarified. We compiled a unique dataset of fish, arthropod and macrophyte assemblages from 61 stream ecosystems in two Neotropical biomes: Amazonian rainforest and Uruguayan grasslands. We then tested how the cover of agriculture, pasture, urbanization and afforestation affected the taxonomic richness and functional diversity of those three species assemblages, and the consequences of these effects for animal biomass production. Single trait categories and functional diversity were evaluated, combining recruitment and life-history, resource and habitat-use, and body size. The effects of intensive human land-uses on taxonomic and functional diversities were as strong as other drivers known to affect biodiversity, such as local climate and environmental factors. In both biomes, the taxonomic richness and functional diversity of animal and macrophyte assemblages decreased with increasing cover of agriculture, pasture, and urbanization. Human land-uses were associated with functional homogenization of both animal and macrophyte assemblages. Human land-uses reduced animal biomass through direct and indirect pathways mediated by declines in taxonomic and functional diversities. Our findings indicate that converting natural ecosystems to supply human demands results in species loss and trait homogenization across multiple biotic assemblages, ultimately reducing animal biomass production in streams.

Boosting freshwater fish conservation with high-resolution distribution mapping across a large territory.

The lack of high-resolution distribution maps for freshwater species across large extents fundamentally challenges biodiversity conservation worldwide. We devised a simple framework to delineate the distributions of freshwater fishes in a high-resolution drainage map based on stacked species distribution models and expert information. We applied this framework to the entire Chinese freshwater fish fauna (>1600 species) to examine high-resolution biodiversity patterns and reveal potential conflicts between freshwater biodiversity and anthropogenic disturbances. The correlations between spatial patterns of biodiversity facets (species richness, endemicity, and phylogenetic diversity) were all significant (r = 0.43-0.98, p < 0.001). Areas with high values of different biodiversity facets overlapped with anthropogenic disturbances. Existing protected areas (PAs), covering 22% of China's territory, protected 25-29% of fish habitats, 16-23% of species, and 30-31% of priority conservation areas. Moreover, 6-21% of the species were completely unprotected. These results suggest the need for extending the network of PAs to ensure the conservation of China's freshwater fishes and the goods and services they provide. Specifically, middle to low reaches of large rivers and their associated lakes from northeast to southwest China hosted the most diverse species assemblages and thus should be the target of future expansions of the network of PAs. More generally, our framework, which can be used to draw high-resolution freshwater biodiversity maps combining species occurrence data and expert knowledge on species distribution, provides an efficient way to design PAs regardless of the ecosystem, taxonomic group, or region considered.

Potenciación de la conservación de peces de agua dulce con mapeos de distribución de alta resolución a lo largo de un territorio extenso Resumen La falta de mapas de distribución en alta resolución para las especies de agua dulce en grandes extensiones es un reto importante para la conservación mundial de la biodiversidad. Diseñamos un marco simple para delinear la distribución de los peces de agua dulce en un mapa de drenaje en alta resolución basado en los modelos apilados de la distribución de las especies y la información de expertos. Aplicamos este marco a toda la ictiofauna de agua dulce en China (>1600 especies) para analizar los patrones en alta resolución de la biodiversidad y revelar los conflictos potenciales entre la biodiversidad de agua dulce y las perturbaciones antropogénicas. Todas las correlaciones entre los patrones espaciales de las facetas de la biodiversidad (riqueza de especies, endemismo y diversidad filogenética) fueron importantes (r = 0.43-0.98, p < 0.001). Las áreas con valores altos de diferentes facetas de la biodiversidad se traslaparon con las perturbaciones antropogénicas. Las áreas protegidas existentes que actualmente cubren el 22% del territorio de China, protegen 25-2% del hábitat de los peces, 16-23% de las especies y 30-31% de las áreas de conservación prioritarias. Además, 6-21% de las especies se encontraban totalmente desprotegidas. Estos resultados sugieren que se necesita extender la red de áreas protegidas para asegurar la conservación de los peces de agua dulce de China y los bienes y servicios que proporcionan. En concreto, los niveles medio a bajo de los grandes ríos y sus lagos asociados del noreste al suroeste de China albergaron los ensambles de especies más diversos y por lo tanto deberían ser el objetivo de las futuras expansiones de la red de áreas protegidas. De forma más generalizada, nuestro marco, el cual puede usarse para trazar mapas en alta resolución de la biodiversidad de agua dulce al combinar los datos de presencia de las especies y el conocimiento de los expertos sobre su distribución, proporciona un método eficiente para diseñar las áreas protegidas sin importar el ecosistema, región o grupo taxonómico considerado.

Responses of macroinvertebrate functional trait structure to river damming: From within-river to basin-scale patterns.

Revealing how aquatic organisms respond to dam impacts is essential for river biomonitoring and management. Traditional examinations of dam impacts on macroinvertebrate assemblages were frequently conducted within single rivers (i.e., between upstream vs. downstream locations) and based on taxonomic identities but have rarely been expanded to level of entire basins (i.e., between dammed vs. undammed rivers) and from a functional trait perspective. Here, we evaluated the effects of dams on macroinvertebrate assemblages at both the within-river and basin scales using functional traits in two comparable tropical tributaries of the Lancang-Mekong River. At different scales, maximum body size, functional feeding groups (FFG), voltinism and occurrence in drift respond significantly to dam impact. Armoring categories varied significantly between downstream sites and upstream sites, and oviposition behavior, habits and adult life span significantly differed between rivers. The key traits at the within-river scale resembled to those at the between-river scale, suggesting that within-river trait variation could further shape functional trait structure at the basin scale in dammed rivers. Furthermore, water nutrients and habitat quality induced by dams showed the most important role in shaping trait structure, although trait-environment relationships varied between the two different scales. In addition, the trait-environment relationships were stronger in the dry season than in the wet season, suggesting a more important role of environmental filtering processes in the dry season compared with the wet season. This study highlights the utility of the trait-based approach to diagnose the effects of damming and emphasizes the importance of spatial scale to examine dam impacts in riverine systems.

A global agenda for advancing freshwater biodiversity research.

Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global consultation, we identify 15 pressing priority needs, grouped into five research areas, in an effort to support informed stewardship of freshwater biodiversity. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated actions towards its sustainable management and conservation.

Invasion impacts and dynamics of a European-wide introduced species.

Globalization has led to the introduction of thousands of alien species worldwide. With growing impacts by invasive species, understanding the invasion process remains critical for predicting adverse effects and informing efficient management. Theoretically, invasion dynamics have been assumed to follow an "invasion curve" (S-shaped curve of available area invaded over time), but this dynamic has lacked empirical testing using large-scale data and neglects to consider invader abundances. We propose an "impact curve" describing the impacts generated by invasive species over time based on cumulative abundances. To test this curve's large-scale applicability, we used the data-rich New Zealand mud snail Potamopyrgus antipodarum, one of the most damaging freshwater invaders that has invaded almost all of Europe. Using long-term (1979-2020) abundance and environmental data collected across 306 European sites, we observed that P. antipodarum abundance generally increased through time, with slower population growth at higher latitudes and with lower runoff depth. Fifty-nine percent of these populations followed the impact curve, characterized by first occurrence, exponential growth, then long-term saturation. This behaviour is consistent with boom-bust dynamics, as saturation occurs due to a rapid decline in abundance over time. Across sites, we estimated that impact peaked approximately two decades after first detection, but the rate of progression along the invasion process was influenced by local abiotic conditions. The S-shaped impact curve may be common among many invasive species that undergo complex invasion dynamics. This provides a potentially unifying approach to advance understanding of large-scale invasion dynamics and could inform timely management actions to mitigate impacts on ecosystems and economies.

Distance decay 2.0 - A global synthesis of taxonomic and functional turnover in ecological communities.

Aim: Understanding the variation in community composition and species abundances (i.e., ß-diversity) is at the heart of community ecology. A common approach to examine ß-diversity is to evaluate directional variation in community composition by measuring the decay in the similarity among pairs of communities along spatial or environmental distance. We provide the first global synthesis of taxonomic and functional distance decay along spatial and environmental distance by analysing 148 datasets comprising different types of organisms and environments. Location: Global. Time period: 1990 to present. Major taxa studied: From diatoms to mammals. Method: We measured the strength of the decay using ranked Mantel tests (Mantel r) and the rate of distance decay as the slope of an exponential fit using generalized linear models. We used null models to test whether functional similarity decays faster or slower than expected given the taxonomic decay along the spatial and environmental distance. We also unveiled the factors driving the rate of decay across the datasets, including latitude, spatial extent, realm and organismal features. Results: Taxonomic distance decay was stronger than functional distance decay along both spatial and environmental distance. Functional distance decay was random given the taxonomic distance decay. The rate of taxonomic and functional spatial distance decay was fastest in the datasets from mid-latitudes. Overall, datasets covering larger spatial extents showed a lower rate of decay along spatial distance but a higher rate of decay along environmental distance. Marine ecosystems had the slowest rate of decay along environmental distances. Main conclusions: In general, taxonomic distance decay is a useful tool for biogeographical research because it reflects dispersal-related factors in addition to species responses to climatic and environmental variables. Moreover, functional distance decay might be a cost-effective option for investigating community changes in heterogeneous environments.

From meta-system theory to the sustainable management of rivers in the Anthropocene.

Regional-scale ecological processes, such as the spatial flows of material, energy, and organisms, are fundamental for maintaining biodiversity and ecosystem functioning in river networks. Yet these processes remain largely overlooked in most river management practices and underlying policies. Here, we propose adoption of a meta-system approach, where regional processes acting at different levels of ecological organization - populations, communities, and ecosystems - are integrated into conventional river conservation, restoration, and biomonitoring. We also describe a series of measurements and indicators that could be assimilated into the implementation of relevant biodiversity and environmental policies. Finally, we highlight the need for alternative management strategies that can guide practitioners toward applying recent advances in ecology to preserve and restore river ecosystems and the ecosystem services they provide, in the context of increasing alteration of river network connectivity worldwide.

Anthropogenic land‒use impacts on the size structure of macroinvertebrate assemblages are jointly modulated by local conditions and spatial processes.

Body size descriptors and associated resemblance measurements may provide useful tools for forecasting ecological responses to increasing anthropogenic land‒use disturbances. Yet, the influences of agriculture and urbanisation on the size structure of biotic assemblages have seldom been investigated in running waters. Using a comprehensive dataset on stream macroinvertebrates from 21 river basins across Western Finland, we assessed whether the structure of assemblages via changes in taxonomic composition and body size distributions responded predictably to anthropogenic land‒use impacts. Specifically, we applied a combination of resemblance measurements based on cumulative abundance profiles and spatially constrained null models to understand faunal impairment by agricultural and urban development, and the most likely mechanisms underlying the observed shifts in assemblage size structure. Anthropogenically impacted stream sites showed less variation in assemblage composition and size distributions compared with least‒disturbed sites, with strong declines in internal variation also occurring for the transition from near‒pristine to moderately impacted landscapes. These results were consistent whether based on species‒level or genus‒level data. Variation in assemblage size structure seemed to be more predictable than taxonomic composition, supporting the notion that resemblance measurements based on body size distributions can represent an improvement to more traditional approaches based on taxonomic identities alone. In addition, we showed that macroinvertebrate assemblages resulted from effects of land‒use degradation mediated through local conditions and spurious spatial structures in the distribution of anthropogenic activities across the landscape. Overall, our findings suggest that existing water policies and agri‒environment schemes should be guided not only by understanding the individual effects of agricultural and urban development on taxonomic composition at a given stream site. Rather, we should also acknowledge the size structure of stream assemblages and whether concomitant changes in local conditions and the non‒random distribution of human infrastructures are likely to mitigate or accelerate these effects.

Loss of lateral hydrological connectivity impacts multiple facets of molluscan biodiversity in floodplain lakes.

Lateral hydrological connectivity (LHC) is a key process in maintaining aquatic biodiversity in river floodplain ecosystems. However, the effects of LHC loss on aquatic biodiversity are rarely studied. Here, we evaluated, for the first time, the responses of multiple facets (i.e., taxonomic, functional and phylogenetic) of alpha and beta diversity of freshwater molluscs to the LHC loss in 23 floodplain lakes in the Yangtze River Basin in China. Our results showed that taxonomic and functional alpha diversities were all significantly higher in connected lakes (CLs) than in disconnected lakes (DLs), whereas phylogenetic alpha diversity (Δ+) was lower in CLs than in DLs. For beta diversity facets, taxonomic (Tßsor) and phylogenetic (Pßsor) dissimilarities were slightly more contributed by the turnover component or equally contributed by the turnover and nestedness-resultant components both in CLs and DLs. Instead, functional beta diversity (Fßsor), generally showing much lower values than Tßsor and Pßsor, was mainly contributed by the nestedness-resultant component (76.6-84.0%), especially in DLs. We found that only functional dissimilarities were significantly higher in DLs than CLs, indicating a high level of functional diversity loss without replacement of species possessing traits sensitive to hydrological disconnection (i.e., large body size, lamellibranch body form, filter feeding, ovoviviparity and burrowing habits). In general, lake area, hydrological connectivity, aquatic vegetation coverage and nutrient levels (TN and TP) played important roles in structuring variation in molluscan alpha and beta diversities, although the three diversity facets responded to different environmental factors. Our results suggest that loss of connectivity to the mainstem river has negative impacts on molluscan assemblages in floodplain lakes. More importantly, as taxonomic, functional and phylogenetic diversities responded somewhat differently to the loss of hydrological connectivity, all of these biodiversity facets should be better incorporated into aquatic biodiversity assessment and conservation programs in large river floodplains.

Does trait-based joint species distribution modelling reveal the signature of competition in stream macroinvertebrate communities?

The occupancy and abundance of species are jointly driven by local factors, such as environmental characteristics and biotic interactions, and regional-scale factors, such as dispersal and climate. Recently, it has been shown that biotic interactions shape species occupancies and abundances beyond local extents. However, for small ectothermic animals, particularly for those occurring in freshwater environments, the importance of biotic interactions remains understudied. Species-to-species associations from joint species distribution models (i.e. species associations while controlling for environmental characteristics) are increasingly used to draw hypotheses of which species possibly show biotic interactions. We studied whether species-to-species associations from joint species distribution models show signs of competition using a hypothesis testing framework in stream macroinvertebrate communities at regional extent. We sampled aquatic macroinvertebrates from 105 stream sites in western Finland encompassing a latitudinal gradient of c. 500 kilometres. We hypothesized that if competition drives these associations (H1) functionally, similar species are mostly negatively associated, whereas functionally dissimilar species show random associations. We further hypothesized that the relationship between functional dissimilarity and the strength of association is more pronounced (H2) for abundances rather than occupancies, (H3) at small grain (i.e. stream site) rather than at large grain (i.e. river basin), and (H4) among species having weak dispersal ability than among species with high dispersal ability. Stream macroinvertebrates showed both negative and positive species-to-species associations while controlling for habitat characteristics. However, the negative associations were mostly at large grain (river basin) rather than at small grain (stream site), in occupancy rather than abundance, and not related to species functional dissimilarity or to their dispersal ability. Thus, all our hypotheses considering possible competition (H1-H4) were rejected. Competition does not appear to be a major driving force of stream macroinvertebrate communities at the spatial grain sizes considered. The observed positive associations in occupancy at small grain (stream site) may be attributed to species' similar microhabitat preferences, whereas at large grain (river basin), they may stem from metacommunity dynamics. Our results highlight that species traits were necessary to interpret whether or not species-to-species associations from joint species distribution models resulted from biotic interactions.

Effects of dam construction and fish invasion on the species, functional and phylogenetic diversity of fish assemblages in the Yellow River Basin.

An understanding of the consequences of human-mediated disturbances from multi-facet diversity (i.e. species, functional and phylogenetic) perspectives is of great significance in biodiversity assessment and conservation planning. Most previous studies have concentrated on anthropogenic effects on species diversity in the Yellow River Basin (YRB) in China, but information on anthropogenic effects on phylogenetic and functional facets is still pending. Here, we identified the temporal changes in species, functional, and phylogenetic alpha diversity of fish assemblages in 18 reaches (i.e. 15 mainstream reaches and 3 tributaries) of the YRB under the background of long-term cascade hydropower construction and widespread introduction of non-native fish species. The results showed that native fishes experienced a sharp decline through time, with an average of 25.6 (extirpation rate 46.7%) native species extirpated per sub-region, and 89 of 182 (48.9%) native species extirpated across the whole basin during the period considered. However, the number of non-native fish species substantially increased, with an average increase of 8.6 species (invasion rate 26.9%) per sub-region. Furthermore, the percentage of non-native species showed a significant unimodal relationship with average altitude, with highest invasion rates (ca. 70%) in upstream reaches. The extirpation rate was negatively related to altitude, increasing from upstream to downstream reaches. Interestingly, the functional diversity indices (FEve, FDiv, FDis, RaoQ) and phylogenetic diversity indices (Δ+ and Λ+) of the entire fish fauna significantly increased through time, whereas these indices based on native fish fauna only did not change. Such increases in functional and phylogenetic diversities were mainly triggered by introductions of non-native species, which were functionally distinct and phylogenetically distant from native species, and extirpation of congeneric endemic species. In general, the present study revealed anthropogenic impacts on the multi-faceted diversity of fish assemblages in a large river and highlighted the negative effects of cascaded hydropower developments and non-native fish invasions on native fish. Moreover, evaluating the responses of multi-faceted diversity to anthropogenic disturbances is a suitable means to understand assemblage reorganization and to assess how such impacts lead to the decline of biodiversity. The complementary information derived from using the multi-faceted diversity approach indicate functional and phylogenetic diversity measures could be implemented in biodiversity planning in the sediment-laden and ecologically important Yellow River Basin.

A Metacommunity Approach to Improve Biological Assessments in Highly Dynamic Freshwater Ecosystems.

Rapid shifts in biotic communities due to environmental variability challenge the detection of anthropogenic impacts by current biomonitoring programs. Metacommunity ecology has the potential to inform such programs, because it combines dispersal processes with niche-based approaches and recognizes variability in community composition. Using intermittent rivers-prevalent and highly dynamic ecosystems that sometimes dry-we develop a conceptual model to illustrate how dispersal limitation and flow intermittence influence the performance of biological indices. We produce a methodological framework integrating physical- and organismal-based dispersal measurements into predictive modeling, to inform development of dynamic ecological quality assessments. Such metacommunity-based approaches could be extended to other ecosystems and are required to underpin our capacity to monitor and protect ecosystems threatened under future environmental changes.

Choice of field and laboratory methods affects the detection of anthropogenic disturbances using stream macroinvertebrate assemblages.

Accurate and precise detection of anthropogenic impacts on stream ecosystems using macroinvertebrates as biological indicators depends on the use of appropriate field and laboratory methods. We assessed the responsiveness to anthropogenic disturbances of assemblage metrics and composition by comparing commonly employed alternative combinations of field sampling and individuals counting methods. Four datasets were derived by, in the field 1) conducting multihabitat sampling (MH) or 2) targeting samples in leaf packs (single-habitat sampling - SH) and, in the laboratory A) counting all individuals of the samples, or B) simulating subsampling of 300 individuals per sample. We collected our data from 39 headwater stream sites in a drainage basin located in the Brazilian Cerrado. We used a previously published quantitative integrated disturbance index (IDI), based on both local and catchment disturbance measurements, to characterize the intensity of anthropogenic alterations at each site. Family richness and % Ephemeroptera, Plecoptera and Trichoptera (% EPT) individuals obtained from each dataset were tested against the IDI through simple linear regressions, and the differences in assemblage composition between least- and most-disturbed sites was tested using Permutational Multivariate Analysis of Variance (PERMANOVA). When counting all individuals, differences in taxonomic richness and assemblage composition of macroinvertebrate assemblages between least- and most-disturbed sites were more pronounced in the MH than in the SH sampling method. Leaf packs seemed to concentrate high abundance and diversity of macroinvertebrates in highly disturbed sites, acting as 'biodiversity hotbeds' in these situations, which likely reduced the response of the assemblages to the disturbance gradient when this substrate was targeted. However, MH sampling produced weaker results than SH when subsampling was performed. The % EPT individuals responded better to the disturbance gradient when SH was employed, and its efficiency was not affected by the subsampling procedure. We conclude that no single method was the best in all situations, and the efficiency of a sampling protocol depends on the combination of field and laboratory methods being used. Although the total count of individuals with multihabitat sampling obtained the best results for most of the evaluated variables, the decision of which procedures to use depends on the amount of time and resources available, on the variables of interest, on the availability of habitat types in the sites sampled, and on the other methods being employed in the sampling protocol.

Correlates of different facets and components of beta diversity in stream organisms.

Recently, community ecology has emphasized the multi-facetted aspects of biological diversity by linking species traits and the environment. Here, we explored environmental correlates of taxonomically-based and traits-based compositional distances using a comprehensive data set of diatom and macroinvertebrate communities. We also explored the responses of different beta diversity components (i.e., overall beta diversity, turnover, and nestedness) of beta diversity facets (i.e., taxonomically and traits-based beta diversity) to environmental distances. Partial Mantel tests were used to test the relationships between beta diversity and environmental distance (while controlling for spatial distances). Taxonomically-based beta diversity varied much more than traits-based beta diversity, indicating strong functional convergence. We found that taxonomically-based beta diversity was largely driven by the turnover component. However, the nestedness component contributed more to overall traits-based beta diversity than the turnover component. Taxonomically-based beta diversity was significantly correlated with environmental distances for both diatoms and macroinvertebrates. Thus, we found support for the role of environmental filtering as a driver of community dissimilarities of rather different biological groups. However, the strength of these relationships between beta diversity and environmental distances varied depending on the biological group, facet, component, and the way which the environmental variables were selected to calculate the explanatory (distance) matrix. Our results indicated that both taxonomically and traits-based approaches are still needed to better understand patterns and mechanisms affecting the organization of biological communities in streams. This is because different facets of biological communities may be driven by different mechanisms.

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 SAD-mainly longitudinal in the United States but latitudinal in Finland-were 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.