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.

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'.

Multi-decadal improvements in the ecological quality of European rivers are not consistently reflected in biodiversity metrics.

Humans impact terrestrial, marine and freshwater ecosystems, yet many broad-scale studies have found no systematic, negative biodiversity changes (for example, decreasing abundance or taxon richness). Here we show that mixed biodiversity responses may arise because community metrics show variable responses to anthropogenic impacts across broad spatial scales. We first quantified temporal trends in anthropogenic impacts for 1,365 riverine invertebrate communities from 23 European countries, based on similarity to least-impacted reference communities. Reference comparisons provide necessary, but often missing, baselines for evaluating whether communities are negatively impacted or have improved (less or more similar, respectively). We then determined whether changing impacts were consistently reflected in metrics of community abundance, taxon richness, evenness and composition. Invertebrate communities improved, that is, became more similar to reference conditions, from 1992 until the 2010s, after which improvements plateaued. Improvements were generally reflected by higher taxon richness, providing evidence that certain community metrics can broadly indicate anthropogenic impacts. However, richness responses were highly variable among sites, and we found no consistent responses in community abundance, evenness or composition. These findings suggest that, without sufficient data and careful metric selection, many common community metrics cannot reliably reflect anthropogenic impacts, helping explain the prevalence of mixed biodiversity trends.

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.

Eutrophication increases the similarity of cyanobacterial community features in lakes and reservoirs.

Eutrophication of inland waters is a mostly anthropogenic phenomenon impacting aquatic biodiversity worldwide, and might change biotic community structure and ecosystem functions. However, little is known about the patterns of cyanobacterial community variations and changes both on alpha and beta diversity levels in response to eutrophication. Here, we investigated cyanobacterial communities sampled at 140 sites from 59 lakes and reservoirs along a strong eutrophication gradient in eastern China through using CPC-IGS and 16S rRNA gene amplicon sequencing. We found that taxonomic diversity increased, but phylogenetic diversity decreased significantly along the eutrophication gradient. Both niche width and niche overlap of cyanobacteria significantly decreased from low- to high-nutrient waterbodies. Cyanobacterial community distance-decay relationship became weaker from mesotrophic to hypereutrophic waterbodies, while ecological uniqueness (i.e., local contributions to beta diversity) tended to increase in high-nutrient waterbodies. Latitude and longitude were more important in shaping cyanobacterial community structure than other environmental variables. These findings suggest that eutrophication affects alpha and beta diversity of cyanobacterial communities, leading to increasingly similar community structures in lakes and reservoirs with a higher level of eutrophication. Our work highlights how cyanobacterial communities respond to anthropogenic eutrophication and calls for an urgent need to develop conservation and management strategies to control lake eutrophication and protect freshwater biodiversity.

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.

Connecting distinct realms along multiple dimensions: A meta-ecosystem resilience perspective.

Resilience research is central to confront the sustainability challenges to ecosystems and human societies in a rapidly changing world. Given that social-ecological problems span the entire Earth system, there is a critical need for resilience models that account for the connectivity across intricately linked ecosystems (i.e., freshwater, marine, terrestrial, atmosphere). We present a resilience perspective of meta-ecosystems that are connected through the flow of biota, matter and energy within and across aquatic and terrestrial realms, and the atmosphere. We demonstrate ecological resilience sensu Holling using aquatic-terrestrial linkages and riparian ecosystems more generally. A discussion of applications in riparian ecology and meta-ecosystem research (e.g., resilience quantification, panarchy, meta-ecosystem boundary delineations, spatial regime migration, including early warning indications) concludes the paper. Understanding meta-ecosystem resilience may have potential to support decision making for natural resource management (scenario planning, risk and vulnerability assessments).

Biotic homogenisation and differentiation as directional change in beta diversity: synthesising driver-response relationships to develop conceptual models across ecosystems.

Biotic homogenisation is defined as decreasing dissimilarity among ecological assemblages sampled within a given spatial area over time. Biotic differentiation, in turn, is defined as increasing dissimilarity over time. Overall, changes in the spatial dissimilarities among assemblages (termed 'beta diversity') is an increasingly recognised feature of broader biodiversity change in the Anthropocene. Empirical evidence of biotic homogenisation and biotic differentiation remains scattered across different ecosystems. Most meta-analyses quantify the prevalence and direction of change in beta diversity, rather than attempting to identify underlying ecological drivers of such changes. By conceptualising the mechanisms that contribute to decreasing or increasing dissimilarity in the composition of ecological assemblages across space, environmental managers and conservation practitioners can make informed decisions about what interventions may be required to sustain biodiversity and can predict potential biodiversity outcomes of future disturbances. We systematically reviewed and synthesised published empirical evidence for ecological drivers of biotic homogenisation and differentiation across terrestrial, marine, and freshwater realms to derive conceptual models that explain changes in spatial beta diversity. We pursued five key themes in our review: (i) temporal environmental change; (ii) disturbance regime; (iii) connectivity alteration and species redistribution; (iv) habitat change; and (v) biotic and trophic interactions. Our first conceptual model highlights how biotic homogenisation and differentiation can occur as a function of changes in local (alpha) diversity or regional (gamma) diversity, independently of species invasions and losses due to changes in species occurrence among assemblages. Second, the direction and magnitude of change in beta diversity depends on the interaction between spatial variation (patchiness) and temporal variation (synchronicity) of disturbance events. Third, in the context of connectivity and species redistribution, divergent beta diversity outcomes occur as different species have different dispersal characteristics, and the magnitude of beta diversity change associated with species invasions also depends strongly on alpha and gamma diversity prior to species invasion. Fourth, beta diversity is positively linked with spatial environmental variability, such that biotic homogenisation and differentiation occur when environmental heterogeneity decreases or increases, respectively. Fifth, species interactions can influence beta diversity via habitat modification, disease, consumption (trophic dynamics), competition, and by altering ecosystem productivity. Our synthesis highlights the multitude of mechanisms that cause assemblages to be more or less spatially similar in composition (taxonomically, functionally, phylogenetically) through time. We consider that future studies should aim to enhance our collective understanding of ecological systems by clarifying the underlying mechanisms driving homogenisation or differentiation, rather than focusing only on reporting the prevalence and direction of change in beta diversity, per se.

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.

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.

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.

Shifts in food webs and niche stability shaped survivorship and extinction at the end-Cretaceous.

It has long been debated why groups such as non-avian dinosaurs became extinct whereas mammals and other lineages survived the Cretaceous/Paleogene mass extinction 66 million years ago. We used Markov networks, ecological niche partitioning, and Earth System models to reconstruct North American food webs and simulate ecospace occupancy before and after the extinction event. We find a shift in latest Cretaceous dinosaur faunas, as medium-sized species counterbalanced a loss of megaherbivores, but dinosaur niches were otherwise stable and static, potentially contributing to their demise. Smaller vertebrates, including mammals, followed a consistent trajectory of increasing trophic impact and relaxation of niche limits beginning in the latest Cretaceous and continuing after the mass extinction. Mammals did not simply proliferate after the extinction event; rather, their earlier ecological diversification might have helped them survive.

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.

Human pressure drives biodiversity-multifunctionality relationships in large Neotropical wetlands.

Many studies have shown that biodiversity regulates multiple ecological functions that are needed to maintain the productivity of a variety of ecosystem types. What is unknown is how human activities may alter the 'multifunctionality' of ecosystems through both direct impacts on ecosystems and indirect effects mediated by the loss of multifaceted biodiversity. Using an extensive database of 72 lakes spanning four large Neotropical wetlands in Brazil, we demonstrate that species richness and functional diversity across multiple larger (fish and macrophytes) and smaller (microcrustaceans, rotifers, protists and phytoplankton) groups of aquatic organisms are positively associated with ecosystem multifunctionality. Whereas the positive association between smaller organisms and multifunctionality broke down with increasing human pressure, this positive relationship was maintained for larger organisms despite the increase in human pressure. Human pressure impacted multifunctionality both directly and indirectly through reducing species richness and functional diversity of multiple organismal groups. These findings provide further empirical evidence about the importance of aquatic biodiversity for maintaining wetland multifunctionality. Despite the key role of biodiversity, human pressure reduces the diversity of multiple groups of aquatic organisms, eroding their positive impacts on a suite of ecological functions that sustain wetlands.

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.

Characterising functional strategies and trait space of freshwater macroinvertebrates.

We examined the functional strategies and the trait space of 596 European taxa of freshwater macroinvertebrates characterized by 63 fuzzy coded traits belonging to 11 trait groups. Principal component analysis was used to reduce trait dimensionality, to explain ecological strategies, and to quantify the trait space occupied by taxa. Null models were used to compare observed occupancy with theoretical models, and randomization-based analyses were performed to test whether taxonomic relatedness, a proxy of phylogenetic signal, constrains the functional trait space of freshwater macroinvertebrates. We identified four major strategies along which functional traits of the taxa examined show trade-offs. In agreement with expectations and in contrast to existing evidence we found that life cycles and aquatic strategies are important in shaping functional structure of freshwater macroinvertebrates. Our results showed that the taxonomic groups examined fill remarkably different niches in the functional trait space. We found that the functional trait space of freshwater macroinvertebrates is reduced compared to the range of possibilities that would exist if traits varied independently. The observed decrease was between 23.44 and 44.61% depending on the formulation of the null expectations. We demonstrated also that taxonomic relatedness constrains the functional trait space of macroinvertebrates.

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.

Responses of multiple facets of macroinvertebrate alpha diversity to eutrophication in floodplain lakes.

The accelerated eutrophication of freshwater lakes has become an environmental problem worldwide. Increasing numbers of studies highlight the need to incorporate functional and phylogenetic information of species into bioassessment programms, but it is still poorly understood how eutrophication affects multiple diversity facets of freshwater communities. Here, we assessed the responses of taxonomic, phylogenetic and functional diversity of benthic macroinvertebrates to water eutrophication in 33 lakes in the Yangtze River floodplain in China. Our results showed that macroinvertebrate assemblage structure was significantly different among four lake groups (river-connected, macrophyte-dominated, macrophyte-algae transition, and algae-dominated). Three taxonomic, two phylogenetic and two functional diversity indices were significantly different among the lake groups. Except for the increasing trend of Lambda+, these metrics showed a clear decreasing trend with increasing levels of eutrophication, with highest values detected in river-connected and macrophyte-dominated lakes, followed by macrophyte-algae transition lakes and algal-dominated lakes. Although differing in the number and identity of key environmental and spatial variables among the explanatory models of different diversity indices, environmental factors (eutrophication-related water quality variables) played more important role than spatial factors in structuring all three facets of alpha diversity. The predominant role of environmental filtering can be attributed to the strong eutrophication gradient across the studied lakes. Among the three diversity facets, functional diversity indices performed best in portraying anthropogenic disturbances, with variations in these indices being solely explained by environmental factors. Spatial factors were mostly weak or negligible in accounting for the variation in functional diversity indices, implying that trait-based indices are robust in portraying anthropogenic eutrophication in floodplain lakes. However, variation in some taxonomic and phylogenetic diversity indices were also affected by spatial factors, indicating that conservation practitioners and environmental managers should use these metrics with caution when providing solutions for addressing eutrophication in floodplain lakes.