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Revealing the mechanisms underlying community organization has long been a central interest for ecologists and biogeographers. Recent findings have suggested that different dimensions of biodiversity may be shaped by contrasting ecological processes, offering complementary insights about community assembly. However, studies integrating multiple diversity facets across the Qinghai‐Tibetan Plateau (QTP) remain insufficient. We combined multiple analytical frameworks to unravel the patterns (taxonomic, functional and phylogenetic) and correlates (local environment, land use and dispersal pathways) of aquatic arthropod diversity in lotic (stream) and lentic (wetland) ecosystems of the QTP. We observed strong phylogenetic signals in most functional traits, pointing to the influence of evolutionary processes on these faunas. Null models indicated that community structure in most streams and wetlands was mostly the result of random draws from the regional functional and phylogenetic species pool. The prevalence of stochasticity was most likely associated with the interplay of the paleogeographical history, the extremely harsh environmental conditions at high elevations and the subsequent impoverishment of the regional species pool. However, some streams and wetlands also exhibited phylogenetic overdispersion and functional clustering, emphasizing the potential importance of competitive exclusion and habitat filtering, respectively. Variation partitioning further revealed that both environmental filtering and dispersal limitation accounted for the spatial variation of diversity measures, with local environment overriding the effects of space and catchment land use. Overall, this study improves our understanding of community organization and diversity patterns in environmentally extreme alpine catchments, with broad implications for the conservation and management of one of the world’s most important high‐altitude treasures. [ABSTRACT FROM AUTHOR]

Identifying naturally-regulated spatial and temporal variations of benthic macroinvertebrates is critical to effective assessment and conservation of aquatic ecosystems, but little is known about these variations in large rivers in East Asian monsoon region. Here, we address this issue by measuring within-one-year longitudinal and seasonal variability in macroinvertebrate assemblages in such a broadly natural river across its whole watershed. Along longitudinal gradients, taxon richness, Shannon–Wiener diversity and mayflies and caddisflies significantly decreased downstream but chironomids and oligochaeta increased. Taxon richness, diversity indices, and abundance of most taxa all had lowest value in summer. Assemblage structure showed both significant but larger longitudinal than seasonal variations, with a clear separation of upstream and most midstream sites from downstream ones in ordination plot. Different environmental and spatial variables were significant for distinguishing macroinvertebrate assemblages among four seasons, although substrate and PCNM1 emerged as important in all seasons. Variance partitioning analyses indicated stronger environmental control than spatial structuring of community composition in all seasons, with pure environmental factors explaining most community variation. These observed patterns contribute to understanding of sources of uncertainty in bioassessment and thus have implications for ecological monitoring and assessment using macroinvertebrates in rivers in monsoon regions. [ABSTRACT FROM AUTHOR]

Aim Introductions of exotic species have globally modified the structure and function of native assemblages and are recognized as one of the major threats to biodiversity. The current patterns, processes and consequences of invasion have been intensively studied globally, but studies reporting the long-term dynamics of invasions over large areas are rare. Here, we measured how the temporal changes in fish assemblage composition in a Chinese highland isolated-lake landscape drive taxonomic dissimilarity and its turnover component over three successive time periods spanning the last 75 years. Location Yun-Gui Plateau, 15 isolated lakes. Methods The Sørensen and Simpson indices were used to quantify changes in taxonomic dissimilarity and its turnover component over 1940-2015. Results We report a decline of taxonomic dissimilarity between lakes through time, mainly due to a decrease in species turnover. Such a homogenization process was due to the combined effects of the invasion of the same non-native species in most lakes and of extirpation of narrow endemic species. The strong decline in species dissimilarity and turnover was triggered by a high historical level of dissimilarity among assemblages. At a regional scale, the combined effect of introductions and extirpations modified the distance decay of taxonomic similarity between lakes. Surprisingly, this beta-diversity gradient is currently no longer supported by biogeographic and evolutionary processes, but by the human-mediated introduction of distinct exotic species in some lakes. Moreover, an extinction debt process was evident as extirpations sometimes occurred many years after the introduction of non-native species. Main conclusions Our study highlights that high historical differentiation of fishes in isolated lakes has turned to homogenization with dramatic loss of endemic species due to intensive introductions. This provides a striking example of human domination over an extended lake landscape and its associated irreparable biodiversity damages on isolated systems historically dominated by narrow endemic species. [ABSTRACT FROM AUTHOR]

Aim: Understanding the mechanisms underlying the structure and connectivity of ecological communities is a central issue in biogeography. Dispersal syndromes are tightly woven into organisms' life history seen across populations and communities, but measuring dispersal is still complicated in practice. We investigated the role of dispersal syndromes (here, associated with body size, adult flying ability and voltinism) to predict phylogenetic distance decay relationships (DDRs) of aquatic insect assemblages in dendritic stream networks. Location: Du River Basin, China. Taxon: Aquatic insects (Coleoptera, Diptera, Ephemeroptera, Hemiptera, Lepidoptera, Megaloptera, Odonata, Plecoptera and Trichoptera). Methods: We applied multiple methods (i.e. deconstruction approach, null models, Mantel tests and partial Mantel tests) to enhance our basic understanding of phylogenetic distance decay patterns. To provide additional insights into correlates of phylogenetic dissimilarity between stream sites, we modelled potential dispersal routes based on overland, watercourse and cost distances. Results: Overland distances were among the main correlates of phylogenetic distance decay in the stream networks studied, suggesting that aquatic insects disperse overland seeking for habitats suitable for survival and reproduction. However, local environmental filtering was generally more important for phylogenetic DDRs than geographical distances alone. The interaction between environmental vs. dispersal processes in driving spatial patterns of phylogenetic dissimilarity was contingent on different dispersal syndromes. More specifically, significant phylogenetic DDRs were detected only for subsets of large‐bodied, univoltine taxa with strong adult flying abilities, such as dragonflies. Main Conclusions: Overall, historical constraints affect the phylogenetic DDRs in aquatic insects. Dispersal syndromes associated with body size, adult flying ability and voltinism are key features underlying distance decay in phylogenetic assemblage similarity and the evolutionary legacies of aquatic insects in dendritic stream networks. [ABSTRACT FROM AUTHOR]

Aim: Disentangling how stochastic and deterministic processes contribute to variation in beta diversity is a common goal for ecologists and biogeographers. However, such studies are scarce in alpine streams, especially when different diversity facets are considered. Here, we combined different approaches to examine the drivers of taxonomic, phylogenetic and functional beta diversities, and discussed how our results can inform community assembly and biodiversity conservation in Tibetan streams. Location: Tibet plateau. Taxon: Macroinvertebrates. Methods: We first partitioned multiple facets of beta diversity (Btotal) into species replacement (Brepl) and richness difference (Brich) as well as local (LCBD) or species (SCBD) contributions. Then, we applied ordination methods to examine the relative importance of local, climatic and spatial factors on Btotal, Brepl and Brich, respectively. We explored community assembly rules using null models based on trait and phylogeny structure. Results: Btotal displayed high values and was primarily driven by Brepl. Local, climatic and spatial factors were poor predictors of the different facets of beta diversity. Null models showed that the diversity metrics did not differ from those of null expectations, suggesting that most individual streams might be occupied by species that were merely random draws from the functional or phylogenetic pools available in this region. Partitioning beta diversity into LCBD and SCBD implied that the upper canyon streams were more unique than those at lower elevations and can be valuable for biodiversity conservation. Main Conclusions: Analysing multiple facets of beta diversity provide important insights into community assembly that cannot be acquired by focusing on taxonomic diversity only. Using a multi‐faceted approach involving species, phylogenetic and trait data, our study not only sheds light on the assembly mechanisms of macroinvertebrate communities in alpine streams, but also bring inspirations for biodiversity conservation in the 'World's Third Pole' that is highly sensitive to global change. [ABSTRACT FROM AUTHOR]

Accurate assessment of life history and population ecology of widespread species in ultra‐eutrophic freshwater lakes is a prerequisite for understanding the mechanisms by which widespread species respond to eutrophication. Freshwater pulmonate (Radix swinhoei) is widespread and abundant in many eutrophic water bodies in Asia. Despite its key roles in eutrophic lake systems, the information on life history and population ecology of R. swinhoei is lacking, especially in ultra‐eutrophic freshwater plateau lakes. Here, we conducted a 1‐year survey of R. swinhoei with monthly collections to measure the life history traits (life span and growth), annual secondary production, and population size structure of R. swinhoei in nearshore regions with a high seasonally variation of nutrients in Lake Dianchi, a typic hypereutrophic plateau lake in Southwest China. Our results showed that R. swinhoei had the highest biomass in autumn and had the lowest in winter. Its maximum potential life span was 2.5 years, with three recruitment periods (November, March, and July) within a year. Its annual secondary production and P/B ratio were 137.19 g WW/m2 and 16.05, respectively. Redundancy analysis showed that eutrophication‐related environmental factors had weak correlations with population size structure of R. swinhoei. Our results suggested that R. swinhoei is a typical r‐strategist with high secondary production and thrive in eutrophic environment. Our study can help better understand the mechanisms for widespread species to survive eutrophication and could also be relevant for biodiversity conservation and management of eutrophic ecosystems. [ABSTRACT FROM AUTHOR]

The first ever survey of the enchytraeid fauna in the Fanjing Mountain National Nature Reserve (Guizhou, China) yielded a total of eight species, two of them new to science: Xetadrilus prolixglandus sp. nov. and Hemienchytraeus tenuiculus sp. nov. One unidentified and possibly new species of Fridericia and five additional species, Achaeta brevivasa, Enchytraeus buchholzi, Fridericia loretensis, Henlea perpusilla and Hemienchytraeus stephensoni, are recorded and described, based on the collected material. The species records include morphological descriptions and molecular data (the mitochondrial cytochrome c oxidase subunit 1 (COI) gene, the nuclear ribosomal ITS region and the nuclear histone 3 (H3) gene). [ABSTRACT FROM AUTHOR]

Eleven species of terrestrial and aquatic Enchytraeidae are reportedfrom southeastern China. Fridericia multisegmentata and Enchytraeus athecatus are new to science, while most of the others are recorded from the country for the first time. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Community assembly in glacierized rivers remain mostly ignored. • We applied multiple analyses to examine the assembly of multiple aquatic taxa. • Community structure was mainly explained by dispersal and historical biogeography. • The strength of dispersal and niche constraints was mediated by body sizes. • Freshwater bioassessment can benefit from incorporating the metacommunity concept. [ABSTRACT FROM AUTHOR]

Abstract: During April of 2007, macroinvertebrate assemblages were sampled across 43 sites in the Chishui River system, located in southwestern China. The aims are two-fold: (i) to examine the degree to which macroinvertebrate functional feeding groups (FFGs) correspond to prediction of the river continuum concept (RCC), and (ii) to determine the relationships between environmental variables and FFG structure. A synthetic environmental factor (the first axis of a Principal Component Analysis of altitude, distance from source, channel width, and stream order) was used as a measure of stream longitudinal gradient to examine RCC prediction. The RCC prediction held for richness, shredders, and scrapers by decreasing and increasing. Collector-filters and predators did not present any significant trend along the longitudinal gradient. Collector-gatherers significantly increased along the Chishui river continuum, which seems not exactly fall into with the prediction of the RCC, but is accordant with the central RCC theme: longitudinal distributions of FFGs follow longitudinal patterns in basal resources. After redundancy analysis (RDA), four variables (altitude, channel width, silt and clay, and cobble) were significant predictors of community variance. The RCC generally applies to running waters on this subtropical Asian river system. Additional theoretical and field studies across a broad array of Asian streams could be done to refine RCC and FFG classification in the future. [Copyright &y& Elsevier]

The extent to which the sequence and timing of important events on Earth have influenced biological evolution through geological time is a matter of ongoing debate. In this context, the phylogenetic history of aquatic insects remains largely elusive, and our understanding of their chronology is fragmentary and incomplete at best. Here, after gathering a comprehensive data matrix of 3125 targeted rRNA and protein-coding gene sequences from nine independent gene portions, we built a well-supported time-calibrated phylogenetic tree comprising almost 1200 genera that represent a large proportion of extant families of dragonflies and damselflies (Odonata), mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera). We reviewed the main evolutionary and historical scenarios for each aquatic insect lineage as revealed by our best-scoring molecular tree topology, major ancient radiations, calibrated divergence estimates, and important events in geological history related to the spatial arrangement of land masses, continental drift, and mass extinctions. Molecular dating using the birth-death model of speciation, with a lognormal-relaxed model of sequence evolution informed by transcriptomic constraints, suggested that (i) dragonflies and damselflies first radiated approximately 220 million years (Ma) ago and most extant lineages thrived independently after the Triassic–Jurassic (Tr–J) extinction event; (ii) mayflies underwent bursts of diversification during the Cretaceous; (iii) ancestral divergence separating the stonefly suborders Arctoperlaria and Antarctoperlaria was consistent with geographical isolation after vicariant fragmentation and tectonic splitting of the supercontinent Pangaea around 170 Ma ago; and (iv) the most recent common ancestors of caddisflies extended back to the time of Pangaea, supporting the earliest offshoot of the 'retreat-making' Annulipalpia and a sister relationship between the predatory free-living Rhyacophilidae and Hydrobiosidae. Our 'Tree of Life' of aquatic insects also resolved shallow phylogenetic relationships related to key evolutionary innovations, such as the convergent evolution of exophytic oviposition in dragonflies or the Jurassic origins of the burrowing lifestyle in mayflies. In this study, we also illustrate how our time-calibrated phylogeny can help to integrate phylogenetic aspects in biogeographical and ecological research across the world. To do so, we used three empirical datasets of stream insects from subarctic Finland, northeastern Spain, and southeastern Tibet as exemplary cases. These examples of application tested ecogeographical mechanisms related to (i) the responses of size structural resemblances to phylogenetic constraints, and patterns of (ii) phylogenetic relatedness and (iii) phylogenetic uniqueness along elevational and flow-intermittence gradients, respectively. We emphasise how specific details capturing different aspects of phylogenetic variation are dependent on the geological, geographical, and environmental contexts in different drainage basins. We finally highlight potential venues for future research, including evaluations of geographical patterns of phylogenetic diversity in space and time, evolution of ecological characters in relation to palaeoclimatic variation, and development of complementary algorithms for conservation prioritisation of evolutionarily valuable bioregions for aquatic insects. Overall, we hope that this work will stimulate multidisciplinary research efforts among different areas of the biogeosciences towards safeguarding the phylogenetic heritage of extant aquatic insects across the world. • Mapping the evolutionary pathway of aquatic insects has proven to be a complex task. • We present the largest time-calibrated phylogeny for key groups of aquatic insects. • Important events in Earth's geological history shaped aquatic insect macroevolution. • Phylogenetic variation is dependent on the geographical and environmental context. • This 'Tree of Life' contains a great deal of useful information for biogeosciences. [ABSTRACT FROM AUTHOR]

Bacterioplankton are both primary producers and primary consumers in aquatic ecosystems, which were commonly investigated to reflect environmental changes, evaluate primary productivity, and assess biogeochemical cycles. However, there is relatively less understanding of their responses to anthropogenic disturbances such as constructions of dams/tunnels/roads that may significantly affect the aquatic ecosystem. To fill such gap, this study focused on the bacterioplankton communities' diversity and turnover during a tunnel construction across an urban lake (Lake Donghu, Wuhan, China), and five batches of samples were collected within 2 months according to the tunnel construction progress. Results indicated that both resources and predator factors contributed significant to the variations of bacterioplankton communities, but the closed area and open areas showed different diversity patterns due to the impacts of tunnel construction. Briefly, the phytoplankton, TN, and TP in water were still significantly correlated with the bacterioplankton composition and diversity like that in normal conditions. Additionally, the organic matter, TN, and NH4-N in sediments also showed clear effects on the bacterioplankton. However, the predator effects on the bacterioplankton in the closed-off construction area mainly derived from large zooplankton (i.e., cladocerans), while small zooplankton such as protozoa and rotifers are only responsible for weak predator effects on the bacterioplankton in the open areas. Further analysis about the ecological driving forces indicated that the bacterioplankton communities' turnover during the tunnel construction was mainly governed by the homogeneous selection due to similar environments within the closed area or the open areas at two different stages. This finding suggests that bacterioplankton communities can quickly adapt to the environmental modifications resulting from tunnel construction activities. This study can also give references to enhance our understanding on bacterioplankton communities' response to ecological and environmental changes due to intensification of construction and urbanization in and around lake ecosystems. [ABSTRACT FROM AUTHOR]

As a less time-consuming procedure, subsampling technology has been widely used in biological monitoring and assessment programs. It is clear that subsampling counts affect the value of traditional biodiversity indices, but its effect on taxonomic distinctness (TD) indices is less well studied. Here, we examined the responses of traditional (species richness, Shannon-Wiener diversity) and TD (average taxonomic distinctness: Δ +, and variation in taxonomic distinctness: Λ +) indices to subsample counts using a random subsampling procedure from 50 to 400 individuals, based on macroinvertebrate datasets from three different river systems in China. At regional scale, taxa richness asymptotically increased with fixed-count size; ≥250–300 individuals to express 95% information of the raw data. In contrast, TD indices were less sensitive to the subsampling procedure. At local scale, TD indices were more stable and had less deviation than species richness and Shannon-Wiener index, even at low subsample counts, with ≥100 individuals needed to estimate 95% of the information of the actual Δ + and Λ + in the three river basins. We also found that abundance had a certain effect on diversity indices during the subsampling procedure, with different subsampling counts for species richness and TD indices varying by regions. Therefore, we suggest that TD indices are suitable for biodiversity assessment and environment monitoring. Meanwhile, pilot analyses are necessary when to determine the appropriate subsample counts for bioassessment in a new region or habitat type. [ABSTRACT FROM AUTHOR]

Understanding biotic assemblage variations resulting from water diversions and other pressures is critical for aquatic ecosystem conservation, but hampered by limited research. Mechanisms driving macroinvertebrate assemblages were determined across five lakes along China's South-to-North Water Diversion Project, an over 900-km water transfer system connecting four river basins. We assessed macroinvertebrate patterns from 59 sites in relation to water quality, climatic, spatial, and hydrologic factors. Macroinvertebrate density, biomass, and species richness increased from upriver to downriver lakes, and were higher during the water transfer period than in the non-water transfer period. Non-native species including Nephtys sp., Paranthura japonica , Potamillacf acuminata , Capitekkidae spp. and Novaculina chinensis , were distributed along the entire study system, some become dominant in upriver lakes. High species turnover occurred in two upriver lakes. Hydrology and water quality are critical factors in shaping these macroinvertebrate patterns. Hydrological disturbance by water transfer boosted macroinvertebrate abundance during the water transfer period while facilitated non-native species dispersals and increased biotic homogenization. This study indicates the need for: 1) an effective ecosystem monitoring system; 2) unified system management standards; 3) external pollution controls; and 4) limiting the dispersal of non-native species. [Display omitted] • Macroinvertebrate had an increasing gradient from upriver to downriver lakes. • Macroinvertebrate were more abundant and diverse during the water transfer period. • Non-native Nephtys sp. and Paranthura japonica spread along the diversion system. • Hydrology and water quality were critical in driving macroinvertebrate patterns. [ABSTRACT FROM AUTHOR]

• Beta diversity weighted by incidence vs abundance data varied differently along urbanization gradient. • Richness difference contributed more to beta diversity weighted by abundance than incidence data. • Stochasticity was more dominant in shaping beta diversity weighted by abundance than incidence data. • Homogenization studies should consider the roles of rare and abundant taxa. Urbanization is one of the major drivers of biotic homogenization (i.e., decrease in beta diversity) in freshwater systems. However, only a few studies have simultaneously examined how urbanization affects multiple facets (i.e., taxonomic, functional and phylogenetic) of beta diversity and its underlying ecological drivers in urban river macroinvertebrates. Here, we distinguished the patterns and ecological mechanisms of multiple facets of macroinvertebrate beta diversity weighted by incidence and abundance data in a subtropical river system with a distinct urbanization gradient. We also investigated how total beta diversity patterns stem from replacement versus richness difference among sites. Our results showed that taxonomic and phylogenetic beta diversities weighted by incidence data were primarily driven by replacement of taxa, whereas the richness difference contributed more to multiple facets of beta diversity based on abundance data. Furthermore, multiple facets of beta diversity decreased with urbanization for both incidence-weighted and abundance-weighted data, but the former showed more substantial decreases. Both replacement and richness difference components contributed roughly equally to the decline of incidence-weighted beta diversity. In contrast, the losses of abundance-weighted beta diversity were mainly associated with replacement of taxa. Variation partitioning results revealed that all beta diversity measures based on incidence data were governed primarily by local and land-use variables, whereas spatial variables were more relevant in driving beta diversity weighted by abundance data. Overall, by comparing different facets and components of beta diversity weighted by incidence versus abundance data, we suggest that incidence-weighted data may be more sensitive in portraying the impacts of urbanization on macroinvertebrate diversity. This likely resulted from the fact that incidence-weighted data shows the importance of rare taxa in shaping homogenization induced by urbanization. [ABSTRACT FROM AUTHOR]

[Display omitted] • We tested temporal aspects of metacommunity structure in a large freshwater lake using complementary approaches. • Macroinvertebrate metacommunities showed distinct best-fit patterns throughout the four hydrological periods. • The relative importance of environmental and spatial variables also differed among hydrological periods. • Shifts in metacommunity dynamics mainly resulted from considerable changes in hydrological conditions. • Taking temporal aspects into account gives a better insight into metacommunity organization. To improve our understanding on the temporal aspects of metacommunity structure, we focused on benthic macroinvertebrates collected seasonally (i.e., wet, drying, dry and rewetting seasons) in Dongting Lake, a large subtropical floodplain lake in China. We employed the elements of metacommunity structure (EMS) framework and variation partitioning to examine whether metacommunity structure and its underlying mechanisms vary among seasons with distinct biotic and abiotic features. We found gradual shifts in the main assembly mechanisms throughout the year, from apparent spatial structuring (potentially indicative of mass effects) in the wet season to more environmental filtering dynamics in the dry season. When the degree of connectivity was high in the wet season, the benthic metacommunity was characterized by nested structure associated with clumped species loss, and was shaped mainly by spatial processes. However, quasi-Clemensian structure was assigned to metacommunities in the transitional seasons with intermediate connectivity, during which environmental variables were more important than spatial factors in describing community structure. When the degree of connectivity was low in the dry season, the benthic metacommunity displayed Clementsian structure, which was configured solely by environmental variables. The rapid shifts in metacommunity dynamics between seasons mainly result from the considerable changes in the hydrological conditions of Dongting Lake, as the studied system varies from lacustrine to fluvial phases within a single year. Taken together, our results revealed that taking temporal aspects into account gives a better insight into metacommunity organization, especially when the studied systems embrace remarkable variability in hydrological regimes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Human activities contribute to the loss of evolutionary history and functional space. • Anthropogenic impacts threaten phylogenetically unique clades. • Different dimension biodiversity metrics are important to preserving evolutionary history, adaptive potential and ecological function. Under a global change scenario, human-induced impacts alter multiple facets of river biodiversity (i.e., taxonomic, functional and phylogenetic). Hence, focusing on changes in community assembly and different diversity dimensions along anthropogenic impact gradients is of paramount importance for ecological research. Here, we classified stream sites into near-pristine (NP), moderately impacted (MI) and highly impacted (HI) categories based on a comprehensive anthropogenic impact score for the Hanjiang River Basin (China), and tested for differences in patterns of functional (FD) and phylogenetic diversity (PD). Our study suggests that NP sites showed higher FD and PD than impacted streams (MI and HI), with their communities being phylogenetically overdispersed and mostly shaped by random processes. Anthropogenically impacted sites mostly harbored closely related and functionally similar species, although the degree of clustering varied between NP, MI and HI streams, thereby confirming predictions that human activities contribute to the loss of evolutionary history and functional space in running waters. Importantly, we identified the influence of underlying deterministic mechanisms on the homogenization of both functional and phylogenetic facets of diversity. Similarly, NP sites exhibited the greatest proportion of evolutionarily distinct lineages, suggesting that anthropogenic impacts also threaten phylogenetically unique clades. Overall, this study contributed to a better understanding of multiple diversity patterns in aquatic insect communities by generating new empirical evidence of human-induced degradation of subtropical stream ecosystems in China. [ABSTRACT FROM AUTHOR]

The highly endemic diversity of the Yun-Gui plateau lakes has decreased severely in recent decades. Protecting these native species is a challenge, in part because their biology and population ecology remain unexplored. We investigated 1 focal endangered gastropod species (Margarya melanioides) in 1 plateau lake: 1) to quantify spatiotemporal variation in population abundance and size structure, and 2) to identify the key variables influencing these variations. Density was 0.068 individuals/m2 with an estimated total population size of 2.1 × 107 individuals. The size-frequency distribution was skewed toward larger, mature individuals (40.0-60.0 mm), a result indicating that the population is aging. Population size structure showed high spatial heterogeneity, and density was highest in the north-central region of the lake. Redundancy analysis indicated that human-induced environmental degradation strongly controlled the spatial patterns in size-structure. This species has experienced a remarkable decrease in range and population size over the past 50 y, and the population probably will collapse by 2015. The decline could be attributed to demographic drift, environmental filtering, human harvesting, and its limited dispersal ability. Our studies should give useful information for building efficient conservation strategies for M. melanioides and other threatened plateau gastropods. Further studies are needed on the population ecology and reproductive biology of M. melanioides, particularly on its reproductive behavior and size-specific survivorship. [ABSTRACT FROM AUTHOR]

Environmental heterogeneity and dispersal limitation are important drivers of beta diversity; however, their relative influence on the two fundamental components of beta diversity (i.e., species replacement and richness difference) has not been fully examined in montane streams. Here, we examined the relative importance of local environmental gradients and three physical distance matrices (i.e., overland, watercourse and cost distances) on beta diversity and its two components for a macroinvertebrate metacommunity in a stream network. To provide additional insights into community assembly, we also analysed variation in two deconstructed sub-communities based on dispersal ability (i.e., weak and strong dispersers). Both environmental filters and physical distances (dispersal limitation) drove patterns of overall beta diversity, with the former generally prevailing over the latter. Species replacement components showed stronger correlations with environmental gradients than physical distances, while the opposite is true for the richness difference components. Overland distances were generally more important than cost and watercourse distances for community dissimilarity of stream macroinvertebrates, implying that lateral dispersal out of stream corridors through flight was the major dispersal route in the studied steam network. As expected, community dissimilarity of strong dispersers was primarily shaped by environmental filtering, while community dissimilarity of weak dispersers was associated with the joint effects of environmental filtering and dispersal limitation. Our findings demonstrate that partitioning overall dissimilarity into species replacement and richness difference provides more insights into the processes driving spatial variability in biological communities compared with the utilization of total beta diversity alone. Our results support the notion that maintaining environmental heterogeneity and natural connectivity of stream networks should be effective measures to conserve regional biodiversity. Unlabelled Image • We tested DDRs between beta diversity and environmental/physical distances. • Environmental heterogeneity was the major driver of total beta diversity and replacement component. • Overland distance was more influential for beta diversity than watercourse and cost distances • Dispersal ability determined how communities responded to environmental and physical distances. • Maintaining environmental heterogeneity and natural connectivity are important to conserve stream biodiversity. [ABSTRACT FROM AUTHOR]

• We examined the relative role of environmental filtering, mass effects and dispersal limitation. • Overall metacommunity was decomposed into nine sub-metacommunities based on traits. • The relative importance of the three ecological processes depended on biological traits considered. • Different spatial processes and trait-based approaches improved our understanding of community assembly in river networks. Metacommunity ecology highlights the importance of integrating simultaneously environmental filtering and spatial processes, such as mass effects and dispersal limitation, into investigation of community assembly. However, few studies to date have tried to examine mass effects and dispersal limitation as independent ecological mechanisms along with environmental filtering in shaping biological communities in river networks. We examined the relative importance of three factor groups, i.e., environmental variables, within-river spatial factors (indicative of mass effects) and basin identity (referring to dispersal limitation) on a macroinvertebrate metacommunity and nine trait-based deconstructed sub-metacommunities from seven subtropical rivers. We applied redundancy analysis and variance partitioning to reveal the pure and shared effects of the three groups of factors on community variation. Environmental filtering, mass effects and dispersal limitation were all significant mechanisms affecting variation in macroinvertebrate communities, but their relative importance depended on biological traits. Environmental filtering explained more of the variation in the whole metacommunity, tolerant taxa and macroinvertebrate groups with weak dispersal ability (i.e., aquatic dispersal, aerial passive dispersal and large body size). In contrast, mass effects accounted for more variation in the communities of intolerant taxa and macroinvertebrate groups with strong dispersal ability (i.e., aerial active dispersal mode and medium body size). Dispersal limitation was more influential for sub-communities of moderately tolerant taxa and large-sized taxa. Our study highlights that simultaneously accounting for different spatial processes and using a trait-based approach are essential to improve our understanding of community assembly in river networks. [ABSTRACT FROM AUTHOR]

Unraveling the ecological factors that control variation in local community structure in space and time is fundamental to metacommunity ecology. In this scenario, environmental filtering and spatial processes are recognized as important drivers of community assembly, yet their relative importance is anticipated to vary for biological communities in different seasons, network positions and organisms with distinct dispersal modes. In this study, we used a dataset (macroinvertebrate communities and environmental variables) collected in different seasons from the Ganjiang River in China to test the above ideas. We divided the whole metacommunity in each season into mainstream communities, tributary communities, strictly aquatic dispersers and aquatic/aerial dispersers, and subsequently used variation partitioning to examine the relative contribution of environmental and spatial factors separately for the overall and decomposed components of the metacommunity. Our results showed that both environmental filtering and spatial processes were important drivers of variation in community structure, yet their explanatory powers varied considerably among seasons. Environmental filtering was the primary driver of metacommunity organization in most scenarios, while the effects of spatial processes surpassing environmental filtering occurred only sporadically. For communities in different network positions, tributary communities were structured by both strong environmental filtering and profound effects of spatial processes via dispersal limitation. However, communities in mainstream sites were mainly determined by environmental filtering, and the effects of spatial processes were almost negligible. Moreover, environmental filtering was clearly more important for aquatic/aerial dispersers, while spatial processes were more influential for strictly aquatic dispersers. We thus concluded that environmental filtering, spatial processes, network position and dispersal mode can interact to regulate metacommunity organization of riverine macroinvertebrates. Considering that the relative contribution of these factors varied among seasons, we strongly uphold the idea that community ecology research should go beyond one-season snapshot surveys in river networks. Unlabelled Image • We tested seasonal variation in assembly mechanisms of macroinvertebrate communities. • Environmental filtering dominated in controlling community assembly in all seasons. • Network position can affect the relative importance of environmental and spatial factors. • Dispersal mode of organisms can also exert controls on community dynamics. • Seasonal surveys should be highlighted when conducting community assembly research. [ABSTRACT FROM AUTHOR]

Disentangling the mechanisms underlying community assembly is a central topic in community ecology and an important prerequisite for bioassessment. The relative importance of deterministic and stochastic processes is expected to change among organisms relying on different dispersal modes and may vary considerably through time. However, how seasonal change and dispersal modes will interplay to influence community assembly remains to be demonstrated. Here, we examined seasonal dynamics in the relative role of environmental filtering and potential dispersal pathways (overland vs. watercourse) on community assembly of aquatic macroinvertebrates in a Chinese river experiencing monsoon oscillations. We also investigated if and how community assembly processes are dependent on dispersal modes. To do this, we divided the entire metacommunity into three groups: strictly aquatic dispersers (G1), aquatic/aerial dispersers with weak dispersal ability (G2), aquatic/aerial dispersers with strong dispersal ability (G3). Our results showed strong changes in environmental conditions and community structure before, during and after the monsoon. Watercourse distances were more relevant for strictly aquatic dispersers (i.e., G1), whereas overland distances were more strongly related with taxa able to fly during their adult phase (i.e., G2 and G3). Environmental filtering was consistently predominant across seasons. Moreover, mechanisms underlying community assembly of strictly aquatic dispersers remained relatively stable among seasons. On the other hand, ecological correlates of aquatic/aerial dispersers exhibited pronounced seasonal dynamics, probably as a result of their changing dispersal abilities in the transition from larvae to adulthood. Overall, our findings suggest that the relative importance of environmental filtering and spatial processes are mediated by dispersal modes and the hydrological dynamics imposed by seasonal monsoons. Hence, we argue that incorporating the temporal aspect of intra-annual hydrological variation and considering multiple dispersal modes are crucial for unravelling the dynamic nature of community assembly and for improving river bioassessment and management., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Although environmental filtering and spatial structuring are commonly regarded as two key factors shaping community dynamics, their relative contribution remains unknown for numerous aquatic ecosystems, particularly highly dynamic floodplain lakes. This issue is here addressed by examining the seasonal metacommunity dynamics of freshwater fishes in Lake Dongting, a large subtropical lake of the middle Chang-Jiang basin in southern China. Physicochemical variables and fish assemblages were recorded at 20 sampling sites during the wet, normal, and dry seasons. Distance-based redundancy analysis and associated variation partitioning were used to examine the relative role of environmental variables and spatial factors in fish community assembly in each season. Analysis results demonstrated that the relative contribution of environmental filtering and spatial structuring varied depending on environmental features and the extent of hydrological connectivity in different seasons. Intensified physicochemical parameters in the dry season convinced the enhanced environmental filtering, whereas high hydrological connectivity in the wet season favored the stronger spatial process. Specifically, the community assembly processes were temporally dynamic; spatial structuring (or mass effects), resulting from excessively high dispersal rates, was dominant during the flooding season, and environmental filtering was stronger than spatial structuring (or dispersal limitation) during the non-flooding season. These findings highlight the importance of conserving local habitats of Lake Dongting during the dry and normal seasons, and maintaining of the flood pulse of the lake and its natural variability during the wet season. Apparently, the construction of a water-level regulation project at the Chenglingji Channel, the outlet watercourse of Lake Dongting, is not supported because it will change the flood pulse of this lake and thus impact habitat heterogeneity or variability., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

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., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Expansion of agricultural and urban areas and intensification of catchment land-use increasingly affect different facets of biodiversity in aquatic communities. However, understanding the responses of taxonomic and functional diversity to specific conversion from natural forest to agriculture and urban land-use remains limited, especially in subtropical streams where biomonitoring programs and using functional traits are still under development. Here, we conducted research in a subtropical stream network to examine the responses of macroinvertebrate taxonomic and functional diversity to different types of land-use in central China. Our results showed that medium body size, univoltine, gill respiration, and slow seasonal development were much higher in natural forest sites, while certain traits related to strong resilience and resistance (e.g., small body size, fast seasonal development, bi-or multivoltine, abundant occurrence in drift, sprawler) dominated in high-intensity agriculture and urbanization sites. We further found that land-use compromised water quality (e.g., increases in total phosphate, conductivity and water temperature) and habitat conditions (e.g., high proportion of sand and silt, gravel, and channel width) accounted for the changes in trait composition based on a combination of RLQ and fourth-corner analysis. Moreover, natural forest sites presented relatively high values of functional richness than other land-use, demonstrating the importance of natural forest maintenance to promote high levels of functional diversity. However, taxonomic diversity indexes showed higher sensitivity to distinguish different types of land-use compared to functional diversity measures. Even so, given that certain trait categories showed significant relationships with specific local environmental stressors, trait-based approaches can provide reliable evidence to diagnose the cause of impairment and complement the results of the taxonomic-based approaches. Our findings support the idea that taxonomic and functional approaches should be integrated in river restoration and land-use management., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Hemienchytraeus wuhanensis sp. nov. is described from hardwood forest soil in Wuhan, China. This moderately sized enchytraeid species of 6-9 mm body length is characterized by: (1) an oesophageal appendage with tertiary branches, (2) three pairs of secondary pharyngeal gland lobes in V, VI, VII, (3) five pairs preclitellar nephridia, from 5/6 to 9/10, (4) dorsal vessel originating in clitellar segments, (5) a girdle-shaped clitellum, (6) a relatively small male reproductive apparatus without seminal vesicle, and (7) spermathecae that extend to VI-VII. DNA barcodes of paratype specimens of the new species are provided. Previous species records of Hemienchytraeus from China are critically discussed., (Juanjuan Chen, Rüdiger M. Schmelz, Zhicai Xie.)

Effects of commercial sand mining on aquatic diversity are of increasing global concern, especially in parts of some developing countries. However, understanding of this activity on the diversity of macroinvertebrates remains focused on the α component of species diversity, rather than community functioning. Thus, there remains much uncertainty regarding how each component of taxonomic (TD) and functional (FD) diversity respond to the activity both in freshwater and marine environments. Here, we assessed the effect of sand dredging on α, β and γ components of TD and FD during different dredging periods based on the response of macroinvertebrate communities over 4 years in the second largest freshwater lake in China. After three years of active dredging, substantial reductions in each component (α, β and γ) of TD and FD were observed within the dredged area. Moreover, after one year of natural recovery, a distinct restoration was observed with an obvious return in multiple facets of TD and FD indices. No such changes were observed within the adjacent and reference areas. Decreases in the multiple components of TD and FD within the dredged area were most likely associated with the direct extraction of substrate and associated benthic fauna and indirect variations of the water and sediment environment (e.g., increases in water depth and decreases in %Clay). Furthermore, dispersal processes and mass effects mainly contributed to the maintenance of TD and FD during the dredged and recovery stages. In addition, the fast recovery of TD and FD was also related to the simple taxonomic structure and highly connected nature of the study area. Our results suggest that a more precise experimental design (BACI) should be pursued to avoid potentially confounding effects (e.g., natural disturbance) because the sensitivity of diversity indices depends upon different experimental designs. Moreover, measurement of the impacts of sand dredging on macroinvertebrate diversity can be undertaken within a rigorous framework for better understanding the patterns and processes of each component of TD and FD under the sand dredging disturbance., Competing Interests: Author contribution statement All author provided valuable suggestions and comments for the manuscript and contributed significantly to the writing of the paper. Dr. Meng Xingliang contributed to specimen collection and identification, data analysis and article writing; Chen Juanjuan, Li Zhengfei, Liu Zhenyuan, Ge Yihao, Jiang Xuankong helped in specimen collection, measurement of environmental variables and contributed ideas. Dr. Keith M. Cooper and Professor Xie Zhicai provided valuable suggestions and comments for the manuscript., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In parts of developing countries, the over-exploitation of sands from inland waters has led to serious environmental concerns. However, understanding of the impacts of commercial sand dredging on inland water ecosystem functions remains limited. Herein, we assess the effects of this activity on the functional structure of the macroinvertebrate community and its recovery processes based on a 4-year survey, in the South Dongting Lake in China. Our result showed a simplified macroinvertebrate functional structures within the dredged area, as evidenced by a loss of certain trait categories (e.g., oval and conical body form) and a significant reduction in trait values due to the direct removal of macroinvertebrates and indirect alternations to physical environmental conditions (e.g., water depth and %Medium sand). Moreover, clear increases were observed in certain trait categories (e.g., small body size and swimmer) resulting from the dredging-related disturbance (e.g., increased turbidity) within the adjacent area. Furthermore, one year after the cessation of dredging, a marked recovery in the taxonomic and functional structure of macroinvertebrate assemblages was observed with most lost trait categories returning and an increase in the trait values of eight categories (e.g., body size 1.00-3.00 cm and oval body form) within the dredged and adjacent area. In addition, dispersal processes and sediment composition were the main driver for the structuring of the macroinvertebrate taxonomic and functional assemblages during the dredging stages, whilst water environmental conditions dominated the taxonomic structure and dispersal processes determined the functional structure during the recovery stage. Implications of our results for monitoring and management of this activity in inland waters are discussed., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The Yungui Plateau lakes, which are characterized by a highly endemic biodiversity, have been suffering severely from anthropogenic intervention in the recent decades. Studies on the response of these biodiversity to human-mediated effects are still limited. Here, we selected the typical Lake Dianchi to investigate the correlation between macroinvertebrate spatiotemporal dynamics and human-induced eutrophication across a 2-year span (2009-2010). A total of 26 taxa were recorded, and the assemblage pattern of the macroinvertebrate community was mainly controlled by the spatiotemporal (region, season, and year) density fluctuations of some pollution-tolerant species (Limnodrilus hoffmeisteri, Tubifex tubifex, Branchiura sowerbyi, and Chironomus plumosus). Taxon richness, total density, biomass, and the abundance of Oligochaeta and Chironomidae decreased from the north to the south of the lake but were much higher in 2009 than in 2010. Moreover, the high densities of total assemblages and oligochaete occurred during spring and/or autumn, whereas that of chironomids was only high during summer. The contributions of important factors varied in different seasons, but the community variations were mainly shaped by eutrophication-related factors (e.g., Chla, N, and P). Variance partitioning analyses showed that aquatic factors were able to explain more community variations than sediment (6.9-36.6 vs. 5.3-14.7%) across seasons, but their interactive effects were negligible. The results of this study will be beneficial for restoring and managing hypereutrophic lakes in the Yungui Plateau and imply the necessity of long-term monitoring in bioassessment projects involving intensively disturbed lakes.

Land use change is one of the major factors impacting freshwater biodiversity. Afforestation could convert new lands from agriculture or urban land uses to reduce erosion and lead to landscape alterations and biodiversity changes. Here, we examined the changes in the three facets of macroinvertebrate alpha diversity (i.e., taxonomic, functional, and phylogenetic diversity) and further explored possible mechanisms driving their variations before (2007) and after (2016) afforestation along the undammed Chishui River, the core of the National Nature Reserve of Rare and Endemic Fishes in the Upper Yangtze River. We found that taxonomic diversity measures (e.g., species richness, Shannon-Wiener index and Simpson index) increased but all measures of functional diversity (e.g., FRic, FEve, FDiv, and RaoQ) and phylogenetic diversity (e.g., indices of taxonomic distinctness) exhibited stability after the afforestation practice. We also found that only significant taxonomic diversity variation was detected and it showed a relationship to alterations of land use rather than local environmental condition changes across the 10-year afforestation practice. Moreover, hydrology and nutrients levels showed changes after afforestation, but these changes had no effect on the biodiversity changes based on multiple linear regression models. In each survey, the three facets of alpha diversity were significantly explained by natural physical factors and showed inconsistent responses to these underlying environmental variables. In addition, the biodiversity-environment relationships remained stable before and after afforestation, indicating that the inherent mechanisms that drive macroinvertebrate community variation have not changed. Our findings highlight that different alpha diversity measures of lotic macroinvertebrates provide different information about biodiversity and respond differently to various environmental variables. Thus, it is necessary to integrate them into one framework when applying routine monitoring, assessment, and conservation procedures based on lotic macroinvertebrates.

This study was conducted to determine effect and mechanism of exogenous silicon (Si) on salt and drought tolerance of Glycyrrhiza uralensis seedling by focusing on the pathways of antioxidant defense and osmotic adjustment. Seedling growth, lipid peroxidation, antioxidant metabolism, osmolytes concentration and Si content of G. uralensis seedlings were analyzed under control, salt and drought stress [100 mM NaCl with 0, 10 and 20% of PEG-6000 (Polyethylene glycol-6000)] with or without 1 mM Si. Si addition markedly affected the G. uralensis growth in a combined dose of NaCl and PEG dependent manner. In brief, Si addition improved germination rate, germination index, seedling vitality index and biomass under control and NaCl; Si also increased radicle length under control, NaCl and NaCl-10% PEG, decreased radicle length, seedling vitality index and germination parameters under NaCl-20% PEG. The salt and drought stress-induced-oxidative stress was modulated by Si application. Generally, Si application increased catalase (CAT) activity under control and NaCl-10% PEG, ascorbate peroxidase (APX) activity under all treatments and glutathione (GSH) content under salt combined drought stress as compared with non-Si treatments, which resisted to the increase of superoxide radicals and hydrogen peroxide caused by salt and drought stress and further decreased membrane permeability and malondialdehyde (MDA) concentration. Si application also increased proline concentration under NaCl and NaCl-20% PEG, but decreased it under NaCl-10% PEG, indicating proline play an important role in G. uralensis seedling response to osmotic stress. In conclusion, Si could ameliorate adverse effects of salt and drought stress on G. uralensis likely by reducing oxidative stress and osmotic stress, and the oxidative stress was regulated through enhancing of antioxidants (mainly CAT, APX and GSH) and osmotic stress was regulated by proline.