Hydrological and environmental variables outperform spatial factors in structuring species, trait composition, and beta diversity of pelagic algae

Ecological restoration enhanced the stability of epiphytic microbial food webs of submerged macrophytes: Insights from predation characteristics of epiphytic predators

The application of various submerged macrophytes for ecological restoration has gained increasing attention in urban lake ecosystems. The multitrophic microbial communities that colonized in various submerged macrophytes constitute microbial food webs through trophic cascade effects, which affect the biogeochemical cycles of the lake ecosystem and directly determine the effects of ecological restoration. Therefore, it is essential to reveal the diversity, composition, assembly processes, and stability of the microbial communities within epiphytic food webs of diverse submerged macrophytes under eutrophication and ecological restoration scenarios. In this study, we explored the epiphytic microbial food webs of Vallisneria natans and Hydrilla verticillata in both eutrophic and ecological restoration regions. The obtained results indicated that the two regions with different nutrient levels remarkably affected the diversity and composition of epiphytic multitrophic microbial communities of submerged macrophytes, among them, the community composition of epiphytic predators were more prone to change. Secondly, environmental filtering effects played a more important role in driving the community assembly of epiphytic predators than that of prey. Furthermore, the generality and intraguild predation of epiphytic predators were significantly improved within ecological restoration regions, which increased the stability of epiphytic microbial food webs. Additionally, compared with Hydrilla verticillata, the epiphytic microbial food webs of Vallisneria natans exhibited higher multitrophic diversity and higher network stability regardless of regions. Overall, this study focused on the role of the epiphytic microbial food webs of submerged macrophytes in ecological restoration and uncovered the potential of epiphytic predators to enhance the stability of microbial food webs, which may provide new insights into the development of ecological restoration strategies.

Spatial distribution of benthic taxonomic and functional diversity in the Yellow River Basin: From ecological processes to associated determinant factors

One of the fundamental objectives in ecology is to investigate the ecological processes and associated factors governing the abundance and spatial distribution patterns of biodiversity. However, the reaction of biological communities to environmental degradation remains relatively unknown, even for ecologically crucial communities like macroinvertebrates in aquatic ecosystems. Here, we sampled 117 locations to quantify relative contributions of geographical and environmental factors, including water quality, land use, climate, and hydrological factors, to determine the absolute and relative compositions of macroinvertebrate communities and their spatial distribution in the Yellow River Basin (YRB), the sixth-longest river system on Earth. We assessed relative roles of species sorting and dispersal in determining macroinvertebrate community structure along YRB. Our results demonstrated that alpha and beta diversity indices showed an increase from the up- to low-reaches of YRB. The middle and low-reaches exhibited elevated species diversity and both regions exhibited relatively stable community compositions. The biodiversity of macroinvertebrates was influenced by a combination of geographical factors and environmental variables, with environmental factors predominantly serving as the principal determinants. Results of multiple linear regression and variance decomposition showed that the effect of environmental factors was approximately three times greater than that of spatial factors. These findings provide support for the hypothesis that species sorting, driven by environmental gradients, plays a significant role in shaping the community structure of macroinvertebrates in running water ecosystems at the basin scales. Moreover, the factors contributing to substantial shifts in biodiversity across different segments of YRB indicate that distinct river sections have been influenced by varying stressors, with downstream areas being more susceptible to the impacts of water pollution and urbanization resulting from human activities.

Taxonomic and functional β-diversity patterns reveal stochastic assembly rules in microbial communities of seagrass beds

Microorganisms are important members of seagrass bed ecosystems and play a crucial role in maintaining the health of seagrasses and the ecological functions of the ecosystem. In this study, we systematically quantified the assembly processes of microbial communities in fragmented seagrass beds and examined their correlation with environmental factors. Concurrently, we explored the relative contributions of species replacement and richness differences to the taxonomic and functional β-diversity of microbial communities, investigated the potential interrelation between these components, and assessed the explanatory power of environmental factors. The results suggest that stochastic processes dominate community assembly. Taxonomic β-diversity differences are governed by species replacement, while for functional β-diversity, the contribution of richness differences slightly outweighs that of replacement processes. A weak but significant correlation (p < 0.05) exists between the two components of β-diversity in taxonomy and functionality, with almost no observed significant correlation with environmental factors. This implies significant differences in taxonomy, but functional convergence and redundancy within microbial communities. Environmental factors are insufficient to explain the β-diversity differences. In conclusion, the assembly of microbial communities in fragmented seagrass beds is governed by stochastic processes. The patterns of taxonomic and functional β-diversity provide new insights and evidence for a better understanding of these stochastic assembly rules. This has important implications for the conservation and management of fragmented seagrass beds.

Temperature and nutrients alter the relative importance of stochastic and deterministic processes in the coastal macroinvertebrates biodiversity assembly on long-time scales

Macroinvertebrates play a vital role in coastal ecosystems and are an important indicator of ecosystem quality. Both anthropogenic activity and environmental changes may lead to significant changes in the marine macroinvertebrate community. However, the assembly process of benthic biodiversity and its mechanism driven by environmental factors at large scales remains unclear. Here, using the benthic field survey data of 15 years at large spatial and temporal scales from the Yellow Sea Large Marine Ecosystem, we investigated the relative importance of environmental selection, dispersal processes, random-deterministic processes of macroinvertebrates community diversity assembly, and the responses of this relative importance driven by temperature and nutrients. Results showed that the macroinvertebrates community diversity is mainly affected by dispersal. Nitrogen and phosphorus are the most important negative factors among environmental variables, while geographical distance is the main limiting factor of β diversity. Within the range of 0.35-0.70 mg/L of nutrients, increasing nutrient concentration can significantly facilitate the contribution of the decay effect to β diversity. Within the temperature range studied (15.0-18.0°C), both warming and cooling can lead to a greater tendency for species diversity assembly processes to be dominated by deterministic processes. The analysis contributes to a better understanding of the assembly process of the diversity of coastal marine macroinvertebrates communities and how they adapt to global biogeochemical processes.

Zeta diversity patterns in metabarcoded lotic algal assemblages as a tool for bioassessment

Assessments of the ecological health of algal assemblages in streams typically focus on measures of their local diversity and classify individuals by morphotaxonomy. Such assemblages are often connected through various ecological processes, such as dispersal, and may be more accurately assessed as components of regional-, rather than local-scale assemblages. With recent declines in the costs of sequencing and computation, it has also become increasingly feasible to use metabarcoding to more accurately classify algal species and perform regional-scale bioassessments. Recently, zeta diversity has been explored as a novel method of constructing regional bioassessments for groups of streams. Here, we model the use of zeta diversity to investigate whether stream health can be determined by the landscape diversity of algal assemblages. We also compare the use of DNA metabarcoding and morphotaxonomy classifications in these zeta diversity-based bioassessments of regional stream health. From 96 stream samples in California, we used various orders of zeta diversity to construct models of biotic integrity for multiple assemblages of diatoms, as well as hybrid assemblages of diatoms in combination with soft-bodied algae, using taxonomy data generated with both DNA sequencing as well as traditional morphotaxonomic approaches. We compared our ability to evaluate the ecological health of streams with the performance of multiple algal indices of biological condition. Our zeta diversity-based models of regional biotic integrity were more strongly correlated with existing indices for algal assemblages classified using metabarcoding compared to morphotaxonomy. Metabarcoding for diatoms and hybrid algal assemblages involved rbcL and 18S V9 primers, respectively. Importantly, we also found that these algal assemblages, independent of the classification method, are more likely to be assembled under a process of niche differentiation rather than stochastically. Taken together, these results suggest the potential for zeta diversity patterns of algal assemblages classified using metabarcoding to inform stream bioassessments.

SER: An R package to characterize environmental regimes

Environmental regimes (or environmental legacy or historical legacy) are the dynamics of environmental characteristics over a given (either long or short) time period, such as frequency of mean or extreme events and rate of change, which might be absent by using only contemporary variables. We present SER, an R package for estimating environmental regimes for different environmental variables. Using the data included in the package, several examples are shown. SER is suitable for any type of environmental or biotic variables, including nutrient concentration, light, and dissolved oxygen. In addition, by changing the argument "days_bf," it is possible to compute environmental regimes over any time period, such as days, months, or years. Our case study showed that the inclusion of environmental regimes increased the explained variation of temporal β-diversity and its components. Environmental regimes are expected to advance the "environment-community" relationships in ecological studies. They can further be implemented in other subjects such as social science, socioeconomics, and epidemiology.

Lake morphological characteristics and climatic factors affect long-term trends of phytoplankton community in the Rotorua Te Arawa lakes, New Zealand during 23 years observation

Monitoring the long-term dynamics of lake phytoplankton can help understand their natural temporal variability, as well as assess potential impacts of interventions aimed at improving lake ecological condition. However, investigating long-term changes in lake ecosystems has received scant attention. In the present study, we analyzed a long-term dataset of phytoplankton communities collected from 1990 to 2013 from eleven of the 12 Rotorua Te Arawa lakes in New Zealand, to explore their responses to changing abiotic conditions. We used a sequential algorithm to examine the likelihood of regime shifts in abiotic and biotic factors during the study period that could be attributable to lake interventions. Our analysis suggests that lake interventions have improved the abiotic factors, whereas the response of biotic factors was less clear. Total phosphorus levels were implicated in the decline in lake condition, including in two lakes subject to lake interventions, and in four control lakes. Both abiotic and biotic factors showed diverse trends (e.g., increase, decrease or no change), and abiotic factors had more regime shifts than biotic factors. Shifts in biotic indices also displayed time lags to shifts in abiotic factors. Long-term responses of abiotic and biotic factors were also influenced by lake morphological characteristics and climatic variables. This latter finding underscores the importance of considering lake morphological characteristics and climate changes when planning management practices. A sound understanding of resilience and threshold of phytoplankton shifts to environmental changes are needed to assess the effectiveness of previous management strategies and prioritize the future conservation efforts toward water quality goals.

Environmental DNA metabarcoding reveals the impact of different land use on multitrophic biodiversity in riverine systems

Human-induced changes in land use drive an alarming decline in river biodiversity and related ecosystem services worldwide. However, how different land use shapes aquatic multitrophic communities is still not well understood. Here, we used the biodiversity dataset from bacteria to fish captured by the environmental DNA (eDNA) approach in the four riverine systems with spatially different land use (i.e., Slightly disturbed group, Upstream disturbed group, Downstream disturbed group, and Strongly disturbed group) to reveal the changes in multitrophic biodiversity in relation to human land use. Firstly, our data showed that spatially different land use determined the pollutant loads of the riverine systems, most pollutants (e.g., TN and NH₃-N) had significant differences among the four riverine systems. Secondly, taxonomic α diversity across multitrophic levels did not necessarily change significantly, yet the change in community structure can be considered as a more sensitive indicator to reflect different land use, because different land use shaped the unique structure of multitrophic communities, and the dissimilarity of community structure was closely associated with land use gradient (e.g., positive relationships in the Slightly disturbed group, negative relationships in the Strongly disturbed group). Thirdly, different land use induced the shifts of key taxa, resulting in the variation of community structure and the change of co-occurrence network. Overall, these findings suggest that spatially different land use plays a critical role in shaping aquatic multitrophic communities, and an in-depth understanding of the interdependences between biodiversity and land use is a critical prerequisite for formulating river management strategies.

Distinct indicators of land use and hydrology characterize different aspects of riverine phytoplankton communities

Given the many threats to freshwater biodiversity, we need to be able to resolve which of the multiple stressors present in rivers are most important in driving change. Phytoplankton are a key component of the aquatic ecosystem, their abundance, species richness and functional richness are important indicators of ecosystem health. In this study, spatial variables, physiochemical conditions, water flow alterations and land use patterns were considered as the joint stressors from a lowland rural catchment. A modeling approach combining an ecohydrological model with machine learning was applied. The results implied that land use and flow regime, rather than nutrients, were most important in explaining differences in the phytoplankton community. In particular, the percentage of water body area and medium level residential urban area were key to driving the rising phytoplankton abundance in this rural catchment. The proportion of forest and pasture area were the leading factors controlling the variations of species richness. In this case deciduous forest cover affected the species richness in a positive way, while, pasture share had a negative effect. Indicators of hydrological alteration were found to be the best predictors for the differences in functional richness. This integrated model framework was found to be suitable for analysis of complex environmental conditions in river basin management. A key message would be the significance of forest area preservation and ecohydrological restoration in maintaining both phytoplankton richness and their functional role in river ecosystems.

Environmental DNA Biomonitoring Reveals the Interactive Effects of Dams and Nutrient Enrichment on Aquatic Multitrophic Communities

Dam construction and nutrient enrichment are two pervasive stressors in rivers worldwide, which trigger a sharp decline in biodiversity and ecosystem services. However, the interactive effects of both stressors on multitrophic taxonomic groups remain largely unclear. Here, we used the multitrophic datasets captured by the environmental DNA (eDNA) approach to reveal the interactions between dams and nutrient enrichment on aquatic communities from the aspects of taxonomic α diversity, β diversity, and food webs. First, our data showed that dams and nutrient enrichment jointly shaped a unique spatial pattern of aquatic communities across the four river systems, and the dissimilarity of community structure significantly declined (i.e., structural homogenization) under both stressors. Second, dams and nutrients together explained 40-50% of the variations in aquatic communities, and dams had a stronger impact on fish, aquatic insects, and bacteria, yet nutrients had a stronger power to drive protozoa, fungi, and eukaryotic algae. Finally, we found that additive, synergistic, and antagonistic interactions of dams and nutrient enrichment were common and coexisted in river systems and led to significantly simplified aquatic food webs, with decreases in modularity (synergistic) and robustness (additive) and an increase in coherence (synergistic). Overall, our study highlights that eDNA-based datasets can provide multitrophic perspectives for fostering the understanding of the interactive effects of multiple stressors on rivers.

Effect of Gated Weir Opening on the Topography and Zooplankton Community of Geum River, South Korea

Hydrological changes affect not only the physicochemical factors and habitat structure of river ecosystems, but also the structure of biological communities sensitive to environmental changes, such as zooplankton. In this study, we investigate the effects of weir opening on environmental variables and topographic structures at Sejong Weir in South Korea and monitor the resulting changes in the structure and distribution of the zooplankton community. Weir opening led to increased dissolved oxygen and decreased conductivity, turbidity, chlorophyll a, total phosphorus, and total nitrogen and increased the diversity of topographic structures (reduced pool area and increase riffle and grassland/bare land areas) in the section downstream of Sejong Weir. Prior to weir opening (2015–2016), the cladoceran community was dominated by Chydrous spaeericus and Moina microcopa. After opening (2018–2019), the abundance of other cladoceran communities such as Bosmina groups (Bosmina longiseta, Bosmina fatalis, and Bosminopsis deitersi), Ceriodaphnia sp., and Daphnia obtusa increased. In contrast, the copepod species (Cyclops vicinus and Mesocyclops leukarti) were abundant before weir opening. We conclude that artificial weir opening helped maintain the unique environmental characteristics of the river ecosystem in terms of river continuity and led to a different zooplankton community composition in the new river environment.

Relative importance of climate and spatial processes in shaping species composition, functional structure and beta diversity of phytoplankton in a large river

Although metacommunity dynamics of lentic phytoplankton are relatively well-documented, studies on the role of environmental and spatial processes in shaping phytoplankton communities of large rivers are still scarce. Here, we examined six phytoplankton data sets, which were collected in 1978-2017 from large river-scale segments (mean spatial extent 1117 km) in the Danube River. Our aim was to elucidate role of climatic, spatial and temporal predictors in variation of phytoplankton beta diversity using variance partitioning for compositions of species and functional groups sensu Reynolds. We hypothesised that phytoplankton beta diversity (measured as average distance to group centroid) would be positively related to both climatic heterogeneity and spatial extent used as a proxy for dispersal limitation. Additionally, we tested alternative dispersal models to evaluate different spatial processes structuring phytoplankton community. Our results revealed that spatial variables were more important than climatic factors in controlling both species and functional group composition. Climatic heterogeneity showed significant positive relationship with beta diversity. In contrast, there was no significant relationship between beta diversity and spatial extent, suggesting that spatial effect on beta-diversity was attenuated by anthropogenic disturbance. The better performance of non-directional model compared to model of water directionality suggested that spatial dynamics of phytoplankton metacommunity was in large part regulated by differences in the regional species pools. Spatial and temporal variables outperformed environmental (including climatic) factors in explaining phytoplankton metacommunity structure, indicating that phytoplankton exhibited strong biogeographical patterns. Thus, dispersal limitation interfered with species-sorting processes in determining phytoplankton community structure. In conclusion, our findings revealed that the development of a more reliable bioassessment program of the Danube River should be based on separation into basin regions.

Influences of pesticides, nutrients, and local environmental variables on phytoplankton communities in lentic small water bodies in a German lowland agricultural area

Agrochemicals such as pesticides and nutrients are concurrent chemical stressors in freshwater aquatic ecosystems surrounded by agricultural areas. Lentic small water bodies (LSWB) are ecologically significant habitats especially for maintaining biodiversity but highly understudied. Phytoplankton are ideal indicator species for stress responses. Functional features of the phytoplankton are important in revealing the processes that determine the structure of the communities. In this study, we investigated the effects of pesticides, nutrients, and local environmental variables on the species composition and functional features of phytoplankton communities in LSWB. We studied pesticide toxicity of ninety-four pesticides, three nutrients (NH₄-N, NO₃-N and PO₄-P) and local environment variables (precipitation, water level change, temperature, dissolved oxygen concentration, electrical conductivity, pH) in five LSWB over twelve weeks during the spring pesticide application period. We explored respective changes in species composition of phytoplankton community and functional features. Redundancy analysis and variance partitioning analysis were applied to correlate phytoplankton community compositions with the pesticide toxicity (as maximum toxicity in toxic units), nutrients and local environment variables. We used multiple linear regression models to identify the main environmental variables driving the functional features of phytoplankton communities. Pesticide toxicity, nutrients and local environmental variables significantly (p < 0.001) contributed to shaping phytoplankton community composition individually. Local environment variables showed the highest pure contribution for driving phytoplankton composition (12%), followed by nutrients (8%) and pesticide toxicity (2%). Functional features (represented by functional diversity and functional redundancy) of the phytoplankton community were significantly affected by pesticide toxicity and nutrients concentrations. The functional richness and functional evenness were negatively affected by PO₄-P concentrations. Pesticide toxicity was positively correlated with functional redundancy indices. Our findings emphasized the relative importance of concurrent multiple stressors (e.g., pesticides and nutrients) on phytoplankton community structure, directing potential effects on metacommunity structures in aquatic ecosystems subjected to agricultural runoff.

Human activities' fingerprint on multitrophic biodiversity and ecosystem functions across a major river catchment in China

Human-induced global change dramatically alters individual aspects of river biodiversity, such as taxonomic, phylogenetic or functional diversity, and is predicted to lead to losses of associated ecosystem functions. Understanding these losses and dependencies are critical to human well-being. Until now, however, most studies have only looked either at individual organismal groups or single functions, and little is known on the effect of human activities on multitrophic biodiversity and on ecosystem multifunctionality in riverine ecosystem. Here we profiled biodiversity from bacteria to invertebrates based on environmental DNA (hereafter, 'eDNA') samples across a major river catchment in China, and analysed their dependencies with multiple ecosystem functions, especially linked to C/N/P-cycling. Firstly, we found a spatial cross-taxon congruence pattern of communities' structure in the network of the Shaying river, which was related to strong environmental filtering due to human land use. Secondly, human land use explained the decline of multitrophic and multifaceted biodiversity and ecosystem functions, but increased functional redundancy in the riverine ecosystem. Thirdly, biodiversity and ecosystem function relationships at an integrative level showed a concave-up (non-saturating) shape. Finally, structural equation modeling suggested that land use affects ecosystem functions through biodiversity-mediated pathways, including biodiversity loss and altered community interdependence in multitrophic groups. Our study highlights the value of a complete and inclusive assessment of biodiversity and ecosystem functions for an integrated land-use management of riverine ecosystems.

Phytoplankton diversity in relation to physicochemical attributes and water quality of Mandakini River, Garhwal Himalaya

Phytoplankton are important biological indicators of water quality. This current study assessed the physicochemical parameters and phytoplankton diversity of Mandakini River, an important tributary of the River Ganga. Water and phytoplankton samples were collected from three sampling sites located at three different altitudes for a period of twelve months (July 2018-June 2019). Water samples were analyzed for fourteen important physicochemical parameters along with the identification of phytoplankton by following the standard methodology. A total of 21 species of phytoplankton under three major groups Bacillariophyceae (Cymbella aequalis, Diatoma vulgaris, Fragilaria arcus, Frustulia rhomboids, Gomphonema geminatum, Navicula confervacea, Nitzchia diversa, and Synedra ulna); Chlorophyceae (Volvox sp., Cladophora glomerata, Closterium longissima, Hydrodictyon sp., Microspora amoena, Spirogyra sp., Oedogonium sp., Ulothrix zonata, and Zygnema cylindrospermum); and Cyanophyceae (Anabaena ambigua, Chlorococcum humicola, Nodularia sp., and Oscillatoria sancta) were observed and recorded during the study period. Site S₃ (Rudraprayag) had the highest species diversity. From this study, the effect of physicochemical parameters on the diversity and density of phytoplankton was observed. It also includes the overall significance of phytoplankton and physicochemical parameters to the water quality of the Mandakini River along with the key factors that were responsible for the degradation of water quality. The current study also provides baseline information to future researchers working in a similar discipline.

Short-period hydrological regimes override physico-chemical variables in shaping stream diatom traits, biomass and biofilm community functions

Despite increasing interest in hydrological effects on riverine ecosystems, few studies have documented the impact of hydrology on biofilm community functions, and those existing have typically focused on annual-based hydrological indices. In this study, we conducted monthly samplings during a year in five lowland streams with different flow regimes and investigated the impacts of hydrological conditions and physico-chemical variables on the trait composition of diatoms growing on artificial substrates, biomass (chlorophyll a and ash free dry weight), and biofilm community functions (biochemical processes, i.e., biofilm metabolism and nutrient uptake rates measured in the laboratory). Instead of the commonly used annual-based hydrological indices, we calculated indices for shorter periods (14 and ~28 days) of the hydrological regimes. Results of species-based variation partitioning showed that short-period hydrological indices (10.10 ± 7.18%) contributed more to explain species distribution than physico-chemical variables (5.90 ± 3.83%), indicating the dominant role of hydrology in structuring the diatom community. Specifically, we found different response patterns for different guilds and size classes to the hydrological and physico-chemical variables, and our results demonstrated that species tolerating high disturbance may be more appropriate as indicators of environmental disturbance than low-tolerant species. We also found dominant effects of short-period hydrological events on biomass and biofilm community functions. Despite an overall negative effect of high flow events and flow variations on biomass and biofilm community functions, positive effects on function-biomass ratios were also observed, indicating that the effects of flow regimes on biofilm are complex. In conclusion, our study highlights the importance of including short-period hydrological conditions in studies on environmental factors shaping benthic algae. Based on our results, we recommend use of short-period hydrological conditions when investigating the effects of flow regime on biofilm community composition and functions.

Downstream transport processes modulate the effects of environmental heterogeneity on riverine phytoplankton

Environmental heterogeneity (EH) in space and time promotes niche-partition, which leads to high variation in biological communities, such as in algae. In streams, EH is highly related to the intensity of the water flow and may lead to community variation mainly during the low flow conditions. Despite the wide knowledge on the responses of phytoplankton communities to EH in lentic and semi-lentic systems, studies of riverine phytoplankton community variation are still scarce. Here, we first investigated the relationship between phytoplankton community variation and EH in different courses of the river and between seasons. We expected that under low or intermediate flow conditions, there is a positive correlation between community variation and EH. Alternatively, we did not expect any relationship between EH and community variation under high flow condition because stronger downstream transport would mask environmental filtering. We sampled nine sites monthly (May 2012 to April 2013) in a tropical river of Brazilian Southeast. We calculated EH from abiotic data whereas for community variation, here community distinctiveness (CD), we used Sorensen (CD_Sor) and Bray-Curtis (CD_Bray) dissimilarities. Differences in EH, CD_Sor and CD_Bray were tested at between-season and among-course levels. We found lower distinctiveness during the dry season when EH was the highest. Contrastingly, phytoplankton CD was the highest even when EH was low during the wet season. We found that this pattern raised from the increasing in individuals dispersal during the wet season, promoting mass effects. Finally, our results thus reject the first hypothesis and show a negative relationship between EH and distinctiveness. However, results support our alternative hypothesis and show that during the wet season, distinctiveness is not driven by EH. These results provide new insights into how EH drives community variation, being useful for both basic research about riverine algal communities and biomonitoring programs using phytoplankton communities as bioindicators.

Taxonomic and functional anuran beta diversity of a subtropical metacommunity respond differentially to environmental and spatial predictors

Anurans exhibit limited dispersion ability and have physiological and behavioural characteristics that narrow their relationships with both environmental and spatial predictors. So, the relative contributions of environmental and spatial predictors in the patterns of taxonomic and functional anuran beta diversity were examined in a metacommunity of 33 ponds along the coast of south Brazil. We expected that neutral processes and, in particular, niche-based processes could have similar influence on the taxonomic and functional beta diversity patterns. Distance-based methods (db-RDA) with variation partitioning were conducted with abundance data to examine taxonomic and functional facets and components (total, turnover and nestedness) in relation to environmental and spatial predictors. Processes determining metacommunity structure differed between the components of beta diversity and among taxonomic and functional diversity. While taxonomic beta diversity was further accounted by both environmental and spatial predictors, functional beta diversity responded more strongly to spatial predictors. These two contrasting patterns were different to what we had predicted, suggesting that while there is a taxonomic turnover mediated by environmental filters, the spatial distance promotes the trait dissimilarity between sites. In addition, our data confirm that neutral and niche-based processes operate on anuran metacommunities even at short geographic scales. Our results reinforce the idea that studies aiming to evaluate the patterns of structure in metacommunities should include different facets of diversity so that better interpretations can be achieved.

Everything is not everywhere: can marine compartments shape phytoplankton assemblages?

The idea that 'everything is everywhere, but the environment selects' has been seminal in microbial biogeography, and marine phytoplankton is one of the prototypical groups used to illustrate this. The typical argument has been that phytoplankton is ubiquitous, but that distinct assemblages form under environmental selection. It is well established that phytoplankton assemblages vary considerably between coastal ecosystems. However, the relative roles of compartmentalization of regional seas and site-specific environmental conditions in shaping assemblage structures have not been specifically examined. We collected data from coastal embayments that fall within two different water compartments within the same regional sea and are characterized by highly localized environmental pressures. We used principal coordinates of neighbour matrices (PCNM) and asymmetric eigenvector maps (AEM) models to partition the effects that spatial structures, environmental conditions and their overlap had on the variation in assemblage composition. Our models explained a high percentage of variation in assemblage composition (59-65%) and showed that spatial structure consistent with marine compartmentalization played a more important role than local environmental conditions. At least during the study period, surface currents connecting sites within the two compartments failed to generate sufficient dispersal to offset the impact of differences due to compartmentalization. In other words, our findings suggest that, even for a prototypical cosmopolitan group, everything is not everywhere.

The seasonal and spatial variations in diatom communities and the influence of environmental factors on three temperate reservoirs in Shandong province, China

Diatoms play an important role as ecological indicators, and some species of diatoms can easily cause water blooms, thereby decreasing the production capacity of water treatment plants and endangering drinking water safety. Mastering the diatom community dynamics is crucial for water supply. In this study, diatom composition, spatial distribution and succession were investigated in Datun Reservoir, Donghu Reservoir and Shuangwangcheng Reservoir, which are important drinking water sources in Shandong province, China. Results showed that the three reservoirs could be classified as being between mesotrophic and moderately eutrophic. The diatom community in each of the three reservoirs exhibited no obvious seasonal succession. The diatom communities in the three reservoirs were relatively simple in composition, with Synedra and Cyclotella being the most dominant groups all year round. Synedra had a negative relationship with NO₂-N. Cyclotella had a positive association with NO₃-N, but was negatively associated with NH₄-N and COD_Mn in the three reservoirs. Through the analysis of diatom and environmental factors, the three reservoirs have the potential of hosting diatom blooms in summer, when the higher temperature combines with reduced water flow.

Beta Diversity Partitioning and Drivers of Variations in Fish Assemblages in a Headwater Stream: Lijiang River, China

Beta diversity partitioning has currently received much attention in research of fish assemblages. However, the main drivers, especially the contribution of spatial and hydrological variables for species composition and beta diversity of fish assemblages are less well studied. To link species composition to multiple abiotic variables (i.e., local environmental variables, hydrological variables, and spatial variables), the relative roles of abiotic variables in shaping fish species composition and beta diversity (i.e., overall turnover, replacement, and nestedness) were investigated in the upstream Lijiang River. Species composition showed significant correlations with environmental, hydrological, and spatial variables, and variation partitioning revealed that the local environmental and spatial variables outperformed hydrological variables, and especially abiotic variables explained a substantial part of the variation in the fish composition (43.2%). The overall species turnover was driven mostly by replacement (87.9% and 93.7% for Sørensen and Jaccard indices, respectively) rather than nestedness. Mantel tests indicated that the overall species turnover (ßSOR and ßJAC) and replacement (ßSIM and ßJTU) were significantly related to hydrological, environmental, and spatial heterogeneity, whereas nestedness (ßSNE or ßJNE) was insignificantly correlated with abiotic variables (P > 0.05). Moreover, the pure effect of spatial variables on overall species turnover (ßSOR and ßJAC) and replacement (ßSIM and ßJTU), and the pure effect of hydrological variables on replacement (ßSIM and ßJTU), were not important (P > 0.05). Our findings demonstrated the relative importance of interactions among environmental, hydrological, and spatial variables in structuring fish assemblages in headwater streams; these fish assemblages tend to be compositionally distinct, rather than nested derivatives of one another. Our results, therefore, indicate that maintaining natural flow dynamics and habitat continuity are of vital importance for conservation of fish assemblages and diversity in headwater streams.

Determining the macroinvertebrate community indicators and relevant environmental predictors of the Hun-Tai River Basin (Northeast China): A study based on community patterning

It is essential to understand the patterning of biota and environmental influencing factors for proper rehabilitation and management at the river basin scale. The Hun-Tai River Basin was extensively sampled four times for macroinvertebrate community and environmental variables during one year. Self-Organizing Maps (SOMs) were used to reveal the aggregation patterns of the 355 samples. Three community types (i.e., clusters) were found (at the family level) based on the community composition, which showed a clearly gradient by combining them with the representative environmental variables: minimally impacted source area, intermediately anthropogenic impacted sites, and highly anthropogenic impacted downstream area, respectively. This gradient was corroborated by the decreasing trends in density and diversity of macroinvertebrates. Distance from source, total phosphorus and water temperature were identified as the most important variables that distinguished the delineated communities. In addition, the sampling season, substrate type, pH and the percentage of grassland were also identified as relevant variables. These results demonstrated that macroinvertebrates communities are structured in a hierarchical manner where geographic and water quality prevail over temporal (season) and habitat (substrate type) features at the basin scale. In addition, it implied that the local-scale environment variables affected macroinvertebrates under the longitudinal gradient of the geographical and anthropogenic pressure. More than one family was identified as the indicator for each type of community. Abundance contributed significantly for distinguishing the indicators, while Baetidae with higher density indicated minimally and intermediately impacted area and lower density indicated highly impacted area. Therefore, we suggested the use of abundance data in community patterning and classification, especially in the identification of the indicator taxa.