Influence of environmental variables on macroinvertebrate community structure in Lianhuan Lake

The structural characteristics of the macroinvertebrate community can effectively reflect the health status of lake ecosystems and the quality of the lake ecological environment. It is therefore important to identify the limiting factors of macroinvertebrate community structure for the maintenance of lake ecosystem health. In this study, the community composition of macroinvertebrate assemblages and their relationships with environmental variables were investigated in 13 small lakes within Lianhuan Lake in northern China. A self‐organizing map and K‐means clustering analysis grouped the macroinvertebrate communities into five groups, and the indicator species reflected the environmental characteristics of each group. Principal component analysis indicated that the classification of the macroinvertebrate communities was affected by environmental variables. The Kruskal–Wallis test results showed that environmental variables (pH, total phosphorus, nitrate, water temperature, dissolved oxygen, conductivity, permanganate index, and ammonium) had a significant effect on the classification of the macroinvertebrate communities. Redundancy analysis showed that mollusks were significantly negatively correlated with pH and chlorophyll a, while annelids and aquatic insects were significantly positively correlated with chlorophyll a and dissolved oxygen. Spearman correlation analysis showed that the species richness and Shannon''s diversity of macroinvertebrates were significantly negatively correlated with total phosphorus, while the biomass of macroinvertebrates was significantly negatively correlated with pH. High alkalinity and lake eutrophication have a serious impact on the macroinvertebrate community. Human disturbances, such as industrial and agricultural runoff, negatively impact the ecological environment and affect macroinvertebrate community structure. Thus, macroinvertebrate community structure should be improved by enhancing the ecological environment and controlling environmental pollution at a watershed scale.     

Characterization of benthic habitat settings in a lagoonal ecosystem using free-living nematodes as proxy

Free-living nematodes are sensitive to most of the disturbances and therefore have ability to reflect direct structural and functional changes in an ecosystem. We studied nematode assemblages of Chilika Lagoon, the largest lagoon of Asia, across spatio-temporal scales in link with environmental variables and evaluated nematode assemblages as a proxy to characterize lagoonal benthic habitat settings. Our results revealed that nematode communities showed significant variation spatially and temporally in terms of mean density (16–854/10 cm²) and mean number of species (7–74). Salinity is the key factor that controls nematode community structure across this lagoon and was strongly supported by statistical analyses. The observed nematode assemblages were further used as a proxy to assign benthic habitats of Chilika into distinct biological, topographical and hydrological settings. This study showed that nematode assemblages could be effectively used for long term ecological monitoring of dynamic sedimentary environment of lagoons globally.     

Fishes of Indiana streams: current and historic assemblage structure

We examined Indiana fish assemblages using taxonomy and ecological categories to assess temporal shifts in community structure and recent environmental relationships. Historic (1945) and recent (1996–2007) presence/absence data were compiled by subbasin and analyzed with Nonmetric Multidimensional Scaling (NMS) ordination and by species richness. Canonical Correspondence Analysis (CCA) was used to test taxonomic identity and ecological category abundance data for explanation with recent (1996–2007) environmental variables. We found a decrease in assemblage heterogeneity for recent assemblages and an increase in the number of tolerant species per subbasin. Recent Indiana streams are dominated by tolerant fishes with generalist life history strategies and low functional variation. The use of ecological categories resulted in weaker relationships with environmental variables than analyses with taxonomic identities. Analyses using taxonomy resulted in strong assemblage explanation from stream size and flow variation, while analyses using ecological categories resulted in strong assemblage explanation from habitat variation in silt substrates and flow. Analyses of recent assemblage structure using ecological categories resulted in decreased assemblage variation among subbasins than in analyses using taxonomic identities. We found that fish assemblages of Indiana streams are structured primarily by habitat complexity and have been altered during the past 50 years through multiple disturbances including fragmentation, siltation, and species introductions.     

An approach to analysis of functional redundancy in protozoan communities for bioassessment in marine ecosystems

It is necessary to detect how much ecological redundancy or response units (RUs) exist in communities for reducing the “signal-to-noise” ratios of the observed full species data in community-based ecological research and monitoring programs. To reveal the functional redundancy in ciliated protozoan communities in marine ecosystems for both ecological research and monitoring programs, a multivariate approach (peeling procedure) was used to identify the response units to the environmental changes using a dataset of biofilm-dwelling ciliates from coastal waters of the Yellow Sea, northern China. From the full 141-species dataset, three subsets with sufficient information of the whole community (correlation coefficient >0.75) were identified as response units (RUs 1–3) at three levels of functional redundancy, which comprised 20, 26 and 27 species, respectively. These response units appeared to be interchangeable between functional equivalents on both spatial and temporal scales. In terms of relative abundance, RU1, which predominated the ciliate communities over 1-year period, and RU2, which occurred only in warm seasons (except winter) with a peak in summer, presented a decreasing trend, while RU3, which distributed all four seasons with two peaks in summer and autumn, increased with the increase of pollution level. Furthermore, high proportions of bacterivores were found in RU1 during warm seasons and represented an increase trend, while high relative abundances of algivores occurred in RUs 2 and 3 appeared to be decreasing along the pollution gradient. These results demonstrated that the ciliated protozoan assemblages have high functional redundancy in response to environmental changes in marine ecosystems.     

Environmental DNA metabarcoding reveals winners and losers of global change in coastal waters

Studies of the ecological effects of global change often focus on one or a few species at a time. Consequently, we know relatively little about the changes underway at real-world scales of biological communities, which typically have hundreds or thousands of interacting species. Here, we use COI mtDNA amplicons from monthly samples of environmental DNA to survey 221 planktonic taxa along a gradient of temperature, salinity, dissolved oxygen and carbonate chemistry in nearshore marine habitat. The result is a high-resolution picture of changes in ecological communities using a technique replicable across a wide variety of ecosystems. We estimate community-level differences associated with time, space and environmental variables, and use these results to forecast near-term community changes due to warming and ocean acidification. We find distinct communities in warmer and more acidified conditions, with overall reduced richness in diatom assemblages and increased richness in dinoflagellates. Individual taxa finding more suitable habitat in near-future waters are more taxonomically varied and include the ubiquitous coccolithophore Emiliania huxleyi and the harmful dinoflagellate Alexandrium sp. These results suggest foundational changes for nearshore food webs under near-future conditions.     

Local and regional determinants of stream fish assemblage structure: inferences based on taxonomic vs. functional groups

Aim  To examine the roles of local and regional environmental variables and biotic interactions in determining the structure of local stream fish assemblages, and to compare results derived from analyses based on taxonomic and functional groups.
Location  Texas, USA.
Methods  Species abundance data were compiled for 157 stream fish assemblages in several river basins across Texas. Species were condensed into functional groups based on trophic and life-history characteristics. Local and regional environmental variables were either measured at each location or determined from scale maps and public-access data bases. The original taxonomic and functional group data sets were analysed using similarity indices, null models of co-occurrence, and direct and indirect ordination techniques. Results derived from taxonomic and functional group data sets are compared.
Results  Inferences regarding the relative roles of local and larger-scale factors in determining stream fish assemblage structure differ dramatically between analyses of taxonomic and functional groups. Taxonomic analyses suggest a prominent role of regional-scale environmental factors, and local assemblages sorted according to a biogeographic pattern. Functional group analyses suggest almost equal roles of factors representative of local and larger scales, and assemblages were distinguished by a habitat template irrespective of geographic region.
Main conclusions  The structure of local stream fish assemblages is determined ultimately by factors representing multiple scales, with the relative importance of each depending on the biological unit employed (species or functional groups). We suggest that analyses using functional groups can more directly infer ecological responses to environmental variation, and therefore may provide a more fruitful avenue for developing and testing ecological theory of community organization across biogeographic scales.     

Paleoecology of the Greater Phyllopod Bed community,Burgess Shale

To better understand temporal variations in species diversity and composition, ecological attributes, and environmental influences for the Middle Cambrian Burgess Shale community, we studied 50,900 fossil specimens belonging to 158 genera (mostly monospecific and non-biomineralized) representing 17 major taxonomic groups and 17 ecological categories. Fossils were collected in situ from within 26 massive siliciclastic mudstone beds of the Greater Phyllopod Bed (Walcott Quarry — Fossil Ridge). Previous taphonomic studies have demonstrated that each bed represents a single obrution event capturing a predominantly benthic community represented by census- and time-averaged assemblages, preserved within habitat. The Greater Phyllopod Bed (GPB) corresponds to an estimated depositional interval of 10 to 100 KA and thus potentially preserves community patterns in ecological and short-term evolutionary time.The community is dominated by epibenthic vagile deposit feeders and sessile suspension feeders, represented primarily by arthropods and sponges. Most species are characterized by low abundance and short stratigraphic range and usually do not recur through the section. It is likely that these are stenotopic forms (i.e., tolerant of a narrow range of habitats, or having a narrow geographical distribution). The few recurrent species tend to be numerically abundant and may represent eurytopic organisms (i.e., tolerant of a wide range of habitats, or having a wide geographical distribution). Rarefaction curves demonstrate variation in species richness through the GPB and suggest that more stenotopic species could still be discovered with additional sampling. Comparisons between richness and evenness trends suggest that the community is relatively stable overall, despite gradual species turnover through time, especially in assemblages from younger beds. Less diverse assemblages with low species evenness possibly represent the onset of less favourable environmental conditions.Fossil occurrences in individual beds were analysed using a range of statistical techniques (Correspondence Analysis, Canonical Correspondence Analysis, Minimum Spanning Tree, Indicator Species Analysis, Mantel Test) to extract community patterns. Results suggest the presence of four fossil assemblages based on distinct species associations. The different assemblages presumably reflect variations in environmental and ecological conditions, some acting through time, leading to species turnover. “Disturbances” (e.g., changes in paleo-redox conditions), differences in substrate firmness, and limited taphonomic biases are probably the main factors contributing to community structure. The influence of ecological factors, however, is also predicted from non-random patterns of species recurrences in successive events. Preliminary comparisons with Lower Cambrian Chengjiang-type assemblages of southern China suggest that the overall structure and ecology of Cambrian communities remained relatively stable until at least the Middle Cambrian in subtidal siliciclastic soft substrate environments.Comparisons with modern marine benthic ecosystems further suggest the Burgess Shale community was probably highly dependent on immigration from a regional pool of species after each burial event. This could support the view that species availability, habitat characteristics, and recolonisation processes were more important in structuring the community in the long-term than species interactions or environmental variations at a local scale.     

庞泉沟自然保护区华北落叶松林的自组织特征映射网络分类与排序

自组织特征映射网络（SOM）是新近引入植物生态学的分析方法,对复杂问题和非线性问题具有较强的分析和求解功能。本研究应用SOM分类和排序研究了庞泉沟自然保护区华北落叶松林。研究结果表明,SOM将120个样方分为7个植物群落类型,分类结果具有明确的生态意义;样方和物种在SOM训练图上呈现一定规律的分布;7个群落类型各有其分布范围和界限,揭示了群落间的生态关系。在此基础上,通过引入一种在SOM训练图上可视化环境因子梯度的方法,能够较好地完成样方、物种和环境因子相互关系的分析,揭示了海拔是影响该区华北落叶松林生长和分布的最主要因子。生态分析表明SOM分类和排序是一种有效的梯度分析方法,适用于表征生态特征和探索群落和环境相互关系的研究。     

Sea temperature is the primary driver of recent and predicted fish community structure across Northeast Atlantic shelf seas

Climate change has strongly influenced the distribution and abundance of marine fish species, leading to concern about effects of future climate on commercially harvested stocks. Understanding the key drivers of large-scale spatial variation across present-day marine assemblages enables predictions of future change. Here we present a unique analysis of standardised abundance data for 198 marine fish species from across the Northeast Atlantic collected by 23 surveys and 31,502 sampling events between 2005 and 2018. Our analyses of the spatially comprehensive standardised data identified temperature as the key driver of fish community structure across the region, followed by salinity and depth. We employed these key environmental variables to model how climate change will affect both the distributions of individual species and local community structure for the years 2050 and 2100 under multiple emissions scenarios. Our results consistently indicate that projected climate change will lead to shifts in species communities across the entire region. Overall, the greatest community-level changes are predicted at locations with greater warming, with the most pronounced effects at higher latitudes. Based on these results, we suggest that future climate-driven warming will lead to widespread changes in opportunities for commercial fisheries across the region.     

Environmental factors and underlying mechanisms of tree community assemblages of pine-oak mixed forests in the Qinling Mountains,China

Understanding the mechanisms of assembly of tree communities is very important for restoring and managing pine-oak mixed forests in the Qinling Mountains, China, but the essential mechanisms remain largely unexplored. The objective of this research was to uncover the underlying mechanisms of species coexistence and to identify the key environmental factors influencing the tree community assemblages in these forests. We investigated tree species and 15 environmental factors of topography, soil properties, and stand development of pine-oak mixed forests at an elevation of 1000-2000 m a.s.l. in the Qinling Mountains. Six classical models for the distribution of species abundance were used to fit the observed distributions; a clustering analysis was conducted to divide the ecological species groups, and a redundancy analysis examined the relationship between species assemblages and various environmental factors. Zipf-Mandelbrot, neutral-theory, log-normal, and Zipf models performed well in fitting the patterns of species-abundance distribution in the pine-oak mixed forests, which was related to the complexity of the community structure of the forests. A special combination of the Zipf-Mandelbrot and neutral-theory models, however, best explained the mechanism of species coexistence for the forests and indicated that these forests were progressive successional communities able to maintain stable development during succession. In addition, multiple factors controlled the tree community assemblage of pine-oak mixed forests in the mountainous regions, although available potassium, slope aspect, average tree DBH, and slope position were significant environmental variables.     

Are landscape attributes a useful shortcut for classifying vegetation in the tropics? A case study of La Amistad International Park

Effective vegetation classification schemes identify the processes determining species assemblages and support the management of protected areas. They can also provide a framework for ecological research. In the tropics, elevation‐based classifications dominate over alternatives such as river catchments. Given the existence of floristic data for many localities, we ask how useful floristic data are for developing classification schemes in species‐rich tropical landscapes and whether floristic data provide support for classification by river catchment. We analyzed the distribution of vascular plant species within 141 plots across an elevation gradient of 130 to 3200 m asl within La Amistad National Park. We tested the hypothesis that river catchment, combined with elevation, explains much of the variation in species composition. We found that annual mean temperature, elevation, and river catchment variables best explained the variation within local species communities. However, only plots in high‐elevation oak forest and Páramo were distinct from those in low‐ and mid‐elevation zones. Beta diversity did not significantly differ in plots grouped by elevation zones, except for low‐elevation forest, although it did differ between river catchments. None of the analyses identified discrete vegetation assemblages within mid‐elevation (700–2600 m asl) plots. Our analysis supports the hypothesis that river catchment can be an alternative means for classifying tropical forest assemblages in conservation settings.     

Lake regionalization and diatom metacommunity structuring in tropical South America

Lakes and their topological distribution across Earth's surface impose ecological and evolutionary constraints on aquatic metacommunities. In this study, we group similar lake ecosystems as metacommunity units influencing diatom community structure. We assembled a database of 195 lakes from the tropical Andes and adjacent lowlands (8°N–30°S and 58–79°W) with associated environmental predictors to examine diatom metacommunity patterns at two different levels: taxon and functional (deconstructed species matrix by ecological guilds). We also derived spatial variables that inherently assessed the relative role of dispersal. Using complementary multivariate statistical techniques (principal component analysis, cluster analysis, nonmetric multidimensional scaling, Procrustes, variance partitioning), we examined diatom–environment relationships among different lake habitats (sediment surface, periphyton, and plankton) and partitioned community variation to evaluate the influence of niche‐ and dispersal‐based assembly processes in diatom metacommunity structure across lake clusters. The results showed a significant association between geographic clusters of lakes based on gradients of climate and landscape configuration and diatom assemblages. Six lake clusters distributed along a latitudinal gradient were identified as functional metacommunity units for diatom communities. Variance partitioning revealed that dispersal mechanisms were a major contributor to diatom metacommunity structure, but in a highly context‐dependent fashion across lake clusters. In the Andean Altiplano and adjacent lowlands of Bolivia, diatom metacommunities are niche assembled but constrained by either dispersal limitation or mass effects, resulting from area, environmental heterogeneity, and ecological guild relationships. Topographic heterogeneity played an important role in structuring planktic diatom metacommunities. We emphasize the value of a guild‐based metacommunity model linked to dispersal for elucidating mechanisms underlying latitudinal gradients in distribution. Our findings reveal the importance of shifts in ecological drivers across climatic and physiographically distinct lake clusters, providing a basis for comparison of broad‐scale community gradients in lake‐rich regions elsewhere. This may help guide future research to explore evolutionary constraints on the rich Neotropical benthic diatom species pool.     

Local factors control the community composition of cyanobacteria in lakes while heterotrophic bacteria follow a neutral model

1. Neutral community models are derived from the proposition that basic probabilities of species loss (extinction, emigration) and gain (immigration, speciation) explain biological community structure, such that species with many individuals are very likely to be widespread. Niche models on the other hand assume that interactions between species and differential resource use mediate species coexistence, thus invoking environmental factors to explain community patterns. 2. In this study, we compared neutral and niche models to test how much of the spatial variability of assemblages of heterotrophic bacteria and phytoplankton in 13 lakes they could explain. Analysis of phytoplankton was restricted to cyanobacteria, so that they could be studied with the same molecular fingerprinting method, automated ribosomal intergenic spaces analysis (ARISA), as heterotrophic bacteria. We determined local biotic and abiotic lake variables as well as lake age, glacial history and distance between sites. 3. The neutral community model had a good fit to the community composition of heterotrophic bacteria (R² = 0.69), whereas it could not produce a significant model for the community composition of cyanobacteria. 4. The community composition of cyanobacteria was instead correlated to environmental variables. The best model, a combination of total organic carbon, biomass of eukaryotic phytoplankton, pH and conductivity, could explain 8% of the variation. In contrast, variation in the community composition of heterotrophic bacteria was not predicted by any of the environmental variables. Historical and spatial variables were not correlated to the community composition of either group. 5. The pattern found for heterotrophic bacteria suggests that stochastic processes are important. The correlation of cyanobacteria with local environmental variables alone is consistent with the niche model. We suggest that cyanobacteria, a group of organisms containing bloom‐forming species, may be less likely to fit a neutral community model, since these blooms are usually triggered by a particular combination of environmental conditions.     

Regional and local drivers of macroinvertebrate assemblages in boreal springs

Aim To identify the most important environmental drivers of benthic macroinvertebrate assemblages in boreal springs at different spatial scales, and to assess how well benthic assemblages correspond to terrestrially derived ecoregions. Location Finland. Methods Benthic invertebrates were sampled from 153 springs across four boreal ecoregions of Finland, and these data were used to analyse patterns in assemblage variation in relation to environmental factors. Species data were classified using hierarchical divisive clustering (twinspan ) and ordinated using non‐metric multidimensional scaling. The prediction success of the species and environmental data into a priori (ecoregions) and a posteriori (twinspan ) groups was compared using discriminant function analysis. Indicator species analysis was used to identify indicator taxa for both a priori and a posteriori assemblage types. Results The main patterns in assemblage clusters were related to large‐scale geographical variation in temperature. A secondary gradient in species data reflected variation in local habitat structure, particularly abundance of minerogenic spring brooks. Water chemistry variables were only weakly related to assemblage variation. Several indicator species representing southern faunistic elements in boreal springs were identified. Discriminant function analysis showed poorer success in classifying sites into ecoregions based on environmental than on species data. Similarly, when classifying springs into the twinspan groups, classification based on species data vastly outperformed that based on environmental data. Main conclusions A latitudinal zonation pattern of spring assemblages driven by regional thermal conditions is documented, closely paralleling corresponding latitudinal patterns in both terrestrial and freshwater assemblages in Fennoscandia. The importance of local‐scale environmental variables increased with decreasing spatial extent. Ecoregions provide an initial stratification scheme for the bioassessment of benthic macroinvertebrates of North European springs. Our results imply that climate warming, landscape disturbance and degradation of spring habitat pose serious threats to spring biodiversity in northern Europe, especially to its already threatened southern faunistic elements.     

Disentangling the roles of spatial and environmental variables in shaping benthic algal assemblages in rivers of central and northern China

Benthic algae were collected from central and northern Chinese rivers to test the hypothesis that geographic location has significant contributions in shaping algal assemblages. We used Moran’s eigenvector maps (MEM) to model spatial components and variation partitioning to quantify the influences of spatial and environmental variables on regional patterns of algal richness and community composition, respectively. We found that variation in algal richness was attributed to MEM component 2, 8, and 9 and the quadratic term of N–NO₃. Regarding abundance data, latitude, longitude, and MEM component 1, 2, and 7 were important spatial variables. Although P–PO₄, pH, and annual mean temperature were significant environmental variables influencing algal community composition, they were all spatially structured. Among the total explained variance in both algal metrics, spatial proportions were higher than that of environmental variables. We also found that abundant species of Achnanthidium minutissimum, Cocconeis placentula, Cymbella delicatula, Cymbella affinis, Cymbella turgidula, and Synedra ulna displayed clear spatially related patterns. In conclusion, the contributions of spatial and environmental variables to regional variation of algal assemblages are scale-dependent. As for our study scale (~1,000 km), spatial control may be more important. Since spatial effects could obscure local environmental impacts on algal communities, appropriate study scale and statistical methods should be taken into account in algal bioassessment. We recommend inclusion of both algal richness and community composition in study of algal biogeography, due to their different relationships with spatial and environmental variables.     

A pathway for multivariate analysis of ecological communities using copulas

We describe a new pathway for multivariate analysis of data consisting of counts of species abundances that includes two key components: copulas, to provide a flexible joint model of individual species, and dissimilarity‐based methods, to integrate information across species and provide a holistic view of the community. Individual species are characterized using suitable (marginal) statistical distributions, with the mean, the degree of over‐dispersion, and/or zero‐inflation being allowed to vary among a priori groups of sampling units. Associations among species are then modeled using copulas, which allow any pair of disparate types of variables to be coupled through their cumulative distribution function, while maintaining entirely the separate individual marginal distributions appropriate for each species. A Gaussian copula smoothly captures changes in an index of association that excludes joint absences in the space of the original species variables. A permutation‐based filter with exact family‐wise error can optionally be used a priori to reduce the dimensionality of the copula estimation problem. We describe in detail a Monte Carlo expectation maximization algorithm for efficient estimation of the copula correlation matrix with discrete marginal distributions (counts). The resulting fully parameterized copula models can be used to simulate realistic ecological community data under fully specified null or alternative hypotheses. Distributions of community centroids derived from simulated data can then be visualized in ordinations of ecologically meaningful dissimilarity spaces. Multinomial mixtures of data drawn from copula models also yield smooth power curves in dissimilarity‐based settings. Our proposed analysis pathway provides new opportunities to combine model‐based approaches with dissimilarity‐based methods to enhance understanding of ecological systems. We demonstrate implementation of the pathway through an ecological example, where associations among fish species were found to increase after the establishment of a marine reserve.     

Structure of ground-dwelling arthropod assemblages in vegetation units of Área Natural Protegida Península Valdés,Patagonia, Argentina

Knowing the spatial variation of insect and arachnid assemblages and their relationship with habitat variables is critical to understand the structure and dynamics of these communities in arid environments. The aim of this paper was to analyze the variation in ground-dwelling arthropod assemblages across three representative vegetation units of the Área Natural Protegida Península Valdés (Patagonia, Argentina). We asked whether environmental differences among representative vegetation units were associated to distinct arthropod assemblages. We selected three plant communities: grass, dwarf-shrub, and shrub steppes, and established three sampling sites within each of them. We measured variables of vegetation structure and soil characteristics and collected the arthropods using 10 pitfall traps per site. We analyzed the structure of arthropod assemblages at both family and ant species taxonomic levels. Each plant community displayed a distinctive assemblage, with differences in diversity, taxa abundance, trophic structure and functional groups of ants. Vegetation variables explained a higher proportion of the variation in the structure of the ground-dwelling arthropod assemblages than the soil variables. This work highlights the importance of the different vegetation units for the conservation of ground-dwelling arthropod biodiversity in Península Valdés.