Community-environment Relationships Research Articles

Ecological Study of the Vegetation in the Loka Abaya National Park, Ethiopia

An ecological study of the vegetation in the Loka Abaya National Park, in the Central Rift Valley of Ethiopia, was conducted. Vegetation data and some environmental variables including physical and chemical properties of the soil, altitude, slope, and ecological disturbance were collected and subjected to the agglomerative hierarchical classification and ordination with the canonical correspondence analysis. For each of the community groups, the mean and standard errors were calculated from the environmental parameters to characterize the community types and quantitative relationships between environmental variables were analyzed by calculating Pearson’s product-moment correlation coefficient using the SAS computer software programme. A total of 198 plant species representing 79 families and 139 genera were collected and documented. Seven plant community types, namely, Vachellia brevispica Harms–Rhus natalensis Krauss, Ficus sur Forssk.–Vachellia albida (Del.) A. Chev., Panicum subalbidum Kunth–Cyperus latifolius Poir, Dodonaea angustifolia L. f.–Ximenia americana L., Combretum molle R.Br ex. G.Don–Combretum collinum Fresen., Ilex mitis (L.) Radlk–Olea europaea L. subsp. cuspidata, and Dichrostachys cinerea (L.) Wight & Arn, were identified. Ilex mitis–Olea europaea L. subsp. cuspidata community had the highest species richness, whereas the least species richness was recorded for the Panicum subalbidum–Cyperus latifolius community. The results of vegetation-environment relationships indicated that the measured environmental variables explained 74.99% of the total variation in floristic data. The results of the canonical correspondence analysis (CCA) of community-environment relationships indicated that among measured environmental variables, altitude (r2 0.0548, P<0.01), slope (r2 = 0.0241, P<0.01), pH (r2 = 0.01855, P<0.01), sodium (r2 = 0.01316, P<0.04), CEC (r2 = 0.01424, P<0.03), magnesium (r2 = 0.01282, P<0.04), potassium (r2 = 0.0152, P<0.02), and soil moisture content (SMC) (r2 = 0.01537, P<0.05) significantly explained the variation in species composition of the communities and their distribution. Therefore, ecosystem-oriented biodiversity conservation and restoration strategies will be implemented by considering these significant environmental variables.

Planktic diatom responses to spatiotemporal environmental variation in high‐mountain tropical lakes

Abstract Tropical lakes harbour high levels of biodiversity, but the temporal and spatial variability of biological communities are still inadequately characterised, making it difficult to predict the impact of accelerated rates of environmental change in these regions. Our goal was to identify the spatiotemporal dynamics of the planktic diatom community in the Cajas Massif in the tropical Andes. We analysed seasonal diatom and environmental data over a period of 1 year from 10 lakes located in geologically distinct basins and modelled community–environment relationships using multivariate ordination and variation partitioning techniques. Generalised additive models with a full‐subset information theoretic approach also were used to determine which environmental variables explain single‐species abundance. Although the lakes are monomictic and thus have variable thermal structure across the year, seasonal variability of water chemistry conditions was negligible, and seasonal differences in diatom community composition were small. Across space, diatom community composition was correlated primarily with ionic content (divalent cations and alkalinity), related to bedrock composition, and secondly with lake thermal structure and productivity. The ionic gradient overrode the effect of the thermal structure–productivity gradient at the diatom community level, whereas individual diatom species responded more sensitively to variables related to in‐lake and catchment productivity, including chlorophyll‐a and iron, and the proportion of wetlands in the catchment. Our results indicate that the spatiotemporal variability of Cajas lakes and their diatom communities is the result of multiple intertwined environmental factors. The emergence of the ionic and thermal structure–productivity gradients in a rather small tropical lake district suggests segregation of ecological niches for diatoms that also may be important in other high‐elevation lake regions. Future studies that track tropical Andean lakes under natural and anthropogenically mediated change, both in contemporary times and in palaeoenvironmental reconstructions, would benefit from the modelling approach (community and species levels) developed here.

Local environmental and spatial factors are associated with multiple facets of riverine fish β‐diversity across spatial scales and seasons

Abstract Disentangling the factors governing community structure across various spatial and temporal scales is a core task in community ecology and biogeography, because it could provide valuable insights into biodiversity conservation and management. The relative role of environmental (a proxy for niche‐based mechanism) and spatial (a proxy for dispersal) effects in shaping ecological communities depends on diversity facets, network positions, seasonality and biological characteristics of the focal organisms. However, such patterns are not well understood for fish communities in large river systems, especially if all of these patterns are examined simultaneously. We investigated fish taxonomic, functional and phylogenetic total β‐diversity (and their turnover and nestedness phenomena) at different spatial scales (basin vs. section scales) and seasons (wet vs. dry seasons) in a subtropical river system (the Chishui River basin, China). We also quantified the relative importance of environmental variables and spatial factors in shaping fish β‐diversity by using generalised dissimilarity modelling. At the basin scale, fish taxonomic and phylogenetic β‐diversity across seasons mainly reflected turnover, yet turnover and nestedness contributed likewise to total functional β‐diversity. Taxonomic and phylogenetic β‐diversity were strongly correlated (r from 0.39 to 0.87), whereas functional and both taxonomic and phylogenetic facets were relatively weakly correlated (r from 0.27 to 0.65). Generalised dissimilarity modelling suggested that phylogenetic β‐diversity phenomena were consistently more influenced by environmental variables (wet 16.1%, dry 22.4%) than by spatial factors (wet 6.7%, dry 4.8%). However, for both taxonomic and functional facets, environmental variables (turnover 13.8%, nestedness 6.4%) and spatial factors (turnover 4.3%, nestedness 9.4%) accounted for a greater proportion of variations in turnover and nestedness, respectively. At the section scale, only phylogenetic total β‐diversity and nestedness, as well as taxonomic nestedness significantly differed between the headwater and downstream sections. Furthermore, headwater communities were primarily explained by spatial (15.7%) and environmental (12.7%) variables in the wet season, while environmental factors (25.9%; spatial 7.7%) dominated in the dry season. By contrast, downstream communities were more influenced by environmental factors (17.9%; spatial 8.3%) in the wet season, whereas environmental (11.0%) and spatial variables (11.5%) contributed likewise to β‐diversity in the dry season. Our results highlight that, compared with taxonomic β‐diversity, accounting for turnover and nestedness of functional and phylogenetic β‐diversity helps to reveal distinct biodiversity patterns, and potential environmental and spatial controls. Given that community–environment relationships and the relative contribution of environmental and spatial factors varied between seasons and between the basin and section scales, our study underlines the importance of long‐term dynamics and spatial scales in metacommunity studies. Our findings also suggest that maintaining environmental heterogeneity and adequate hydrological connectivity would be essential for the conservation of fish diversity. Overall, our study advances current knowledge of fish biodiversity patterns and their maintenance mechanisms by adding insights from multi‐faceted diversity and seasonality, which has rarely been done in large subtropical rivers.

High compositional dissimilarity among small communities is decoupled from environmental variation

Communities composed of small populations are predicted to be strongly influenced by stochastic demographic events and, thus, less affected by environmental selection than those composed of large populations. However, this prediction has only been tested with computer simulations, simplified controlled experiments, and limited observational data. Here, using multiple datasets on fish abundance in 541 streams we tested 1) if communities composed of small populations are more spatially variable and 2) less related to the environment variation than communities composed of large populations. We used process‐based simulations to identify β‐diversity metrics and community–environment measures that were appropriate to investigate the role of assembly processes along a gradient of community size. We show that variation in species composition among small communities is higher than among large communities and that the strength of community–environment relationships is weaker in small communities. Our results indicate that community size affects the strength of ecological drift and environmental selection in metacommunities. We thus suggest that further declines in the size of populations and ecosystems can make spatial variation in biodiversity more unpredictable.

The power of metabarcoding: Can we improve bioassessment and biodiversity surveys of stream macroinvertebrate communities?

Most stream bioassessment and biodiversity surveys are currently based on morphological identification of communities. However, DNA metabarcoding is emerging as a fast and cost-effective alternative for species identification. We compared both methods in a survey of benthic macroinvertebrate communities across 36 stream sites in northern Finland. We identified 291 taxa of which 62% were identified only by DNA metabarcoding. DNA metabarcoding produced extensive species level inventories for groups (Oligochaeta, Chironomidae, Simuliidae, Limoniidae and Limnephilidae), for which morphological identification was not feasible due to the high level of expertise needed. Metabarcoding also provided more insightful taxonomic information on the occurrence of three red-listed vulnerable or data deficient species, the discovery of two likely cryptic and potentially new species to Finland and species information of insect genera at an early larval stage that could not be separated morphologically. However, it systematically failed to reliably detect the occurrence of gastropods that were easily identified morphologically. The impact of mining on community structure could only be shown using DNA metabarcoding data which suggests that the finer taxonomic detail can improve detection of subtle impacts. Both methods generally exhibited similar strength of community-environment relationships, but DNA metabarcoding showed better performance with presence/absence data than with relative DNA sequence abundances. Our results suggest that DNA metabarcoding holds a promise for future anthropogenic impact assessments, although, in our case, the performance did not improve much from the morphological species identification. The key advantage of DNA metabarcoding lies in efficient biodiversity surveys, taxonomical studies and applications in conservation biology.

Congruency between two traditional and eDNA-based sampling methods in characterising taxonomic and trait-based structure of fish communities and community-environment relationships in lentic environment

Recent developments in environmental DNA (eDNA) metabarcoding suggest that eDNA-based representation of ecological communities can be a promising tool in both fundamental ecological research and environmental assessment. However, it is less known, how eDNA performs in characterising ecological communities and community-environment relationships at the regional scale compared with traditional sampling methods. Here, we used electrofishing (EF), gillnetting (GN) and eDNA-based surveys to compare their congruency in characterising the taxonomic and trait-based structure of (oxbow) lake fish communities and their structuring mechanisms. eDNA proved to be more effective in detecting taxa in the total samples and by traits than EF and GN. Principal coordinate analysis and multiple factor analysis showed a moderate separation of communities according to sampling methods for the taxon and the trait-based structures, respectively, but eDNA samples were always located in intermediate position in the ordination plots. Procrustes analyses indicated significant among-method congruency in community structure. However, in general, eDNA-based community patterns always showed higher correlation with either the EF or the GN-based community patterns, than the two traditional methods to each other. Variance partitioning in redundancy analyses indicated large differences among the sampling methods in the importance of environmental and spatial variables in shaping metacommunity structure. These results thus suggest that the sampling method can largely influence the identified mechanisms which govern fish metacommunity organisation. Our results suggest, that eDNA metabarcoding can be the best universal method for understanding the taxonomic and trait-based organisation of lake fish metacommunities.

DNA metabarcoding and morphological methods show complementary patterns in the metacommunity organization of lentic epiphytic diatoms

Diatoms are important organisms in freshwater ecosystems due to their position as primary producers and therefore, analyzing their assemblages provides relevant information on ecosystem functioning. Diatoms have historically been identified based on morphological traits, which is time-consuming and requires well-trained specialists. Nevertheless, DNA barcoding offers an alternative approach to overcome some limitations of the morphological method. Here, we assess if both approaches are comparable methods to study patterns and mechanisms (including environmental filtering and dispersal limitation) of epiphytic diatom metacommunities using a comprehensive dataset from 22 Mediterranean ponds at different taxonomic resolutions. We used a fragment of rbcL barcode gene combined with High-Throughput Sequencing to infer diatom community composition. The overall degree of correspondence between both approaches was assessed by Procrustean rotation analysis and Procrustean randomization tests, whereas the role of local environmental variables and geographical distances was studied using a comprehensive combination of BIOENV, Mantel tests and distance-based redundancy analysis. Our results showed a relatively poor correspondence in the compositional variation of diatom metacommunity between both approaches. We speculate that the incompleteness of the reference database and the bioinformatics processing are the biases most likely affecting the molecular approach, whereas the limited counting effort and the presence of cryptic species are presumably the major biases related with the morphological method. On the other hand, variation in diatom community composition detected with both approaches was strongly related to the environmental template, which may be related with the narrow community-environment relationships in diatoms. Nevertheless, we found no significant relationship between compositional variation and geographical distances. Overall, our work shows the complementary nature of both approaches and highlights the importance of DNA metabarcoding to address empirical research questions of community ecology in freshwaters, especially once the reference databases include most genotypes of occurring taxa and bioinformatics biases are overcome.

Land snail community patterns related to regional habitat conservation status of European spring fens

Human activities have enormous impact on current biodiversity distribution across all spatial scales. Despite the numerous studies showing the difference between preserved and impaired sites, only little is known about the regional scale. Therefore, we selected four European regions differing in habitat conservation status (HCS) to explore if the variation in land snail communities reflects regional differences. We collected quantitative land snail samples at 169 isolated spring fen sites and measured environmental parameters. The species richness of habitat specialists expressed low variation and weak associations with local conditions in the two regions of adequate HCS, presumably because of their common occurrence throughout most sites. In contrast, the richness of matrix-derived species, i.e. predominantly habitat generalists, was highly variable in these two regions and also tightly associated with local conditions, especially moisture. In both the intermediate and the inadequate HCS region, these associations were much weaker as the fens are less extreme and allow for penetration of matrix-derived species. Population densities of Vertigo geyeri, an umbrella species internationally protected by the EU Habitats Directive, were highest in the two adequate HCS regions. Species composition was primarily controlled by moisture in the regions of adequate HCS, while in the remaining regions, those predictors that are less easily jeopardized by human impact, such as climate, water chemistry and terrain topography, gained importance. In the inadequate HCS region, none of the analysed predictors was associated with the main compositional gradient, suggesting a complete disruption of community-environment relationships. Our results suggest that the species richness and community responses to natural gradients might be substantially modified by human impact, although the effect of some other region-specific factors cannot be easily disentangled because of inevitably low number of studied regions.

Spatial and temporal trends in different dimensions of macrophyte biodiversity in boreal lakes

To comprehensively understand the impact of anthropogenic activities on biodiversity, we must understand how biodiversity has changed over time and its underlying processes. Regardless of a recent increase in scientific interest towards changes in community composition, i.e. beta diversity, these changes have not been studied comprehensively in lake environments in a spatio-temporal framework. In addition, although biotic homogenisation has gained much attention in recent decades, it is still unclear how this process acts at different levels of biodiversity through time.
 The main aim of this thesis is to study temporal and spatial biodiversity patterns of vascular aquatic macrophyte communities in small boreal lakes during a period of 70 years. The focus is on beta diversity-environment relationships and different dimensions of biodiversity, with special attention to functional features. This thesis is based on three separate case studies that all have utilised temporal presence-absence data of vascular aquatic macrophytes from 27 to 28 lakes from the 1940s to the 2010s.
 Vascular aquatic macrophyte communities showed only moderately different spatial beta diversity patterns in relation to human impact across decades. The patterns of different dimensions of spatial beta diversity diverged only slightly from each other. The temporal change in aquatic macrophyte communities at the lake level has beenmodest since the 1940s. Nevertheless, it seems that even relatively modest changes in the environment affect temporal gains and losses of species at the lake level. There were no signs of either biotic homogenisation or biotic differentiation (taxonomic, phylogenetic or functional), but the changes in the environment have affected functional community composition and changes in functional richness to some extent.
 By using the spatial and temporal beta diversity perspective, this thesis highlights the fact that even though biotic homogenisation is a pervasive problem globally, it is not an unambiguous process acting similarly at all spatial and temporal scales or in different environments and different organism groups. There are likely five partly interdependent reasons why no signs of biotic homogenisation were detected in the study area during the 70-year study period: the modest changes in the environment from the 1940s to the 2010s, high ecological resilience of the lakes, information on species presence and absence was used instead of abundance data, biotic interactions and complex community-environment relationships together with stochastic processes and climate change.
 The results highlight that relying on only one or two survey points in time can result in limited knowledge of the ecological phenomenon under study, and an exceptional year in terms of weather conditions can hinder detecting overall long-term trends in compositional changes, especially under ongoing climate change. The patterns detected in macrophyte beta diversity are likely to represent situations in the extensive boreal and glaciated areas of Eurasia and North America, with largely similar species pools in many regions. Therefore, lakes across the boreal region and areas that have faced glaciation and postglacial processes might be resistant against moderate levels of human pressure.

The role of environmental conditions, climatic factors and spatial processes in driving multiple facets of stream macroinvertebrate beta diversity in a climatically heterogeneous mountain region

There is a growing recognition that examining patterns of ecological communities and their underlying determinants is not only feasible based on taxonomic data, but also functional and phylogenetic approaches. This is because these additional facets can enhance the understanding of the relative contribution of multiple processes in shaping biodiversity. However, few studies have focused on multifaceted beta diversities in lotic macroinvertebrates, especially when considering driving factors operating at multiple spatial scales. Here, we examined the spatial patterns of multi-faceted (i.e., taxonomic, functional and phylogenetic) beta diversity and their components (i.e., turnover and nestedness) of macroinvertebrates in 50 sites in 10 streams situated in the north and south slope of the Qinling Mountains, the geographical dividing line of Northern and Southern China. We found that the streams draining the north slope showed significantly lower values of beta diversity based on all three facets than the streams draining the south slope. Such north-to-south increases of beta diversity were caused by the distinct climatic and local environmental conditions between the sides of the mountain range. Moreover, spatial variables generally played the most important role in structuring all facets and components of beta diversity, followed by local environmental and climatic variables, whereas catchment variables were less important. Despite the similar results of relative contribution of explanatory variables on each beta diversity facet, the details of community-environment relationships (e.g., important explanatory variables and explanatory power) were distinct among different diversity facets and their components. In conclusion, measuring functional and phylogenetic beta diversity provides complementary information to traditional taxonomic approach. Therefore, an integrative approach embracing multiple facets of diversity can better reveal the mechanisms shaping biodiversity, which is essential in assessing and valuing aquatic ecosystems for biodiversity management and conservation.

Global patterns and determinants of lake macrophyte taxonomic, functional and phylogenetic beta diversity

Documenting the patterns of biological diversity on Earth has always been a central challenge in macroecology and biogeography. However, for the diverse group of freshwater plants, such research program is still in its infancy. Here, we examined global variation in taxonomic, functional and phylogenetic beta diversity patterns of lake macrophytes using regional data from six continents. A data set of ca. 480 lake macrophyte community observations, together with climatic, geographical and environmental variables, was compiled across 16 regions worldwide. We (a) built the very first phylogeny comprising most freshwater plant lineages; (b) exploited a wide array of functional traits that are important to macrophyte autoecology or that relate to lake ecosystem functioning; (c) assessed if different large-scale beta diversity patterns show a clear latitudinal gradient from the equator to the poles using null models; and (d) employed evolutionary and regression models to first identify the degree to which the studied functional traits show a phylogenetic signal, and then to estimate community-environment relationships at multiple spatial scales. Our results supported the notion that ecological niches evolved independently of phylogeny in macrophyte lineages worldwide. We also showed that taxonomic and phylogenetic beta diversity followed the typical global trend with higher diversity in the tropics. In addition, we were able to confirm that species, multi-trait and lineage compositions were first and foremost structured by climatic conditions at relatively broad spatial scales. Perhaps more importantly, we showed that large-scale processes along latitudinal and elevational gradients have left a strong footprint in the current diversity patterns and community-environment relationships in lake macrophytes. Overall, our results stress the need for an integrative approach to macroecology, biogeography and conservation biology, combining multiple diversity facets at different spatial scales.

Ecological fidelity and spatiotemporal resolution of arthropod death assemblages from rodent middens in the central Atacama Desert (northern Chile)

Evaluating the magnitude and direction of biases affecting the ecological information captured by death assemblages is an important prerequisite for understanding past, present, and future community-environment relationships. Here, we establish the ecological fidelity and spatiotemporal resolution of an overlooked source of fossil remains: the soil arthropod assemblages found in rodent middens (that span from the present to >44,420 cal yr BP) collected in the central Atacama Desert of northern Chile. We evaluated the “live-dead agreement” across four sources of soil arthropod data; two contemporary surveys of live communities (i.e., live), and two sources of death assemblages (i.e., dead). Although live-dead agreements and diversity indices are highly variable among samples (live and dead assemblages), our results consistently demonstrate that an average fossil midden (i) better captures the structure and composition of living communities than species richness per se; (ii) offers a spatially-resolved picture of those communities at local scales; and (iii) is only weakly affected by time-averaging. The fine spatiotemporal resolution of fossil midden records in the Atacama, and most likely other areas of the world where rodent middens occur offers ecological information on the structure and composition of fossil arthropod assemblages potentially over many thousands of years. This information is reliable enough to establish historical baselines before past and ongoing anthropogenic impacts.

Assessing the ecological value of small testate amoebae (

Methodological advances are essential for robust ecological research. Quantitative reconstructions of environmental conditions using testate amoebae rely on sound taxonomy. While the taxonomy of large species is relatively well resolved, this is not the case for most small taxa (typically <45 μm long). In New Zealand, peatlands contain a diversity of both cosmopolitan and characteristic large southern endemic taxa, but also have a high abundance of small taxa. The latter are often lumped into morphotypes reducing their value as ecological indicators. In this study, we demonstrate how (a) lumping small taxa versus splitting them into unique types, and (b) including or excluding them from community analysis influenced their ecological inference. We assessed testate amoeba composition in six peat bogs from New Zealand, three that were moderately-to-highly impacted, and three that were non-impacted. Environmental variables were measured at each sampling site and the surface testate amoeba community patterns and community-environment relationships compared. We found a clear division between impacted and non-impacted sites. Several distinct small taxa were more strongly related to water-table depth and conductivity, while the larger taxa were more correlated to pH. These results show that improved taxonomic resolution of small taxa can provide more informed environmental assessment.

Global patterns in the metacommunity structuring of lake macrophytes: regional variations and driving factors

We studied community–environment relationships of lake macrophytes at two metacommunity scales using data from 16 regions across the world. More specifically, we examined (a) whether the lake macrophyte communities respond similar to key local environmental factors, major climate variables and lake spatial locations in each of the regions (i.e., within-region approach) and (b) how well can explained variability in the community–environment relationships across multiple lake macrophyte metacommunities be accounted for by elevation range, spatial extent, latitude, longitude, and age of the oldest lake within each metacommunity (i.e., across-region approach). In the within-region approach, we employed partial redundancy analyses together with variation partitioning to investigate the relative importance of local variables, climate variables, and spatial location on lake macrophytes among the study regions. In the across-region approach, we used adjusted R2 values of the variation partitioning to model the community–environment relationships across multiple metacommunities using linear regression and commonality analysis. We found that niche filtering related to local lake-level environmental conditions was the dominant force structuring macrophytes within metacommunities. However, our results also revealed that elevation range associated with climate (increasing temperature amplitude affecting macrophytes) and spatial location (likely due to dispersal limitation) was important for macrophytes based on the findings of the across-metacommunities analysis. These findings suggest that different determinants influence macrophyte metacommunities within different regions, thus showing context dependency. Moreover, our study emphasized that the use of a single metacommunity scale gives incomplete information on the environmental features explaining variation in macrophyte communities.

Anthropogenic disturbances strengthened tree community-environment relationships at the temperate-boreal interface

Knowledge of how environmental gradients generate changes in community composition across forest landscapes (β-diversity) represents a critical issue in the era of global change, which exerts especially powerful impacts by shifting disturbance regimes. We analyzed the response of tree communities to increased disturbance rates that were linked to European settlement at the temperate-boreal interface of eastern Canada. We tested whether disturbance has led to spatial homogenization or heterogenization, and to decoupling or strengthening of community-environment relationships. We used a reconstruction of pre-industrial tree communities based on historical land survey records (1854–1935), together with modern data, to assess changes in tree β-diversity patterns. Then, β-diversity was partitioned into fractions explained by spatial (dbMEM) and environmental variables (latitude, elevation, slope, drainage and surface deposits) in order to assess changes in spatial structures and community-environment relationships. In pre-industrial times, environmental variables explained only a small proportion of β-diversity since dominant taxa were present across the range of environmental gradients, whereas habitat specialists were very rare. Between pre-industrial and modern times, our analysis highlights an increase in β-diversity and the proportion of β-diversity that was explained by environmental variables. Increased disturbance rates have favored early-successional habitat specialist taxa and reduced the habitat breadth of pre-industrial generalists, thereby increasing the strength of community-environment relationships. Our results support that disturbance can alter the strength of community-environment relationships and also suggest that functional traits of species within the regional pool could predict whether or not disturbance alters such relationships.

Effect of landscape context on fish metacommunity structuring in stream networks

Summary The metacommunity framework has shed light upon the significance of local and regional processes in shaping ecological communities. However, our knowledge is limited how landscape context (i.e. type and positioning of habitats) influences the structuring of metacommunities. We examined the role of environmental selection (niche‐based species sorting), dispersal and drift (i.e. stochastic changes in species abundance) mechanisms on the structuring of fish metacommunities in riverscapes. We used a hierarchical design and examined metacommunity structuring (i) in individual running water habitat types, namely highland streams, lowland streams, highland rivers and lowland rivers; (ii) in landscape types, where patterns in highland and in lowland types were examined separately and (iii) at the level of the whole riverscape, where samples from all running water types were pooled. Elements of metacommunity structure (EMS) analysis, community–environmental relationships in redundancy analysis, and decay of community similarity with distance (distance decay) complemented with partial Mantel tests were used to reveal the mechanisms behind the observed patterns. Both the EMS framework and community–environment relationships revealed the prevalent role of selection (niche‐based species sorting mechanisms) on fish metacommunity structuring, although stochastic variability also influenced the results. Metacommunity structures reflecting niche‐based mechanisms (Clementsian or quasi‐Clementsian) were observed at higher hierarchical levels (i.e. at the riverscape and the landscape type levels), while quasi‐Clementsian or random patterns were found within single running water types. Distance decay relationships indicated that dispersal limitation did not clearly affect metacommunity structuring in any combination of running water types. Partial Mantel tests showed that some part of the variation in distance decay could be explained by the correlation between environmental variables and fish assemblage structure in some habitat types, which further suggests the importance of niche‐based mechanisms in metacommunity structuring. Our study shows that different metacommunity structures can arise in a hierarchy of habitat types in riverscapes, and niche‐based species sorting mechanisms are more influential in their structuring than dispersal ones. Landscape classifications are useful for a better understanding of the structuring of metacommunities in both the freshwater and terrestrial realms.

Evaluating community-environment relationships along fine to broad taxonomic resolutions reveals evolutionary forces underlying community assembly.

We propose a method for detecting evolutionary forces underlying community assembly by quantifying the strength of community-environment relationships hierarchically along taxonomic ranks. This approach explores the potential role of phylogenetic conservatism on habitat preferences: wherein, phylogenetically related taxa are expected to exhibit similar environmental responses. Thus, when niches are conserved, broader taxonomic classification should not diminish the strength of community-environment relationships and may even yield stronger associations by summarizing occurrences and abundances of ecologically equivalent finely resolved taxa. In contrast, broader taxonomic classification should weaken community-environment relationships when niches are under great divergence (that is, by combining finer taxa with distinct environmental responses). Here, we quantified the strength of community-environment relationships using distance-based redundancy analysis, focusing on soil and seawater prokaryotic communities. We considered eight case studies (covering a variety of sampling scales and sequencing strategies) and found that the variation in community composition explained by environmental factors either increased or remained constant with broadening taxonomic resolution from species to order or even phylum level. These results support the niche conservatism hypothesis and indicate that broadening taxonomic resolution may strengthen niche-related signals by removing uncertainty in quantifying spatiotemporal distributions of finely resolved taxa, reinforcing the current notion of ecological coherence in deep prokaryotic branches.

Temporal variation in community–environment relationships and stream classifications in benthic diatoms: Implications for bioassessment

Diatom based biomonitoring tools are proven to be a practical way to indicate stream conditions, but only little is known how stable diatom inferred stream classifications are in time. We studied annual variation in diatom community–environment relationships, community structure and diatom indices (Index of Pollution Sensitivity, IPS and Trophic Diatom Index, TDI) during three consecutive years (2010–2012) in four drainage basins distributed in Finland. We also used a cluster analysis to examine if stream classifications resulted in distinct and temporally stable community types. We found only subtle temporal variation in community–environment relationships, nutrient concentrations (N, P) and conductivity consistently being the main factors structuring communities. According to Mantel tests, diatom communities resembled each other significantly at different years, and the values of IPS and TDI indices remained relatively stable in the basins through time. The stream classification based on diatoms also resulted in temporally stable and statistically distinct community types. We thus suggest that sampling of diatoms, e.g., in every three years seems to be a reliable procedure to assess biological water quality. Generally, to choose the correct metrics to assess water quality is essential, and both biological and physicochemical factors should be considered.

Mediated spatio-temporal patterns of macroinvertebrate assemblage associated with key environmental factors in the Qinghai Lake area, China

The Qinghai Lake area is one of key regions in the Qinghai–Tibet Plateau for supporting a highly specific array of biodiversity. However, little is known about the composition and spatio-temporal patterns of benthic assemblages across this region. Herein, we examined how the community structure and community–environment relationships of macroinvertebrates varied over three consecutive years (2012–2014) across its three distinct water types of the saline main-body (MB) and sub-lakes (SSLs) and the freshwater bodies (FWBs). These waters harbored a poor benthic fauna, with identification of 30 taxa (6 in MB, 6 in SSLs and 23 in FWBs). There were distinct differences of assemblage composition among three water bodies, whereas weak (inter-year) or insignificant (seasons) differences at temporal scales. The CCA models indicated that there were highly naturally-driven environmental-assemblage relationships through time, with constant environmental factors of salinity, water depth and nutrients being the key environmental factors affecting macroinvertebrate variations. The currently overall benthic community composition and structure remains quite stable through years, indicating their suffering less from human activities. These results provide implications for projecting comprehensive benthic biomonitoring and conservation planning for those fragile and under-investigated lakes in the Qinghai–Tibet Plateau.

Community–environment relationships of riverine invertebrate communities in central Chinese streams

Chinese rivers are both highly biodiverse and highly under pressure, hence an urgent need exists to understand ecological drivers and disentangle different scales of stressors to support water management. Our aims were to (1) determine the most influential variables for benthic invertebrate occurrence, (2) compare results related to communities as opposed to metrics and (3) examine the role of spatial scales with relevance to management. Benthic invertebrate sampling was performed at 37 sites in selected tributaries of the middle reaches of the Yangtze, covering an environmental gradient with a focus on organic pollution (stratified sampling design). Ten metrics commonly used in biomonitoring were derived and analysed in parallel to assemblage data. Environmental variables covered 74 parameters from three different spatial scales, namely local, reach and catchment scale. We ran a CCA with each of the three subsets to find out the significant determining/explanatory variables, followed by pCCA and pRDA (for metric data) with these variables with forward selection to determine single variables important for each subset; we further used variation portioning for benthic invertebrate data. A high percentage of overall variability (70 %) of the assemblage structure was explained, with catchment- and local-scale variables being almost equally important. Small-scale variables tended to be more important than large-scale variables for the metric-based approach but not for the assemblage approach. Our results emphasise the need for spatially explicit regional studies in freshwater systems and suggest testing multi-metric assessment approaches to tackle water management and environmental health questions in China.