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Owing to a long history of anthropogenic pressures, freshwater ecosystems are among the most vulnerable to biodiversity loss1. Mitigation measures, including wastewater treatment and hydromorphological restoration, have aimed to improve environmental quality and foster the recovery of freshwater biodiversity2. Here, using 1,816 time series of freshwater invertebrate communities collected across 22 European countries between 1968 and 2020, we quantified temporal trends in taxonomic and functional diversity and their responses to environmental pressures and gradients. We observed overall increases in taxon richness (0.73% per year), functional richness (2.4% per year) and abundance (1.17% per year). However, these increases primarily occurred before the 2010s, and have since plateaued. Freshwater communities downstream of dams, urban areas and cropland were less likely to experience recovery. Communities at sites with faster rates of warming had fewer gains in taxon richness, functional richness and abundance. Although biodiversity gains in the 1990s and 2000s probably reflect the effectiveness of water-quality improvements and restoration projects, the decelerating trajectory in the 2010s suggests that the current measures offer diminishing returns. Given new and persistent pressures on freshwater ecosystems, including emerging pollutants, climate change and the spread of invasive species, we call for additional mitigation to revive the recovery of freshwater biodiversity.

Community ecology has had a strong focus on single snapshots of species compositional variation in time. However, environmental change often occurs slowly at relatively broad spatio‐temporal scales, which requires historically explicit assessments of long‐term metacommunity dynamics, such as the order of species arrival during community assembly (i.e., priority effects), a theme that merits further empirical quantification. In this study, we applied the Bayesian inference scheme of Hierarchical Modeling of Species Communities together with information on functional traits and evolutionary dependencies to efficiently explore the question of how ecological communities are organized in space and time. To do this, we used a comprehensive time‐series dataset from boreal lake plants and adopted the perspective that more sound conclusions on metacommunity dynamics can be gained from studies that consider a historically integrative approach over long timeframes. Our findings revealed that historical contingency via priority effects can profoundly shape community assembly under the influence of environmental change across decades (here, from the 1940s to the 2010s). Similarly, our results supported the existence of both positive and negative species‐to‐species associations in lake plants, suggesting that functional divergence can switch the inhibition–facilitation balance at the metacommunity level. Perhaps more importantly, this proof‐of‐concept study supports the notion that community ecology should include a historical perspective and suggests that ignoring priority effects may risk our ability to identify the true magnitude of change in present‐day biotic communities.

Identifying the hierarchical spatial levels that show the greatest dissimilarities between communities and how these patterns are generated is essential to provide insights into the monitoring and protection of biodiversity. In this study, we additively partitioned diversity of macroinvertebrates into alpha, beta, and gamma diversity across multiple scales in typical and semi‐arid tropical estuaries. We also determined which components of the total beta diversity, in terms of species replacement or richness difference (presence‐absence data) and abundance difference (relative abundance data), had the greatest relative importance in structuring the composition of benthic macrofauna. In typical and semi‐arid tropical estuaries, a non‐random spatial pattern was observed in additive partitioning of diversity, with higher values of beta diversity obtained at the largest scales analyzed. When considering the presence‐absence data, in general there was no clear trend which components of beta diversity had greater relative importance in typical estuaries. In the semi‐arid tropical estuaries, the richness difference component showed greater relative importance in the rainy season, whereas the species replacement presented greater proportions in the dry season. When considering abundance data, in general the abundance difference component showed greater relative importance in typical and semi‐arid tropical estuaries in the two seasonal periods. Therefore, approaches based on the presence/absence and on the relative abundance of species provided complementary answers about the distribution patterns of benthic macroinvertebrate communities. We demonstrated that environmental filtering and dispersal limitation may affect the patterns of distribution of benthic macrofauna in estuaries located in regions with different climatic conditions.

Environmental filtering and spatial processes have been associated with variation in ecological communities and biodiversity; however, their relative importance on multiple dimensions of beta diversity has not been fully explored in montane streams. Here, we examined the relative contribution of local, catchment and climate environmental variables and spatial factors to variation in three dimensions of macroinvertebrate beta diversity in the upper Han River Basin. Taxonomic, functional, and phylogenetic beta diversities and their respective turnover and nestedness components were calculated for macroinvertebrate assemblages sampled in a total of 130 stream sites across a large mountainous landscape. We investigated the correlations between beta diversity facets using MSR‐Mantel procedure and then examined the relative influence of each set of ecological factors through redundancy analysis and variance partitioning. Our results revealed relatively low spatial congruence among beta diversity dimensions, indicating these diversity dimensions are independent measures which offer complementary information of community assembly. Beta diversity dimensions and components were best explained by spatial and local environmental factors, whereas the large‐scale catchment and climate factors appeared less influential. Moreover, spatial and environmental factors generally exerted different controls on beta diversity depending on the dimensions under consideration. Taxonomic and phylogenetic beta diversities were more strongly determined by spatial factors via dispersal limitation, while functional beta diversity was mainly associated to local environments through habitat filtering. Our results challenge the perspective that using one diversity facet as a surrogate for others is enough, and highlight the need to integrate multiple diversity dimensions in metacommunity and biodiversity research.

Documenting the patterns of biological diversity on Earth has always been a central challenge in macroecology and biogeography. However, we are only beginning to generate an understanding of the global patterns and determinants of macrophyte diversity. Here, we studied large‐scale variation and community‐environment relationships of lake macrophytes along climatic and geographical gradients using regional data from six continents. We applied statistical routines typically used in the context of metacommunity studies to provide novel insights into macrophyte community compositional patterns within regions worldwide. We found that lake macrophyte metacommunities followed clumped species replacement structures, suggesting that two or more species groups were responding similarly to the environment within regions. Underlying such general convergence, our results also provided evidence that community‐environment relationships were largely context‐dependent, stressing that no single mechanism is enough to account for the complex nature of compositional variation. Surprisingly, we found no general relationships between functional or phylogenetic composition and main metacommunity types, suggesting that linking multi‐trait and evolutionary information to the elements of metacommunity structure is not straightforward. Our findings highlight that global conservation initiatives and biodiversity protection need to capture environmental variation at the metacommunity level, and acknowledge the highly context‐dependent patterns in the community‐environment relationships of lake macrophytes. Overall, we emphasize the need to embrace the potential complexity of ecological inferences in metacommunity organization across the globe.

Eutrophication alters the trophic dynamics in lakes and may result in biotic homogenization. How nutrient enrichment drives patterns of taxonomic and functional (i.e., trait‐based) homogenization of macroinvertebrate assemblages at within‐lake (local) and among‐lake (regional) scales is, however, not well understood. Taxonomic and functional compositions of macroinvertebrate assemblages in 41 lakes of the middle and lower reaches of the Yangtze River and Huaihe River were analyzed at within‐lake and among‐lake scales. Our results indicated that there was a significant difference in macroinvertebrate assemblages among lakes under different trophic status, and that total phosphorus was the major environmental factor that regulated both taxonomic and functional beta diversity of macroinvertebrate assemblages. That the abundances of pollution‐tolerant species (e.g., Limnodrilus hoffmeisteriand Microchironomus tabarui) increased with trophic state contributed the most to among‐lake dissimilarity. Functional beta diversity was significantly positively correlated with taxonomic beta diversity, while functional beta diversity was on average lower than taxonomic beta diversity. A combination of univariate and multivariate techniques revealed that nutrient enrichment homogenized taxonomic and functional diversity of benthic macroinvertebrate assemblages in shallow lakes at within‐lake and among‐lake scales, and that there was an overall trend toward taxonomic homogenization that exceeded the trend of functional homogenization. Thus, taxonomic and functional compositions should be considered simultaneously to improve understanding of the response of aquatic communities to anthropogenic disturbance, as the loss and gain of species may be influenced by species‐specific features, and functional composition may exhibit a relatively high correspondence with changes in environmental conditions.

Community ecology has broadened considerably with the recognition that it is not only at the species‐level data where biological patterns and their determinants should be studied. Rather, also functional and phylogenetic data should be examined, as they may provide important information for both basic ecology and applied fields such as conservation and bioassessment. We thus explored the distance decay of taxonomic, functional, and phylogenetic community compositions along spatial and environmental gradients within a boreal lake metacommunity. We used distance‐based methods (i.e., Mantel test, Mantel correlograms and db‐RDA) to examine different facets (i.e., taxonomic, functional, and phylogenetic) and components (i.e., total, turnover and nestedness‐resultant) in relation to spatial and environmental variables. We found that the species compositions of lake benthic invertebrate communities varied mostly along environmental gradients, but were also weakly related to spatial distances between lakes. We also showed that functional and phylogenetic compositions were solely related to environmental variation across the lakes, but these relationships were generally weak. Our exploration of different facets and components of beta diversity added to the knowledge of lake invertebrate communities by adding functional and phylogenetic views, which has rarely been done in studies of aquatic metacommunities. Such information is also important in valuing lakes for conservation and bioassessment because it is not only at the species‐level data where ecological patterns and underlying mechanisms should be explored.

•Behavioral, population and large-scale processes are typically studied in isolation.•Integration of these processes is an important means to advance community ecology.•An approach to such integration is to examine variation in behavioral trait groups.•Increased understanding of stream insect communities benefits applied research.

AbstractNestedness is a widely studied pattern in ecology and biogeography. Nestedness has been termed perfect when sites harbouring low-diversity assemblages contain subsets of species in progressively more diverse assemblages. Nestedness has been studied in various regional and environmental contexts, but few studies have rigorously examined environmental factors underlying this pattern. We studied the degree and determinants of nestedness in insect assemblages of headwater streams. We hypothesized that nested habitat characteristics and nested niche structure generate nestedness in these organisms and tested this hypothesis in 8 boreal drainage basins (63–70° N, 23–29° E). Stream insect assemblages were significantly nested in all 8 regions based on the nestedness temperature calculator and in 5 regions based on discrepancy analysis. Nestedness was weak, however, as suggested by high matrix temperature values. Site ranks in the maximally packed nestedness matrix were significantly correlated to stream size in 2 of the regions and to environmental gradients in 5 of the regions. Nestedness was primarily governed by stream size and local environmental gradients. The relationships of nestedness to environmental gradients suggest that, at least in some regions, stream insects show nested niche structure with regard to their responses to environmental gradients. These environmental relationships are highly region-specific, however, suggesting strong context- dependency in nested subset patterns.

AbstractWe examined the determinants of zooplankton and phytoplankton metacommunity structure across 25 boreal wetland ponds. Our objective was to determine whether plankton metacommunities exhibit spatial structuring, thus suggesting neutrality, or are merely structured by local environmental features, suggesting that they are under niche-based control. According to Redundancy Analysis (RDA), zooplankton community structure was primarily controlled by concentration of major ions and geographical location of the pond, while phytoplankton community structure was primarily controlled by major ion concentration, nitrogen concentration, and geographical location. According to variance partitioning in RDA, zooplankton community structure was attributed more to pure spatial position of the pond (16.7% of variance) than to pure environmental factors (4.7% of variance). For phytoplankton, community composition was controlled by both spatial and environmental factors, although the effect of pure spatial position (11.1% of variance) on phytoplankton community structure was somewhat weaker than for zooplankton. For zooplankton, community similarity was negatively (P< 0.01) related to both geographical and environmental distance. For phytoplankton, community similarity was negatively (P < 0.05) related only to geographical distance. Finally, cluster analyses showed that zooplankton and phytoplankton communities formed highly dissimilar groupings, thus implying low community concordance. Our results suggest that both zooplankton and phytoplankton comply with both neutral and niche-based models. Our results further imply that even across small spatial scales and even for small organisms such as plankton, communities might be strongly spatially structured. The finding that spatial configuration was even more important than local environmental factors in controlling zooplankton community composition suggests that zooplankton may be dispersal-limited within relatively small spatial scales or that zooplankton metacommunities might be related to mass effects.

Abstract:Many ecological assemblages show a nested subset pattern of species distribution, i.e.,common species occur in all assemblages, whereas rare species tend to occur in progressively more diverse assemblages. We examined the determinants of nestedness and assemblage composition of lake-dwelling snails and clams in a boreal landscape using nestedness calculator, rank correlation, and canonical correspondence analysis (CCA). Both snail and clam assemblages were highly nested, and the nested subset pattern correlated with an index of isolation and habitat suitability (mainly water chemistry) for snails and with habitat suitability for clams. Habitat suitability and isolation were themselves highly correlated, thus obscuring the detection of their relative importance to nestedness. Yet, it appears that nestedness in this molluscan fauna is due mainly to nested tolerance of abiotic factors. Partial CCA showed that isolation and habitat suitability were almost equally important correlates of species composition for snails, whereas lake area was the key factor related to clam assemblage composition, followed by habitat suitability. It thus appears that while the degree of nestedness in species composition of lake-dwelling clams and snails may be highly correlated with a single variable, the overall pattern of species composition among lakes requires multiple explanatory variables.