A framework for quantifying geodiversity at the local scale: a case study from the Rokua UNESCO Global Geopark.

Geoconservation and related quantitative and qualitative geodiversity assessments are gaining increasing attention. However, methodologies for measuring geodiversity at local scale are currently rare. Here, we present a framework for assessing local-scale geodiversity of different landforms using field-based and digital elevation model (DEM-) derived data from the Rokua UNESCO Global Geopark in Finland. We observed the presence or absence of various geodiversity elements, such as geological or topographical elements in our study sites, and used these data to quantify alpha (α), gamma (γ) and beta (ß) geodiversity of various landforms. In addition, we measured topographical heterogeneity in the field and from DEMs. The results showed distinct patterns in the geodiversity and topographical variation of the landforms. The differences between α, γ and ß geodiversity of different landforms were particularly clear. According to the results, measures of topographical variability can be used to some extent as surrogates for geodiversity, but the choice of optimal variables is context and scale dependent. These results provide perspectives for further local-scale geodiversity assessments in different study areas and are applicable for a range of purposes, from scientific research to practical management and geoconservation. This article is part of the Theo Murphy meeting issue 'Geodiversity for science and society'.

Quantitative measurement of geodiversity uniqueness: research implications and conservation applications.

Quantitative approaches are needed to complement qualitative explorations to identify sites with unique geodiversity and thereby guide geoconservation and geoheritage programmes. Here, we introduce the concept and associated index of 'geodiversity uniqueness'. This index is based on a numerical analysis of geofeatures and allows the identification of sites with unique geodiversity in a study area. We applied this approach to geofeature data from three areas in Finland. Our results showed that patterns of geodiversity uniqueness varied profoundly among the three study areas and across sites within each area. This was due to different sets of geofeatures and distinct characteristics of each study area. More importantly, the approach presented here was robust across the datasets and selection criteria for sets of sites, showing potential for geoconservation in each study area. The geodiversity uniqueness approach is a promising starting point to identify and map sites with unique geodiversity that can be further verified using field observations. To improve our knowledge of geodiversity variation, complementary approaches providing objective information on contributions to total beta geodiversity are needed to advance geoconservation programmes across areas and different spatial scales. This article is part of the Theo Murphy meeting issue 'Geodiversity for science and society'.

Towards a taxonomy of geodiversity.

Geodiversity is a topical concept in earth and environmental sciences. Geodiversity information is needed to conserve nature, use ecosystem services and achieve sustainable development goals. Despite the increasing demand for geodiversity data, there exists no comprehensive system for categorizing geodiversity. Here, we present a hierarchically structured taxonomy that is potentially applicable in mapping and quantifying geodiversity across different regions, environments and scales. In this taxonomy, the main components of geodiversity are geology, geomorphology, hydrology and pedology. We propose a six-level hierarchical system where the components of geodiversity are classified at progressively lower taxonomic levels based on their genesis, physical-chemical properties and morphology. This comprehensive taxonomy can be used to compile geodiversity information for scientific research and various applications of value to society and nature conservation. Ultimately, this hierarchical system is the first step towards developing a global geodiversity taxonomy. This article is part of the Theo Murphy meeting issue 'Geodiversity for science and society'.

Disentangling the effects of geographic distance, environment and history on beta diversity of freshwater fish at a biogeographical crossroads.

Examining assemblage turnover and variation along geographic and environmental distances is a useful approach to evaluate beta diversity patterns and associated driving mechanisms. However, such studies are relatively limited in freshwater systems. Here, we compared the relationships between freshwater fish beta diversity and geographic distances among 165 hydrological units (HUs) in four zoogeographical regions (PA, Palearctic Region; CA, High Central Asia; EA, East Asia, SA, South Asia) across China and adjacent areas. This area can be considered a biogeographical crossroads, where faunal composition shares elements with different biogeographic and evolutionary origins. We found a considerably high level of between-HU overall dissimilarity (ßsor, range from ca. 0.60 to 0.85) in all four regions, mainly due to the turnover component (the relative contribution of ßsim to ßsor ranged from 60% to 90%). In general, ßsor and ßsim both significantly increased with geographic distance (except in PA), whereas the nestedness-resultant component (ßsne) decreased with geographic distance. The intercepts and slopes of the relationships between dissimilarities and distance (RDDs) both varied significantly among the four regions. The intercepts of ßsor and ßsim were both highest in SA, followed by CA, PA and EA, implying different levels of fish faunal heterogeneity at short distances. In contrast, the slopes of these two dissimilarities followed the decreasing trend from EA > CA > SA > PA, suggesting different environmental suitability and dispersal ability of fish species among regions. Variation partitioning in distance-based redundancy analysis showed that the spatial and historical factors were more important than area-heterogeneity and energy factors across all HUs and within three individual ecoregions (EA, SA and CA), but spatial factors were non-significant in PA. Our study highlighted the usefulness of RDDs in understanding biogeographical patterns and enhancing the biodiversity conservation of freshwater fishes.

Distance decay 2.0 - A global synthesis of taxonomic and functional turnover in ecological communities.

Aim: Understanding the variation in community composition and species abundances (i.e., ß-diversity) is at the heart of community ecology. A common approach to examine ß-diversity is to evaluate directional variation in community composition by measuring the decay in the similarity among pairs of communities along spatial or environmental distance. We provide the first global synthesis of taxonomic and functional distance decay along spatial and environmental distance by analysing 148 datasets comprising different types of organisms and environments. Location: Global. Time period: 1990 to present. Major taxa studied: From diatoms to mammals. Method: We measured the strength of the decay using ranked Mantel tests (Mantel r) and the rate of distance decay as the slope of an exponential fit using generalized linear models. We used null models to test whether functional similarity decays faster or slower than expected given the taxonomic decay along the spatial and environmental distance. We also unveiled the factors driving the rate of decay across the datasets, including latitude, spatial extent, realm and organismal features. Results: Taxonomic distance decay was stronger than functional distance decay along both spatial and environmental distance. Functional distance decay was random given the taxonomic distance decay. The rate of taxonomic and functional spatial distance decay was fastest in the datasets from mid-latitudes. Overall, datasets covering larger spatial extents showed a lower rate of decay along spatial distance but a higher rate of decay along environmental distance. Marine ecosystems had the slowest rate of decay along environmental distances. Main conclusions: In general, taxonomic distance decay is a useful tool for biogeographical research because it reflects dispersal-related factors in addition to species responses to climatic and environmental variables. Moreover, functional distance decay might be a cost-effective option for investigating community changes in heterogeneous environments.

Loss of lateral hydrological connectivity impacts multiple facets of molluscan biodiversity in floodplain lakes.

Lateral hydrological connectivity (LHC) is a key process in maintaining aquatic biodiversity in river floodplain ecosystems. However, the effects of LHC loss on aquatic biodiversity are rarely studied. Here, we evaluated, for the first time, the responses of multiple facets (i.e., taxonomic, functional and phylogenetic) of alpha and beta diversity of freshwater molluscs to the LHC loss in 23 floodplain lakes in the Yangtze River Basin in China. Our results showed that taxonomic and functional alpha diversities were all significantly higher in connected lakes (CLs) than in disconnected lakes (DLs), whereas phylogenetic alpha diversity (Δ+) was lower in CLs than in DLs. For beta diversity facets, taxonomic (Tßsor) and phylogenetic (Pßsor) dissimilarities were slightly more contributed by the turnover component or equally contributed by the turnover and nestedness-resultant components both in CLs and DLs. Instead, functional beta diversity (Fßsor), generally showing much lower values than Tßsor and Pßsor, was mainly contributed by the nestedness-resultant component (76.6-84.0%), especially in DLs. We found that only functional dissimilarities were significantly higher in DLs than CLs, indicating a high level of functional diversity loss without replacement of species possessing traits sensitive to hydrological disconnection (i.e., large body size, lamellibranch body form, filter feeding, ovoviviparity and burrowing habits). In general, lake area, hydrological connectivity, aquatic vegetation coverage and nutrient levels (TN and TP) played important roles in structuring variation in molluscan alpha and beta diversities, although the three diversity facets responded to different environmental factors. Our results suggest that loss of connectivity to the mainstem river has negative impacts on molluscan assemblages in floodplain lakes. More importantly, as taxonomic, functional and phylogenetic diversities responded somewhat differently to the loss of hydrological connectivity, all of these biodiversity facets should be better incorporated into aquatic biodiversity assessment and conservation programs in large river floodplains.

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.

Metacommunity ecology meets biogeography: effects of geographical region, spatial dynamics and environmental filtering on community structure in aquatic organisms.

Metacommunity patterns and underlying processes in aquatic organisms have typically been studied within a drainage basin. We examined variation in the composition of six freshwater organismal groups across various drainage basins in Finland. We first modelled spatial structures within each drainage basin using Moran eigenvector maps. Second, we partitioned variation in community structure among three groups of predictors using constrained ordination: (1) local environmental variables, (2) spatial variables, and (3) dummy variable drainage basin identity. Third, we examined turnover and nestedness components of multiple-site beta diversity, and tested the best fit patterns of our datasets using the "elements of metacommunity structure" analysis. Our results showed that basin identity and local environmental variables were significant predictors of community structure, whereas within-basin spatial effects were typically negligible. In half of the organismal groups (diatoms, bryophytes, zooplankton), basin identity was a slightly better predictor of community structure than local environmental variables, whereas the opposite was true for the remaining three organismal groups (insects, macrophytes, fish). Both pure basin and local environmental fractions were, however, significant after accounting for the effects of the other predictor variable sets. All organismal groups exhibited high levels of beta diversity, which was mostly attributable to the turnover component. Our results showed consistent Clementsian-type metacommunity structures, suggesting that subgroups of species responded similarly to environmental factors or drainage basin limits. We conclude that aquatic communities across large scales are mostly determined by environmental and basin effects, which leads to high beta diversity and prevalence of Clementsian community types.

Average niche breadths of species in lake macrophyte communities respond to ecological gradients variably in four regions on two continents.

Different species' niche breadths in relation to ecological gradients are infrequently examined within the same study and, moreover, species niche breadths have rarely been averaged to account for variation in entire ecological communities. We investigated how average environmental niche breadths (climate, water quality and climate-water quality niches) in aquatic macrophyte communities are related to ecological gradients (latitude, longitude, altitude, species richness and lake area) among four distinct regions (Finland, Sweden and US states of Minnesota and Wisconsin) on two continents. We found that correlations between the three different measures of average niche breadths and ecological gradients varied considerably among the study regions, with average climate and average water quality niche breadth models often showing opposite trends. However, consistent patterns were also found, such as widening of average climate niche breadths and narrowing of average water quality niche breadths of aquatic macrophytes along increasing latitudinal and altitudinal gradients. This result suggests that macrophyte species are generalists in relation to temperature variations at higher latitudes and altitudes, whereas species in southern, lowland lakes are more specialised. In contrast, aquatic macrophytes growing in more southern nutrient-rich lakes were generalists in relation to water quality, while specialist species are adapted to low-productivity conditions and are found in highland lakes. Our results emphasise that species niche breadths should not be studied using only coarse-scale data of species distributions and corresponding environmental conditions, but that investigations on different kinds of niche breadths (e.g., climate vs. local niches) also require finer resolution data at broad spatial extents.

Elements of regional beetle faunas: faunal variation and compositional breakpoints along climate, land cover and geographical gradients.

Regional faunas are structured by historical, spatial and environmental factors. We studied large-scale variation in four ecologically different beetle groups (Coleoptera: Dytiscidae, Carabidae, Hydrophiloidea, Cerambycidae) along climate, land cover and geographical gradients, examined faunal breakpoints in relation to environmental variables, and investigated the best fit pattern of assemblage variation (i.e. randomness, checkerboards, nestedness, evenly spaced, Gleasonian, Clementsian). We applied statistical methods typically used in the analysis of local ecological communities to provide novel insights into faunal compositional patterns at large spatial grain and geographical extent. We found that spatially structured variation in climate and land cover accounted for most variation in each beetle group in partial redundancy analyses, whereas the individual effect of each explanatory variable group was generally much less important in accounting for variation in provincial species composition. We also found that climate variables were most strongly associated with faunal breakpoints, with temperature-related variables alone accounting for about 20% of variation at the first node of multivariate regression tree for each beetle group. The existence of faunal breakpoints was also shown by the 'elements of faunal structure' analyses, which suggested Clementsian gradients across the provinces, that is, that there were two or more clear groups of species responding similarly to the underlying ecological gradients. The four beetle groups showed highly similar biogeographical patterns across our study area. The fact that temperature was related to faunal breakpoints in the species composition of each beetle group suggests that climate sets a strong filter to the distributions of species at this combination of spatial grain and spatial extent. This finding held true despite the ecological differences among the four beetle groups, ranging from fully aquatic to fully terrestrial and from herbivorous to predaceous species. The existence of Clementsian gradients may be a common phenomenon at large scales, and it is likely to be caused by crossing multiple species pools determined by climatic and historical factors on the distributions of species.

Responses of multiple facets of macroinvertebrate alpha diversity to eutrophication in floodplain lakes.

The accelerated eutrophication of freshwater lakes has become an environmental problem worldwide. Increasing numbers of studies highlight the need to incorporate functional and phylogenetic information of species into bioassessment programms, but it is still poorly understood how eutrophication affects multiple diversity facets of freshwater communities. Here, we assessed the responses of taxonomic, phylogenetic and functional diversity of benthic macroinvertebrates to water eutrophication in 33 lakes in the Yangtze River floodplain in China. Our results showed that macroinvertebrate assemblage structure was significantly different among four lake groups (river-connected, macrophyte-dominated, macrophyte-algae transition, and algae-dominated). Three taxonomic, two phylogenetic and two functional diversity indices were significantly different among the lake groups. Except for the increasing trend of Lambda+, these metrics showed a clear decreasing trend with increasing levels of eutrophication, with highest values detected in river-connected and macrophyte-dominated lakes, followed by macrophyte-algae transition lakes and algal-dominated lakes. Although differing in the number and identity of key environmental and spatial variables among the explanatory models of different diversity indices, environmental factors (eutrophication-related water quality variables) played more important role than spatial factors in structuring all three facets of alpha diversity. The predominant role of environmental filtering can be attributed to the strong eutrophication gradient across the studied lakes. Among the three diversity facets, functional diversity indices performed best in portraying anthropogenic disturbances, with variations in these indices being solely explained by environmental factors. Spatial factors were mostly weak or negligible in accounting for the variation in functional diversity indices, implying that trait-based indices are robust in portraying anthropogenic eutrophication in floodplain lakes. However, variation in some taxonomic and phylogenetic diversity indices were also affected by spatial factors, indicating that conservation practitioners and environmental managers should use these metrics with caution when providing solutions for addressing eutrophication in floodplain lakes.

Shifts in food webs and niche stability shaped survivorship and extinction at the end-Cretaceous.

It has long been debated why groups such as non-avian dinosaurs became extinct whereas mammals and other lineages survived the Cretaceous/Paleogene mass extinction 66 million years ago. We used Markov networks, ecological niche partitioning, and Earth System models to reconstruct North American food webs and simulate ecospace occupancy before and after the extinction event. We find a shift in latest Cretaceous dinosaur faunas, as medium-sized species counterbalanced a loss of megaherbivores, but dinosaur niches were otherwise stable and static, potentially contributing to their demise. Smaller vertebrates, including mammals, followed a consistent trajectory of increasing trophic impact and relaxation of niche limits beginning in the latest Cretaceous and continuing after the mass extinction. Mammals did not simply proliferate after the extinction event; rather, their earlier ecological diversification might have helped them survive.

Acknowledging geodiversity in safeguarding biodiversity and human health.

Our existence on Earth is founded on a vital nature, which supports human physical and mental health. However, nature is often depicted only through biodiversity, whereas geodiversity-the diversity of non-living nature-has so far been neglected. Geodiversity consists of assemblages, structures, and systems of geological, geomorphological, soil, and hydrological components that fundamentally underlie biodiversity. Biodiversity can support overall human health only with the foundation of geodiversity. Landscape characteristics, such as varying topography or bodies of water, promote aesthetic and sensory experiences and are also a product of geodiversity. In this Personal View, we introduce the concept of geodiversity as a driver for planetary health, describe its functions and services, and outline the intricate relationships between geodiversity, biodiversity, and human health. We also propose an agenda for acknowledging the importance of geodiversity in health-related research and decision making. Geodiversity is an emerging topic with untapped potential for ensuring ecosystem functionality and good living conditions for people in a time of changing environments.

Rarity in freshwater vascular plants across Europe and North America: Patterns, mechanisms and future scenarios.

Patterns of species rarity have long fascinated ecologists, yet most of what we know about the natural world stems from studies of common species. A large proportion of freshwater plant species has small range sizes and are therefore considered rare. However, little is known about the mechanisms and geographical distribution of rarity in the aquatic realm and to what extent diversity of rare species in freshwater plants follows their terrestrial counterparts. Here, we present the first in-depth analysis of geographical patterns, potential deterministic ecogeographical factors and projected scenarios of freshwater vascular plant rarity using 50 × 50 km grid cells across Europe (41°N-71°N) and North America (25°N-78°N). Our results suggest that diversity of rare species shows different patterns in relation to latitude on the two continents, and that hotspots of rarity concentrate in a relatively small proportion of the European and North American land surface, especially in mountainous as well as in climatically rare and stable areas. Interestingly, we found no differences among alternative rarity definitions and measures when delineating areas with notably high diversity of rare species. Our findings also indicate that few variables, namely a combination of current climate, Late Quaternary climate-change velocity and human footprint, are able to accurately predict the location of continental centers of rare species diversity. However, these relationships are not geographically homogeneous, and the underlying factors likely act synergistically. Perhaps more importantly, we provide empirical evidence that current centers of rare species diversity are characterized by higher anthropogenic impacts and might shrink disproportionately within this century as the climate changes. Our reported distributional patterns of species rarity align with the known trends in species richness of other freshwater organisms and may help conservation planners make informed decisions mitigating the effects of climate change and other anthropogenic impacts on biodiversity.

Lakes in the era of global change: moving beyond single-lake thinking in maintaining biodiversity and ecosystem services.

The Anthropocene presents formidable threats to freshwater ecosystems. Lakes are especially vulnerable and important at the same time. They cover only a small area worldwide but harbour high levels of biodiversity and contribute disproportionately to ecosystem services. Lakes differ with respect to their general type (e.g. land-locked, drainage, floodplain and large lakes) and position in the landscape (e.g. highland versus lowland lakes), which contribute to the dynamics of these systems. Lakes should be generally viewed as 'meta-systems', whereby biodiversity is strongly affected by species dispersal, and ecosystem dynamics are contributed by the flow of matter and substances among locations in a broader waterscape context. Lake connectivity in the waterscape and position in the landscape determine the degree to which a lake is prone to invasion by non-native species and accumulation of harmful substances. Highly connected lakes low in the landscape accumulate nutrients and pollutants originating from ecosystems higher in the landscape. The monitoring and restoration of lake biodiversity and ecosystem services should consider the fact that a high degree of dynamism is present at local, regional and global scales. However, local and regional monitoring may be plagued by the unpredictability of ecological phenomena, hindering adaptive management of lakes. Although monitoring data are increasingly becoming available to study responses of lakes to global change, we still lack suitable integration of models for entire waterscapes. Research across disciplinary boundaries is needed to address the challenges that lakes face in the Anthropocene because they may play an increasingly important role in harbouring unique aquatic biota as well as providing ecosystem goods and services in the future.

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.

Untangling the assembly of macrophyte metacommunities by means of taxonomic, functional and phylogenetic beta diversity patterns.

Metacommunity ecology has broadened considerably with the recognition that measuring beta diversity beyond the purely taxonomic viewpoint may improve our understanding of the dispersal- and niche-based mechanisms across biological communities. In that perspective, we applied a novel multidimensional approach including taxonomic, functional and phylogenetic data to enhance our basic understanding of macrophyte metacommunity dynamics. For each beta diversity metric, we calculated the mean overall value and tested whether the mean value was different from that expected by chance using null models. We also employed evolutionary and spatially constrained models to first identify the degree to which the studied functional traits showed a phylogenetic signal, and then to estimate the relative importance of spatial and environmental effects on metacommunity structure. We first found that most individual ponds were inhabited by species that were merely random draws from the taxonomic and phylogenetic species pool available in the study region. Contrary to our expectations, not all measured traits were conserved along the phylogeny. We also showed that trait and phylogenetic dimensions strongly increased the amount of variation in beta diversity that can be explained by degree of environmental filtering and dispersal limitation. This suggests that accounting for functional traits and phylogeny in metacommunity ecology helps to explain idiosyncratic patterns of variation in macrophyte species distribution. Importantly, phylogenetic and functional analyses identified the influence of underlying mechanisms that would otherwise be missed in an analysis of taxonomic turnover. Together, these results let us conclude that macrophyte species have labile functional traits adapted to dispersal-based processes and some evolutionary trade-offs that drive community assembly via species sorting. Overall, our exploration of different facets of beta diversity showed how functional and phylogenetic information may be used with species-level data to test community assembly hypotheses that are more ecologically meaningful than assessments of environmental patterns based on the purely taxonomic viewpoint.

Environmental Characteristics and Anthropogenic Impact Jointly Modify Aquatic Macrophyte Species Diversity.

Species richness and spatial variation in community composition (i.e., beta diversity) are key measures of biodiversity. They are largely determined by natural factors, but also increasingly affected by anthropogenic factors. Thus, there is a need for a clear understanding of the human impact on species richness and beta diversity, the underlying mechanisms, and whether human-induced changes can override natural patterns. Here, we dissect the patterns of species richness, community composition and beta diversity in relation to different environmental factors as well as human impact in one framework: aquatic macrophytes in 66 boreal lakes in Eastern Finland. The lakes had been classified as having high, good or moderate status (according to ecological classification of surface waters in Finland) reflecting multifaceted human impact. We used generalized least square models to study the association between different environmental variables (Secchi depth, irregularity of the shoreline, total phosphorus, pH, alkalinity, conductivity) and species richness. We tested the null hypothesis that the observed community composition can be explained by random distribution of species. We used multivariate distance matrix regression to test the effect of each environmental variable on community composition, and distance-based test for homogeneity of multivariate dispersion to test whether lakes classified as high, good or moderate status have different beta diversity. We showed that environmental drivers of species richness and community composition were largely similar, although dependent on the particular life-form group studied. The most important ones were characteristics of water quality (pH, alkalinity, conductivity) and irregularity of the shoreline. Differences in community composition were related to environmental variables independently of species richness. Species richness was higher in lakes with higher levels of human impact. Lakes with different levels of human impact had different community composition. Between-lake beta diversity did not differ in high, good or moderate status groups. However, the variation in environmental variables shaping community composition was larger in lakes with moderate status compared to other lakes. Hence, beta diversity in lakes with moderate status was smaller than what could be expected on the basis of these environmental characteristics. This could be interpreted as homogenization.

A comparative analysis of metacommunity types in the freshwater realm.

Most metacommunity studies have taken a direct mechanistic approach, aiming to model the effects of local and regional processes on local communities within a metacommunity. An alternative approach is to focus on emergent patterns at the metacommunity level through applying the elements of metacommunity structure (EMS; Oikos, 97, 2002, 237) analysis. The EMS approach has very rarely been applied in the context of a comparative analysis of metacommunity types of main microbial, plant, and animal groups. Furthermore, to our knowledge, no study has associated metacommunity types with their potential ecological correlates in the freshwater realm. We assembled data for 45 freshwater metacommunities, incorporating biologically highly disparate organismal groups (i.e., bacteria, algae, macrophytes, invertebrates, and fish). We first examined ecological correlates (e.g., matrix properties, beta diversity, and average characteristics of a metacommunity, including body size, trophic group, ecosystem type, life form, and dispersal mode) of the three elements of metacommunity structure (i.e., coherence, turnover, and boundary clumping). Second, based on those three elements, we determined which metacommunity types prevailed in freshwater systems and which ecological correlates best discriminated among the observed metacommunity types. We found that the three elements of metacommunity structure were not strongly related to the ecological correlates, except that turnover was positively related to beta diversity. We observed six metacommunity types. The most common were Clementsian and quasi-nested metacommunity types, whereas Random, quasi-Clementsian, Gleasonian, and quasi-Gleasonian types were less common. These six metacommunity types were best discriminated by beta diversity and the first axis of metacommunity ecological traits, ranging from metacommunities of producer organisms occurring in streams to those of large predatory organisms occurring in lakes. Our results showed that focusing on the emergent properties of multiple metacommunities provides information additional to that obtained in studies examining variation in local community structure within a metacommunity.