Shaping Local Communities Research Articles

Vertical exchange versus horizontal dispersal in structuring local planktonic and sedimentary bacterial communities in polluted lotic ecosystems

Elucidating the mechanisms underlying community assembly remains a central question in community ecology, especially in aquatic ecosystems disrupted by human activities. Understanding the causes and consequences of community responses to changing environmental conditions is essential for revealing the ecological effects of anthropogenic disturbances and proposing practical strategies for ecological restoration. While stochastic dispersal and species sorting are known to influence local biological communities, most studies have focused on horizontal dispersal, often neglecting the vertical exchange of organisms between planktonic and sedimentary communities when studying stochastic dispersal. We used a highly disturbed urban river in Beijing as a model system to investigate the relative roles of stochastic dispersal versus species sorting driven by local pollution, as well as two components of stochastic dispersal, vertical exchange and horizontal dispersal, in structuring local bacterial communities. Our integrated analyses of planktonic and sedimentary bacterial communities revealed that, despite different spatial patterns along the river, both types of bacterial communities were primarily shaped by stochastic dispersal processes rather than species sorting influenced by the environmental gradient. Notably, in addition to the effect of horizontal dispersal along the river, the vertical exchange between planktonic and sedimentary bacterial communities significantly contributed to the formation of local communities. These findings suggest that both vertical exchange and horizontal dispersal should be considered when assessing the role of stochastic dispersal in shaping local community structure in microbial communities.

Relational values shape people’s connectedness to nature in a former military protected area of Ecuador

SummaryRelational values are a way of recognizing and valuing the complex and interconnected relationships between people and nature, such as caregiving, place attachment and spiritual meaning, as well as the social and cultural impacts of degradation and environmental and conservation efforts. However, the implications of these values for the management and conservation of protected areas are little known. We explored the role of relational values in shaping local communities’ connectedness to a protected area of Ecuador that had been used by the military in the past and the implications of the values for well-being. Four hundred individual face-to-face surveys in the surroundings of Arenillas Ecological Reserve (south-west Ecuador) indicated high levels of connectedness towards this natural reserve amongst local communities through multiple values of nature. However, relational values were identified as the most prominent value explaining the strength of connectedness to nature, followed by intrinsic and instrumental values. We also showed that combinations of different natural values (instrumental, intrinsic and relational) might explain the support for specific well-being components. Our findings offer understanding of human behaviour towards protected areas with a military past and represent a first step in Ecuador towards comprehending how relational values shape the connectedness of local communities to nature.

Consistent imprints of elevation, soil temperature and moisture on plant and arthropod communities across two subarctic landscapes

Abstract Factors shaping arthropod and plant community structure at fine spatial scales are poorly understood. This includes microclimate, which likely plays a large role in shaping local community patterns, especially in heterogeneous landscapes characterised by high microclimatic variability in space and in time. We explored differences in local microclimatic conditions and regional species pools in two subarctic regions: Kilpisjärvi in north‐west Finland and Varanger in north‐east Norway. We then investigated the relationship between fine‐scale climatic variation and local community characteristics (species richness and abundance) among plants and arthropods, differentiating the latter into two groups: flying and ground‐dwelling arthropods collected by Malaise and pitfall traps, respectively. Arthropod taxa were identified through DNA metabarcoding. Finally, we examined if plant richness can be used to predict patterns in arthropod communities. Variation in soil temperature, moisture and snow depth proved similar between regions, despite differences in absolute elevation. For each group of organisms, we found that about half of the species were shared between Kilpisjärvi and Varanger, with a quarter unique to each region. Plants and arthropods responded largely to the same drivers. The richness and abundance of both groups decreased as elevation increased and were positively correlated with higher soil moisture and temperature values. Plant species richness was a poor predictor of local arthropod richness, in particular for ground‐dwelling arthropods. Our results reveal how microclimatic variation within each region carves pronounced, yet consistent patterns in local community richness and abundance out of a joint species pool.

Local eukaryotic and bacterial stream community assembly is shaped by regional land use effects

With anticipated expansion of agricultural areas for food production and increasing intensity of pressures stemming from land-use, it is critical to better understand how species respond to land-use change. This is particularly true for microbial communities which provide key ecosystem functions and display fastest responses to environmental change. However, regional land-use effects on local environmental conditions are often neglected, and, hence, underestimated when investigating community responses. Here we show that the effects stemming from agricultural and forested land use are strongest reflected in water conductivity, pH and phosphorus concentration, shaping microbial communities and their assembly processes. Using a joint species distribution modelling framework with community data based on metabarcoding, we quantify the contribution of land-use types in determining local environmental variables and uncover the impact of both, land-use, and local environment, on microbial stream communities. We found that community assembly is closely linked to land-use type but that the local environment strongly mediates the effects of land-use, resulting in systematic variation of taxon responses to environmental conditions, depending on their domain (bacteria vs. eukaryote) and trophic mode (autotrophy vs. heterotrophy). Given that regional land-use type strongly shapes local environments, it is paramount to consider its key role in shaping local stream communities.

EcoPhyloMapper: An r package for integrating geographical ranges, phylogeny and morphology

Abstract Spatial patterns of species richness, phylogenetic and morphological diversity are key to answering many questions in ecology and evolution. Across spatial scales, geographical and environmental features, as well as evolutionary history and phenotypic traits, are thought to play roles in shaping both local species communities and regional assemblages. By examining these geographical patterns, it is possible to infer how different axes of biodiversity influence one another, and how their interaction with abiotic factors has led to the spatial distribution of species assemblages—and their attributes—that we observe in the present. Although there has been interest in this area of research for some time, it has recently become more tractable to include multivariate shape data in such analyses. Shape information has the potential to provide a more direct measure of the functional morphology of species as compared to individual trait measurements and might be more relevant to understanding community composition. However, few tools currently exist to explore geographical patterns of both phylogenetic and shape diversity. We present the EcoPhyloMapper r package (epm) that aims to streamline the handling of geographical range polygons or point occurrences and integration of resulting species metacommunities with phylogenetic trees and morphological shape. Geographical maps can be generated that demonstrate spatial patterns in diversity metrics pertaining to phylogenetic similarity, multivariate shape similarity and disparity, and combinations of the two. Patterns of taxonomic, phylogenetic and shape disparity turnover can also be visualized. Biodiversity indices summarized across grid cells can easily be exported to GIS software as well as to other r packages that specialize in community assembly or geospatial statistics. This r package will facilitate the geographical exploration of multivariate shape data in concert with phylogenetic diversity, which will, in turn, support macroecological research exploring how species assemblages are structured. Furthermore, this r package should prove useful across a wide range of macroecological applications that extend beyond the study of morphology.

Host plant environmental filtering drives foliar fungal community assembly in symptomatic leaves.

Foliar fungi (defined as all fungal species in leaves after surface sterilization; hereafter, 'FF') are of great importance to host plant growth and health, and can also affect ecosystem functioning. Despite this importance, few studies have explicitly examined the role of host filtering in shaping local FF communities, and we know little about the differences of FF community assembly between symptomatic (caused by fungal pathogens) and asymptomatic leaves, and whether there is phylogenetic congruence between host plants and FF. We examined FF communities from 25 host plant species (for each species, symptomatic and asymptomatic leaves, respectively) in an alpine meadow of the Tibetan Plateau using MiSeq sequencing of ITS1 gene biomarkers. We evaluated the phylogenetic congruence of FF-plant interactions based on cophylogenetic analysis, and examined α- and β-phylogenetic diversity indices of the FF communities. We found strong support for phylogenetic congruence between host plants and FF for both asymptomatic and symptomatic leaves, and a host-caused filter appears to play a major role in shaping FF communities. Most importantly, we provided independent lines of evidence that host environmental filtering (caused by fungal infections) outweighs competitive exclusion in driving FF community assembly in symptomatic leaves. Our results help strengthen the foundation of FF community assembly by demonstrating the importance of host environmental filtering in driving FF community assembly.

At the heart of controversies

PurposeThe purpose of this paper is to discuss and evaluate the role of hybrid forums as tools to address specific controversies related to sustainable practices in localized agro-food systems (LAFS).Design/methodology/approachIn contrast with other conventional public engagement methods, such as citizen juries, consensus conferences, focus groups or deliberative processes, hybrid forums entail a more dynamic and democratic mechanism to reflect and act together, with the aim of constructing a common project around a defined challenge (Callon et al., 2001, 2009). They can offer an enriching and challenging methodological approach in the context of LAFS, especially in the discussion of controversial issues around food chain sustainability. The authors present here a new generation of hybrid forums: HF 2.0.FindingsHF 2.0. represent both a methodological tool and a real experience of dialogic democracy, two interactive aspects which are closely interlinked and rest upon each other. The authors argue that the attractiveness of HF 2.0. is notable in at least two ways: first, they provide a solid democratic and reflective mechanism to stimulate effective dialogue and knowledge-exchange among different stakeholders; second, they contribute as an important methodological evidence-based tool, which can be used as a launching pad for shaping local action groups and community partnerships’ strategies aimed at fostering local development.Originality/valueThis paper attempts to provide a methodological discussion over the experimental use of HF 2.0. in the context of LAFS and assesses their effectiveness in the co-construction of knowledge. The authors explore their pragmatic validity in addressing controversies over local and sustainable seafood via empirical applications in Norway and the UK.

Carabid activity‐density increases with forest vegetation diversity at different spatial scales

Abstract More diverse forests are generally more resistant to insect herbivores. This might be due to positive effects of tree diversity on predation. Although the enemies hypothesis has received conflicting evidence in forest ecosystems. Carabids were sampled by pitfall trapping in a tree diversity experiment, at the centre of plots ranging from one to five tree species mixtures. The composition and vertical structure of the vegetation was assessed at three scales, in the understorey, in the canopy of the experimental plots, and in the surrounding area of each plot. None of the tested vegetation variables had an effect on the species richness of carabids. In contrast, the vegetation compositional diversity at the understorey, canopy and surrounding scales had additive and positive effects on the activity‐density of the carabids. Our findings indicate that more diverse forests can host a higher activity‐density of predatory carabids, as a result of the combined effect of horizontal and vertical vegetation diversity, which might increase both habitat quality and the amount of feeding resources. This highlights the relevance of manipulative tree diversity experiments to identify the ecological filters shaping local carabid communities.

Choices of sampling method bias functional components estimation and ability to discriminate assembly mechanisms

Abstract The understanding and prediction of species distributions have been advanced by the development of community assembly theories and functional trait‐based approaches. Coupled with null models, trait dispersion patterns are commonly used to gauge the relative importance of niche versus neutral‐based processes on shaping local communities. However, asymmetrical trait dispersion patterns of identical communities may artificially arise as a result of sampling methods choice. This non‐random filtering on traits is overlooked, and it may bias the estimation of functional components as well as the detection of underlying assembly mechanisms—especially for species‐rich arthropod communities. We sampled subtropical ground‐dwelling ant communities using a paired treatment design comprising pitfall traps and Winkler extractors (Winklers), two commonly used sampling techniques for terrestrial arthropods, in 17 shrublands and 33 secondary forest 400 m2 plots in Hong Kong to determine the effect of sampling filters on functional composition (community means of six morphological traits) and functional diversity (range and variance of individual traits; size and filling properties of multidimensional trait space) using a null model approach for each habitat. We found, as hypothesized, that sampling filters from different methods affected the trait composition and diversity of ant communities asymmetrically. In shrublands and forests, the trait compositions of communities sampled by pitfall traps were dominated by larger sized, slender‐shaped and long‐legged ants as compared to those sampled by Winklers. The latter method also underestimated the diversity of individual traits related to body size as well as the size and filling properties of multidimensional trait space. Our results highlight that the usage of particular sampling methods without prior knowledge on their potential filtering effects on traits can affect the detection of assembly processes, and interpretation of functional proxies, such as body size. Additional care should be taken when comparing trait components obtained from studies using different sampling methods, so as to distinguish the sampling artefacts from actual ecological phenomena. Hence, it is important to consider the potential biases that different sampling methods may introduce to functional trait‐based research.

Phylogenetic diversity in the Western Ghats biodiversity hotspot reflects environmental filtering and past niche diversification of trees

AbstractAimWe examined how contrasted climatic conditions influenced the ecological and phylogenetic diversity of tropical trees at the regional scale. Beyond the basic expectation of greater environmental filtering in currently stressful contexts, we addressed how biogeographic history and past climates contributed to shaping the distribution and diversity of extant taxa.LocationEvergreen forests of Western Ghats, India.MethodsWe evaluated the relative importance of niche‐based, historical, and spatial processes on community phylogenetic structure and turnover in 297 plots including 459 species. If niche conservatism prevails, we expected greater phylogenetic clustering under harsher or historically less stable climates, and overdispersion in opposite conditions. To test the role of environmental filtering in shaping local communities, we assessed species’ climatic niches and congruence between niche and phylogenetic diversity. To assess the imprint of ancient versus recent evolutionary constraints, we calculated mean pair‐wise (MPD) and nearest‐taxon (MNTD) phylogenetic distances, respectively.ResultsWe found non‐random phylogenetic structure depending on both current and past climatic variation. Basal community phylogenetic structure (MPD) was related to niche diversity and varied according to hydric stress: (a) northern environments filtered more closely related species, while (b) phylogenetic overdispersion suggested greater niche differentiation in stable, least‐seasonal southern habitats and at high elevations. Terminal phylogenetic structure (MNTD) did not show overdispersion. Phylogenetic turnover was driven by current abiotic factors, not space.Main conclusionsThe patterns of ecological and phylogenetic diversity likely reflect the Miocene climate shift to increasing seasonality northwards. Phylogenetic clustering under hydric stress or historical instability suggests the influence of functional conservatism, whereas overdispersion in southern forests supports the persistence of old lineages in an ancient rain forest refugium as an evolutionary museum. Overdispersion in fragmented montane forests reflects a mixture of biogeographically distinct species pools, both tropical and temperate, that characterise environmentally contrasted cores and fringes. Low phylogenetic turnover along the seasonality gradient suggests recent ecological diversification across forests with contrasted rainfall seasonality.

The National Map of Security Threats as a tool to monitor security and public order

Threats to public order compromise the personal security of the individual, forcing him to take action to improve it, and thus to guarantee it to the closest people. The right to ensure the security of the individual, society is one of the duties of a state whose omission can be considered a violation of human rights. By implementing this obligation, a threat monitoring system was created in Poland – the National Safety Threat Map. It is a tool used by the Police which in 2016 was initially piloted, then already throughout the country introduced this mechanism to monitor and counteract local threats, affecting the safety of residents. This tool uses the Internet as a source of information about threats from citizens. The instruction was issued for both users – citizens, as well as for policemen of users and local administrators, and instructions for proper and reliable implementation. They impose on the Police officers’ specific tasks in the system for the implementation of applications. The work is an attempt to answer the question: What tool is KMZB in the system of monitoring by the state of public security and order? National Map of Security Threats (KMZB) – functions of the National Map of Security Threats in shaping local community safety, constitutes an element of the process of managing the public safety, as well as inspiring the local community in this respect. The Police as the formation serving the society and opened for its needs implemented the additional channel of the information exchange about the most troublesome threats defined on the local level.

Między lokalnością a wspólnotowością, czyli o wspólnototwórczych właściwościach scen miejskich

Artykuł podejmuje problem procesów emergencji, reprodukcji i rekonstrukcji wspólnot lokalnych oraz relacji między wspólnotowością i lokalnością w kształtowaniu społeczności lokalnych we współczesnych miastach. Wychodząc od omówienia nurtu środowiskowego i psychospołecznego w analizie społeczności lokalnych oraz ich ewolucji w kierunku koncepcji nowej lokalności i nowej wspólnotowości, artykuł wskazuje na swoistą przepaść w analizowaniu zjawisk wspólnotowych we współczesnych miastach między tymi dwoma podejściami, a tym samym podkreśla konieczność rein­tegracji obu aspektów dla lepszego zrozumienia miejskich procesów wspólnototwórczych. Zapropo­nowana zostaje koncepcja scen miejskich jako wartościowego konceptualnie pola dla eksploracji tych procesów, w których przenikają się zjawiska z zakresu nowej lokalności, jak i nowej wspólnotowości. W konkluzji sformułowana zostaje koncepcja lokalnej struktury możliwości społeczno-kulturowych. Tym samym artykuł udziela odpowiedzi na pytanie o istotę mechanizmów kulturowych, za pomocą których praktyki kulturowe strukturują terytorialne całości społeczne.

Zooplankton community structure along a pollution gradient at fine geographical scales in river ecosystems: The importance of species sorting over dispersal.

The release of anthropogenic pollution into freshwater ecosystems has largely transformed biodiversity and its geographical distribution patterns globally. However, for many communities including ecologically crucial ones such as zooplankton, it is largely unknown how different communities respond to environmental pollution. Collectively, dispersal and species sorting are two competing processes in determining the structure and geographical distribution of zooplankton communities in running water ecosystems such as rivers. At fine geographical scales, dispersal is usually considered as the dominant factor; however, the relative role of species sorting has not been evaluated well, mainly because significant environmental gradients rarely exist along continuously flowing rivers. The Chaobai River in northern China represents a rare system, where a significant environmental gradient exists at fine scales. Here, we employed high-throughput sequencing to characterize complex zooplankton communities collected from the Chaobai River, and tested the relative roles of dispersal and species sorting in determining zooplankton community structure along the pollution gradient. Our results showed distinct patterns of zooplankton communities along the environmental gradient, and chemical pollutant-related factors such as total phosphorus and chlorophyll-a were identified as the major drivers for the observed patterns. Further partial redundancy analyses showed that species sorting overrode the effect of dispersal to shape local zooplankton community structure. Thus, our results reject the dispersal hypothesis and support the concept that species sorting caused by local pollution can largely determine the zooplankton community structure when significant environmental gradients exist at fine geographical scales in highly polluted running water ecosystems.

Factors shaping community assemblages and species co-occurrence of different trophic levels.

Species assemblages are the results of various processes, including dispersion and habitat filtering. Disentangling the effects of these different processes is challenging for statistical analysis, especially when biotic interactions should be considered. In this study, we used plants (producers) and leafhoppers (phytophagous) as model organisms, and we investigated the relative importance of abiotic versus biotic factors that shape community assemblages, and we infer on their biotic interactions by applying three‐step statistical analysis. We applied a novel statistical analysis, that is, multiblock Redundancy Analysis (mbRA, step 1) and showed that 51.8% and 54.1% of the overall variation in plant and leafhopper assemblages are, respectively, explained by the two multiblock models. The most important blocks of variables to explain the variations in plant and leafhopper assemblages were local topography and biotic factors. Variation partitioning analysis (step 2) showed that pure abiotic filtering and pure biotic processes were relatively less important than their combinations, suggesting that biotic relationships are strongly structured by abiotic conditions. Pairwise co‐occurrence analysis (step 3) on generalist leafhoppers and the most common plants identified 40 segregated species pairs (mainly between plant species) and 16 aggregated pairs (mainly between leafhopper species). Pairwise analysis on specialist leafhoppers and potential host plants clearly revealed aggregated patterns. Plant segregation suggests heterogeneous resource availability and competitive interactions, while leafhopper aggregation suggests host feeding differentiation at the local level, different feeding microhabitats on host plants, and similar environmental requirements of the species. Using the novel mbRA, we disentangle for the first time the relative importance of more than five distinct groups of variables shaping local species communities. We highlighted the important role of abiotic processes mediated by bottom‐up effects of plants on leafhopper communities. Our results revealed that in‐field structure diversification and trophic interactions are the main factors causing the co‐occurrence patterns observed.

Trees as islands: canopy ant species richness increases with the size of liana‐free trees in a Neotropical forest

The physical characteristics of habitats shape local community structure; a classic example is the positive relationship between the size of insular habitats and species richness. Despite the high density and proximity of tree crowns in forests, trees are insular habitats for some taxa. Specifically, crown isolation (i.e. crown shyness) prevents the movement of small cursorial animals among trees. Here, we tested the hypothesis that the species richness of ants (Sa) in individual, isolated trees embedded within tropical forest canopies increases with tree size. We predicted that this pattern disappears when trees are connected by lianas (woody vines) or when strong interactions among ant species determine tree occupancy. We surveyed the resident ants of 213 tree crowns in lowland tropical forest of Panama. On average, 9.2 (range = 2–20) ant species occupied a single tree crown. Average (± SE) Sa was ca 25% higher in trees with lianas (10.2 ± 0.26) than trees lacking lianas (8.0 ± 0.51). Sa increased with tree size in liana‐free trees (Sa = 10.99A0.256), but not in trees with lianas. Ant species composition also differed between trees with and without lianas. Specifically, ant species with solitary foragers occurred more frequently in trees with lianas. The mosaic‐like pattern of species co‐occurrence observed in other arboreal ant communities was not found in this forest. Collectively, the results of this study indicate that lianas play an important role in shaping the local community structure of arboreal ants by overcoming the insular nature of tree crowns.

Phylogenetic turnover along local environmental gradients in tropical forest communities.

While the importance of local-scale habitat niches in shaping tree species turnover along environmental gradients in tropical forests is well appreciated, relatively little is known about the influence of phylogenetic signal in species' habitat niches in shaping local community structure. We used detailed maps of the soil resource and topographic variation within eight 24-50ha tropical forest plots combined with species phylogenies created from the APG III phylogeny to examine how phylogenetic beta diversity (indicating the degree of phylogenetic similarity of two communities) was related to environmental gradients within tropical tree communities. Using distance-based redundancy analysis we found that phylogenetic beta diversity, expressed as either nearest neighbor distance or mean pairwise distance, was significantly related to both soil and topographic variation in all study sites. In general, more phylogenetic beta diversity within a forest plot was explained by environmental variables this was expressed as nearest neighbor distance versus mean pairwise distance (3.0-10.3% and 0.4-8.8% of variation explained among plots, respectively), and more variation was explained by soil resource variables than topographic variables using either phylogenetic beta diversity metric. We also found that patterns of phylogenetic beta diversity expressed as nearest neighbor distance were consistent with previously observed patterns of niche similarity among congeneric species pairs in these plots. These results indicate the importance of phylogenetic signal in local habitat niches in shaping the phylogenetic structure of tropical tree communities, especially at the level of close phylogenetic neighbors, where similarity in habitat niches is most strongly preserved.

Determinants of community structure of zooplankton in heavily polluted river ecosystems.

River ecosystems are among the most affected habitats globally by human activities, such as the release of chemical pollutants. However, it remains largely unknown how and to what extent many communities such as zooplankton are affected by these environmental stressors in river ecosystems. Here, we aim to determine major factors responsible for shaping community structure of zooplankton in heavily polluted river ecosystems. Specially, we use rotifers in the Haihe River Basin (HRB) in North China as a case study to test the hypothesis that species sorting (i.e. species are “filtered” by environmental factors and occur at environmental suitable sites) plays a key role in determining community structure at the basin level. Based on an analysis of 94 sites across the plain region of HRB, we found evidence that both local and regional factors could affect rotifer community structure. Interestingly, further analyses indicated that local factors played a more important role in determining community structure. Thus, our results support the species sorting hypothesis in highly polluted rivers, suggesting that local environmental constraints, such as environmental pollution caused by human activities, can be stronger than dispersal limitation caused by regional factors to shape local community structure of zooplankton at the basin level.

Soil resources and topography shape local tree community structure in tropical forests

Both habitat filtering and dispersal limitation influence the compositional structure of forest communities, but previous studies examining the relative contributions of these processes with variation partitioning have primarily used topography to represent the influence of the environment. Here, we bring together data on both topography and soil resource variation within eight large (24-50 ha) tropical forest plots, and use variation partitioning to decompose community compositional variation into fractions explained by spatial, soil resource and topographic variables. Both soil resources and topography account for significant and approximately equal variation in tree community composition (9-34% and 5-29%, respectively), and all environmental variables together explain 13-39% of compositional variation within a plot. A large fraction of variation (19-37%) was spatially structured, yet unexplained by the environment, suggesting an important role for dispersal processes and unmeasured environmental variables. For the majority of sites, adding soil resource variables to topography nearly doubled the inferred role of habitat filtering, accounting for variation in compositional structure that would previously have been attributable to dispersal. Our results, illustrated using a new graphical depiction of community structure within these plots, demonstrate the importance of small-scale environmental variation in shaping local community structure in diverse tropical forests around the globe.

Fish assemblages of an African river floodplain: a test of alternative models of community structure

AbstractIn the Oueme River, a lowland river in Benin, Africa, artificial ponds constructed in the floodplain (whedos) are colonised during the high‐water period by a presumably random sample of fishes from the river channel. As water slowly recedes from the floodplain, fishes are isolated in whedos until they are harvested near the end of the dry season. We surveyed fishes in whedos and adjacent main‐channel and floodplain habitats during two low‐water periods (2008 and 2009) and one falling‐water period (2010–2011) to evaluate the relevance of four alternative metacommunity models to these systems. In 2010–2011, we also measured a suite of physicochemical variables including dissolved oxygen, temperature, specific conductivity and per cent cover of aquatic vegetation. Whedos were covered with dense growth of aquatic vegetation, and dissolved oxygen concentrations were lower in whedos and a natural floodplain depression compared with the main channel. Multivariate analyses revealed that habitat types were distinct with regard to assemblage structure and abiotic conditions. Assemblages in whedos and natural floodplain depressions were differentiated from those of the river channel, with the floodplain habitats being dominated by piscivorous fishes that tolerate aquatic hypoxia. Dispersal, aquatic hypoxia and predation act in concert to shape local community structure. Patch dynamics, species sorting and mass effect models all were consistent with patterns in fish assemblage structure in this system. We conclude that the underlying mechanisms of drift, speciation, selection and dispersal ultimately may be more useful for explaining patterns in ecological communities than alternative metacommunity models.

The influence of species pools and local processes on the community structure: a test case with woody plant communities in China's mountains

Understanding how patterns of biodiversity vary among taxonomic levels can provide insights into the mechanisms that regulate the assembly of ecological communities. In this study, we examined the scale and environmental dependence of the relationship between number of species and number of genera/families in woody plant communities to investigate the influences of species pool and local ecological processes on the taxonomic structures of local communities. The data we used are based on a large number of forest plots collected across the eastern part of China and the globe. The results showed that the ratio of the number of genera/families:species and the taxonomic exponents, i.e. the exponents of the genus/family–species relationship, were generally lower than null expectations based on the regional species pool, suggesting that abiotic filtering (e.g. environmental filtering and dispersal limitation) is more important than interspecific competition in shaping local communities. The extent of species pool and the area sampled for local communities both influenced our ability to infer whether local ecological processes were important. In particular, the deviation of the taxonomic ratios and exponents between empirical and null patterns increased as the extent of species pool increased, and the taxonomic exponents declined as area of the local community increased, due partly to the reduced effect of interspecific competition. We conclude that regional species pools and local processes both influenced the taxonomic structure of local woody plant communities, but their effects vary substantially among spatial scales.