Characterising functional trait diversity and trait–environment relationships in fish assemblages of boreal lakes

1. Characterisation of biodiversity is typically based on taxonomic approaches, while much less is known about other related aspects. Functional trait diversity is one such component of biodiversity that has not been addressed rigorously in ecological research until recently. We tested the congruence between taxonomic‐ and trait‐based approaches, and examined how spatial configuration, local abiotic environmental factors and biotic effects interact to influence taxonomic‐ and trait‐based characterisation of freshwater fish assemblages. 2. Fish assemblage data were compiled for 124 lakes in southern Finland. Variance partitioning in both linear regression analyses and redundancy analysis was used to quantify the relative contribution of spatial and environmental variables to taxonomic and functional trait diversity and structure. Additionally, a null model analysis was used to test for the potential effects of interspecific segregation and biotic interactions on the co‐occurrence of species. 3. The species pool was relatively poor. However, trait‐based classification of species indicated that most species belonged to unique functional entities, which suggested low redundancy in species composition. Correlation analysis indicated a very strong relationship between species richness (SR) and the number of unique trait combinations (UTC). Ecoregion‐level heterogeneity in SR and UTC were well represented in a relatively small group of randomly selected lakes (c. 30 lakes). Multiple regressions indicated moderate roles for abiotic environmental variables (i.e. lake surface area, depth, total phosphorous, colour and pH) in determining SR, UTC and the distribution of single trait categories, whereas geographical location was not generally influential. 4. Redundancy analysis revealed similar patterns to those of diversity analyses for taxonomic and associated trait‐based structure, emphasising the effect of abiotic environmental variables and the negligible effect of geographical position. 5. Co‐occurrence analysis indicated significant checkerboard distribution at the whole assemblage level, but interspecific segregation proved to be of relatively minor importance in the constrained analyses, where species pair combinations within trait category groups were evaluated. 6. Our results suggest that taxonomic‐ and trait‐based patterns of boreal lake fish assemblages are strongly interrelated. Environmental filtering through the effects of local abiotic variables seems to have the most prominent role in determining trait‐based assemblage patterns among lakes, which may also be secondarily shaped by biotic interactions. 7. From the applied perspective, it may not necessarily matter whether traditional taxonomic or more novel trait‐based approaches are used in characterising spatial patterns in boreal fish assemblages. However, trait‐based approaches may provide complementary information which cannot be directly revealed by taxonomic data.     

河流鱼类分类群和功能群的纵向梯度格局——以新安江流域为例

确定鱼类群落的空间格局是保护和管理河流鱼类多样性的基础。尽管河流鱼类分类群（基于物种组成）的纵向梯度格局已得到大量报道,但其功能群（基于功能特征）的空间格局研究较少。以皖南山区新安江为研究流域,沿其"正源-下游"梯度共设置27个调查样点,分别于2017年5月和10月完成2次调查取样,着重研究了鱼类分类群和功能群结构的纵向梯度格局及其形成机制。共采集鱼类44种,可分为5个运动功能群和4个营养功能群,构成14个"营养-运动"复合功能群。双因素交互相似性分析结果显示,鱼类分类群和功能群均随河流级别显著变化,但两者均无显著的季节变化;根据相似性百分比分析,由1级至3级河流,数量优势物种和功能群的空间变化主要呈嵌套格局,而由3级至5级河流其变化主要呈周转格局。方差分解结果显示,局域栖息地、陆地景观和支流空间位置3类解释变量对分类群和功能群空间变化的解释率分别为33.6%和38.5%,其中,分类群受局域栖息地和支流空间位置变量的显著影响,而功能群受局域栖息地和陆地景观变量的显著影响。研究表明,沿着新安江的"上游-下游"纵向梯度,鱼类分类群和功能群的空间格局基本一致,但两者的形成机制不同：分类群的纵向梯度变化受环境过滤和扩散过程的联合影响,而功能群则主要受环境过滤影响。     

What governs the functional diversity patterns of fishes in the headwater streams of the humid forest enclaves: environmental conditions,taxonomic diversity or biotic interactions?

The relationship between functional and taxonomic diversity is a major issue in ecology. Biodiversity in aquatic environments is strongly influenced by environmental gradients that act as dispersion and niche barriers. Environmental conditions act as filters to select functional traits, but biotic interactions also play a role in assemblage structure. In headwater streams, the relationship between functional and taxonomic diversity remains unclear. In this study we investigated how environmental conditions, taxonomic diversity and biotic interactions influence the spatial distribution of traits and functional diversity in stream fish species. Standardized sampling of fish species was carried out in 50 m sections of 16 streams located in rainforest enclaves in a semiarid region of Brazil (Caatinga biome). The functional diversity indices displayed different responses to the predictor variables used. Functional richness was mainly influenced by environmental conditions, while functional evenness was mostly determined by taxonomic diversity. On the other hand, functional dispersion was explained by a combination of environmental conditions and taxonomic diversity. The spatial distribution of fish species with the same functional traits was random, indicating that biotic interactions are not a strong predictor in these ecosystems. Channel width, pH and substrate were the most important variables in the spatial distribution of the functional traits of the fish species. Our results suggest that the functional structure of fish assemblages in headwater streams depends mainly on environmental conditions and taxonomic diversity.     

Temporal variability in the spatial and environmental determinants of functional metacommunity organization – stream fish in a human‐modified landscape

1. Quantifying the relative importance of environmental filtering versus regional spatial structuring has become an intensively studied area in the context of metacommunity ecology. However, most studies have evaluated the role of environmental and spatial processes using taxonomic data sets of single snapshot surveys. 2. Here, we examined temporal changes in patterns and possible processes behind the functional metacommunity organization of stream fishes in a human‐modified landscape. Specifically, we (i) studied general changes in the functional composition of fish assemblages among 40 wadeable stream sites during a 3‐year study period in the catchment area of Lake Balaton, Hungary, (ii) quantified the relative importance of spatial and environmental factors as determinants of metacommunity structure and (iii) examined temporal variability in the relative role of spatial and environmental processes for this metacommunity. 3. Partial triadic analysis showed that assemblages could be effectively ordered along a functional gradient from invertebrate consuming species dominated by the opportunistic life‐history strategy, to assemblages with a diverse array of functional attributes. The analysis also revealed that functional fish assemblage structure was moderately stable among the sites between the sampling periods. 4. Despite moderate stability, variance partitioning using redundancy analyses (RDA) showed considerable temporal variability in the contribution of environmental and spatial factors to this pattern. The analyses also showed that environmental variables were, in general, more important than spatial ones in determining metacommunity structure. Of these, natural environmental variables (e.g. altitude, velocity) proved to be more influential than human‐related effects (e.g. pond area, % inhabited area above the site, nutrient enrichment), even in this landscape with relatively low variation in altitude and stream size. 5. Pond area was, however, the most important human stressor variable that was positively associated with the abundance of non‐native species with diverse functional attributes. The temporal variability in the relative importance of environmental and spatial factors was probably shaped by the release of non‐native fish from fish ponds to the stream system during flood events. 6. To conclude, both spatial processes and environmental control shape the functional metacommunity organization of stream fish assemblages in human‐modified landscapes, but their importance can vary in time. We argue, therefore, that metacommunity studies should better consider temporal variability in the ecological mechanisms (e.g. dispersal limitation, species sorting) that determine the dynamics of landscape‐level community organization.     

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

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

Regional and local drivers of macroinvertebrate assemblages in boreal springs

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

Exploring taxonomic filtering in urban environments

Question: Several mechanisms have been proposed that control the spatio‐temporal pattern of species coexistence. Among others, the species pool hypothesis states that the large‐scale species pool is an important factor in controlling small‐scale species richness through filtering of species that can persist within a species assemblage on the basis of their tolerance of the abiotic environment. Because of the process of environmental filtering, co‐occurring species that experience similar environmental conditions are likely to be more taxonomically similar than ecologically distant species. This is because, due to the conservatism of many species traits during evolutionary diversification, the ability of species to colonize the same ecological space is thought to depend at least partially on their taxonomic similarity. The question for this study is: Under the assumption of trait conservatism, does environmental filtering lead to nonrandom species assemblages with respect to their taxonomic structure? Methods: The significance of taxonomic filtering in regulating species coexistence is tested using data from 15 local species assemblages from the urban flora of Rome (Italy). To find out whether the taxonomic structure of the selected’ local’ species assemblages was significantly different from random, we used a Monte Carlo simulation in which for each local species assemblage, the actual taxonomic diversity was compared to the taxonomic diversity of 1000 virtual species lists of the same size extracted at random from a larger ‘regional’ species pool. Results: We found that in most cases the local species assemblages have a higher degree of taxonomic similarity than would be expected by chance showing a phenomenon of ‘species condensation’ in a small number of higher‐level taxa. Conclusions: Our observations support the species pool hypothesis and imply that environmental filtering is an important mechanism in shaping the taxonomic structure of species assemblages. Therefore, the incorporation of taxonomic diversity into landscape and community ecology may be beneficial for a better understanding of the processes that regulate species coexistence.     

Scale-related patterns in the spatial and environmental components of stream macroinvertebrate assemblage variation

Aim We examined the relative contributions of spatial gradients and local environmental conditions to macroinvertebrate assemblages of boreal headwater streams at three hierarchical extents: bioregion, ecoregion and drainage system. We also aimed to identify the environmental variables most strongly related to assemblage structure at each study scale, and to assess how the importance of these variables is related to regional context and spatial structuring at different scales. Location Northern Finland ( 62 – 68° N, 25–32° E). Methods Variation in macroinvertebrate data was partitioned using partial canonical correspondence analysis into components explained by spatial variables (nine terms from the cubic trend surface regression), local environmental variables (15 variables) and spatially structured environmental variation. Results The strength of the relationship between assemblage structure and local environmental variables increased with decreasing spatial extent, whereas assemblage variation related to spatial variables and spatially structured environmental variation showed the opposite pattern. At the largest extents, spatial variation was related to latitudinal gradients, whereas spatial autocorrelation among neighbouring streams was the likely mechanism creating spatial structure within drainage systems. Only stream size and water acidity were consistently important in explaining assemblage structure at all study scales, while the importance of other environmental variables was more context‐dependent. Main conclusions The importance of local environmental factors in explaining macroinvertebrate assemblage structure increases with decreasing spatial extent. This scale‐related pattern is not caused solely by changes in study extent, however, but also by variable sample sizes at different regional extents. The importance of environmental gradients is context‐dependent and few factors are likely to be universally important correlates of macroinvertebrate assemblage structure. Finally, our results suggest that bioassessment should give due attention to spatial structuring of stream assemblages, because important assemblage gradients may not only be related to local factors but also to biogeographical constraints and neighbourhood dispersal processes.     

Evolution of termite functional diversity: analysis and synthesis of local ecological and regional influences on local species richness

Aim To (1) describe termite functional diversity patterns across five tropical regions using local species richness sampling of standardized areas of habitat; (2) assess the relative importance of environmental factors operating at different spatial and temporal scales in influencing variation in species representation within feeding groups and functional taxonomic groups across the tropics; (3) achieve a synthesis to explain the observed patterns of convergence and divergence in termite functional diversity that draws on termite ecological and biogeographical evidence to‐date, as well as the latest evidence for the evolutionary and distributional history of tropical rain forests. Location Pantropical. Methods A pantropical termite species richness data set was obtained through sampling of eighty‐seven standardized local termite diversity transects from twenty‐nine locations across five tropical regions. Local‐scale, intermediate‐scale and large‐scale environmental data were collected for each transect. Standardized termite assemblage and environmental data were analysed at the levels of whole assemblages and feeding groups (using components of variance analysis) and at the level of functional taxonomic groups (using correspondence analysis and canonical correspondence analysis). Results Overall species richness of local assemblages showed a greater component of variation attributable to local habitat disturbance level than to region. However, an analysis accounting for species richness across termite feeding groups indicated a much larger component of variation attributable to region. Mean local assemblage body size also showed the greater overall significance of region compared with habitat type in influencing variation. Ordination of functional taxonomic group data revealed a primary gradient of variation corresponding to rank order of species richness within sites and to mean local species richness within regions. The latter was in the order: Africa > south America > south‐east Asia > Madagascar > Australia. This primary gradient of species richness decrease can be explained by a decrease in species richness of less dispersive functional taxonomic groups feeding on more humified food substrates such as soil. Hence, the transects from more depauperate sites/regions were dominated by more dispersive functional taxonomic groups feeding on less humified food substrates such as dead wood. Direct gradient analysis indicated that ‘region’ and other large‐scale factors were the most important in explaining patterns of local termite functional diversity followed by intermediate‐scale geographical and site variables and, finally, local‐scale ecological variables. Synthesis and main conclusions Within regions, centres of termite functional diversity lie in lowland equatorial closed canopy tropical forests. Soil feeding termite evolution further down food substrate humification gradients is therefore more likely to have depended on the long‐term presence of this habitat. Known ecological and energetic constraints upon contemporary soil feeders lend support for this hypothesis. We propose further that the anomalous distribution of termite soil feeder species richness is partly explained by their generally very poor dispersal abilities across oceans. Evolution, radiation and dispersal of soil feeder diversity appears to have been largely restricted to what are now the African and south American regions. The inter‐regional differences in contemporary local patterns of termite species richness revealed by the global data set point to the possibility of large differences in consequent ecosystem processes in apparently similar habitats on different continents.     

Algal epiphytes of Zostera marina: Variation in assemblage structure from individual leaves to regional scale

Data from a hierarchical study of four Zostera marina beds in Wales were used to identify the spatial scales of variation in epiphyte assemblages. There were significant within and among bed differences in assemblage structure. The differences in assemblage structure with spatial scale generally persisted when species identifications were aggregated into functional groups. There was also significant within and among bed variability in Zostera density and average length. Local variations in Zostera canopy variables at the quadrat scale (total leaf length, average leaf length and leaf density per quadrat) were not related to epiphyte species richness nor to the structure of the assemblage. In contrast, individual leaf length was significantly related to species richness in two of the beds and the structure of epiphyte assemblages was always related to individual leaf lengths. The absence of links between quadrat scale measurements of canopy variables and assemblage structure may reflect the high turnover of individual Zostera leaves. Experimental work is required to discriminate further between the potential causes of epiphyte assemblage variation within and between beds. No bed represented a refuge where a rare species was abundant. If a species was uncommon at the bed scale, it was also uncommon in beds where it occurred. The heterogeneous assemblages found in this study suggest that a precautionary approach to conservation is advisable. As much of a bed as possible should be retained, both to protect the integrity of local assemblages and to retain rare species at regional scales.     

Biome transitions as centres of diversity: habitat heterogeneity and diversity patterns of West African bat assemblages across spatial scales

It is widely accepted that species diversity is contingent upon the spatial scale used to analyze patterns and processes. Recent studies using coarse sampling grains over large extents have contributed much to our understanding of factors driving global diversity patterns. This advance is largely unmatched on the level of local to landscape scales despite being critical for our understanding of functional relationships across spatial scales. In our study on West African bat assemblages we employed a spatially explicit and nested design covering local to regional scales. Specifically, we analyzed diversity patterns in two contrasting, largely undisturbed landscapes, comprising a rainforest area and a forest‐savanna mosaic in Ivory Coast, West Africa. We employed additive partitioning, rarefaction, and species richness estimation to show that bat diversity increased significantly with habitat heterogeneity on the landscape scale through the effects of beta diversity. Within the extent of our study areas, habitat type rather than geographic distance explained assemblage composition across spatial scales. Null models showed structure of functional groups to be partly filtered on local scales through the effects of vegetation density while on the landscape scale both assemblages represented random draws from regional species pools. We present a mixture model that combines the effects of habitat heterogeneity and complexity on species richness along a biome transect, predicting a unimodal rather than a monotonic relationship with environmental variables related to water. The bat assemblages of our study by far exceed previous figures of species richness in Africa, and refute the notion of low species richness of Afrotropical bat assemblages, which appears to be based largely on sampling biases. Biome transitions should receive increased attention in conservation strategies aiming at the maintenance of ecological and evolutionary processes.     

Fishes of Indiana streams: current and historic assemblage structure

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

Local species assemblages are influenced more by past than current dissimilarities in photosynthetic activity

Most land on Earth has been changed by humans and past changes of land can have lasting influences on current species assemblages. Yet few globally representative studies explicitly consider such influences even though auxiliary data, such as from remote sensing, are readily available. Time series of satellite‐derived data have been commonly used to quantify differences in land‐surface attributes such as vegetation cover, which will among other things be influenced by anthropogenic land conversions and modifications. Here we quantify differences in current and past (up to five years before sampling) vegetation cover, and assess whether such differences differentially influence taxonomic and functional groups of species assemblages between spatial pairs of sites. Specifically, we correlated between‐site dissimilarity in photosynthetic activity of vegetation (the enhanced vegetation index) with the corresponding dissimilarity in local species assemblage composition from a global database using a common metric for both, the Bray–Curtis index. We found that dissimilarity in species assemblage composition was on average more influenced by dissimilarity in past than current photosynthetic activity, and that the influence of past dissimilarity increased when longer time periods were considered. Responses to past dissimilarity in photosynthetic activity also differed among taxonomic groups (plants, invertebrates, amphibians, reptiles, birds and mammals), with reptiles being among the most influenced by more dissimilar past photosynthetic activity. Furthermore, we found that assemblages dominated by smaller and more vegetation‐dependent species tended to be more influenced by dissimilarity in past photosynthetic activity than prey‐dependent species. Overall, our results have implications for studies that investigate species responses to current environmental changes and highlight the importance of past changes continuing to influence local species assemblage composition. We demonstrate how local species assemblages and satellite‐derived data can be linked and provide suggestions for future studies on how to assess the influence of past environmental changes on biodiversity.     

The Influence of Environmental,Biotic and Spatial Factors on Diatom Metacommunity Structure in Swedish Headwater Streams

Stream assemblages are structured by a combination of local (environmental filtering and biotic interactions) and regional factors (e.g., dispersal related processes). The relative importance of environmental and spatial (i.e., regional) factors structuring stream assemblages has been frequently assessed in previous large-scale studies, but biotic predictors (potentially reflecting local biotic interactions) have rarely been included. Diatoms may be useful for studying the effect of trophic interactions on community structure since: (1) a majority of experimental studies shows significant grazing effects on diatom species composition, and (2) assemblages can be divided into guilds that have different susceptibility to grazing. We used a dataset from boreal headwater streams in south-central Sweden (covering a spatial extent of ∼14000 km²), which included information about diatom taxonomic composition, abundance of invertebrate grazers (biotic factor), environmental (physicochemical) and spatial factors (obtained through spatial eigenfunction analyses). We assessed the relative importance of environmental, biotic, and spatial factors structuring diatom assemblages, and performed separate analyses on different diatom guilds. Our results showed that the diatom assemblages were mainly structured by environmental factors. However, unique spatial and biological gradients, specific to different guilds and unrelated to each other, were also evident. We conclude that biological predictors, in combination with environmental and spatial variables, can reveal a more complete picture of the local vs. regional control of species assemblages in lotic environments. Biotic factors should therefore not be overlooked in applied research since they can capture additional local control and therefore increase accuracy and performance of predictive models. The inclusion of biotic predictors did, however, not significantly influence the unique fraction explained by spatial factors, which suggests low bias in previous assessments of unique regional control of stream assemblages.     

Taxonomic relatedness and spatial structure of a shelf benthic gastropod assemblage

Aim Phylogenetically related species share attributes that lead to common responses to environmental conditions, but which could also produce the exclusion of species by its relatives. These processes could generate the patterns of phylogenetic attraction or repulsion in local communities, where related species would tend to coexist more or less than expected by chance. This paper aims to (1) analyse the phylogenetic structure of a benthic gastropod assemblage in the south‐western Atlantic Ocean (SAO); (2) explore the linkages between phylogenetic structure and spatial distribution patterns; (3) compare outcomes driven by the analysis of presence‐only data and predictive species distribution models; and (4) explore which aspects of the gained knowledge can be useful to the design of sound conservation and/or management actions. Location Uruguayan shelf and slope in the SAO. Methods Spatial patterns in taxonomical relatedness were assessed using (1) raw presence/absence data (i.e. realized niche approach) and (2) reconstruction of the potential composition of the assemblage from niche modelling (i.e. fundamental niche approach). Null models were used to test hypotheses on assemblage structure. Results Significant departures from the null hypothesis that all species were drawn from the same assemblage were observed irrespectively of the approach, indicating the existence of non‐random structures. However, a high proportion of local communities can be thought as random subsets of the regional species pool. This lack of a strong signal of a taxonomic effect could be related to the absence of a linkage between taxonomic distances and ecological similarities. Main conclusions Our results suggest a random assembly of local communities from the regional species pool and/or niche filtering independent of phylogeny as main determinants of local community composition. We also suggest that local assemblages displaying significantly higher (or lower) than expected taxonomic relatedness should be taken into consideration for designing spatially explicit conservation measures.     

Control of stream insect assemblages: roles of spatial configuration and local environmental factors

Abstract 1. Current views in ecology emphasise that community structure is the sum of multiple processes, with imprints of both regional and local drivers. However, the degree to which stream insect assemblages are structured by spatial configuration (complying with the dispersal‐based neutral hypothesis) and local environmental features (complying with the niche‐based species sorting hypothesis) has not been rigorously examined based on surveys in multiple years. 2. Stream sites in a boreal drainage system were surveyed during three consecutive years and the relative contribution of spatial configuration and local environmental variables to aquatic insect assemblage structure (characterised by both abundance and presence–absence data) was assessed. Separate analyses were conducted for mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera), and non‐biting midges (Diptera: Chironomidae) in each year. 3. There were no relationships between the spatial location and local environmental features of streams in Mantel tests, facilitating exploration of their independent effects on assemblage structure. The study found virtually no effects of spatial location on stream insect assemblages across the study drainage system, as evidenced by Mantel tests and canonical correspondence analyses (CCA). The environmental variables were also rather weakly associated with assemblage structure, with the total amount of explained variation ranging from 9.8% to 31.7% in the CCAs. There were no appreciable differences in the amount of environment‐related explained variation in assemblage structure between mayflies, stoneflies, caddisflies, and midges, but some between‐year differences were noticeable in most insect groups. The environmental variables that were significantly related to assemblage structure exhibited some between‐group and between‐year variability. In general, patterns shown by abundance and presence–absence data were highly similar. 4. It appears that stream insect assemblages comply with the niche‐based species sorting hypothesis in the context of metacommunity ecology. In contrast, the absence of spatial structuring suggests that stream insect assemblages do not comply with the neutral hypothesis, being not strongly dispersal limited at the within‐drainage basin scale.     

Beta diversity of rock-restricted cichlid fishes in Lake Malawi: importance of environmental and spatial factors

The rock-restricted cichlid fish assemblages of Lake Malawi exhibit high spatial diversity in their species composition and relative abundance. However the extent to which this is due to the effects of local environmental differences, dispersal limitation of constituent taxa, and the assignment of allopatric populations to species is uncertain. We examined the factors associated with diversity within an assemblage from the north-western shores, encompassing a spatial scale of 170 km. For both the whole assemblage, and all constituent species-complexes, spatial variance in community structure was significantly dependent upon both geographic distances between locations and local habitat variables. Pronounced effects of distance indicate limited dispersal, but our results also show that that the spatial variance explained by geographic distance alone was strongly linked to proportion of allopatric populations within a species-complex with species status. Thus, the taxonomic status of allopatric populations underlies, at least partially, the biogeographical structure of this assemblage. Substrate composition and habitat depth were also significant determinants of community structure, although spatial variance attributed to these variables was less than that associated with distance alone. Substantial unexplained variance may be a consequence of the effects of unmeasured habitat variables, high ecological similarity between co-occurring species, stochastic influences on population abundance, and the effects of local adaptation. Despite low spatial variance explained by the assessed environmental variables, significant environmental influence on cichlid assemblage structure across a wide spatial scale indicates that even slight future environmental changes may have the capacity to significantly alter species composition.     

Unraveling the effects of water–sediment conditions and spatial patterns on Unionida assemblages in seasonally connected floodplain lakes

Floodplain lakes are good metacommunity systems to study the environmental and spatial processes structuring local assemblages. They are more connected during high-water periods and are more isolated during low-water periods. We evaluated the effects of lake spatial patterning and water and sediment conditions on Unionida species assemblages. Moran Eigenvector Maps were used to generate spatial variables representing spatial patterns at different scales. We sampled 35 lakes from the Pantanal floodplain, Brazil. To understand the effects of environmental and spatial variables, we performed Redundancy Analyses and variation partitioning to separate environmental and spatial pattern effects. Environmental variables explained almost twice the variation in the Pantanal mussel assemblages than did spatial variables. Unionida species presence was driven mainly by variations in sediment coarse sand and silt contents. The weak spatial patterns observed may be related to increased connectivity between lakes during floods, which facilitates mussel host fish dispersal. Mussel abundances were driven mainly by organic matter availability, but varied between species. Changes in lake connectivity can affect the regional sediment dynamics and affect mussel assemblages.

     

Effects of wind‐driven spatial structure and environmental heterogeneity on high‐altitude wetland macroinvertebrate assemblages with contrasting dispersal modes

相似文献   

Concordance among stream assemblages and spatial autocorrelation along a fragmented gradient

Patterns of spatial autocorrelation of biota and distributional similarity (concordance) between assemblages of different organism groups have important implications in both theoretical ecology and biodiversity conservation. Here we report environmental gradients and spatial distribution patterns of taxonomic composition among stream fish, benthic macroinvertebrate, and diatom assemblages along a fragmented stream in south‐western France. We quantified spatial patterns of lotic assemblage structure along this stream, and we tested for concordance in distribution patterns among the three taxonomic groups. Our results showed that both environmental characteristics and stream assemblages were spatially autocorrelated. For stream fish and diatom assemblages, these patterns reflected assemblage changes along the longitudinal stream gradient, whereas environmental variables and benthic macroinvertebrates exhibited a more patchy spatial pattern. Cross‐taxa concordance was significant between stream fish and diatoms, and between stream fish and benthic macroinvertebrates. The assemblage concordance between stream fish and diatoms could be attributed to similar responses along the longitudinal gradient, whereas those between stream fish and benthic macroinvertebrates may result from biotic interactions. Based on potential dispersal capacities of taxa, our results validated the hypotheses that weakly dispersing taxa exhibit greater concordance than highly dispersing ones and that dispersal capacities affect how taxonomic groups respond to their local environment. Both diatoms and highly dispersing stream fish were affected by stream fragmentation (i.e. the number of dams between sites), while the effect of fragmentation was not significant for invertebrates that fly well in their adult stage, thus emphasizing the importance of the way of dispersal. These results suggest that addressing the effects of dispersal capacity on stream assemblage patterns is crucial to identifying mechanisms behind patterns and to better understanding the determinants of stream biodiversity.