Do metacommunity theories explain spatial variation in fish assemblage structure in a pristine tropical river?

相似文献   

The importance of environmental heterogeneity for species diversity and assemblage structure in Bornean stream frogs

1. Several hypotheses have been proposed to explain the structure of multi-species assemblages. Among these, abiotic environmental factors and biotic processes are often favoured. Several recent studies examining anuran communities identified environmental factors to be only of minor importance in the composition of leaf-litter and canopy assemblages in pristine forests. Instead, spatial effects and spatially structured environments were considered more important. 2. In this study, we investigated whether these findings could also be confirmed for very heterogeneous stream habitats in the primary rainforest of the Ulu Temburong National Park, Brunei Darussalam. We thus investigated anuran assemblage compositions on 50 stream sites with regard to environmental and spatial influences. 3. Cross-product correlations indicated that both factors (spatial and environmental parameters) determined assemblage composition of anurans. Environment itself may be spatially structured, yet this interrelation did not contribute to the explainable variation of frog community compositions within the study area. 4. Detailed analyses of the environmental parameters with nonmetric multidimensional scaling revealed that community structure was mostly affected by three major environmental characters: stream turbidity, river size and the density of understorey vegetation. Based on these habitat characteristics, we assigned species to three distinct habitat guilds. 5. The results underline the importance of riparian habitat heterogeneity in pristine forests in structuring anuran assemblages. We conclude that different anuran assemblages, that is, leaf litter, canopy and stream communities, follow different assemblage rules and thus are not directly comparable.     

Mapping forest vegetation patterns in an Atlantic-Mediterranean transitional area by integration of ordination and geostatistical techniques

Aims Forest vegetation variability may be explained by the complex interplay among several spatial structuring factors, including climate and topography. We modelled the spatial variability of forest vegetation assemblages and significant environmental variables along a complex environmental gradient or coenocline to produce a detailed cartographic database portraying the distribution of forests along it.Methods We combined an analysis of ordination coenoclines with kriging over 772 field data plots from the third Spanish National Forest Inventory in an Atlantic–Mediterranean transitional area (northern Spain).Important findings The best fitted empirical semivariogram revealed a strong spatial structure of forest species composition along the complex environmental gradient considered (the climatic–topographic gradient from north to south). The steady and gradual increase of semivariance with a marked lag distance indicates a gradual turnover of forest assemblages according to the climatic–topographic variations (regional or local). Two changes in the slope of the semivariogram suggest the existence of two different scales of spatial variation. The interpolation map by Kriging of forest vegetation assemblages along the main coenocline shows a clear spatial distribution pattern of trees and shrubs in accordance with the spatial variation of significant environmental variables. We concluded that the multivariate geostatistical approach is a suitable technique for spatial analysis of forest systems employing data from national forest inventories based on a regular network of field plots. The development of an assortment of maps describing changes in vegetation assemblages and variation in environmental variables is expected to be a suitable tool for an integrated forest management and planning.     

Environmental watering triggers rapid frog breeding in temporary wetlands within a regulated river system

The Murray–Darling basin is the most extensively regulated river system in Australia and delivery of environmental water is increasingly being used in its management. Due to their sensitivity to hydrological changes, frogs are often targets of environmental watering actions, and site-specific data on their habitat and water requirements are essential for achieving optimal ecological outcomes. I investigated the spatial and temporal response of frogs to the environmental watering of temporary wetlands in the lower River Murray region to determine if watering (timing, duration and quality) triggered a breeding response and provided opportunities for juvenile recruitment. Frog and tadpole surveys were conducted each month from December 2014 to April 2015 at watered temporary wetlands and permanent wetlands along on the River Murray in South Australia. All seven frog species known from the lower Murray valley bred opportunistically after deliberate flooding of temporary wetland sites. Breeding was immediate and was observed at all watered sites. Tadpole development was largely synchronous and rapid, with the majority of frogs metamorphosing 3 to 4 months after wetlands were inundated. The abundance and diversity of tadpoles and frogs was significantly greater in watered wetlands than in permanent wetlands. Wetlands required inundation for a minimum duration of 4 months over summer and autumn to allow sufficient time for tadpoles to complete development. Environmental watering of wetlands via pumping, whilst highly localised, can target key ecological assets in dry conditions, and may provide critical breeding opportunities and refugia for maintaining frog species and their ecological roles.     

Relationships between fish assemblages, macrophytes and environmental gradients in the Amazon River floodplain

During the flood season of 1992–1993, 139 species of fishes were collected from a floodplain lake system in the central Amazon Basin. Fish species distribution was examined relative to abiotic variables in seven vegetation strata on Marchantaria Island, Solimões River. Both environmental variables and species distributions were influenced by a river channel to floodplain-interior gradient. Species diversity was significantly higher in vegetated areas than in unvegetated areas, with deeper water Paspalum repens stands harbouring the highest diversity. As a result, species richness and catches were positively related to habitat complexity, while catch was also negatively related to dissolved oxygen (DO) and water depth. Low DO and shallow waters appeared to act as a refuge from predation. Fish assemblages were related to water chemistry, but species richness was not. Canonical correspondence analysis provided evidence that floodplain fish assemblages formed by the 76 most common species were influenced by physical variables, macrophyte coverage and habitat complexity, which jointly accounted for 67% of the variance of fish species assemblages. Omnivores showed no pattern relative to the river channel to floodplain-interior gradient while detritivores were more likely to be found at interior floodplain sites and piscivores closer to the river. Piscivores could be further separated into three groups, one with seven species associated with free-floating macrophytes in deep water, a second with five species found in shallow waters with rooted grasses and a third with six open water orientated species. The results suggest that fish assemblages in the Amazon floodplain are not random associations of species.     

The effect of local environmental variables on the helminth parasite communities of the pointedbelly frog Leptodactylus podicipinus from ponds in the Pantanal wetlands

Understanding the patterns of species distribution and abundance has been at the core of ecology. In general, these patterns are determined by species dispersion as well as by abiotic and biotic environmental conditions. Similarly, host-parasite relations and the structure of parasite assemblages are also shaped by environmental conditions and landscape composition. Herein, we assessed the influence of environmental variables and parasite species dispersion on the structure of helminth parasites communities in the frog Leptodactylus podicipinus. We sampled 10 ponds and recorded area, depth, altitude, pH, dissolved oxygen, salinity, temperature, and extent of soil, water, and vegetation cover as well as the distances between the ponds. We collected 121 frogs and found 9 helminth taxa; 2 of them were core species (prevalence higher than 50%), which contributed to the relatively high similarity observed among the ponds. Most of the helminths showed some variation in the frequencies of occurrence among communities from different ponds. The change in species composition among ponds was explained by the environmental variables but not by the distance between the ponds. Moreover, the results indicated that local processes (variation in environmental conditions) were more important than the regional processes (species distribution) in determining the structure of parasite communities. The variation in helminth communities among ponds in response to moderate differences in pond environmental characteristics points to the potential of helminth species as indicators of environmental conditions.     

Vegetation types of the upper Madeira River in Rondônia,Brazil

We characterize the vegetation types of the upper basin of the Madeira River in the Brazilan state of Rondônia, a biodiverse region with elevated rates of habitat loss. Vegetation and environmental parameters were recorded from 37 observation points distributed along and near a 160 km stretch of the Madeira River and representing the range of regional environments. Analysis of structure and floristic variables, as well as associated edaphic attributes and water table fluctuation, permitted recognition of five main vegetation types and seven subtypes. Open Ombrophilous Forest was the most frequently encountered vegetation type and occurred on well-drained, nutrient-poor soils, whereas Dense Ombrophilous Forest was seldom recorded. Alluvial Ombrophilous Forests (várzea) were found along a narrow strip of land along the banks of the Madeira River on the most fertile soils in the study area. Semideciduous Forests were found on small areas of rocky outcrops with shallow soils and reduced water availability during the dry season. Campinaranas, which range from open savanna physiognomies to closed canopy forests, were found to be a key environment in the lowlands south of the Madeira River on silty hydromorphic soils, where they harbor a peculiar flora tolerant of flooding during the rainy season. Our classification of the main vegetation types in the upper Madeira River illuminates a high degree of floristic and environmental heterogeneity in a highly threatened region. Our results will be useful for designing conservation strategies aimed at protecting the full range of floristic diversity present in the region.     

Environmental and spatial variables influence the composition of frog assemblages in sub-tropical eastern Australia

In community ecology, contrasting theories suggest that the distribution and abundance of species, and thus the composition of assemblages, are influenced by i) environmental gradients, or ii) contagious biotic processes such as predation, competition, dispersal and disease. In the former case, sites with similar environments would tend to support similar assemblages, while in the latter, geographically proximate sites would tend to support more similar assemblages than widely separated sites. I investigated the relative influence of environmental variables and spatial position on the composition of frog assemblages at forest streams in sub-tropical eastern Australia using redundancy analysis (RDA) and partial RDA. Data on the maximum abundance of the frog species at 65 survey sites were transformed such that RDA would yield the Hellinger distance between sites. The following analysis identified 11 environmental variables that explained 45% of the variation in the abundance of species at the survey sites (the species matrix), as a proportion of total variance. The geographic co-ordinates of the survey sites accounted for 12%, while the environmental and spatial variables combined accounted for 47% of the variation in the species matrix. Partial redundancy analysis indicated that of the explained variation, 74% was purely environmental, 5% was purely spatial and 21% was spatial environmental variation. This study is the first to quantify the relative influence of environmental and spatial variables on the composition of amphibian assemblages. It provides support for both the environmental control model and the biotic control model of species' distributions and assemblage composition, although environmental variables appear to have the greater effect at this scale of analysis.     

Structure and Spatial‐Temporal Dynamics of Chironomidae Fauna (Diptera) in Upland and Lowland Fluvial Habitats of the Chocancharava River Basin (Argentina)

Structure of benthic Chironomidae assemblages and their spatial‐temporal dynamic were analyzed in upland and lowland habitats from the Chocancharava River basin (Córdoba, Argentina). Sampling was performed in three tributary streams and in three lowland reaches of the river during high and low rainfall periods. Characteristic taxa of upland and lowland reaches and of the different habitats in these reaches were identified using the IndVal method. Chironomidae assemblages were different between upland and lowland reaches and among habitats in each reach, as assessed by Multiresponse Permutation Procedure and Canonical Correspondence Analyses. Substrate type and current velocity were the major explanatory variables structuring the assemblages in upland reaches whereas in lowland reaches current velocity and aquatic vegetation were the most important variables. The highest richness was found in the most complex habitat units in both upland and lowland stretches as assessed by Analyses of Variance. Chironomidae larvae responded to longitudinal changes of hydraulic variables and to local variations of fluvial habitats at different reaches. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Metacommunity structure of aquatic gastropods in a river floodplain: the role of niche breadth and drift propensity

相似文献   

The roles of environment,site position,and seasonality in taxonomic and functional organization of chironomid assemblages in a heterogeneous wetland,Kis-Balaton (Hungary)

Environmental heterogeneity plays a determinant role in structuring taxonomic and functional composition of local assemblages via various interacting processes as synthesized in the metacommunity theory. In this study, we evaluate the relative roles of local environmental and landscape filters, spatial constraints and seasonality in organization of assemblages of Chironomidae (Diptera), a diverse aquatic insect group with winged adults, in an extremely heterogeneous wetland system, Kis-Balaton, Hungary. As expected, local environmental variables explained a substantial proportion of assemblage variance mainly along sediment structure, macrophyte coverage, and decomposing plant matter gradients. Considering the narrow spatial range of the study area, pure spatial influence was unexpectedly strong, likely because of the dispersal limitation related to tall terrestrial vegetation patches and mass effect related to the uneven distribution and area of certain microhabitats and their species pools. However, landscape- and season-related variability proved to be low or negligible. Taxonomic and functional feeding guild (FFG)-based approaches revealed the same main trends in assemblage data; however, FFGs seemed to track environmental changes more tightly. We argue for the common use of taxonomic and functional-based approaches and advise the improvement of species optima and tolerance spectra databases to expand bioassessment power.

     

Different roles of environmental variables and spatial factors in structuring stream benthic diatom and macroinvertebrate in Yangtze River Delta,China

Exploring the relative contribution of spatial factors and environmental variables in shaping communities is of widespread interest in biodiversity conservation and environmental management. Stream communities are hierarchically regulated by environmental variables over multiple spatial scales, and the reaction of different organisms to stressors are still equivocal. We sampled both macroinvertebrates and diatom at 80 sites and additional 10 sites for macroinvertebrates, field measured and laboratory analyzed environmental variables, from the tributaries of Qiantang River, Yangtze River Delta China in 2011. We used PCNM (principal coordinates of neighbor matrices) to generate spatial predictors. We applied redundancy analysis and variation partitioning procedures to identify key spatial and environmental factors, and to quantify their relative roles in shaping diatom and macroinvertebrate assemblages. Our results demonstrated the role of spatial and environmental variables differed in shaping benthic diatom and macroinvertebrate. Diatom assemblage variations were better explained by spatial factors, however macroinvertebrate assemblage variations were better explained by environmental variables. In terms of environmental variables, catchment scale variables (e.g., land use estimators, land use diversity) played the primary role in determining the patterns of both diatom and macroinvertebrate assemblages, whereas the influence of reach-scale variables (e.g., pH, substrates, and nutrients) appeared less. However, nutrients were the stronger factors influencing benthic diatom, whereas physical habitat (e.g., substrates) played more important role than water chemistry in structuring macroinvertebrates. Our results provided more evidence to the incorporation of spatial factors interpreting spatial patterns of stream organisms, and highlighted the useful of multiple organisms and environmental variables at different spatial scales in diagnosing mechanism of stream degradation and in building a sound stream conditions monitoring program for Yangtze River Delta.     

赣江水系大型底栖动物多样性与受胁因子初探

赣江是长江的第七大支流, 孕育了极为丰富的大型底栖动物多样性, 而相关的研究明显不足。基于文献调研和2016-2017年现场调查, 本研究系统评估了赣江水系大型底栖动物多样性及其受胁因素。共记录底栖动物5门10纲27目95科204属330种(历史记录138种, 2016-2017年记录267种)。历史记录中国特有软体动物计48种(腹足类17种, 双壳类31种), 目前记录32种。优势种主要是一些耐污种和广布种。中游支流的密度、生物量和丰富度指数要高于赣江干流、上游支流和下游支流。典范对应分析结果表明, 底栖动物的分布主要受海拔、基质、流速、浊度、挖沙等环境因子以及不同尺度空间因子的驱动。偏CCA结果显示, 环境过滤对群落结构的影响高于空间过程。本研究结果可为赣江流域水生生物的保护和管理提供科学依据。     

Altitudinal gradients in stream fish diversity and the prevalence of diadromy in the Sixaola River basin,Costa Rica

Landscape-scale patterns of freshwater fish diversity and assemblage structure remain poorly documented in many areas of Central America, while aquatic ecosystems throughout the region have been impacted by habitat degradation and hydrologic alterations. Diadromous fishes may be especially vulnerable to these changes, but there is currently very little information available regarding their distribution and abundance in Central American river systems. We sampled small streams at 20 sites in the Sixaola River basin in southeastern Costa Rica to examine altitudinal variation in the diversity and species composition of stream fish assemblages, with a particular focus on diadromous species. A set of environmental variables was also measured in the study sites to evaluate how changes in fish assemblage structure were related to gradients in stream habitat. Overall, fish diversity and abundance declined steeply with increasing elevation, with very limited species turnover. The contribution of diadromous fishes to local species richness and abundance increased significantly with elevation, and diadromous species dominated assemblages at the highest elevation sites. Ordination of the sampling sites based on fish species composition generally arranged sites by elevation, but also showed some clustering based on geographic proximity. The dominant gradient in fish community structure was strongly correlated with an altitudinal habitat gradient identified through ordination of the environmental variables. The variation we observed in stream fish assemblages over relatively small spatial scales has significant conservation implications and highlights the ecological importance of longitudinal connectivity in Central American river systems.     

珠江水系鱼类群落多样性空间分布格局

珠江是我国南方第一大河,是我国重要淡水渔业生产基地和水生生物资源基因库。珠江鱼类在维持生物多样性、提供鱼类种质资源方面举足轻重。但是到目前为止,关于其鱼类空间分布格局的研究甚少。特别是近几十年来各种水工建设和过度捕捞使得渔业资源急剧衰退,鱼类空间分布的研究显得尤为重要。2015年对珠江全流域13个站位进行了全面调查,共采集渔获物10119尾,隶属于94种72属17科。鲤科鱼类占显著优势,其次种类较多的依次为鲿科、鳅科。采用非度量多维标度排序(NMDS)方法对鱼类群落空间分布特征进行了分析,结果表明珠江鱼类被划分为3个类群,即以餐、南方拟餐、黄颡鱼等小型鱼类为主的中上游类群、以赤眼鳟、鲮鱼、广东鲂等中型鱼类为主的中下游类群和以罗非鱼为主的重要支流类群。同时发现中下游物种多样性高,上游及河口江段多样性低的格局。采用冗余分析方法(RDA)分析了鱼类多样性与环境因子的关系,发现年均气温、降雨量、年均径流量、河流宽度与透明度是珠江水系河流鱼类群落结构差异的主要影响因子,其中年均气温是影响鱼类群落分布的最关键因子之一。与历史资料对比后发现,珠江鱼类种类明显减少、空间分布也发生了巨大改变。研究是珠江水系野生渔业资源长期调查的一部分,研究结果将对渔业资源的多样性保护和可持续利用具有指导意义。     

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.     

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.

     

Environmental filtering and spatial effects on metacommunity organisation differ among littoral macroinvertebrate groups deconstructed by biological traits

We examined spatial and environmental effects on the deconstructed assemblages of littoral macroinvertebrates within a large lake. We deconstructed assemblages by three biological trait groups: body size, dispersal mode and oviposition behaviour. We expected that spatial effects on assemblage structuring decrease and environmental effects increase with increasing body size. We also expected stronger environmental filtering and weaker spatial effect on the assemblages of flying species compared with assemblages of non-flying species. Stronger effect of environmental filtering was expected on the assemblages with species attaching eggs compared with assemblages of species with free eggs. We used redundancy analysis with variation partitioning to examine spatial and environmental effects on the deconstructed assemblages. As expected, the importance of environmental filtering increased and that of spatial effects decreased with increasing body size. Opposite to our expectations, assemblages of non-flying species were more affected by environmental conditions compared to assemblages of flying species. Concurring with our expectations, the importance of environmental filtering was higher in structuring assemblages of species attaching eggs than in structuring those with freely laid eggs. The amount of unexplained variation was higher for assemblages with small-sized to medium-sized species, flying species and species with free eggs than those with large-sized species, non-flying species and species with attached eggs. Our observations of decreasing spatial and increasing environmental effects with increasing body size of assemblages deviated from the results of previous studies. These results suggest differing metacommunity dynamics between within-lake and among-lake levels and between studies covering contrasting taxonomic groups and body size ranges.