Fish assemblages in Atlantic Forest streams: the relative influence of local and catchment environments on taxonomic and functional species

Streams are under environmental pressures acting at different scales that influence the ecological organisation of their fish assemblages. However, the relative influence of the different scale‐related variables on assemblage composition and function is poorly understood. We evaluated the importance of local‐ and catchment‐scale environmental variables, as well as the spatial structure of the sampling sites, in shaping fish assemblages in Atlantic Forest streams. Local‐scale variables were those measured at the sampling sites, describing the local habitat conditions (e.g. depth, substrate type, altitude). Catchment‐scale variables were those integrating the upstream landscape of the sampling sites (e.g. catchment land use). Spatial distances were calculated from watercourse distance using principal coordinates of neighbour matrices. Altogether, 28 local and seven catchment variables were initially subjected to two processes of eliminating co‐linearity. Redundancy analysis was applied to the three matrices (spatial, local and catchment) to quantify the variance in the structure of the fish assemblages explained by each matrix. Local variables explained more variability in both taxonomic and functional assemblage structure, than catchment and spatial variables. Local variables also changed along the longitudinal gradient, which consequently influenced fish assemblage structure. This pattern was also influenced by anthropogenic alteration and non‐native species, which were more abundant in downstream sites. These results highlight the need to assess Atlantic Forest streams under different environmental scales, especially through the use of quantitative local‐scale metrics, and to consider the effects of longitudinal patterns in structuring fish assemblages when developing and implementing monitoring programmes, impact studies and conservation plans.     

The relative influence of spatial context and catchment‐ and site‐scale environmental factors on stream fish assemblages in a human‐modified landscape

Abstract – Environmental factors act in a hierarchical manner at multiple spatial scales to influence the organisation of ecological assemblages; however, the relative influence of the different scale‐related factor groups is poorly known. We evaluated the importance of catchment‐scale and site‐scale environmental variables, as well as the spatial context of the sampling sites, in shaping stream fish assemblages in an agriculture‐dominated landscape in Hungary. Beside the variables describing spatial context (principal coordinates of a truncated distance matrix among sites), altogether 60 environmental variables were used to predict variability using a variance‐partitioning procedure in redundancy analysis. Presence–absence‐ and relative abundance‐based data were examined at two assemblage levels (entire assemblage and native assemblage) at 54 stream sites. Incorporation of spatial variables increased largely the total explained variability in case of relative abundance, but not for presence–absence data. Of the environmentally explained variance, catchment‐scale variables (e.g., land cover types, patch density) were relatively more influential for the native assemblage‐level analyses, than for analyses at the entire assemblage level, where site‐scale variables (e.g., altitude, depth) proved to be more influential. In addition, pure catchment‐ and pure site‐scale variables have the primary role in determining fish assemblage patterns, whereas the influence of shared variance and that of site‐scale riparian variables proved to be less important. Our findings demonstrate the importance of incorporating the spatial context of the sampling sites in predicting fish assemblage patterns and the effects of channelisation (dikes) in shaping assemblage–environment relationships in this human‐influenced landscape.     

Geographic, terrestrial and aquatic factors: which most influence the structure of stream fish assemblages in the midwestern United States?

Abstract – Effects of environmental or landscape factors on species composition, species richness and complexity of fish assemblages were examined using our collections of fish from 65 sites on streams in 13 drainages across the midwestern United States. Effects of environmental factors were examined at three scales: broad geographic factors included drainage, latitude, and longitude; local terrestrial factors included features of the riparian zone adjacent to the collecting site as well as local climate and land use; within-stream aquatic factors related to structure and hydrology of the stream reach sampled. Each assemblage property was examined for its relationship to factors at each scale separately, and then for relative importance of all factors found to be significant in the separate analyses. Assemblage composition (summarized as sample scores on two axes of a detrended correspondence analysis) varied significantly as a function of factors at all three scales when each scale was considered separately. With simultaneous consideration of all scales, however, only broad geographic factors (particularly latitude) and local terrestrial factors explained significant variation in assemblage composition. Species richness (the number of species we captured) was explained by longitude and within-stream aquatic factors both when considered separately and together. Assemblage complexity (quantified as slope of relative abundance versus rank abundance) was only related to within-stream aquatic factors. Assemblage composition and emergent assemblage properties (richness and complexity), therefore, were explained by factors acting at different scales. The total variation explained for assemblage composition was much greater than that explained for emergent assemblage properties, suggesting that assemblage composition may vary more as a function of environmental and landscape factors than do species richness and complexity. ^NOTE     

Land cover,riparian zones and instream habitat influence stream fish assemblages in the eastern Amazon

The Amazon rainforest has experienced rapid land‐use changes over the last few decades, including extensive deforestation that can affect riparian habitats and streams. The aim of this study was to assess responses of stream fish assemblages to deforestation and land cover change in the eastern Amazon. We expected that percentage of forest in the catchment is correlated with local habitat complexity, which in turn determines fish assemblage composition and structure. We sampled 71 streams in areas with different land uses and tested for relationships between stream fish assemblages and local habitat and landscape variables while controlling for the effect of intersite distance. Fish assemblage composition and structure were correlated with forest coverage, but local habitat variables explained more of the variation in both assemblage composition and structure than landscape variables. Intersite distance contributed to variance explained by local habitat and landscape variables, and the percentage of variance explained by the unique contribution of local habitat was approximately equivalent to the shared variance explained by all three factors in the model. In these streams of the eastern Amazon, fish assemblages were most strongly influenced by features of instream and riparian habitats, yet indirect effects of deforestation on fish assemblage composition and structure were observed even though intact riparian zones were present at most sites. Long‐term monitoring of the hydrographic basin, instream habitat and aquatic fauna is needed to test for potential legacy effects and time lags, as well as assess species responses to continuing deforestation and land‐use changes in the Amazon.     

Habitat relationships with fish assemblages in minimally disturbed Great Plains regions

Abstract – Effects of local environmental influences on the structure of fish assemblages were evaluated from 159 sites in two regions of the Great Plains with limited anthropogenic disturbance. These regions offered an opportunity to evaluate the structure and variation of streams and fish assemblages within the Great Plains. We used canonical correspondence analyses to determine the influence of environmental conditions on species abundances, species occurrences and assemblage characteristics. Analysis of regions separately indicated that similar environmental factors structured streams and fish assemblages, despite differences in environmental conditions and species composition between regions. Variance in fish abundance and assemblage characteristics from both regions was best explained by metrics of stream size and associated metrics (width, depth, conductivity and instream cover). Our results provide a framework and reference for conditions and assemblage structure in North American prairie streams.     

Relative influences of catchment‐ and reach‐scale abiotic factors on freshwater fish communities in rivers of northeastern Mesoamerica

Esselman PC, Allan JD. Relative influences of catchment‐ and reach‐scale abiotic factors on freshwater fish communities in rivers of northeastern Mesoamerica. Ecology of Freshwater Fish 2010: 19: 439–454. © 2010 John Wiley & Sons A/S Abstract – While the abiotic factors important to freshwater fish assemblages at a reach scale are well understood, studies of larger scale constraints have yielded variable conclusions, spurring a need for further studies in new biogeographic contexts. This study investigated the importance of catchment‐ and reach‐scale abiotic factors to variation in freshwater fish assemblages in rivers of northeastern Mesoamerica. Abiotic variables and fish data from 72 sampling sites on main stem rivers of Belize were used with partial constrained ordination to determine the proportion of spatially structured and unstructured variation in fish presence and absence, relative abundance, and community metrics explained by catchment‐ and reach‐scale environmental factors. Results showed that, combined, catchment and reach variables explained a large portion of the total variation in the fish assemblage data (54–75%), and that catchment environment explained a greater portion of variation (42–63%) than reach environment (34–50%). Variables representing landscape position (local elevation, watershed area) and their reach‐level correlates (channel width, depth variation, and substrate) correlated strongly to the fish assemblage data. Our results suggest that landscape‐scale factors have a stronger relative influence on assemblages than environmental conditions at the reach scale within our study area. These results contrast with past findings that showed greater local scale influence in landscapes with low anthropogenic disturbance levels. Our findings suggest that biodiversity conservation efforts should consider assemblage variation across a longitudinal gradient, and that a multi‐catchment region is a biologically relevant scale for fish conservation planning and coordination in northeastern Mesoamerica.     

Fish assemblages structure and function along environmental gradients in rivers of Gabon (Africa)

Abstract –  We examined patterns in fish species assemblages structure and function along environmental gradients in rivers of Gabon. Species presence–absence data from 52 sites were first analysed by canonical correspondence analysis. Results showed that the position of sites along the upstream–downstream gradient, together with elevation and water conductance were the most important predictors of local fish assemblage composition. Assemblage richness and trophic structure were further investigated using regression tree analysis. Results revealed a general increase in species richness from upstream to downstream areas and a transition from insectivorous to omnivorous, herbivorous and piscivorous species along this longitudinal gradient. There were several similarities between these previous patterns and those observed in other temperate streams suggesting a potential convergence in fish assemblage along environmental gradients in tropical and temperate riverine systems. From a conservation standpoint, these results highlight the need to evaluate all habitat types along rivers longitudinal gradient to integrate the full spectrum of species assemblages within conservation plans.     

Seasonal and spatial variation in a prairie stream-fish assemblage

Abstract – Stream-fish assemblage and environmental data for 13 sites in the upper Brazos River, Texas, USA during 1997 and 1998 were used to assess the relationship between environmental conditions, and seasonal and spatial variation in fish species abundance and distribution patterns. There was considerable spatial variation in environmental conditions among sites. Spatial variation in species diversity and species composition was related to variation in conductance (salinity), depth and current velocity among sites and streams. Species diversity increased downstream and species composition shifted from primarily cyprinodontids upstream to cyprinids downstream. Among all dominant species, spatial components of variation in fish abundance were greater than seasonal components, suggesting that assemblage structure is determined more by average or persistent differences in environmental conditions among sites than by seasonal variation in environmental conditions.     

The landscape genetics of syntopic topminnows (Fundulus notatus and F. olivaceus) in a riverine contact zone

The metapopulation dynamics of a species are influenced by the spatial arrangement of preferred habitats across a landscape. Increasing habitat patchiness can result in greater population subdivision, leading to more pronounced population genetic structure. Therefore, even subtle differences in habitat preferences among species could lead to substantial differences in genetic structure. Members of the Fundulus notatus species complex of topminnows include a headwater specialist and a large river specialist with broadly overlapping geographical distributions. Both species are often found in the same drainage systems, but partially isolated by divergent habitat preferences. The purpose of this research was to determine whether distribution along a stream continuum in a contact zone influences population genetic patterns in two species of topminnow (Fundulus olivaceus and Fundulus notatus). Fish were collected in the summers of 2010–2012, and habitat data were collected in summer 2012, within all major tributaries of the Saline River in southern Illinois. In total, 523 fish were genotyped using seven microsatellite loci to assess genetic variation. Species distributions in F. notatus and F. olivaceus were associated with habitat factors that covaried with cumulative drainage area. Populations of F. olivaceus showed a greater level of genetic structure reflected in a significant pattern of isolation by distance, while populations of F. notatus showed no such pattern. Spatial autocorrelation analysis revealed that at an individual level, both species became increasingly divergent with waterway distance. Overall, clear interspecific differences in habitat preferences were translated into measurable but relatively subtle differences in population genetic structure.     

长江安庆新洲江段仔稚鱼的群聚特征

安庆新洲江段是长江下游典型的干流-沙洲生境,为掌握该水域仔稚鱼群聚特征,于2018年4月15日—8月4日开展了逐日调查。调查期间,共采集鉴定仔稚鱼121246尾,隶属于6目8科34种,贝氏䱗（）为第一优势种。新洲南汊、北汊分别采集仔稚鱼79338尾和41908尾,数量占比依次为65.44%和占34.56%。所有渔获物中,产漂流性卵鱼类物种数最多（16种,47.06%）,产浮性卵鱼类数量最多（92623尾,76.39%）。就时间特征而言,南汊、北汊仔稚鱼丰度日变化趋势基本一致,表现出与水位上涨高度关联,共监测到三次高峰,其中7月13日达到峰值（2001.28 ind/100 m³）;就空间特征而言,近岸采样点丰度高于河道中泓采样点,南汊丰度总体高于北汊。冗余分析结果显示,与新洲江段仔稚鱼丰度相关性较强的环境因子为水位、浊度、水温和透明度,其中水位为主要的正相关因子。空间尺度的聚类分析将新洲江段6个采样点分为3个群组,表明新洲江段不同采样点仔稚鱼群聚结构差异显著（=0.017）。研究表明,安庆新洲江段仔稚鱼补充量显著大于上游输入量,新洲对该江段仔稚鱼群聚特征具有显著影响,总体表现为南汊的鱼类繁殖条件显著优于北汊。研究结果补充了安庆新洲江段鱼类早期资源的基础数据,为长江下游渔业资源评估与保护提供了依据。     

The role of oceanographic conditions and plankton availability in larval fish assemblages off the Catalan coast (NW Mediterranean)

In the northwestern Mediterranean, most fish species reproduce in early summer and fewer in the autumn mixing period. This study analyses and compares larval fish assemblages (LFA) in both seasons, and is the first attempt to characterize LFA structure for the autumn period. We analyze horizontal and vertical distribution of fish larvae and the micro- and mesozooplankton biomass and abundance of the main zooplankton groups. The oceanographic situation was analyzed through the study of data from CTD, Nν-Shuttle and ADCP surveys. LFA were determined by ordination analyses based on larval abundance, and the relationships between larval assemblages and environmental variables were investigated through canonical correspondence analysis. The importance of some hydrographic variables (temperature, salinity and stability of the water column), current fields (along-shelf and across-shelf transport) and the abundance of zooplankton are discussed as important factors shaping the structure of larval assemblages. In early summer, LFA were mainly structured by a combination of bathymetry and trophic components, although sea surface temperature also played a role in shaping the horizontal larval distributions. In autumn, trophic variables were the main factors influencing the shelf-dwelling species assemblage. Larvae of oceanic species, on the other hand, were not related to trophic variables but were more affected by current fields.     

Seasonal variation in habitat use by marsh fishes

Abstract— We used I-m² throw traps to examine habitat use by smallsized fishes within a mosaic of wet prairies and sloughs in the headwaters of the St. Johns River, Florida between August 1992 and November 1995. Estimates of total fish density and biomass varied temporally, but did not differ significantly between habitats. Patterns of habitat use, however, differed among the five numerically dominant species. Bluefin killifish, mosquitofish, and golden topminnows were more abundant in sloughs than in wet prairies. In contrast, Everglades pygmy sunfish were more abundant in wet prairies than in sloughs. Finally, the abundance of least killifish did not differ between habitats. Fish densities were positively correlated with plant biomass (i. e., habitat complexity) and negatively correlated with water depth (i. e., hydrology). Species richness and composition were similar among habitats. However, consistent differences in the relative abundance of numerically dominant species between habitats indicated some degree of habitat-specific assemblage structure. Most species were concentrated into deeper sloughs during drying events. This assemblage of small-sized fishes appears to respond relatively rapidly to changes in habitat structure and hydrologic conditions. We therefore recommend that resource managers consider using fishes as indicator taxa to evaluate the efficacy of ongoing restoration and management efforts in wetland systems.     

Influence of offshore breakwaters on fish assemblage structure in the surf zone of a sandy beach in Tokyo Bay,central Japan

To determine the effects of shore-parallel offshore breakwaters on the surf-zone fish assemblage structure of a sandy beach, three study sites (sheltered inshore of breakwater, between adjacent breakwaters, and exposed without breakwaters) were sampled at Ohnuki Beach in Tokyo Bay, central Japan, in September and December 2009 and March and June 2010. Although some physical variables (wave height, turbidity, and water depth) differed among the three sites, no differences were apparent among the sites in the numbers of fish species and individuals, or in the abundance of epibenthic invertebrates (a main fish prey). In addition, species and individual numbers of two dominant feeding groups (mysid and copepod feeders) showed no significant among-site differences. Cluster and ordination analyses confirmed the similarity in fish species composition among the three sites. Furthermore, the mean standard length of all fishes collected throughout the study period did not differ significantly among the sites, the overall results indicating that the presence of breakwaters had little effect on surf-zone fish assemblage structure in the study area, despite some breakwater-related differences in the abiotic environment.     

基于河流网络体尺度的皖河河源溪流鱼类群落的空间格局

2013年7-8月对大别山皖河河源1～3级溪流的鱼类进行了调查,着重从河流网络体空间尺度研究了鱼类多样性及群落结构的空间格局,探讨了局域栖息地条件和支流空间位置对鱼类群落的影响.1～3级溪流间,鱼类物种数随溪流级别增大显著增多,但个体数无显著变化(P＞0.05);长河、潜水和皖水3条支流间鱼类物种数和个体数均无显著差异(P＞0.05).鱼类物种数受局域栖息地条件(海拔)和支流空间位置(河流级别和下游量级)的联合影响,但鱼类个体数仅受局域栖息地条件(海拔)的影响.不同溪流级别和不同支流间的群落结构均无显著差异(P＞0.05).同物种数类似,鱼类群落结构也受局域过程(海拔)和空间过程(汇合量级和下游量级)的联合影响.本研究表明,总体上皖河河源溪流网络体中的鱼类群落是局域过程和空间过程联合作用的产物.因此,为合理保护和管理皖河河源的溪流鱼类物种,有必要兼顾局域栖息地条件与河流网络连通性的保护和恢复.     

Relative importance of local and landscape variables on fish assemblages in streams of Brazilian savanna

Understanding variability in the composition of aquatic assemblages requires a multiscale perspective, since processes operating at different spatial scales (from regional to local) drive the community assembly. Here, the relative importance of environmental variables on fish species composition in streams of the Brazilian savanna (Cerrado) is assessed and quantified at local and landscape scales. The importance of both local and landscape environmental variables in structuring fish assemblages was supported. Local variables explained a substantially higher amount of variance of fish assemblages than landscape variables. However, the shared explanation indicate that landscape variables had a complementary effect. The streams sampled were mostly headwaters at similar altitudes and with similar watershed sizes, so the sensitivity of the fish assemblages, even to small landscape gradients, is highlighted. Maintaining these important instream habitat characteristics close to natural conditions seems to be essential for conserving stream fish species, and for this, the landscape context should be taken into account. Considering the near‐pristine condition of the streams studied, these findings can be used as a reference for further studies addressing the effects of human modifications on stream fish biodiversity of the Cerrado.     

杭州湾—舟山近海春季游泳动物群落结构及与环境因子的关系

杭州湾—舟山近海是许多经济鱼类的传统产卵地和栖息地,环境因子对鱼类群落结构的影响非常显著。本研究根据2016年春季在杭州湾—舟山近海的80个站位的底拖网调查数据,分析了鱼类及大型甲壳类群落数量和平均个体大小的空间分布,并根据典范对应分析法(CCA)研究了鱼类及大型甲壳类主要类群的特征(丰度和个体大小)与环境因子的关系。结果显示,游泳动物可分为5大类群(六丝钝尾虾虎鱼、底层鱼、中上层鱼、虾、蟹),每种类群的丰度平均分别为546、213、83、316和15个/h,平均个体大小分别为0.29、2.19、4.96、0.36和6.66 g/个。根据各类群的丰度、底温、底盐及表层浑浊度,将整个海域分为杭州湾内和舟山近海水域,绝大部分类群的丰度具有显著的区域差异性,而绝大部分类群的个体大小没有区域差异性。受到浑浊度、外海水团交汇的影响,绝大部分类群主要聚集在舟山近海的高生产力水域。CCA分析表明,2个轴的环境因子能解释丰度总变异的25%,而仅能解释个体大小总变异的11.7%,说明环境因子对于鱼类及甲壳类的类群的数量空间分布具有较大影响,而对于个体大小的分布影响较小。     

Evaluating habitat associations of a fish assemblage at multiple spatial scales in a minimally disturbed stream using low‐cost remote sensing

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胶州湾及其邻近海域鱼类群落结构及与环境因子的关系

 为了进一步研究胶州湾及其邻近水域鱼类群落结构及与环境因子的关系, 本文根据2011年冬季(2月)、春季(5月)、夏季(8月)和秋季(11月)在胶州湾及其邻近海域进行的渔业资源和环境调查数据, 应用相对重要性指数、生态多样性指数和多元分析方法等研究了胶州湾鱼类群落结构及其季节变化, 并分析了胶州湾鱼类群落结构与主要环境因子的关系。结果表明: 本次调查共捕获鱼类57种, 隶属于2纲10目31科46属, 种类组成以暖温性和暖水性鱼类为主。主要优势种有方氏云鳚(Pholis fangi)和六丝钝尾虾虎鱼(Amblychaeturichthys hexanema)等。胶州湾鱼类群落物种丰富度指数D的季节变化范围为1.02~1.65, 多样性指数H’变化范围为1.36~1.73, 均匀度指数J′变化范围为0.61~0.76。方差分析表明, 丰富度指数的季节变化显著, 而均匀度指数J′和多样性指数H′无显著性季节变化。单因子相似性(ANOSIM)分析表明, 胶州湾鱼类群落结构和种类组成存在明显的季节更替现象。相似性百分比分析(SIMPER)表明, 方氏云鳚、六丝钝尾虾虎鱼、细纹狮子鱼、斑、赤鼻棱鳀和皮氏叫姑鱼等是造成群落结构季节变化的主要分歧种。典范对应分析表明, 影响胶州湾及其邻近海域鱼类群落结构的主要环境因子为水温、盐度和pH, 其次是底质类型, 条件效应分别为0.310、0.084、0.176和0.256。本研究旨在通过分析胶州湾鱼类群落结构和多样性特征及其与环境因子的关系, 为胶州湾渔业资源的保护和可持续利用提供科学依据。

     

Assemblage patterns of fish functional groups relative to habitat connectivity and conditions in floodplain lakes

Miyazono S, Aycock JN, Miranda LE, Tietjen TE. Assemblage patterns of fish functional groups relative to habitat connectivity and conditions in floodplain lakes.
Ecology of Freshwater Fish 2010: 19: 578–585. © 2010 John Wiley & Sons A/S Abstract – We evaluated the influences of habitat connectivity and local environmental factors on the distribution and abundance patterns of fish functional groups in 17 floodplain lakes in the Yazoo River Basin, USA. The results of univariate and multivariate analyses showed that species–environmental relationships varied with the functional groups. Species richness and assemblage structure of periodic strategists showed strong and positive correlations with habitat connectivity. Densities of most equilibrium and opportunistic strategists decreased with habitat connectivity. Densities of certain equilibrium and opportunistic strategists increased with turbidity. Forested wetlands around the lakes were positively related to the densities of periodic and equilibrium strategists. These results suggest that decreases in habitat connectivity, forested wetland buffers and water quality resulting from environmental manipulations may cause local extinction of certain fish taxa and accelerate the dominance of tolerant fishes in floodplain lakes.