Hierarchical spatial patterns and drivers of change in benthic macroinvertebrate communities in an intermittent Mediterranean river

• 1. The imminent damming of the Odelouca River, an intermittent Mediterranean river situated in the south‐west Algarve region of Portugal with valuable stands of riparian vegetation, has called for the compulsory implementation of compensatory measures.
• 2. In order to assess the primary environmental and human factors that drive change in the benthic macroinvertebrate assemblages of the Odelouca, and the spatial scale at which they occur, 30 sites were sampled for benthic macroinvertebrates and extensively surveyed using River Habitat Survey (RHS) in spring 2005.
• 3. A hierarchical cluster analysis of selected physical and RHS variables clearly indicated gradients of habitat quality (instream and riparian corridor) along both main channel and tributaries. Analysis of macroinvertebrate metrics by parametric and non‐parametric ANOVA showed the derived clusters of groups to be biologically distinct.
• 4. From a total of 64 variables, divided into two explanatory variable groups (environmental or pressure) over three spatial scales (habitat, reach and basin), just 20, predominantly environmental, variables were retained for subsequent analyses.
• 5. Partial canonical correspondence analyses of the selected environmental and pressure variables over the defined spatial scales showed that environmental variables contributed most significantly over all of the spatial scales and that pressure variables related to land‐use only contributed significantly at the level of the river basin.
• 6. Variables recorded by RHS contribute successfully to the detection of habitat quality gradients in a Mediterranean river system and the strongest drivers of macroinvertebrate change are primarily, but not exclusively, environmental factors occurring at middle and higher spatial scales.
• 7. Compensatory measures must therefore be implemented across a range of spatial scales, taking into account abiotic and biotic processes characteristic of disturbance‐driven Mediterranean systems that contribute to habitat heterogeneity and quality and confer functional and trophic diversity to the macroinvertebrate assemblages.

Copyright © 2007 John Wiley & Sons, Ltd.     

Patterns and predictors of fish dispersal in rivers

Quantifying fish dispersal and identifying its general predictors is key for understanding temporal patterns in population dynamics, emigration and immigration, meta‐community dynamics, many ecological processes and predicting recovery time or population responses to environmental changes. This is the first comprehensive quantitative meta‐analysis of heterogeneous freshwater fish movement, aiming to determine mobile and stationary shares of fish communities, their dispersal distances and key predictors of dispersal patterns. By reviewing and analysing 160 empirical data sets from 71 studies covering 62 fishes in streams, it goes beyond previous studies of salmonids’ heterogeneous movement. Based on fitted leptokurtic dispersal kernels, the movement distances of (i) a stationary component (σ_stat) and (ii) a mobile component (σ_mob) as well as the (iii) share of each component (p) were calculated. The median movement distance of the stationary and mobile component of a fish population was 36.4 and 361.7 m, respectively. The share of the stationary individuals was high (median = 66.6%), but unrelated to movement distance. Single and multiple linear regressions as well as mixed‐effects models revealed movement distances positively related to fish length, aspect ratio of the caudal fin, stream size and duration of the study. Furthermore, movement distance differed between taxonomic families. The quantitative parameters of heterogeneous fish movement provided are prerequisite to estimate time lags in fish response to river rehabilitation, temporal patterns in species dispersal, and minimum effective size of potential founder populations for species conservation and stock recovery based on minimum numbers of specimen to disperse.     

Relative influences of environmental and spatial factors on stream fish assemblages in Brazilian Atlantic rainforest

Understanding the role of local and spatial factors in the structuring of aquatic communities is a goal in ecology. The hierarchical structure of stream systems provides opportunities to test the hypothesis that fish assemblages that are more isolated in headwaters are structured by local and/or regional variables. Fishes and abiotic data were collected in 18 stream reaches from two hydrographic basins in the Brazilian Atlantic rainforest. The variance of species composition was partitioned into fractions explained by environmental and spatial factors. The pure environmental fraction explained ≈17% of variance and was represented by regional, habitat availability/heterogeneity and perturbation gradient. The pure spatial fraction explained ≈15% of the individual fraction. Environmental data revealed a species sorting process, and the spatial effect might be a result of different dispersal routes that fish performed during the formation of the hydrographic basins, actual land use and water resources management. The importance of maintaining connectivity in these systems was emphasised because it cannot be guaranteed that the dispersion ability of species is still occurring under current land use change.     

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.     

Density-dependent habitat selection and the ideal free distribution in marine fish spatial dynamics: considerations and cautions

Current methods and theory used in the study of the spatial dynamics of marine fish are problematic. Positive relationships between population abundance and occupied area are typically interpreted as evidence of density‐dependent habitat selection. However, both abundance and area may co‐vary with an un‐parameterized variable, such as a density‐independent effect. In addition, if density‐dependent habitat selection is present, population growth rates in optimal habitats would be expected to be lower than in marginal habitats. This same pattern can also evolve from a large‐scale, spatially autocorrelated change in a density‐independent factor. The theory underlying density‐dependent habitat selection, the ideal free distribution, can be tautological when no a priori information of how habitat suitability changes with density is known. In this case, an ideal free distribution can be defined for any pattern of habitat‐specific population growth rates. However, these problems are not insurmountable and solutions may be found by considering spatial variation in proxies of fitness and explicitly allowing for the relative importance of habitat selection (density dependent) and environmental (density independent) effects to vary with spatial scale.     

Distribution of aquatic plants in the Northern Vosges rivers: implications for biomonitoring and conservation

• 1. The continual confusion over the definition of the term ‘trophic status’ has led to ambiguous demonstrations of the influence of alkalinity versus inorganic N and P on aquatic plant distribution.
• 2. Data from the Northern Vosges rivers (sandstone geology) were reinvestigated to test whether it was possible to separate the effect of (i) spatial isolation from surface water chemistry, and (ii) alkalinity from inorganic N and P on aquatic macrophyte distribution.
• 3. Alkalinity and pH exerted the strongest influence on plant distribution, soluble reactive phosphorus (SRP) and pCO₂ being subordinate. The effect of spatial isolation between catchments was not significant, which may indicate that aquatic plants dispersed well over the area. The effect of longitudinal connectivity on species distribution was strong, although largely confounded by the effects of water chemistry and possibly other physical factors not recorded. The partial effect of SRP (after removing the effect of pH or alkalinity) was still significant. However this was not the case for NH₄.
• 4. The floristic composition was more likely to indicate the role played by alkalinity than inorganic P, with inorganic N being further subordinate. However, the causality of the significant relationships needs to be investigated further. This study questioned the validity of current macrophyte biomonitoring tools striving to indicate the concentrations of inorganic N and P.
• 5. More work is needed to quantify the role of connected and isolated aquatic habitats in the region, in order to understand how to maintain the species pool and to ensure that recolonization rates compensate for the losses due to disturbances. It is not clear how the vegetation would respond to inorganic P enrichment (or control), based on the individual species response observed here, and river P uptake studies from other rivers. Future monitoring should also include measurements of physical degradation.

Copyright © 2007 John Wiley & Sons, Ltd.     

Modelling spatial exclusion of a vulnerable native fish by introduced trout in rivers using landscape features: a new tool for conservation management

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Protected areas and frugivorous fish in tropical rivers: Small-scale fisheries,conservation and ecosystem services

1. Frugivorous fish provide often conflicting ecosystem services of seed dispersal and food provisioning in tropical rivers. Fishing may reduce the size and abundance of frugivorous fish, thus affecting their potential as seed dispersers, which could affect the conservation of these fish and of floodplain forests.
2. The goal of this study was to assess the influence of co-managed protected areas in the form of extractive reserves (RESEX) and small-scale fisheries on frugivorous fish in the Tapajós and Negro rivers, in the Brazilian Amazon. The study examined whether: (i) frugivorous fish are important for fisheries and selectively caught; and (ii) frugivorous fish abundance, size and fisheries catch per unit of effort are higher inside the RESEX than outside.
3. The analyses included fisheries-dependent data (3,753 fish landings) and independent data (12,730 sampled fish) collected in 16 fishing communities (eight for each river). In both rivers, frugivorous fish are among the 10 species caught the most and frugivorous biomass was proportionately higher in landings than in samplings, indicating fisheries selectivity towards these fishes.
4. In both rivers, catches of frugivorous fish were higher outside the RESEX than inside. Catch per unit effort and the proportion of frugivores in the catch were higher outside the RESEX in the Tapajós River but did not vary between sites inside and outside the RESEX in the Negro River. Frugivorous fish were larger inside the RESEX in the Negro, but smaller inside the RESEX in the Tapajós.
5. The results indicated that the ecosystem services of seed dispersal and food source provided by frugivorous fish are not in conflict in the tropical rivers studied. Therefore, these clearwater and blackwater rivers in the Brazilian Amazon show a balance between fisheries and conservation of frugivorous fish, which play an essential role in the functioning of tropical floodplain forest ecosystems.

     

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.     

The importance of spatial scales to analysis of fish diversity in Amazonian floodplain lakes and implications for conservation

The Amazon River Basin has the highest fish species diversity of any region in the world, but is under threat from anthropogenic perturbations including overharvesting, alien species and drought. We asked whether species diversity in this region is more a function of within‐lake species richness (i.e., α diversity) or differences among lakes (β diversity). Although many studies have reported on species richness and diversity in single habitats, the importance of measuring diversity at different spatial scales is not yet well established. We collected fish in 10 floodplain lakes along the Solimões River (Brazil), divided evenly between two lake types: those on islands in the river channel (island lakes) and those on the margins of the river (coastal lakes) during 2006. We partitioned fish diversity into three spatial scales: α = within each lake; β₁ = among lakes of the same type (coastal or island) and β₂ = between the two types of lakes, and compared their relative contributions to regional (γ) diversity. β₁ + β₂ contributed as much or more to γ diversity than did α. Although many of the 116 fish species were shared between lake types (S = 72), 32 species were found exclusively in coastal lakes and 12 species were found exclusively in island lakes. Coastal lakes, which were deeper and cooler than island lakes, consistently had higher fish species richness than island lakes. We suggest that it will be necessary to set areas large enough to contain multiple lakes of both types to preserve regional fish diversity.     

Modelling the habitat requirement of riverine fish species at the European scale: sensitivity to temperature and precipitation and associated uncertainty

Abstract – Species distribution models (SDMs) have been widely used for different purposes such as studying species niche or forecasting the effects of global change on species distribution. Nevertheless, these models are often calibrated on datasets that only cover a fraction of the species’ realised niches, which could lead to unrealistic results. The aim of this study was to model the habitat requirements of 21 freshwater fish species that are native to Europe, using a dataset that accurately reflects their realised niches. Both temperature and precipitation were used as climatic factors to model the habitat requirements of the species, and the uncertainty associated with the fitted environment–occurrence relationships was examined. The results demonstrated the importance of accounting for these two climatic components when estimating the habitat requirements of riverine fish species and whether the uncertainty associated with model expectations varies with the species and the environmental factor considered. These results are discussed with regard to the known ecology of the 21 riverine fish species and within the perspective of climate change.     

Influences of local habitat and stream spatial position on fish assemblages in a dammed watershed,the Qingyi Stream,China

Abstract – Identifying the underlying mechanisms that explain the spatial variation in stream fish assemblages is crucial for the protection of species diversity. The influences of local habitat and stream spatial position on fish assemblages were examined from first‐order through third‐order streams within a dammed watershed, the Qingyi Stream, China. Based on linear regression models, the most important environmental variables influencing fish species richness were water temperature and wetted width, but stream spatial position variables were less important. Using canonical correspondence analysis, five environmental variables were identified to significantly influence fish assemblages, including three habitats (elevation, substrate and water depth) and two spatial variables (C‐link and Link). Our results suggest that, in a heavily dammed watershed, by blocking the migration routes of fishes, dams weaken the influence of stream spatial position on fish species richness. However, fish species compositions are significantly influenced by both local habitat environment and stream spatial position, which is perhaps owing to the distribution of fish species according to ecological requirements not related to spatial processes.     

红枫湖鱼类资源及空间分布的水声学调查研究

于2010年9月～12月和2011年3月～6月对贵阳市红枫湖的鱼类资源进行了调查,捕获鱼类28种,分属于4目6科;鱼类的体长为5.68～116.41 cm,优势体长组为11.00～30.00 cm,其中小型鱼体和中大型鱼体占多数。2011年6月运用BioSonics DT-X（200 kHz）鱼探仪对鱼类密度进行了水声学探测,平均密度为（51.64±36.49）×10-3尾.m-3,不同区域的鱼类密度分布有显著性差异,最大值出现在将军湾[（97.25±12.35）×10-3尾.m-3],最低值位于红枫湖大坝[（14.90±2.56）×10-3尾.m-3],从大坝到将军湾鱼类资源量总体上呈现逐步增长的趋势。红枫湖鱼类分布水层主要在6～15 m,不同水层的鱼类密度分布存在显著差异。     

Environmental requirements and heterogeneity of rheophilic fish nursery habitats in European lowland rivers: Current insights and future challenges

The large-scale degradation of riparian ecotones and of the connectivity between rivers and their floodplains has resulted in a drastic decline of rheophilic fish populations in European temperate lowland rivers. Recent river restoration projects have had variable success in effectively restoring these fish populations. Knowledge on nursery habitat requirements is considered essential for effective population restoration. However, a detailed understanding of the role of habitat heterogeneity in young-of-the-year (YOY) fish population development is limited. Therefore, we carried out a synthesis of the available knowledge on nursery habitat requirements of rheophilic fish species found in European temperate lowland rivers (<200 m elevation). From a total of 603 papers, 77 studies with primary information were selected, containing 390 associations between habitat features and YOY fish. As expected, most studies focused on static components of physical riparian habitat. Generally, YOY fish require habitats of shallow depth (<0.5 m), with slow-flowing water (<0.2 m/s), gentle bank slope (<20°), variety in substratum types (fine sand to gravel), relatively warm water and high food availability. Surprisingly, no clear ontogenetic habitat shifts between larvae and juveniles were found, which may be explained by the limited spatial–temporal resolution of most studies. Since 2011, studies on habitat heterogeneity have increased, but few have explicitly assessed its role in relation to movement patterns of YOY fish for nursery success. Therefore, we recommend that future research focuses on fish movement patterns between habitat patches in heterogeneous (river-floodplain) environments, to increase the knowledge base for effective recovery of rheophilic fish populations.     

No room for dessert: A mechanistic model of prey selection in gut‐limited predatory fish

Predatory fish structure communities through prey pursuit and consumption and, in many marine systems, the gadoids are particularly important. These predators have flexible feeding behaviours and often feed on large prey items. Digestion times of large prey are usually longer than handling times, and gut processing limits feeding rate at high prey density. Optimizing the gut content mix can therefore be an important behavioural strategy. Here, we develop a foraging model that incorporates gut processing and use the model to disentangle internal and external limitations on feeding in the omnivorous cod (Gadus morhua, Gadidae). We extend the traditional definition of prey profitability to consider prey digestive quality, which we quantify for prey of Northeast Atlantic cod populations. We find an important role for gut limitation; within a range of ecologically relevant temperatures and prey densities, predicted feeding rates were strongly reduced compared to feeding constrained by external factors only, and the optimal diet composition under gut limitation differed from predictions from traditional foraging theory. Capelin, a main prey of Northeast Arctic cod, had the highest digestive quality of all prey across ecosystems, but the cold temperatures in the Barents Sea strongly limited feeding rate by slowing down digestion. Baltic cod fed on a higher proportion of poor‐quality prey compared to the other populations, contributing to its slow growth in relation to water temperature. Gut limitation is particularly important to consider in foraging models for fish with many alternative prey species or fish occupying cold waters where digestion is slow.     

北极阿拉斯加水域鱼类生态特征及其重要性评价

为了对北极鱼类的生态特征进行研究,从而科学合理地开发和管理北极鱼类资源,以现有北极阿拉斯加水域鱼类生态科学信息为基础,针对北极阿拉斯加水域104种主要鱼类,从栖息深度、营养级、昼夜垂直移动及季节性洄游、生态重要性、传统文化重要性及商业重要性等多个方面进行了分析。结果显示,大多数北极阿拉斯加海洋鱼类为中上层鱼类或中层鱼类,栖息水域多在1 000 m以浅的陆架或陆坡水域;营养级范围为3.0～4.5,处于较高和较低营养级的鱼种较少;大部分鱼类的重要性知之甚少,目前仅少量鱼种在北极海域生态系统、传统文化以及商业性渔业中起到关键作用;具昼夜垂直移动及季节性洄游特性的鱼种各占一半左右;基于聚类分析,以栖息深度、垂直移动、季节性洄游及营养级4个指标作为变量,该水域属于5个生态类群,而以生态、传统文化以及商业重要性3个指标为变量,则该水域鱼类可划分为3个类群。本研究结果可为进一步开展北极鱼类生态学研究及北极渔业资源的开发潜力评价提供数据支持,并为我国参与北极鱼类资源潜力的开发及国家权益的争取提供参考信息。     

山东近海鱼类群落种类组成与空间结构的周年变化

山东近海渔业资源丰富,但近年来由于过度捕捞等的影响,渔业资源呈现衰退趋势.为全面了解山东近海鱼类群落的组成与结构,为渔业资源的养护提供科学依据,根据2016—2017年在山东近海进行的4个季节的渔业资源底拖网调查数据,采用非度量多维标度排序(NMDS)、单因子相似性分析(ANOSIM)等多元统计方法,对该海域鱼类生态类...     

Prioritizing aquatic conservation areas using spatial patterns and partitioning of fish community diversity in a near‐natural temperate basin

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Temporal and spatial dynamics of fish community structure during watershed alteration in two Ouachita River systems

Fish community composition is highly dynamic, but generally exhibits loose equilibrium within bounds of community structure in upland stream systems with minimal anthropogenic disturbance. Chronic anthropogenic disturbance can exceed ecological thresholds and shift fish community composition to an alternative state. Therefore, long‐term datasets are critical to understand spatiotemporal dynamics of fish community structure. We quantified temporal changes in fish communities in two Ouachita River systems during watershed alteration (i.e., development and reservoir construction) using a suite of multivariate and univariate analyses to assess changes in fish community structure and taxonomic and functional β‐diversity. We found fish community composition shifted in the Saline River basin possibly in response to human disturbance (e.g., development) and hydrologic variability. Furthermore, functional homogenisation occurred through time. In the Ouachita Headwaters basin, taxonomic homogenisation was evident and two fluvial specialists were not detected during the current period. Taxonomic and functional β‐diversity patterns were not consistent across basins demonstrating the complexity of biotic homogenisation. Our retrospective analyses showed human activities played a role in restructuring fish communities despite minimal invasion of exotic species. Ultimately, our study characterised fish community structure across snapshots of time and demonstrates the importance of increasing the frequency of sampling intervals and continuing long‐term collections with similar methods to enhance the understanding of community dynamics.