Detection of ecological change using multiple organism groups: metrics and uncertainty

A number of biological approaches are commonly used to assess the ecological integrity of stream ecosystems. Recently, it is becoming increasingly common to use multiple organism groups in bioassessment. Advocates of the multiple organism approach argue that the use of different organism groups should strengthen inference-based models and ultimately result in lower assessment error, while opponents argue that organism groups often respond similarly to stress implying a high degree of redundancy. Using fish, macroinvertebrate, macrophyte and benthic diatom data, site-specific parameters (e.g., water chemistry and substratum) and catchment variables from European mountain (n = 77) and lowland (n = 85) streams we evaluated the discriminatory power and uncertainty associated with the use of a number of biological metrics commonly used in stream assessment. The primary environmental gradient for both streams types was land use and nutrient enrichment. Secondary and tertiary gradients were related to habitat quality or alterations in hydromorphology. Benthic diatom and macroinvertebrate metrics showed high discriminatory power (R² values often >0.50) and low error (<30%) with the primary (nutrient) gradient, while both fish and macrophyte metrics performed relatively poorly. Conversely, both fish and macrophyte metrics showed higher response (high coefficients of determination) than either benthic diatom or macroinvertebrate metrics to the second (e.g., alteration in habitat/hydromorphology) gradient. However, the discriminatory power and error associated with individual metrics varied markedly, indicating that caution should be exercised when selecting the ‘best’ organism group or metric to monitor stress.     

Assessment of European streams with diatoms, macrophytes, macroinvertebrates and fish: a comparative metric-based analysis of organism response to stress

1. Periphytic diatoms, macrophytes, benthic macroinvertebrates and fish were sampled with standard methods in 185 streams in nine European countries to compare their response to degradation. Streams were classified into two main stream type groups (i.e. lowland, mountain streams); in addition, the lowland streams were grouped into four more specific stream types. 2. Principal components analysis with altogether 43 environmental parameters was used to construct complex stressor gradients for physical–chemical, hydromorphological and land use data. About 30 metrics were calculated for each sample and organism group. Metric responses to different stress types were analysed by Spearman Rank Correlation. 3. All four organism groups showed significant response to eutrophication/organic pollution gradients. Generally, diatom metrics were most strongly correlated to eutrophication gradients (85% and 89% of the diatom metrics tested correlated significantly in mountain and lowland streams, respectively), followed by invertebrate metrics (91% and 59%). 4. Responses of the four organism groups to other gradients were less strong; all organism groups responded to varying degrees to land use changes, hydromorphological degradation on the microhabitat scale and general degradation gradients, while the response to hydromorphological gradients on the reach scale was mainly limited to benthic macroinvertebrates (50% and 44% of the metrics tested correlated significantly in mountain and lowland streams, respectively) and fish (29% and 47%). 5. Fish and macrophyte metrics generally showed a poor response to degradation gradients in mountain streams and a strong response in lowland streams. 6. General recommendations on European bioassessment of streams were derived from the results.     

Ecological assessment of an intermittent Mediterranean river using community structure and function: evaluating the role of different organism groups

1. Reliable lotic ecological monitoring requires knowledge of river typology, environmental factors, the effect of stressors known here as ‘pressures’ and appropriate indicators of anthropogenically induced change. We sampled benthic macroinvertebrate, fish, bird and macrophyte communities along an intermittent Mediterranean river and analysed community structure (relative abundance) and function (metrics) relative to environmental and pressure gradients in order to identify suitable indicator group(s) for future monitoring and mitigation programmes. 2. Principal components analysis revealed that scale‐dependent longitudinal differences in valley form separated narrower higher lying sites and tributaries with good quality habitats from more open degraded sites lower down the river continuum on a small floodplain and large scale pressures describing changes in land use related to agriculture with associated physical bankside and channel impacts. 3. Forward selection of variables in redundancy analysis (RDA) showed that reach scale environmental variables were selected more frequently than pressure variables for each organism group. Altitude and pH were highly redundant within and between groups, indicating essentially longitudinal structural and functional distribution patterns. Redundancy was far lower between selected pressure variables, but single or no pressure variables were retained for some organism groups indicating poor association of functional data, in particular, with the identified pressures. All RDA results indicated a longitudinal pH gradient, highlighting the combined effect of multiple environmental and pressure based mechanisms on organism groups. 4. Large, mobile organisms such as fish and birds provided a reliable link between organism structure and function, environmental factors and physical disturbance of the channel, bankside and wider river corridor. Benthic macroinvertebrate and macrophyte structural data revealed distribution patterns in relation to water velocity, a key parameter for developing appropriate compensation measures. 5. Results clearly show the importance of assessing patterns of both functional and structural change across multiple organism groups in order to identify typologically appropriate links with complex environmental and pressure gradients and develop and implement appropriate monitoring systems.     

An application of canonical correspondence analysis for developing ecological quality assessment metrics for river macrophytes

1. Aquatic macrophyte composition and abundance is required by the European Union's Water Framework Directive for determining ecological status. Five metrics were produced that can be combined to determine the deviation of aquatic macrophytes from reference conditions in Northern Ireland's rivers. 2. Species optima and niche breadths along silt, nitrate, pH, conductivity and dissolved oxygen gradients were generated from aquatic macrophyte and water quality surveys conducted at 273 sites throughout Northern Ireland using Canonical Correspondence Analysis (CCA). Five metric scores based on these environmental gradients were determined at new monitoring sites using the mean optima of the species occurring at the site, weighted by percentage cover and niche breadth of each species. 3. A preliminary reference network of 32 sites of high physico‐chemical and hydromorphological quality, and representative of the range of river types in Northern Ireland, enabled reference metric scores to be produced for each river type. Five unimpacted and twenty impacted sites were used for testing the performance of the metrics. By subtracting reference metric scores from metric scores at a monitoring site measures of ecological impact could be determined along five different impact gradients. Metrics were also combined to give a measure of total ecological change. 4. The metrics system distinguished unimpacted from impacted sites and correctly identified 77% of the known impacts. The metrics distinguished different types of impact, e.g. silt and nitrate. 5. Aquatic macrophyte occurrence and abundance has high natural variability at a site, both temporally and spatially. This method was designed to be sensitive to ecological change whilst reducing noise caused by natural variation.     

Control of freshwater fish and crayfish community structure in Taranaki,New Zealand: dams,diadromy or habitat structure?

1. Freshwater fish and crayfish communities were surveyed along elevational gradients in streams radiating from Mount Taranaki, New Zealand. Six of the 38 streams surveyed had dams or weirs and 32 of the 85 sites were above these barriers. 2. Of the 15 fish and one crayfish species captured, 14 were native. The number of species declined with increasing elevation and distance from the sea. Species richness was also lower above dams even when effects of elevation and distance from the sea were accounted for. 3. Linear regression models using sites without dams were constructed to predict the effect of elevation on fish and crayfish community structure and to allow the effect of dams to be evaluated. The number of species predicted by these models was consistently higher than the number of species found at the above-dam sites. 4. Four fish community groups were classified using two-way indicator species analysis (TWINSPAN). One high elevation group of sites consisted of short steep streams on the west side of the mountain and a second contained longer, lower gradient streams on the east side. The other two groups (3 and 4) consisted of mid-elevation sites and low-elevation sites, respectively. 5. Discriminant analysis was used to predict biotic group membership using the environmental data. Overall, 80% of sites were classified correctly. Correlation of environmental variables with axis scores in the canonical variate analysis revealed that distance from the sea, site elevation and presence of dams were most strongly associated with fish distribution patterns.     

Macrophytes in boreal streams: Characterizing and predicting native occurrence and abundance to assess human impact

Macrophytes are a structurally and functionally essential element of stream ecosystems and therefore indispensable in assessment, protection and restoration of streams. Modelling based on continuous environmental gradients offers a potential approach to predict natural variability of communities and thereby improve detection of anthropogenic community change. Using data from minimally disturbed streams, we described natural macrophyte assemblages in pool and riffle habitats separately and in combination, and explored their variation across large scale environmental gradients. Specifically, we developed RIVPACS-type models to predict the presence and abundance of macrophyte taxa at stream sites in the absence of human influence and, used data from impacted streams to explore the responses of three biotic indices to anthropogenic stress. The indices used, taxonomic completeness (O/E-taxa), a measure of compositional dissimilarity (BC-index) and an index taking into account the abundance of species (AB-index), are based on predicted and observed macrophyte communities. We found that size of the catchment area, altitude, latitude and percentage of lakes in the catchment were the large scale environmental variables that best predicted the natural variation of assemblages. The RIVPACS approach substantially improved both the precision and accuracy to predict the natural communities and the sensitivity to human disturbance. O/E-taxa performed best in relation to the null model decreasing the variation by 20% in pools, 29% in riffles and 32% in combined data. In general, models based on the riffle assemblages performed better than models based on pool assemblages, but including both habitats and predicting abundances instead of only presence/absence yielded the greatest accuracy and sensitivity. Our results support the use of multivariate modelling techniques in predicting reference condition to assess status of stream macrophyte communities.     

Development of dual fish multi-metric indices of biological condition for streams with characteristic thermal gradients and low species richness

Biological indicators based on fish assemblage characteristics are used to assess stream condition worldwide. Fish-based bioassessment poses challenges in Southern New England, the USA, due to the effects of within-watershed thermal gradients on fish assemblage types, low regional species richness, and lack of minimally disturbed sites. Dual multi-metric indices (MMI) of biological condition were developed for wadeable streams based on fish assemblage characteristics sampled across watershed landscapes with varying levels of human disturbance. A coldwater MMI was developed using streams with drainage area of ≤15 km², and a mixed-water MMI for streams with drainage areas of >15 km². For each MMI development, candidate metrics represented by ecological classes were sequentially tested by metric range, within-year precision, correlation with stream size, responsiveness to landscape-level human disturbances, and redundancy. Resultant coldwater and mixed-water MMI were composed of 5 and 7 metrics, respectively. Stream sites tended to score similarly when the two MMI were applied to transitional sites, i.e., drainage areas of 5–40 km². However, some sites received high scores from the mixed-water MMI and intermediate scores from the coldwater MMI. It was thus difficult to ascertain high-quality mixed-water streams from potential coldwater streams which currently support mixed-water assemblages due to ecological degradation. High-quality coldwater streams were restricted to stream sites with drainage areas ≤15 km². The newly developed fish-based MMI will serve as a useful management tool and the dual-MMI development approach may be applicable to other regions with thermal gradients that transition from coldwater to warmwater within watersheds.     

Unravelling the determinants of stream midge biodiversity in a boreal drainage basin

1. Few extensive lotic studies have examined patterns in the biodiversity of non‐biting midges (Diptera: Chironomidae) along major environmental gradients. Our aim was to fill this gap by describing patterns in species diversity, assemblage composition and distributions of midges across a boreal drainage basin. 2. We found that the diversity of midges, as measured by rarefied species richness, Fisher’s α and Pielou’s evenness, responded positively to stream size in regression analysis. By contrast, species density was most strongly correlated to a gradient in suspended solids and phosphorus in stream water, as well as macrophyte cover. Spatial variables were not significantly correlated with species diversity. 3. Midge assemblage composition was best explained by a model incorporating five composite environmental gradients in canonical correspondence analysis. The environmental gradients were stream size, macrophyte cover, alkalinity, nitrogen and suspended solids. Spatial variables did not overcome the effects of environmental gradients on assemblage composition. 4. Cluster analysis divided the 27 study sites into four groups with relatively similar midge assemblages. These groups were statistically significant in multi‐response permutation procedure, and 15 of the 49 midge taxa recorded varied significantly among the groups in indicator value analysis. Discriminant function analysis showed that stream size, macrophyte cover and habitat structure predicted 66.7% of sites into correct groups. 5. The information provided by the present analyses may be of considerable importance in conservation planning at the drainage basin level. The fact that species diversity and assemblage composition varied primarily along the stream size gradient suggests that sites belonging to the different size classes (first to fifth order) are needed to conserve the biodiversity of midges. The other environmental gradients should also be considered in conservation planning, because they explained significant amounts of variability in midge assemblage composition.     

Relationship of fish and macroinvertebrate communities in the mid-Atlantic uplands: Implications for integrated assessments

Indices developed for stream bioassessment are typically based on either fish or macroinvertebrate assemblages. These indices consist of metrics which subsume attributes of various species into aggregate measures reflecting community-level ecological responses to disturbance. However, little is known about the relationship between fish and macroinvertebrate metrics, or about how ecological health assessments are affected by assemblage-specific responses to disturbance. We used principal component analysis (PCA) and regression analysis of existing fish (n = 371) and macroinvertebrate (n = 442) stream bioassessment data from a multi-source dataset to determine broad scale, within-assemblage metric patterns, and to examine the intercorrelation of fish and macroinvertebrate metrics (n = 246) and their response to watershed area and land use/land cover gradients. Fish and macroinvertebrate metrics expressed as principal components (PCs) accounted for 72.4 and 85.4% of dataset variance, respectively, with PC-metric patterns reflecting aspects of stream impairment including water and habitat quality. Model components predicting fish metric response differed among fish PCs, with watershed area and macroinvertebrate metric response strongly correlated with the first fish PC, and remaining fish PC models consisting of watershed area, land use, and macroinvertebrate PCs. Correlation between fish and macroinvertebrate PCs, and models relating fish and macroinvertebrate PCs generally explained less variation (13–27%) than metric response models of fish (25–34%) and macroinvertebrates (8–38%) to watershed area and land use/land cover variables. Best-response models integrating fish and macroinvertebrate PCs, watershed area, and land use/land cover variables accounted for the greatest variation in fish PCs (32–50%) across sites. Because fish and macroinvertebrate metrics provide different information on ecological condition, integrated use of information from multiple groups may be appropriate when developing monitoring programs.     

Revealing the pathways by which agricultural land‐use affects stream fish communities in South Brazilian grasslands

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Assessment of an index of biological integrity (IBI) to quantify the quality of two tributaries of river Chenab,Sialkot, Pakistan

Nullah Aik and Nullah Palkhu, two tributaries of river Chenab, were investigated for the assessment of fish habitat degradation as indicator of stream health. Fish abundance data were collected from 18 sites from September 2004 to April 2006 to develop multimetric indices for fish assemblage integrity and to detect the intensity of habitat degradation. A total of 12 metrics were calculated on the basis of taxonomic richness, habitat preference, trophic guild, stress tolerance and origin of species to develop stepped and continuous index of biological integrity (IBI) criteria. Cluster analysis (CA) classified sites based on species composition into three groups, viz., reference, moderately impaired and impaired groups. Non-metric multidimensional scaling (NMDS) was applied to identify underlying ecological gradient to highlight the habitat degradation. NMDS segregated two sites as less impaired, five sites as moderately impaired and eleven sites as impaired groups. Axes 1 and 2 explained a total variation of 53.3%. First axis explained the level of habitat impairment, whereas axis 2 indicated species richness along longitudinal gradient of streams. Sites located upstream of Nullah Aik showed higher IBI scores which dropped to its lowest in downstream sites near Sialkot city. Lowest values of IBI of sites in close proximity of city indicated the role of anthropogenic activities in catchment areas. The results indicated that variability in water chemistry can be related as a function of stream sites impairments (i.e., unimpaired, moderately impaired, and severely impaired). Water quality parameters showed strong correlation with IBI scores. Significantly negative correlation of IBI scores with COD, TDS, turbidity, Fe, Cr, Zn and positive correlation with DO and pH was found. The results can be used for restoration and future management of small streams passing through urban areas of Pakistan. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. A. Cambray     

Synergy between shading and herbivory triggers macrophyte loss and regime shifts in aquatic systems

Macrophytes play a keystone role in shallow aquatic ecosystems. In lakes, macrophytes stabilize clear‐water conditions with high biodiversity and their decline can cause a shift to a turbid state with lower biodiversity. Various mechanisms have been suggested as triggers of macrophyte collapse. Herbivory by waterfowl and fish seems to be one of the obvious factors, but the response of macrophytes to herbivory is ambiguous. We hypothesized that herbivory alone does not typically cause macrophyte collapse, but that shading from periphyton can enhance the effect of herbivores. Shading of macrophytes is supposed to increase with eutrophication due to changes in the top–down control cascading from fish via macroinvertebrates to periphyton. We elaborated on this idea by fitting a macrophyte growth model with different herbivore grazing and periphyton shading scenarios. In addition, we performed a meta‐analysis on existing experimental herbivore exclosure studies with respect to periphyton growth. The model supported our proposed hypothesis and the reviewed field studies appeared to point in the same direction. We suggest that a significant herbivore impact may indicate a reduced resilience of vegetation to eutrophication, making it an early warning signal for an imminent macrophyte collapse leading to a sudden shift of the system to turbid conditions.     

Physical and biological changes to a lengthening stream gradient following a decade of rapid glacial recession

In mountains, environmental gradients are steep in both terrestrial and aquatic systems, and climate change is causing upward shifts of physical and biological features of these gradients. Glacial streams are an interesting system to evaluate such shifts both because streams have a linear nature (for simplicity of analysis), and because the stream habitat will at least temporarily lengthen as it follows receding glaciers upward. The Tschierva Glacier, Swiss Alps, receded 482 m upstream from 1997 to 2008. We tested the null hypothesis that the physical and biological stream gradient below this glacier maintained the same structure between these time periods, but simply shifted upward following the glacial source. We compared longitudinal patterns of water temperature and zoobenthic community structure in 1997 and 2007–2008 during three seasons (spring, summer, fall) along the uppermost ca. 5 stream km. Upward shifts were evident, including colonization of the newly exposed stream reaches by cold‐adapted taxa, and the appearance in 2007/2008 of four lower‐altitude species that were previously absent. Overall, however, results rejected the null hypothesis, instead revealing significant changes in gradient structures. These included a more steeply increasing temperature profile downstream of the glacier and increased amplitude of seasonal community turnover in 2007/2008 vs. 1997. Long‐term (1955–2007) flow records revealed increasing short‐term and seasonal hydrologic variability, which might have influenced the increased intra‐annual community variability. The steepening of the temperature gradient was likely caused by a warming lake‐outlet tributary upon which glacial influence was diminished between 1997 and 2007/2008. These results suggest that upward‐shifting gradients in glacial streams can involve complex interactions with other landscape elements and that local‐scale climate response can progress even more rapidly than the rate of glacial recession.     

A fisheries acoustic multi-frequency indicator to inform on large scale spatial patterns of aquatic pelagic ecosystems

Fisheries acoustic instruments provide information on four major groups in aquatic ecosystems: fish with and without swim bladder (tertiary and quaternary consumers), fluidlike zooplankton (secondary consumers) and small gas bearing organisms such as larval fish and phytoplankton (predominantly primary producers). We entertain that this information is useable to describe the spatial structure of organism groups in pelagic ecosystems. The proposal we make is based on a multi-frequency indicator that synthesises in a single metric the shape of the acoustic frequency response of different organism groups, i.e. the dependence of received acoustic backscattered energy on emitting echosounder frequency. We demonstrate the development and interpretation of the multi-frequency indicator using simulated data. We then calculate the indicator for acoustic water-column survey data from the Bay of Biscay and use it to create reference maps for the spatial structure of the four scattering groups as well as their small scale spatial variability. These maps provide baselines for monitoring future changes in the structure of the pelagic ecosystem.     

Microfluidic devices for analysis of spatial orientation behaviors in semi-restrained Caenorhabditis elegans

This article describes the fabrication and use of microfluidic devices for investigating spatial orientation behaviors in nematode worms (Caenorhabditis elegans). Until now, spatial orientation has been studied in freely moving nematodes in which the frequency and nature of encounters with the gradient are uncontrolled experimental variables. In the new devices, the nematode is held in place by a restraint that aligns the longitudinal axis of the body with the border between two laminar fluid streams, leaving the animal's head and tail free to move. The content of the fluid streams can be manipulated to deliver step gradients in space or time. We demonstrate the utility of the device by identifying previously uncharacterized aspects of the behavioral mechanisms underlying chemotaxis, osmotic avoidance, and thermotaxis in this organism. The new devices are readily adaptable to behavioral and imaging studies involving fluid borne stimuli in a wide range of sensory modalities.     

Stable isotope measurements confirm consumption of submerged macrophytes by macroinvertebrate and fish taxa

Many macrophyte species in lowland streams exhibit signs of grazing and herbivore damage, even though herbivory by aquatic macroinvertebrates and fish is generally considered to be of little importance. In this study, we collected evidence for the hypothesis that herbivory on macrophytes by macroinvertebrates and fish is more widespread than assumed. We measured the dual stable isotope signatures (δ¹³C and δ¹⁵N) of organic matter, epiphyton, submerged macrophytes, macroinvertebrates and fish in a Belgian lowland stream. There was a clear distinction in isotopic signatures of the different basal resources, allowing the use of the SIAR mixing model. These calculations revealed the consumption of macrophyte tissue not only by the phytophagous larvae of Nymphula nitidulata Hufnagel (Lepidoptera: Crambidae), but also by Baetidae nymphs (Ephemeroptera), Orthocladiinae larvae (Diptera: Chironomidae), the crayfish Orconectus limosus Rafinesque (Decapoda: Cambaridae) and the fish Gobio gobio L. (Cypriniformes: Cyprinidae) which are classified as feeding on other resources. Although the potential share of macrophyte biomass in the diet of macroinvertebrates and fish was demonstrated to be up to 49%, this amount is only a small percentage of the total standing macrophyte biomass in a lowland stream. However, the impact of this herbivory may still be substantial because consumption may comprise a significant fraction of the daily primary production. Additionally, small-scale herbivory may still have a negative impact on macrophyte growth and survival, for example through consumption of apical meristems and the increased susceptibility to diseases and toxins if the macrophyte’s epidermis is damaged.     

The invertebrate species index (ISI) for streams in southeast Queensland,Australia

The invertebrate species index (ISI) is a new biotic index to assess stream health in southeast Queensland, Australia, using benthic macroinvertebrates. The index aims to refine stream monitoring, in particular for eutrophication, as nutrient input is a major stressor of streams in the region. Biotic indices previously used for the region were based on sensitivity scores for macroinvertebrate families and orders, and were valid for all streams across the continent. The ISI is based on species level and tailored to the specific traits of southeast Queensland, thus yielding an increased level of detection of biological change. This will improve monitoring of environmental impact on a regional and local scale. The ISI is a site-specific index calculated as the weighted average (WA) of species’ sensitivity scores (S₁₀), with a species-specific indicator weight (W) and the abundance (A) of each species used as weights. S₁₀ scores for 203 species of benthic macroinvertebrates ranging from 10 (species most sensitive to pollution) to 1 (tolerant of excessive pollution) were derived by means of WA regression and calibration using site scores representing an environmental impact gradient. W measures the indicator strength of the species, and was derived from the weighted standard deviation of the S₁₀. The initial site scores for the WA modeling were derived using canonical correspondence analysis (CCA) to ordinate the sites along a gradient associated with 12 abiotic variables. The data on benthic macroinvertebrates are based on 212 quantitative samples collected in wadeable freshwater streams in southeast Queensland. Two major stream types, (1) small creeks, mainly of uplands and (2) larger streams and rivers of lowlands, were recognised for the region, and for both types the ISI range representing reference condition was established. These reference conditions can be used to establish ecological quality ratios by comparing observed to expected indices and to define ecological quality classes. The ISI is the first biotic index for streams in Australia that uses sensitivity scores and indicator weights for macroinvertebrate species. There is a growing trend in Australia to identify stream macroinvertebrates to species level and to study their specific traits and ecological requirements. The reasons for this are manifold; assessing and monitoring stream health is only one of them. For most regions of Australia, no common ground exists, so far, on how to use species data for stream health assessment. The new biotic index fills this gap for southeast Queensland in providing a standard for the use of species level data in stream health assessment.     

Effects of fish presence and simulated moonlight gradients on night-time horizontal movements of a predatory zooplankter, Chaoborus punctipennis

Some zooplankton, including Chaoborus punctipcnnis, have recentlybeen reported to undergo die1 horizontal migrations in additionto their widely known vertical migrations. In a series of laboratoryand field experiments, we tested the influences of gradientsin light intensity and fish presence on horizontal migrationin C.Punctipennis. In a small chamber, C.punctipennis showedno response to simulated moonlight gradients. They did, however,show significant movement away from fish held at one end ofthe chamber under uniform moonlight. A field experiment in alarge chamber indicated that the response to fish was inducedby chemical cues. When tested in the laboratory chamber withboth moonlight gradients and fish present, C.punctipennis becamepositively phototactic. This response increased the movementaway from fish when the fish were at the darker end of the gradient,or reduced it when the fish were at the brighter end. Ln combination,these experiments demonstrate that C.punctipennis show directedhorizontal movements in response to fish presence and moonlightgradients, suggesting a potential for these stimuli to influencehorizontal migrations observed in the field. Present address: Department of Biology, University of CaliforniaLos Angeles, CA 90095-1606, USA     

River fish assemblages along an elevation gradient in the eastern extremity of Europe

Studies on assemblages of freshwater fishes along elevational gradients of rivers are lacking, even in Europe. In this paper we have explored the entire range of elevational gradients existing in the European part of Russia. We analyzed how fish biodiversity (species richness, abundance, diversity indices) at 435 river sites differed by elevation. The impact of elevation on the distribution of freshwater fish species was analyzed using regression and ordination methods. For the first time for a large area of Eastern Europe, optimum points and niche breadth for fish species along altitude gradients were estimated. Our analyses showed: (1) species richness and Shannon index decreased in the upper part of the gradient; fish abundance showed a unimodal response to elevation; highest numbers were found at elevations between 250 and 500 m; (2) ordination analysis demonstrated an upstream-downstream gradient of the fish assemblages; (3) regression analysis showed significant preferences for elevation by 19 species, all of which were monotonic; (4) optimum and niche breadth (tolerance) were highly variable between species; only five species (brown trout, grayling, common minnow, bullhead and stone loach) were encountered at elevations above 650 m; and (5) in our region, the habitat of grayling was higher in the mountains, and its abundance (numbers) at extreme elevations was greater, than brown trout. These results show how fish assemblages differ with elevation. Our findings identify the data that can be used for regional environmental monitoring of the state of small rivers and for aquatic conservation.