Influence of abiotic variables on the diversity and co-occurrence of fish assemblages in streams of the paranapanema basin, Brazil

Urbanization affects the taxonomic and functional alpha and beta diversity of fish assemblages in streams of subtropical China

Studies on fish assemblages in streams point out, that understanding the relationship between species and their environment is crucial for conservation. The present study aimed at evaluating the effects of changes in abiotic variables on the composition and structure of fish assemblages in Neotropical urban streams from southern Brazil with different levels of urbanization. The composition and structure of fish assemblages showed significant differences along the urbanization gradient observed in the streams. Tolerant and non-native species were found in more urbanized sites. A matrix correlation revealed a relationship between abiotic variables and the spatial pattern of structure and composition of fish assemblages. Abiotic variables, such as total phosphorus, dissolved oxygen, and conductivity, determined the distribution of fish assemblages. Streams without urban influence exhibited intrinsically low species richness, suggesting that they are highly susceptible to species loss and diversity reduction. Thus, changes in water quality or hydrological conditions induced by urbanization may intensify these impacts.

BackgroundAgriculture has greatly influenced water quality, habitats, and fish assemblages in streams of the Mississippi Alluvial Plain (MAP) ecoregion. However, MAP streams have historically been understudied compared to streams in other agricultural regions of the USA. In this study, water quality, habitat, and fish assemblage composition were assessed seasonally (spring, summer, and fall) in eight representative MAP streams located across three U.S. states. The study design included four streams containing highly agricultural watersheds (herein termed “agriculture” streams) and four streams containing mostly forested watersheds (herein termed “forest” streams), which were intended to represent reference conditions for MAP streams.ResultsIn general, forest streams contained significantly better instream and riparian habitats than agriculture streams (P = 0.010–0.040) whereas agriculture streams contained significantly greater levels of primary nutrients (P < 0.001–0.010). Differences between agriculture and forest streams with respect to other physical and chemical variables were intermittent and season dependent. Fish assemblages in agriculture and forest streams were structured primarily along an environmental gradient reflecting instream habitat conditions, water nutrient concentrations, and benthic chlorophyll-a production. Structurally, fish assemblages in both stream types contained many regionally common species, though some species appeared to exhibit affinities for a particular stream type. Functionally, fish assemblages in agriculture streams contained more tolerant species, more omnivores, and fewer insectivores compared to forest stream assemblages, which were nearly all insectivores. Overall, one-third of the fish specimens collected in forest streams classified as intolerant species.ConclusionsOur results suggested that stream water quality, habitat, and fish assemblages differed between agriculture and forest streams in the MAP, with fish assemblages exhibiting both structural and functional differences. Results were consistent with a larger body of literature from smaller, headwater streams whereby land-use changes (e.g., row-crop agriculture) impacted the physical, chemical, and biological characteristics of stream ecosystems. Results further highlight the importance of land use management and its effects on habitat diversity in stream ecosystems, and that protecting the few remaining undisturbed or less-disturbed streams should be a priority.

The aim of this study was to verify structure patterns in fish assemblages in mountain streams of the Rio Tibagi basin through the characterization of spatial and temporal variations in the composition of fish species. Samples were collected in three segments of the Varanal, João Pinheiro and Rio Preto streams. We collected 1154 specimens belonging to 21 species. The most abundant orders were Characiformes (59.01 ± 2.84%) and Siluriformes (39.34 ± 2.82%). Phalloceros harpagos was the most abundant species with 433 individuals, followed by Trichomycterus aff.davisi, with 292 individuals. No temporal variations (between seasons) were detected, but the cluster analysis suggests a separation of species composition between the segments closer to the headwaters and those more distant. The first two axes of the Canonical Correspondence Analysis (CCA) explained 80.09% of the variation in species abundance, and the variables that structured the fish assemblages in those streams were the stream width, depth, water speed, flow rate, conductivity and pH.

Effects of natural hydrological variability on fish assemblages in small Mediterranean streams: Implications for ecological assessment

Considering the increasing importance of analysing spatial structure in ecological studies, the aims of the present study were to test whether fluvial distances and environmental factors are important drivers of the ß-diversity of stream fish assemblages, and whether ß-diversity is different in distinct hydrological periods. Specimens were sampled at 33 stream sites in the eastern Amazon. Eight environmental variables were measured at each site and fluvial distances between pairs of stream sites were determined. Environmental variables were the main factors structuring fish assemblages in both periods. However, fluvial distances were important only during the flood period. This can be related to the formation of extensive flood plains in this period, which increases connectivity between streams, breaking habitat isolation and increasing the regional signal for fish species. The higher correlation of ß-diversity with environmental variables during the flood period may be related to decreased dispersal limitations and intermediate dispersal. Finally, ß-diversity was higher during the flood period, highlighting the importance of the heterogeneity of the flood plain to stream biota. The results of the present study indicate that spatial and environmental factors play complementary roles in structuring fish assemblages in Amazon streams, and that ß-diversity was affected by changes in the habitat connectivity experienced in different hydrological periods.

Fish are important in the structuring of other communities and may have large effects on the functioning of aquatic ecosystems. The structure of fish communities, in turn, seems to differ with climate. We compared the characteristics of fish assemblages in lowland streams located in two contrasting climates (cold-temperate Europe and subtropical South America) by use of published and unpublished data on streams of similar depth, width, and slope (n total = 91 streams). We also selected a subset of seven comparable little-affected streams in the two contrasting climates: temperate (Denmark, 55°–57°N, Dk) and subtropical (Uruguay, 30°–35°S, Uy) and compared the fish community structures in relation to environmental characteristics. We then analysed a series of potential explanatory factors behind the patterns observed, in particular the effect of ambient temperature, by comparing temperature-corrected community metabolism. Significantly higher species richness, higher densities, lower biomass, smaller mean body size, and lower mean weight of fish were observed for the subtropical streams than for the temperate streams, both in the literature review and in the subset of streams. Several characteristics of fish assemblages in streams may be explained by direct and indirect effects of temperature. Accordingly, fish in subtropical systems had a temperature-corrected community metabolism I m−2 equal to that of fish in temperate systems, indicating that temperature, besides historical factors, is an important driver of different size structures. Our findings concur with differences previously found in littoral areas of shallow lakes, suggesting that these patterns are not restricted to running waters. Our results elucidate how fish community structure might be affected by increases in temperature triggered by climate warming.

The effects of local and regional environmental factors on the structure of fish assemblages in the Pirapó Basin, Southern Brazil

Assemblage Organization of Stream Fishes: The Effect of Rivers on Adventitious Streams

Surface waters across much of New York’s Adirondack Mountains were acidified in the late 20th century but began to recover following the 1990 amendments to the Clean Air Act. Little data, however, are available to characterize biological impacts and predict recovery of fish assemblages in streams of the region. Quantitative fish and chemistry surveys were completed in 47 headwater streams during summer 2014–2016 to develop logistic (probabilistic) models that characterize the status of contemporary fish assemblages and predict how different nitrogen (N) and sulfur (S) deposition loads may affect future fish assemblages. Models for inorganic monomeric aluminum (Ali) and richness ≥1 species and for acid neutralizing capacity (ANC) and total density &gt;400 fish/0.1 ha, total biomass &gt;1500 g/0.1 ha, brook trout (Salvelinus fontinalis) density &gt;0 or &gt;200 fish/0.1 ha, and brook trout biomass &gt;1000 g/0.1 ha were suitable for evaluating community and population responses to changes in acid–base chemistry. Anticipated changes in national (US) secondary standards for atmospheric emissions of nitrogen oxides (NOx) and sulfur oxides (SOx) to achieve target N and S deposition loads will alter acid–base chemistry and the probabilities for observing various levels of fish metrics in streams across the region and elsewhere.

Unsaturated Fish Communities in African Rivers

Local environmental and anthropogenic variables play a key role in determining the species distribution across the riverscape. The upstream of River Ganga flows through the Western Himalaya that is unique due to wide variation in hydro-geomorphological features, which offer microhabitats for many fish species. Thus the present study was aimed to investigate the role of environmental and anthropogenic variables on taxonomic and guild structures of the fish assemblages in streams of the Western Himalaya. We documented fish assemblages along the altitudinal gradients in streams of Western Himalaya with 20 sampling sites covering both Bhagirathi and Alakhnanda basins of the upper Ganga river. We documented 40 species of fishes belonging to 12 ecological guilds. We observed high species turnover in streams that flow between 400 and 800 m altitude, while there was no fish species recorded in streams located above 2400 m altitude. Twelve environmental and three anthropogenic variables were subjected to PCA for removing redundant variables, and the linearly uncorrelated variables were then used in the redundancy analysis (RDA) to test the effects of environmental and anthropogenic variables on structuring the species and guild assemblages. We found four distinct fish species assemblages groups in three distinct guilds. The RDA results revealed more number of species associated in sites that were faraway distance from the source with greater catchment areas. Greater number of species inhabited the deep and wide stream with high substrate diversity. The ordination of environmental and anthropogenic variables with ecological guild showed that the upstream basin area and water velocity were highly correlated for members of BISSL guild (Benthic dweller-Insectivore-Small size-Simple reproduction strategy-Local migrant). The members of typical rheophilic minnows belonging to SISSL guild (Surface dweller-Insectivore-Small size-Simple reproduction strategy-Local migrant) were strongly related to close proximity to dams. Further, the proximity of dam was negatively correlated with native snow trout, Schizothorax richardsonii distribution, and the dam presence was positively correlated with the presence of non-native carp, Cyprinus carpio in the Western Himalaya. We could confirm the increase in species richness with decreasing altitude in Western Himalaya.

Understanding patterns in taxonomic congruency and the importance of environmental variables as drivers of these patterns is a prerequisite for analyzing changes in regional species pools. Here we evaluated the spatial correspondence of benthic diatoms, invertebrates, macrophytes, and fish assemblages in minimally disturbed lowland (n=38) and mountain (n=32) streams and, using constrained ordination and variance decomposition, determined how environmental and biological variables related to these patterns. Using different measures of diversity, abundance, and community composition, principal components analysis failed to reveal a single gradient in lowland and mountain streams. This was due to differences in the relationships between individual diversity measures and environmental variables characterizing habitat diversity (number of debris dams, silt and cobble substratum) in lowland streams, and catchment area and oxygen saturation in mountain streams. Despite the low spatial coherence of individual measures, integral multivariate analyses of community structure revealed coherent patterns between taxonomic groups. From 31.0% to 47.7% of the variance in diversity of fish, invertebrate, and macrophyte assemblages in mountain streams and from 11.9% to 33.7% of the variance in diversity in lowland streams were explained by one or more of the remaining three groups. Partial redundancy analyses showed that composition of other taxonomic groups was generally a better predictor of assemblage diversity than interactions with environmental variables, lending support to the importance of species interactions for spatial coherence. Finally, although we found little support for a single biodiversity gradient, correlations between fish diversity and macrophyte and invertebrate diversity in mountain streams and between macrophyte diversity and invertebrate and diatom diversity in lowland streams suggest that these two groups (i.e., fish in mountain and macrophytes in lowland streams) may function as surrogate indicators for the diversity of other taxonomic groups.

ABSTRACTIdentifying the spatial pattern of fish assemblages and the correlation between fish assemblages and environmental factors is basic for conserving and managing stream fishes. Based on data collected from 91 sampling segments within first-order through third-order streams of the Xin'an basin, China, we examined the spatial variation of fish assemblages in this area and related it to local, river-network and catchment factors. We found that fish species richness significantly increased from first-order to second- and third-order streams, but assemblage structures showed no among-stream variation. When the independent influence of the three categories of factors was considered, fish assemblages were significantly related to local habitat (e.g. wetted and substrate heterogeneity), tributary spatial position (e.g. confluence link and distance from mouth) and land use (e.g. agriculture and urbanization areas), respectively. However, when the effects of the these factors were considered jointly, local habitat and tributary spatial position were more important in influencing fish assemblages than land use. Our results suggest that fish assemblages in the headwater streams of the Xin'an basin were mainly determined by both local and spatial factors. The landscape data should be further refined in the future to provide more information for assessing how land use influence stream fishes.

This study evaluated the ecomorphological patterns of fish assemblages in oligotrophic headwater streams of northwestern Amazonia. Our aims were: 1) identify correlations between morphological variables of fish species and habitat use, trophic structure and distance to the main river; 2) examine ecomorphological patterns that reflect ecological aspects of locomotion, habitat use and trophic ecology. A total of 34 species were analyzed using 27 ecomorphological indices to test if they were related to fish assemblage. Significant correlations were found between anatomical traits and trophic guilds and habitat use regardless of phylogenetic relationships. Two trends were identified in the ecomorphological space. First, nektonic insectivores-piscivores with lateral compressed bodies, large eyes, superior-terminal mouth without barbels and larger anal fins were associated to species with continuous swimming, and the use of vision to capture prey. Second, benthic periphytivores-invertivores with depressed bodies, small eyes, ventral or inferior mouth with presence of barbels, and developed pectoral fins were related to species that exploit streams substrate. This study shows that fish assemblages in the oligotrophic headwater streams are ecomorphologically structured by trophic guilds and habitat use. These findings highlight the use of ecomorphology as a tool to predict ecological patterns in these streams.