Factors affecting the transferability of bioindicators based on stream fish assemblages.

The development of multimetric indices (MMIs) to measure the biotic condition of aquatic habitats is based on metrics derived from biological assemblages. Considering fish assemblages, the inconsistencies in metrics responses outside of the places where they were developed limit MMI transferability and applicability to other locations, requiring local calibration. The factors behind the low transferability of these MMIs are still poorly understood. We investigated how environmental dissimilarity and spatial distance influence the transferability of metrics generated from local stream fish assemblages to other regions. We also tested whether functional and taxonomic metrics respond differently to the spatial distance. We used data from 239 fish assemblages from streams distributed across a Brazilian, the upper Parana basin and characterized each site according to the level of anthropogenic disturbance at the landscape scale using an Anthropogenic Pressure Index (API). We divided the upper Parana basin into sub-basins and used two of them to create template response models of the metrics in relation to the API. We used these response models to predict the responses outside the template sub-basins. Our response variable representing a metric of transferability was the absolute difference between metric's predicted and observed value for each site (prediction error). We thus modeled the prediction error in relation to the predictor variables that were i) the environmental dissimilarity between each site with the average of the sites from template sub-basins (climatic, topographic and soil type variables) and ii) the spatial distance (overland and watercourse distance) between each site and the center of the template sub-basin. We found that errors in metric predictions were associated with both environmental dissimilarity and spatial distance. Furthermore, functional and taxonomic metrics responded equally to spatial distance. These results indicate the need for local calibration of metrics when developing MMIs, especially if the protocols already available come from distant and environmentally dissimilar places.

Elements of fish metacommunity structure in Neotropical freshwater streams.

The identification of the mechanisms underlying patterns of species co-occurrence is a way to identify which process(es) (niche, neutral, or both) structure metacommunities. The current paper had the goal of identifying patterns of co-occurrence in Neotropical stream fish and determining which processes structure the fish metacommunity, and identifying any gradients underlying this structure. Results indicated that the metacommunity formed by the species pool was structured by a pattern of nested co-occurrence (hyperdispersed species loss) and a mass-effect mechanism. However, a set of core species, displaying a Clementsian pattern, was structured by a species-sorting mechanism. Both, hyperdispersed species loss and the Clementsian patterns point to a discrete set of communities within the metacommunity. These communities could be isolated by the water physicochemical conditions or morphological characteristics of the stream channel.

Stream fish metacommunity organisation across a Neotropical ecoregion: The role of environment, anthropogenic impact and dispersal-based processes.

Understanding how assemblages are structured in space and the factors promoting their distributions is one of the main goals in Ecology, however, studies regarding the distribution of organisms at larger scales remain biased towards terrestrial groups. We attempt to understand if the structure of stream fish metacommunities across a Neotropical ecoregion (Upper Paraná-drainage area of 820,000 km2) are affected by environmental variables, describing natural environmental gradient, anthropogenic impacts and spatial predictors. For this, we obtained 586 sampling points of fish assemblages in the ecoregion and data on environmental and spatial predictors that potentially affect fish assemblages. We calculated the local beta diversity (Local Contribution to Beta Diversity, LCBD) and alpha diversity from the species list, to be used as response variables in the partial regression models, while the anthropogenic impacts, environmental gradient and spatial factors were used as predictors. We found a high total beta diversity for the ecoregion (0.41) where the greatest values for each site sampled were located at the edges of the ecoregion, while richer communities were found more centrally. All sets of predictors explained the LCBD and alpha diversity, but the most important was dispersal variables, followed by the natural environmental gradient and anthropogenic impact. However, we found an increase in the models' prediction power through the shared effect. Results suggest that environmental filters (i.e. environmental variables such as climate, hydrology and anthropogenic impact) and dispersal limitation together shape fish assemblages of the Upper Paraná ecoregion, showing the importance of using multiple sets of predictors to understand the processes structuring biodiversity distribution.

Relationships Between Environmental Conditions And Fish Assemblages In Tropical Savanna Headwater Streams.

Riparian vegetation plays an important role in providing energy to small watercourses and maintaining ecological processes through organic matter input and together with hydrological and geomorphological watercourse characteristics influence on fish assemblages. The goal of this paper was partitioning and quantifying the influence of riparian zone (type of riverbank substrate, bank slope, type of riparian vegetation cover and percentage of riparian vegetation cover on the main channel), physical habitat (stream channel width and depth, type of substrate and aquatic habitat in channel, water velocity and organic matter), water quality (turbidity, temperature, conductivity, pH, dissolved oxygen and chlorophyll concentration) and spatial variables (linear distances between sampled points) on fish assemblages (richness and abundance per species) in headwater streams of the Upper Paraná River basin, Central Brazil. For this purpose, it was performed a variation partitioning analysis between riparian, physical habitat, water and spatial variables sets and a Redundancy Analysis to quantify the influence of variables on the fish assemblages. Only the physical habitat and water quality variables influenced the fish assemblages (richness and abundance per species).

A multiple hypothesis approach to explain species richness patterns in neotropical stream-dweller fish communities.

Several hypotheses are used to explain species richness patterns. Some of them (e.g. species-area, species-energy, environment-energy, water-energy, terrestrial primary productivity, environmental spatial heterogeneity, and climatic heterogeneity) are known to explain species richness patterns of terrestrial organisms, especially when they are combined. For aquatic organisms, however, it is unclear if these hypotheses can be useful to explain for these purposes. Therefore, we used a selection model approach to assess the predictive capacity of such hypotheses, and to determine which of them (combined or not) would be the most appropriate to explain the fish species distribution in small Brazilian streams. We perform the Akaike's information criteria for models selections and the eigenvector analysis to control the special autocorrelation. The spatial structure was equal to 0.453, Moran's I, and require 11 spatial filters. All models were significant and had adjustments ranging from 0.370 to 0.416 with strong spatial component (ranging from 0.226 to 0.369) and low adjustments for environmental data (ranging from 0.001 to 0.119) We obtained two groups of hypothesis are able to explain the richness pattern (1) water-energy, temporal productivity-heterogeneity (AIC = 4498.800) and (2) water-energy, temporal productivity-heterogeneity and area (AIC = 4500.400). We conclude that the fish richness patterns in small Brazilian streams are better explained by a combination of Water-Energy + Productivity + Temporal Heterogeneity hypotheses and not by just one.

Trace elements: water-sediment interactions in tropical rivers.

This research aimed to determine the water-sediment interaction (partition coefficient Kd) of trace element (Cd, Cu, total Cr, Pb, and Zn) in tropical rivers of the Upper Paraná River basin, Central Brazil. Three trace elements (Cu, total Cr, and Zn) presented quantifiable concentration values in the water and sediment. Neither the element trace considered nor the rivers displayed a similar water-sediment interaction. The evaluation of Kd values indicates the tendency of total Cr to be adsorbed into the sediment (min Kd = 6.244, max Kd = 131.389), mainly in one sampling station (São Francisco River, Kd = 131.389) and the availability of Zn in the water column in all sampling stations (min Kd = 0.234, max Kd = 1.289). The sediment concentrations of Cr in the São Francisco sampling station (0.118 mg L-1) are above international reference values suggesting a risk of contamination for the biota, whereas in four rivers, Cr concentrations represent a risk. The water-sediment interaction of Cu is influenced by water temperature, whereas the pH influenced the Zn interaction.

The influence of environmental variables on the functional structure of headwater stream fish assemblages: a study of two tropical basins in Central Brazil

We investigated functional patterns of fish assemblages of two adjacent basins (Araguaia and Tocantins) to test whether their headwater stream fish assemblages are more functionally (dis)similar than expected by chance and whether these (dis)similarities are related to differences of environmental conditions between basins. We used an analysis of similarities (ANOSIM) on a functional dissimilarity matrix to test for (dis)similarities between fish assemblages of both basins. We performed RLQ and fourth-corner analyses to determine fish species trait-environment relationship. Our results revealed functional dissimilarities between fish assemblages of both basins and significant species trait-environment relationships, suggesting that environmental conditions are driving such dissimilarities. Inter-basin dissimilarities are mainly driven by altitudinal and water temperature gradients, whereas dissimilarities among streams within the basins are influenced by channel depth, turbidity and conductivity. These five environmental variables mostly affected six fish species traits (body mass, water column position, substrate preference, parental care, foraging locality and migration) in different manners. This study is an attempt to understand functional trends of fish assemblages in a tropical region that remains poorly known but severely threatened.

Nós investigamos os padrões funcionais das assembleias de peixes de duas bacias adjacentes (Araguaia and Tocantins) para testar se as assembleias de peixes de seus riachos de cabeceira são funcionalmente mais (dis)similares do que o esperado ao acaso e se estas (dis)similaridades estão relacionadas a diferenças nas condições ambientais entre as bacias. Nós utilizamos uma análise de similaridades (ANOSIM) sobre uma matriz de dissimilaridade funcional para testar por (dis)similaridades entre as assembleias de peixes das duas bacias. Nós realizamos análises de RLQ e fourth-corner para determinar a relação entre o ambiente e a estrutura funcional das assembleias de peixes. Nossos resultados revelaram dissimilaridades funcionais entre as assembleias de peixes de ambas as bacias e relações significativas entre atributos das espécies e o ambiente, sugerindo que as condições ambientais estão direcionando tais dissimilaridades. As dissimilaridades entre bacias são influenciadas principalmente pelos gradientes de altitude e temperatura da água, enquanto as dissimilaridades entre os riachos na bacia pela profundidade do canal, turbidez e condutividade. Estas cinco variáveis ambientais afetaram principalmente seis atributos das espécies de peixes (massa corporal, posição na coluna de água, preferência por substrato, cuidado parental, local de forrageio e migração) de diferentes maneiras. Este estudo é uma tentativa para entender os padrões funcionais das assembleias de peixes de uma região ainda pouco conhecida, mas, seriamente ameaçada.

Flow seasonality and fish assemblage in a tropical river, French Guiana, South America

The objective of this study is to verify the existence of a seasonal pattern of variation in the fish assemblages of a tropical river using taxonomic and functional descriptors. Fish were sampled using gillnets at two sites on the Comté River, a large-sized river 254.8 km long, flowing entirely through rainforest areas of French Guiana. Samplings were conducted every other month from August 1998 to July 2000. Four types of fish assemblage descriptors were used: the species descriptor (number of individual fish of each species in the sample); the family descriptor (number of individual fish of each family in the sample); the trophic descriptor (distribution of the fish biomass in each feeding guild) and the specific maximum observed size - MOS (number of individual fish in each of four classes of MOS: < 100 mm; 101-200 mm; 201-300 mm; > 300 mm). Results point out that changes in the fish assemblage are related to water level oscillations. The role of migration seems to be weak and is limited to trophic displacements characteristic of few species. In the low-water season, characterized by weak water level oscillation, fish species and families belonging to piscivorous or aquatic invertivorous guilds were predominant, whereas in the high-water season the environment is submitted to strong variations caused by fast and large water level oscillations, and the fish assemblage was characterized by species or families with an opportunistic omnivorous diet.

O objetivo deste estudo é verificar a existência de um padrão sazonal da variabilidade das assembleias de peixes de um rio tropical utilizando descritores taxonômicos e funcionais. Os peixes foram amostrados em duas estações localizadas ao longo dos 254,8 km do rio Comté, o qual drena regiões de floresta úmida da Guiana Francesa. As amostragens foram realizadas bimensalmente de agosto de 1998 a julho de 2000 utilizando-se redes de espera. Quatro tipos de descritores da assembleia de peixes foram utilizados: espécies (número de indivíduos de cada espécie na amostra); família (número de indivíduos de cada família na amostra); trófico (distribuição da biomassa de peixes de cada grupo trófico presente na amostra) e o tamanho máximo observado - TMO (número de indivíduos em cada uma das quatro classes de TMO: < 100 mm; 101-200 mm; 201-300 mm; > 300 mm). Os resultados indicam que as mudanças na assembleia de peixes estão relacionadas à oscilação sazonal do nível da água. O papel desempenhado pelas migrações parece fraco e é limitado a deslocamentos tróficos característicos de determinadas espécies. No período da seca, caracterizado por uma fraca oscilação do nível da água, as espécies e famílias predominantes são piscívoras ou invertívoras aquáticas, enquanto que no período da chuva, o ambiente é submetido a fortes mudanças, provocadas por rápidas e amplas oscilações do nível da água, onde as espécies ou famílias características são omnívoras.

Changes in the structure of fish assemblages in streams along an undisturbed-impacted gradient, upper Paraná River basin, Central Brazil

The João Leite River is located in the upper Paraná basin, Central Brazil. It drains areas covered by Cerrado vegetation interspersed with urban and agricultural areas. This study aims to asses changes of the fish assembleges structure along a undisturbed-impacted gradient in ten stream stretches using ecological descriptors, a similarity index and the abundance-biomass relationship (ABC curves). The fish were collected during the dry period using electrofishing gear in stretches of 50 m. Results show that the environmental variation observed along the undisturbed-impacted gradient considered influences on fish assemblage structure. Both richness and diversity differences between fish assemblages are partially influenced by stream stretch orthonian order and anthropogenic impacts. ABC curves classified six stream stretches located in preserved or impacted areas as undisturbed while four stretches were classified as disturbed. This is attributed to the influence of the undisturbed habitat within the conservation unit and the presence of K- or r- strategist species. This type of study contributes to an understanding of the effects of aquatic environment conservation on the Brazilian Cerrado core area, where the choice of conservation areas prioritizes terrestrial over aquatic aspects.

O ribeirão João Leite está localizado no alto da bacia do rio Paraná, Brasil Central, onde drena áreas cobertas por vegetação tipo Cerrado intercaladas com áreas urbanas e agrícolas. Este estudo objetiva avaliar as mudanças na estrutura das assembleias de peixes ao longo de um gradiente ambiental (não perturbado-impactado) em trechos de dez riachos utilizando descritores ecológicos, um índice de similaridade e a relação abundância-biomassa (curvas ABC). Os peixes foram coletados durante o período da estiagem em trechos de 50 m utilizando a pesca elétrica. Os resultados indicam que a variabilidade ambiental observada ao longo do gradiente considerado influencia na estrutura das assembleias de peixes. As diferenças observadas entre a riqueza e diversidade das assembleias de peixes são parcialmente influenciadas pela ordem do riacho e os impactos antropogênicos. As curvas ABC classificam seis trechos localizados em áreas preservadas ou impactadas como não perturbados e quatro como perturbados. Isto é atribuído à influência do habitat preservado presente na unidade de conservação e à presença de espécies com estratégias K- ou r-. Este tipo de estudo contribui ao entendimento dos efeitos da conservação do ambiente aquático na área central do Cerrado brasileiro, onde as escolhas de áreas de conservação dão prioridade aos aspectos terrestres em detrimento dos aquáticos.

Influence of environmental parameters on fish assemblage of a neotropical river with a flood pulse regime, Central Brazil

This study aims to determine which of twelve environmental parameters (five physicochemical and seven hydromorphological) influence on the fish assemblage structure of the lower Mortes River basin located in the Bananal floodplain of the Araguaia River basin, Central Brazil. Sampling was conducted in six stretches of 1000 m each during the high and low waters. Fish were captured using gill nets and environmental parameters were measured by portable equipment or determined visually. The co-inertia analysis indicated that two physicochemical (dissolved oxygen and water transparency), and four hydromorphological (channel width and depth, riparian vegetation cover and type of the riverside substrate) parameters structure the fish assemblages, both driven by the regional hydrological patterns (flood pulse). These results are explained by fish-environmental parameters relationship characteristic of the aquatic Neotropical systems.(AU)

Este estudo determinou quais entre doze parâmetros ambientais (cinco físico-químicos e sete hidromorfológicos) influenciam na estrutura da assembleia de peixes do baixo rio das Mortes localizado na planície de inundação do Bananal, bacia do rio Araguaia, Brasil Central. As coletas foram realizadas em seis trechos de 1000 m cada durante os períodos de chuva e estiagem, nos quais 1036 peixes foram coletados utilizando-se redes de malhar e medidos os parâmetros ambientais utilizando equipamentos portáteis ou determinados visualmente. A análise de coinércia indicou que dois parâmetros físicos e químicos (oxigênio dissolvido e a transparência da água) e quatro hidromorfológicos (largura e profundidade da calha principal, cobertura da mata ripária e tipo de substrato da margem) estruturam a assembleia de peixes, ambos influenciados pelo regime hidrológico regional (pulso de inundação). Estes resultados são discutidos considerando a interação entre peixes e os parâmetros ambientais característicos dos sistemas aquáticos Neotropicais.(AU)

Effects of natural and anthropogenic environmental changes on riverine fish assemblages: a framework for ecological assessment of rivers

A água dos rios constituem um recurso básico para a humanidade. Instrumentos biológicos eficaces (com fundamento ecológico, eficientes, rápidos e aplicáveis à regiões ecologicamente diferentes) são necessários para medir a "saúde" destes. Adaptar tais instrumentos a uma grande área geográfica requer uma compreensão detalhada dos padrões da composição da assembléia de organismos e da sua distribuição dentro e entre os corpos da água em condições naturais, e da natureza dos principais gradientes ambientais que causam ou explicam estes padrões. Uma revisão da literatura disponível pode ajudar a identificar os fatores ambientais mais consistentes que estruturam a assembléia de peixes de ambientes lóticos em condições naturais.