See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/305308573 Effects of area and available energy on fish assemblages of tropical streams Article  in  Marine and Freshwater Research · July 2016 DOI: 10.1071/MF15431 CITATION 1 READS 164 3 authors: Some of the authors of this publication are also working on these related projects: FIRE EFECT ON THE SEASONAL FOREST STRUCTURE IN THE CERRADO BIOME View project Biodiversity Conservation of Forest Fragments in the Fernao Dias APA View project Bruno Goncalves São Paulo State University 31 PUBLICATIONS   57 CITATIONS    SEE PROFILE Francisco Leonardo Tejerina-Garro Pontifícia Universidade Católica de Goiás (PUC Goiás) 65 PUBLICATIONS   630 CITATIONS    SEE PROFILE Rodrigo Assis Carvalho Universidade Estadual de Goiás 24 PUBLICATIONS   179 CITATIONS    SEE PROFILE All content following this page was uploaded by Bruno Goncalves on 19 July 2016. 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BCentro de Biologia Aquática, Departamento de Ciências Biológicas, PUC Goiás, Campus II, Avenida Engler s/n, 74885460, Goiânia, GO, Brazil. CPrograma de Pós-graduação em Sociedade, Tecnologia e Meio Ambiente, UniEVANGÉLICA, Avenida Universitária quilômetro 3.5, Cidade Universitária, 75083515, Anápolis, GO, Brazil. DUniversidade Estadual de Goiás (UEG), Programa de Pós-Graduação em Recursos Naturais do Cerrado (RENAC), Câmpus de Ciências Exatas e Tecnológicas,Henrique Santillo, BR 153, number 3105 Fazenda Barreiro do Meio, 75132400, Anápolis, GO, Brazil. ECorresponding author. Email: decarvalho.ra@gmail.com Abstract. A central issue in fish community ecology is to understand how the size of the drainage area and the available energy influence fish species diversity and their spatial distribution. In the present study, we tested whether the species– area relationship (represented by drainage area) and species–energy association (represented by algal biomass and organic matter) drive taxonomic and functional richness in a regional scale. The results indicated that fish assemblages of the two tropical neighbouring basins sampled responded differently to the size of drainage area. Whereas taxonomic richness was influenced by the size of the drainage area in Tocantins River basin streams, it was not affected in Araguaia River basin streams. Both taxonomic richness and functional richness of the fish assemblages were affected by available energy in the system. A possible explanation for these different responses is related to local conditions, such as the percentage of natural vegetation cover encountered in each basin. Additional keywords: algal biomass, land use, organic matter, vegetation cover. Received 13 November 2015, accepted 16 May 2016, published online 14 July 2016 Introduction Fish species represent 30% of all known vertebrate species on Earth (Strayer and Dudgeon 2010). Considering the totality of fish species described, ,40% of them are encountered in freshwater ecosystems (Dudgeon et al. 2006). With human activities pressuring these systems and leading to unprecedented levels of extinction (Dudgeon et al. 2006; Vörösmarty et al. 2010), there is an urgent need to provide protection for fresh- water habitats. However, the development of conservation actions is directly dependent on our knowledge on how species diversity is distributed along space, and which factors affect this distribution. In the past decade, the number of studies in the Neotropical region focusing on the distribution patterns of fish species diversity in local and regional scales has increased (Bistoni and Hued 2002; Hoeinghaus et al. 2004; Fialho et al. 2007; Súarez et al. 2011; Santana et al. 2014; Carvalho and Tejerina- Garro 2015; Teresa et al. 2015). Themain results of these studies have shown that fish species diversity is associated to different factors, such as variation in the longitudinal gradient of streams coupled with environmental variables, stream features (e.g. stream order), position in the river channel and changes from dry to rainy seasons (seasonality) and the degree of deforestation. Despite such recent effort, only few studies have investigated the patters of fish species distribution at a large scale in the Neotropical region (Súarez et al. 2011). This situation concerns freshwater-fish conservation because it has been estimated that more than 4000–6000 species are present in the Neotropical region (Reis et al. 2003; Lévêque et al. 2008; Albert and Reis 2011). According to classical studies, the following hypotheses were already proposed to explain gradients in species richness: (1) species–area relationship (MacArthur and Wilson 1967); (2) species–energy relationship (Wright 1983); and (3) historical hypothesis (Whittaker et al. 2001). The hypothesis of species– area relationship predicts that larger areas will harbour a higher CSIRO PUBLISHING Marine and Freshwater Research http://dx.doi.org/10.1071/MF15431 Journal compilation � CSIRO 2016 www.publish.csiro.au/journals/mfr number of species than do smaller areas because they are expected to (1) have more habitat heterogeneity and food resources availability (Williamson 1988), (2) reduce the proba- bility of extinction because larger areas have more resources available and tend to support more individuals (MacArthur and Wilson 1967) and (3) present higher speciation rates, given their higher habitat heterogeneity (Losos and Schluter 2000). The species–energy hypothesis predicts that species diversity is a response to energy availability in the system. For example, local and regional fish species diversity may respond to variations in the input of energy along the longitudinal gradient of streams, as proposed by the river-continuum concept (Vannote et al. 1980). Finally, the historical hypothesis predicts that species diversity is a consequence of the potential of system recolonisation and the maturation of such systems after glaciation. At the global scale, patterns of riverine fish diversity are explained by two major factors, namely, energy availability and habitat heterogeneity (Guégan et al. 1998). Here, our main goal relies on the study of patterns of taxonomic richness (species richness) and functional richness (species richness by trophic group) of tropical freshwater fish assemblages. We tested whether the species–area relationship (represented by drainage area) and species–energy association (represented by algal biomass and organic matter) drive taxo- nomic and functional richness of fish assemblages in a regional scale; that is, we expect that both taxonomic and functional richness of fish assemblages will be positively related to the increase of drainage area and available energy in the system. Materials and methods Study area The study area is located in the Goiás State, central Brazil. The Tocantins–Araguaia basin is one of the most developed water- sheds of the Amazonian province (Ribeiro et al. 1995; Lévêque et al. 2008). The Tocantins–Araguaia basin has an estimated size of 767 000 km2 and it presents a mean annual discharge of 11000m3 s�1 (Costa et al. 2003). Our study area is represented by the upper section of the basin that is located in the Goiás State, central Brazil. In this region, the drainage areas of its main tributaries (Tocantins and Araguaia rivers) are geographically separated by mountain chains, such as Serra do Caiapó and Serra dos Pirineus (Tejerina-Garro 2008), and they form two distinct basins, namely, Araguaia River basin (hereafter Araguaia basin) andTocantinsRiver basin (hereafterTocantins basin).Bothbasins have a well-defined dry (May–October) and wet (November– April) season (Albrecht and Pellegrini-Caramaschi 2003; Ques- ada et al. 2004). The original vegetation cover formed mainly by cerrado phytophysiognomies was altered by human occupation (mainly agriculture and cattle-ranching activities), which placed the cerradoas as the second-most modified Brazilian biome (PMDBBS 2016). However, deforestation is not the same in the two basins because differences in topography differently favour the earlier mentioned activities, that is, the Araguaia basin has plane low-altitude areas favourable to agriculture and cattle- ranching, whereas the Tocantins basin has scarped areas with steep slopes that hamper these activities (de Oliveira 2014), being allied to extended areas for conservation or sustainable use (Galinkin 2003). This situation affects also the riparian vegetation, expressed by the absence of this vegetation along many of the stream stretches sampled in the Araguaia basin in relation to those of the Tocantins basin (Table 1). Sampling protocols During the dry season (March to September 2008), we sampled 21 watercourses, 11 being located in the Araguaia River basin and 10 in the Tocantins River basin (Fig. 1). All watercourses sampled belong to 1st or 2nd order, according to the classifi- cation of Strahler (1957). In each watercourse, we delimited and georeferenced (GPS eTrex, Garmin, USA) a stretch of 50 m. Along the stretch, five transects of 10 m each were demarcated and both biotic (fish) and abiotic (environmental variables) data were collected. Fish species were collected using a seine net (4� 1.3 m; 0.1 mm between knots) along the stretch, which was covered 10 times. Fish was fixed with formalin and conserved in containers holding formaldehyde at 20%. In the laboratory of the Centro de Biologia Aquática, PUC Goiás, fish were identi- fied through the use of identification keys (Planquette et al. 1996; Santos et al. 2004; Melo et al. 2005), measured (mm) and weighed (g). Specimens of each species were sent to the Laboratory of Ichthyology of the Pontifı́cia Universidade Católica do Rio Grande do Sul to confirm identification. The trophic guild of each species was determined according to the online database FishBase (R. Froese and D. Pauly, see htpp://www.fishbase.org, accessed 10 September 2015). For the first, third and fifth transects of each stretch, we used a quadrat (0.5� 0.5 m) to collect vegetable organicmatter (leaves, branches, fruits, seeds; hereafter, organic matter, OM). The OM Table 1. Description of the predominant type of riparian vegetation along the stream bank of stretches sampled in the Araguaia and Tocantins basins Stream number follows those displayed in Fig. 1 Basin Stream number Riparian vegetation by stream bank Right Left Araguaia 1 Shrubs Grasses and shrubs 2 No vegetation No vegetation 3 Shrubs and trees Shrub 4 Grasses and shrubs Grasses and shrubs 5 No vegetation No vegetation 6 No vegetation No vegetation 7 Shrubs and trees Shrubs and trees 8 No vegetation No vegetation 9 Shrubs Shrubs 10 No vegetation No vegetation 11 Shrubs and trees Shrubs Tocantins 12 Shrubs Shrubs 13 Shrubs Shrubs and trees 14 Shrubs and trees Shrubs and trees 15 Shrubs Shrubs and trees 16 Shrubs and trees Shrubs and trees 17 Grasses Shrubs 18 No vegetation No vegetation 19 Trees Trees 20 Shrubs Shrubs 21 Grasses Grasses B Marine and Freshwater Research B. Bastos Gonçalves et al. was then dried in the laboratory in an oven for 24 h at 1058C, weighed and calcined (furnace) at 5508C, and weighed again (Silva et al. 1999). The final OM weight was standardised by dividing it by the quadrat area, and expressed in grams per square metre. The algal biomass (AB) was determined through the extrac- tion and measurement of the chlorophyll-a. For that, at the first and the fifth transects of each stretch, the water along the watercourse bank was pumped during 5 min (water pump, P835, Stihl, Brazil), filtered by a plankton net (20-mm mesh) and stored in an amber bottle (1 L) containing 1 mL of magnesium carbonate. In the laboratory, the sample was filtered (Millipore 0.45-mm filter, 25-mm diameter), the chlorophyll was extracted with methanol and the concentration determined by a spectrophotometer (Cary, 50 CONC-UV, Varian, USA) following the protocol of Wetzel and Likens (1991). Algal biomass was expressed in milligrams per litre. The measurements of the drainage area (DA) and the total percentage of vegetation cover (TPVC) of each watercourse were performed in the software ArcGIS (ESRI, USA) using hydrological and land-use maps (scale 1 : 250 000) available on the website of the Sistema Estadual de Estatı́stica e Informações Geográficas do Estado deGoiás (SIEG, see http://www.sieg.go. gov.br/, accessed 21 October 2015). We measured DA as the area (km2) between the headwater of the watercourse and the location of the stretch sampled, respecting the boundaries of the basin. We classified land use into the following five categories: agriculture, urban areas, cerrado sensu stricto, forest (cerradão, mataseca, riparian forest, gallery forest) and pasture, all of them measured in square kilometres. We obtained TPVC accordingly to the following formula: %TPVC ¼ ðCAþ FAÞ=DA� 100 where%TPVC is the total percentage of vegetation cover, CA is the total cerrado area, FA is the total forest area and DA is the drainage area. Statistical analysis Separately, we performed two multiple regressions by basin (Araguaia and Tocantins), considering taxonomic richness (S) or functional richness (richness of the trophic guild) as response variables and area (DA) and available energy (AB and OM) as explanatory variables. We tested the principle of nor- mality using a Shapiro–Wilk test and, whenever necessary, we transformed the data with a logarithm (log10þ1). If the multiple regression analysis was statistically signifi- cant, we performed an analysis of covariance (ANCOVA) between residuals (dependent variable) and two covariates represented by the basins (Araguaia and Tocantins; categorical predictor variable) and the total percentage of vegetation cover (TPVC; continuous predictor variable). All analyses were per- formed using the software STATISTICA 8.0 (StatSoft, Brazil). Results We found 4093 fish specimens from 5 orders, 15 families and 62 species (Table 2). We collected 56 species from eight trophic guilds and 35 species from six trophic guilds in watercourses of Araguaia and Tocantins River basins respectively (Table 2). Taxonomic (S) and functional richness (trophic-guild richness) The multiple regression analysis indicated that the relationship between the taxonomic or functional richness of fish assem- blages and the factor area (DA) and available energy (OM and AB) did not occur in a similar way in the two watercourses grouped by basin (Araguaia and Tocantins). We did not find significant relationships between taxonomic or functional fish richness and area and available energy in the watercourses of the Araguaia River basin (Table 3). For the Tocantins River basin, we found a positive relationship between taxonomic richness and area and available energy (P¼ 0.007; Table 3), that is, taxonomic richness increased as a function of DA and available energy (OM and AB). When we did not consider the DA, AB was negatively related to taxonomic richness (P¼ 0.023; Table 3), that is, taxonomic richness decreased when AB increased. The functional richness was positively related to OM and AB (P¼ 0.023; Table 3), meaning that, an increase in functional richness was due to an increase in OM and AB (available energy) in the system. The ANCOVA analysis indicated that the residuals of the significant relationships described above are not related to the covariates considered (basin and TPVC; Table 4), except for the taxonomic richness–available energy relationship, which is related to the TPVC (Table 4). It means that the relationship increases (the residual tends to diminish) when the TPVC increases, independently of the basin (Fig. 2). Discussion Generally, larger areas are expected to harbour a higher number of species; therefore, species richness is expected to grow as the size of an area increases (Arrhenius 1921; MacArthur and Wilson 1967). Evidence of this positive relationship in aquatic systems has been described at smaller (Eadie et al. 1986; Chittaro 2002) and larger (Watters 1992; Guégan et al. 1998; 1 2 8 11 4 5 7 10 9 17 15 16 20 19 18 21 13 12 146 3 0 65 130 N W E S 260 km Fig. 1. Location of the watercourses sampled in the Araguaia (circles) and Tocantins (triangles) River basins in the Goiás State, central Brazil. Area, energy and fish assemblages in streams Marine and Freshwater Research C http://www.sieg.go.gov.br/ http://www.sieg.go.gov.br/ Matthews and Robison 1998) spatial scales. In the present study, we demonstrated that patterns of taxonomic and func- tional richness of fish assemblages of two tropical neighbouring basins (Araguaia and Tocantins) responded differently to the size of the DA. A possible explanation for such differences is related to the percentage of natural cover observed in each basin. The upper section of the Araguaia and Tocantins River basins are both located in the cerrado, a biodiversity hotspot (Mittermeier et al. 2004, 2011). This biome is mainly threat- ened by the conversion of its original vegetation cover into areas for agriculture and cattle ranching (Klink and Machado 2005), implicating habitat loss and fragmentation, which are listed as major threats to fish diversity (Dudgeon et al. 2006). The vegetation cover is not the same in both basins. There are many isolated or continuous areas of savanna shrub and shrub– tree forests in the Tocantins basin, combined with a larger number of protected areas in its north-eastern region than in the Araguaia basin (Galinkin 2003). Streams with a low per- centage of natural cover are probably affected by other envi- ronmental (e.g. water physicochemical characteristics) and landscape (e.g. presence of a floodplain area) factors than size area, which is the case for Araguaia River basin streams. However, a higher percentage of natural cover could mitigate the effects of agriculture and cattle-ranching, which is the case observed for Tocantins River basin streams, enabling a higher influence of the size of the DA. Table 2. Fish species sampled in the watercourses of the Araguaia and Tocantins basins, central Brazil, in the dry season of 2008 The trophic guild is indicated for each species. Species Trophic guild Basin Species Trophic guild Basin Araguaia Tocantins Araguaia Tocantins Characiformes Characiformes (cont.) Anostomidae Steindachnerina sp. Detritivorous X Leporinus friderici Omnivorous X X Steindachnerina sp. 2 Detritivorous X Characidae Erythrinidae Astyanax abramis Omnivorous X Hoplerithrinus unitaeniatus Omnivorous X Astyanax fasciatus Omnivorous X X Hoplias malabaricus Piscivorous X X Astyanax sp. 1 Omnivorous X X Parodontidae Astyanax sp. 2 Omnivorous X X Apareiodon sp. Algivorous X Astyanax sp. 3 Omnivorous X X Apareiodon sp. 2 Algivorous X Bryconamericus sp. 2 Omnivorous X Cyprinodontiformes Bryconamericus sp. 3 Omnivorous X Poeciliidae Bryconops caudomaculatus Insectivorous X X Pamphorichthys sp. Invertivore X X Charaxgibbosus Piscivorous X Gymnotiformes Creagrutos sp. Insectivorous X X Sternopygidae Galeocharaxgulo Piscivorous X Eigenmannia virescens Insectivorous X X Hemigrammus sp. Insectivorous X X Perciformes Hyphessobrycon sp. Insectivorous X X Cichlidae Iguanodectes spilurus Omnivorous X Aequidens tetramerus Omnivorous X X Jupiaba cf. polylepis Omnivorous X X Apistograma sp. Omnivorous X X Knodus sp. Omnivorous X X Retroculus lapidifer Insectivorous X Moenkhausia collettii Omnivorous X Satanoperca acuticeps Omnivorous X Moenkhausia dichoura Omnivorous X Siluriformes Moenkhausia lepidura Omnivorous X X Aspredinidae Moenkhausia oligolepis Omnivorous X X Bunocephalus coracoideus Insectivorous X Moenkhausia sp. 2 Omnivorous X X Auchenipteridae Moenkhausia sp. 5 Omnivorous X Trachelyopterus galeatus Omnivorous X Odontostilbe sp. Omnivorous X Callichthyidae Phenacogaster sp. Insectivorous X X Aspidoras sp. Invertivore X X Poptella longipinnis Omnivorous X X Corydoras sp. Omnivorous X X Psellogrammus sp. Insectivorous X Heptapteridae Roeboxodon geryi Lepidophagus X Imparfinis sp. Invertivore X X Serrapinnus cf. kriege Omnivorous X Pimelodella cristata Omnivorous X Serrapinus sp. Carnivorous X Pimelodella sp. Omnivorous X Tetragonopterus argenteus Insectivorous X Rhamdella sp. Invertivore X Tetragonopterus chalceus Omnivorous X Loricariidae Thayeria boehlkei Omnivorous X Hypostomus plecostomus Detritivorous X X Ctenoluciidae Hypostomus sp. 1 Detritivorous X X Boulengerella cuvieri Piscivorous X Loricaria cataphracta Omnivorous X X Curimatidae Otocincus tapirape Algivorous X X Curimatella sp. Detritivorous X Rineloricaria sp. Algivorous X X Cyphocharax cf. spiluropsis Detritivorous X Trichomycteridae Trichomycterus sp. Invertivore X D Marine and Freshwater Research B. Bastos Gonçalves et al. Moreover, removal of natural cover, including riparian vegetation, may influence the occurrence of species, because it hampers the input of allochthonous nutrients in the freshwater system (Vannote et al. 1980). This fact can partially explain the results found for the Araguaia River and in an opposite manner in the Tocantins basin (increase of taxonomic and functional richness along with the OM). However, the vegetal cover in the Tocantins basin is not continuous, but interspersed with areas where the riparian vegetation is absent. This situation favours the entry of luminosity into the water column, promoting the rise of algae (Giller and Malmqvist 2000) and, consequently, the primary productivity in the aquatic system measured by the chlorophyll-a (Barroso and Littlepage 1998), as was observed in the present study. Thus, the positive relationship between available energy and taxonomic and functional rich- ness in Tocantins streams indicated that the input of nutrients into the system by the vegetation cover is capable of increasing the number of species and the number of species with different trophic habits in the system, but only when AB and OM are evaluated together. When these two components are evaluated separately, it is observed that an increase in AB has negative effects on taxonomic richness. This result suggests that the fish– AB relationship observed in the Tocantins basin works similarly to the eutrophication phenomenon on fish diversity; that is, it causes changes to the fish assemblage composition or displace- ment, or elimination of fish populations (Lévêque et al. 2008). An additional explanation for the different relationships of the fish assemblages from the two basins with area and available energy is the basin interconnection. In the present study, this was represented by the interconnection between the ‘Vereda Grande’ stream (Tocantins basin) and ‘Brejinho’ stream (Paraná basin; Pavanelli and Britski 1999). These authors stated that this interconnection allows the exchange of fish species between these basins; thus, it influences on taxonomic and functional richness, both of which were measured in the present study. The mentioned differences can be also related to regional and local characteristics of the habitat, such as the physico- chemical characteristics of the water. The Araguaia is classified as a clear-water river and the Tocantins as a white-water one (Rı́os-Villamizar et al. 2014). The type of water results from basin geochemistry that influences the isotopic composition of basal production (Jepsen and Winemiller 2007) and, in conse- quence, the type of available energy for aquatic biota including fish assemblages. Additionally, the Araguaia basin includes a floodplain that provides a greater number of shelters and food for fishes (Agostinho and Zalewski 1995; Junk 1997), increas- ing taxonomic fish richness (Tanaka et al. 2015) and the diversity of morphological, physiological and ethological attri- butes of species (Junk et al. 1989; Lowe-McConnell 1999). This could explain the elevated number of species observed in this basin in relation to Tocantins basin. However, some limita- tions of the present study are necessary to consider; one is related to the number of sampling points and the second to the period of sampling (low-water period). We believe that the sampling effort in the present study was appropriate to give us a first draft of these relationships in regions with little knowledge, and a good first look on how these relationships are structured in regional scales. However, increasing the number of unities and Table 4. Statistics of the total percentage of vegetation cover (TPVC, continuous predictor) by basin (categorical predictor) and results of the ANCOVAanalysis between the residuals of the significant relationships, resulting from multiple linear regression (dependent variable), and the covariates (basin and TPVC) Significant P-values are in bold (P, 0.05). S, taxonomic richness; SGT, functional richness Basin n TPVC (km2) Covariate F1,18 P-value Mean s.d. Basin TPVC Araguaia 11 16.042 23.575 Tocantins 10 40.590 29.283 Residual of the relationship: S v. areaþ available energy 0.089 0.287 3.228 0.089 S v. available energy 0.169 0.013 2.057 0.169 SGT v. available energy 0.369 0.100 0.850 0.369 Table 3. Statistics of the multiple linear regression between the taxonomic richness of fish assemblages (S), functional richness and the factors drainage area (DA), algal biomass (AB) and organic matter (OM) of the watercourses sampled and grouped by basin Significant (P, 0.05) P-values are in bold Basin Richness Estimate Factor Areaþ available energy Available energy Araguaia Taxonomic (S) P 0.618 0.391 R2 0.213 0.209 S¼�19.6852þ 1.1964(DA) �0.4938(AB)þ 9.3619(OM) S¼�18.4216 �0.5636(AB)þ 9.4468(OM) Functional (SGT) P 0.957 0.862 R2 0.041 0.036 SGT¼ 0.8193 �0.2930(DA)þ 0.1526(AB)þ 0.9597(OM) SGT¼ 0.5098þ 0.1697(AB)þ 0.9389(OM) Tocantins Taxonomic (S) P 0.007 0.023 R2 0.848 0.659 S¼�19.1060þ 4.2590(DA) �3.1201(AB)þ 7.8388(OM) S¼�5.6270 �2.0342(AB) Functional (SGT) P 0.065 0.023 R2 0.675 0.658 SGT¼�8.2386þ 0.5471(DA) �0.7609(AB)þ 3.6429(OM) SGT¼�6.5071 �0.6215(AB)þ 3.2932(OM) Area, energy and fish assemblages in streams Marine and Freshwater Research E the sampling effort for both dry andwet seasons in future studies may provide a better picture of the relationships between fish assemblages and area and fish assemblages and energy across space and time. Understanding how the size of the DA and the available energy may affect fish species and their spatial distribution is a cornerstone to fish community ecology. Here, we showed that fish assemblages of two tropical neighbouring basins responded differently to the size of the DA and, this fact may be a consequence of the presence or absence of natural vegetation cover around streams. In other words, impacts caused by human population, as a result of agriculture and cattle-ranching, on natural vegetation cover near streams may affect species occurrence. Moreover, we demonstrated that both taxonomic richness and functional richness of these fish assemblages were affected by available energy in the system, which may also be influenced by the degree of natural vegetation cover near streams. Considering that area and available-energy effects are directly dependent on the presence or absence of natural vegetation cover, it is important to develop conservation actions to protect this highly endangered hotspot. Acknowledgements We thank to the team of the Centro de Biologia Aquática (CBA), especially to:Waldeir Francisco deMenezes, Nicelly Braudes deAraújo, TatianaMelo and Thiago Vieira for collection of field data. We are also grateful to researchers from Pontifı́cia Universidade Católica do Rio Grande do Sul for fish species identification and to the National Council of Technological and Scientific Development (CNPq) for the financial support given for the project (CNPq number 471283/2006-1). References Agostinho, A. A., and Zalewski, M. (1995). The dependence of fish community structure and dynamics on floodplain and riparian ecotone zone in Parana River, Brazil.Hydrobiologia 303, 141–148. doi:10.1007/ BF00034051 Albert, J. E., and Reis, R. E. (2011). 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