Ecomorphological patterns of the fish assemblage from the upper Paraná River floodplain, Brazil, were described and evaluated according to trophic (guilds), spatial (habitats) and phylogenetic (taxonomic distances) structures. The samples were obtained through the Long Term Research Project (LTER-CNPq/UEM/NUPELIA) in August and October 2001. Thirty-five species were analyzed from thirty-one morphological variables. Strong significant correlations (Mantel test) between morphology and trophic guilds and between morphology and taxonomy were found, while morphology and habitat revealed a weak correlation. However, the partial Mantel test showed that the correlations between morphology and trophic guilds persist even when the effect of taxonomy is discounted. The ecomorphological pattern shown by the Principal Component Analysis separated species according to locomotion structures used in feeding. At one extreme there are the piscivores and insectivores that exploit lentic habitats and have compressed bodies and well developed anal fins, while at the other there are detritivores and invertivores that exploit lotic and semi-lotic habitats and have depressed bodies and well developed pectoral, pelvic and caudal fins. Canonical Discriminant Analysis using ecomorphological variables successfully predicted 94.5% of the trophic guild ecomorphotypes, but only 57.1% of the habitat ecomorphotypes. These data indicate that the fish assemblage of the upper Paraná River floodplain is structured ecomorphologically mainly according to trophic structure rather than habitat.Este trabalho objetivou descrever e avaliar os padrões ecomorfológicos da assembleia de peixes da planície de inundação do alto rio Paraná, Brasil, analisando os efeitos das estruturas trófica (guildas), espacial (tipos de habitats) e filogenética (distância taxonômica). Trinta e cinco espécies foram analisadas a partir de 31 variáveis morfológicas obtidas de espécimes coletados em agosto e outubro de 2001 no âmbito do Projeto Ecológico de Longa Duração (PELD-CNPq/UEM/NUPELIA). O teste de Mantel revelou que há correlação significativa das distâncias morfológicas com guildas tróficas e distâncias taxonômicas, enquanto com os tipos de habitats a correlação se mostrou fraca. Contudo, o teste de Mantel parcial demonstrou que a correlação da morfologia com as guildas tróficas independe da filogenia. O padrão de diversificação ecomorfológica apresentado pela Análise de Componentes Principais revelou um gradiente ecomorfológico relacionado à locomoção associada à ecologia trófica. Em um extremo estão espécies de piscívoros e insetívoros que exploram preferencialmente habitats lênticos com corpos comprimidos e nadadeiras anais desenvolvidas, enquanto no outro extremo estão os detritívoros e invertívoros que exploram preferencialmente habitats lóticos e semi-lóticos e apresentam corpos deprimidos e nadadeiras peitorais, pélvicas e caudais desenvolvidas. A Análise Discriminante Canônica realizada com os índices ecomorfológicos previu com sucesso 94,5% dos ecomorfotipos rel...

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Local and turnover patterns of fish diversity in the Itaipu Reservoir were evaluated and related to a longitudinal or river-dam gradient (composed of riverine, transitional, and lacustrine zones) and to transversal or upstream-downstream gradients of the tributaries (composed of lotic and lentic stretches of tributaries and reservoir shores). Thirteen stations were sampled quarterly during 2 years. A total of 85 fish species were caught. Local (alpha) and turnover (beta) patterns of fish diversity showed significant differences in reservoir spatial gradients. Along the longitudinal gradient, total and alpha-diversity were the highest in the riverine and transitional zones of the reservoir and lowest in the lacustrine zone. Along the transversal gradient, total and alpha-diversity increased from the lotic stretches of the tributaries to the reservoir shores. The lotic and lentic stretches of the tributaries presented the highest beta-diversity values, indicating heterogeneity in species compositions among the sub-basins. We conclude with recommendations for reservoir management based on the results of this study.

One of the main issues in community ecology is the detection of structure and the identification of its related causes. In this study, co-occurrence null models were used to identify possible spatio-temporal patterns in the assemblage of aquatic macrophytes in the Upper Paraná River floodplain. The samples were obtained through the Long Term Ecological Research (LTER) Program at two different grains: (1) a coarser spatial grain in January and August 2001 (entire floodplain lagoons); (2) and a finer spatial grain in November 2006 (1 m(2) quadrats). The study was conducted in 36 lagoons, both connected and disconnected to the main river channel, located in the sub-basins of the Baía, Ivinheima and Paraná rivers. Two null models of species co-occurrence, the C-Score and Checkerboard indices, were used to test the null hypothesis of random structure of the aquatic macrophyte assemblages. The null models showed that the aquatic macrophyte assemblages were spatially structured in the distinct spatial grains. However, despite this general pattern, macrophyte assemblages are organized differently depending on the degree of connectivity, seasonal period and, at a finer grain, depth. Species co-occurrences were random in the disconnected lagoons during flood periods, in deep zones of the lagoons of the Baía River and in the shallow littoral zone in the lagoons of the Paraná River. Analysis of the patterns of co-occurrence indicated that competition and/or habitat preferences are probably important influences on the nonrandom structure of assemblages. However, we suppose that at least three important factors (disturbances by water level fluctuation, dispersion and facilitation) counteract potential effects of competition in specific situations, leading macrophyte assemblages to assume random structure.

SynopsisWe assessed the structure of the fish assemblages in the Itaipu Reservoir (Parana´River, Brazil-Paraguay) along a longitudinal or river-dam gradient (composed of riverine, transitional and lacustrine zones) and transversal or upstream-downstream gradients of the tributaries (composed of lotic and lentic stretches of tributaries and reservoir shores). We sampled stations distributed along the environmental gradients quarterly during two years. We caught mostly piscivorous, detritivorous and insectivorous fishes. The structure of the whole fish assemblage both at the regional spatial scale and at the zones of each gradient was significantly non-random according to null models and ordination analysis. When the assemblage was broken into groups, the piscivores and detritivores as well as the predators and prey showed significant nonrandom structure whereas the insectivores, omnivores, herbivores, benthophages and mud-eaters showed random structure. The first groups are those that had more species and the last mentioned are those with fewer species. The tributaries varied more in composition among themselves than the reservoir shores, showing a high heterogeneity in the transversal gradient. The most widespread species was the introduced piscivore Plagioscion squamosissimus. The loricariids were most abundant in the lotic and lentic stretches of the tributaries. We also observed temporal variability in species composition, mainly in the reservoir shores possibly due to the influence of the upstream floodplain on the migratory fish that periodically use the reservoir as feeding habitat. In the tributaries, the temporal changes were less predictable. A combination of habitat preferences and interactions among species, especially predator-prey relations, might be responsible for the observed structure patterns.