Recently, community ecologists are focusing on the relative importance of local environmental factors and proxies to dispersal limitation to explain spatial variation in community structure. Albeit less explored, temporal processes may also be important in explaining species composition variation in metacommunities occupying dynamic systems. We aimed to evaluate the relative role of environmental, spatial and temporal variables on the metacommunity structure of different organism groups in the Upper Paraná River floodplain (Brazil). We used data on macrophytes, fish, benthic macroinvertebrates, zooplankton, periphyton, and phytoplankton collected in up to 36 habitats during a total of eight sampling campaigns over two years. According to variation partitioning results, the importance of predictors varied among biological groups. Spatial predictors were particularly important for organisms with comparatively lower dispersal ability, such as aquatic macrophytes and fish. On the other hand, environmental predictors were particularly important for organisms with high dispersal ability, such as microalgae, indicating the importance of species sorting processes in shaping the community structure of these organisms. The importance of watercourse distances increased when spatial variables were the main predictors of metacommunity structure. The contribution of temporal predictors was low. Our results emphasize the strength of a trait-based analysis and of better defining spatial variables. More importantly, they supported the view that “all-or- nothing” interpretations on the mechanisms structuring metacommunities are rather the exception than the rule.

-(Similarity among periphyton algal communities in a lentic-lotic gradient of the upper Paraná river floodplain, Brazil). Floristic comparison of periphyton communities from three systems with different hydrodynamic regimes (lentic, semilotic, and lotic) was carried out during high and low water periods on the Upper Paraná River floodplain. For each period and system, glass slides were sampled every two days during 18-day periods, and Eichhornia azurea Kunth petioles were sampled three times. A total of 228 species was collected, representing 12 classes, mainly diatoms and desmids. The highest species-richness was found in communities from lentic system and during high water. Species richness in the lotic system was more stable over succession and hydrological periods. Algal taxonomic structure in river community was clearly separated from the other two systems, with 43% of similarity level. The hydrological period was next in importance, followed last by the substratum type, with communities associated at 65-78% similarity levels, depending on system and hydrological period. The type of system, but not the water levels,was the main factor that influenced community richness, followed by disturbances caused by flood pulses and the operation of reservoirs upstream. The periphyton on artificial and natural substrata presented high degree of similarity.RESUMO -(Similaridade entre comunidades de algas perifíticas em um gradiente lêntico-lótico da planície de inundação do alto rio Paraná, Brasil). Comparação florística entre as comunidades perifíticas de três sistemas com distintos regimes hidrodinâmicos (lêntico, semilótico e lótico), abrangendo períodos de águas altas e baixas, foi realizada a partir de substratos artificial e natural. Lâminas de vidro foram coletadas a cada dois dias durante 18 dias e pecíolos de Eichhornia azurea Kunth três vezes em cada ocasião. O perifíton apresentou, como um todo, 228 espécies de algas distribuídas em 12 classes, com a maior representatividade de diatomáceas e desmídias. Maior riqueza foi, invariavelmente, encontrada no sistema lêntico e no período de águas altas. A ficoflórula perifítica foi caracterizada, principalmente, pelo regime hidrodinâmico e pela morfometria do ambiente, havendo nítida separação da comunidade do sistema lótico em relação à dos outros dois sistemas, agrupados a 43% de similaridade. Em seguida, o período hidrológico foi mais importante e, por último, o tipo de substrato, cujas comunidades se associaram a 65-78% de similaridade, dependendo do sistema e período hidrológico. Conclui-se que o tipo de ambiente e não o regime hidrológico exerceu a maior influência sobre a riqueza específica da comunidade; e que as perturbações causadas pelos pulsos de inundação e pela operação dos reservatórios influenciaram, marcadamente, as flutuações da riqueza específica das comunidades perifíticas. Finalmente, as comunidades epifíticas foram floristicamente bem representadas pelos substratos artificiais.

The interannual variation of phytoplankton communities in the three main rivers of the Upper Paraná River floodplain is evaluated in relation to changes in the hydrosedimentological regime. These changes are a result of climatic variability and the formation of Porto Primavera Reservoir, located at the upper Paraná River. Phytoplankton species richness and density were investigated in rivers during a prior period (1993)(1994) and eight years after reservoir impoundment (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007). Multiple analyses were conducted to test the differences between these time periods in order to find predictor variables for phytoplankton attributes. A total of 454 phytoplanktonic taxa were found. The regression analysis revealed significant differences between periods. In the years following construction of the Porto Primavera dam, species richness was lower in the Paraná River and density was higher in the three rivers. In general, the algal density decreased from 2005 to 2007. Diatoms and cyanobacteria contributed significantly to the total density during the period from March 1993 to February 1994. The years 2000-2007 presented the lowest diatom contribution to species richness and the highest cyanobacteria contribution. From 2000 on, cryptomonads and cyanobacteria dominated. The interannual variability of phytoplankton was probably influenced by changes in hydrosedimentological regime due to climatic variations (La Niña and El Niño -Southern Oscillation events -ENSO) and the operational procedures associated with an upstream reservoirs. Studies on climatic variability and its effects on hydrosedimentological regimes of the Paraná, Baía and Ivinhema rivers and the biota therein are necessary to obtain subsidies for management, including decisions related to the operation of dams upstream and downstream of the study area, with the purpose of minimizing risks to the Environmental Protection Area.

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The aim of this study was to analyze the effects of flood pulses (intensity) on the richness and composition of periphytic algae in lentic environments of the Upper Paraná River floodplain, over a six-year period. Other factors, such as connectivity of the environments with the main channel of the river and the availability of substrate for the periphyton, were also evaluated. For qualitative analyses, periphyton community was sampled from adult petioles of Eichhornia azurea Kunth taken from the littoral regions of the lakes studied. A total of 457 taxa of periphytic algae, distributed within 141 genera and 10 classes, were registered in the four environments. The greatest richness of periphytic algae was observed in connected floodplain lakes, especially in 2007 and during high water periods. In both connected and disconnected lakes, richness correlated positively with water levels of the Paraná River. Richness was also positively correlated with the number of taxa of aquatic macrophytes. The specific composition of periphytic algae differed between high and low water periods, and between connected and disconnected lakes. Therefore, among the considered variables, it is evident that flood pulse constitutes the principal force acting on periphytic algae communities of the floodplain, followed by the degree of connectivity and the presence of aquatic macrophytes.Keywords: periphyton, species richness, species composition, flood pulse, floodplain, disturbance, degree of connectivity. Efeito do regime hidrológico e da conectividade na similaridade taxonômica de algas perifíticas: variação interanual ResumoEste trabalho visou analisar o efeito do pulso de inundação (intensidade) sobre a riqueza e composição de algas perifíticas, ao longo de seis anos, em ambientes lênticos da planície de inundação do Alto Rio Paraná. A influência da conectividade dos ambientes com a calha principal do rio e disponibilidade de substratos para a comunidade de algas perifíticas também foi avaliada. Para análise, a comunidade perifítica foi amostrada de pecíolos adultos de Eichhornia azurea Kunth, retirados da região litorânea das lagoas estudadas. Considerando os quatro ambientes, foram registrados 457 táxons de algas, distribuídos em 141 gêneros e 10 classes. A maior riqueza de algas perifíticas foi observada em lagoas conectadas, com destaque para o ano de 2007 e para o período de águas altas. A riqueza apresentou correlação positiva, nas lagoas conectadas e não conectadas, com nível hidrométrico do Rio Paraná. Também esteve correlacionada positivamente com o número de táxons de macrófitas aquáticas. A composição de algas perifíti-cas diferiu entre os períodos de águas altas e águas baixas e entre lagoas conectadas e não conectadas. Ficou evidente que, dentre as variáveis consideradas, o pulso de inundação constitui a principal função de força atuando sobre a comunidade de algas perifíticas na planície, seguido pelo grau de conectividade e presença de macrófitas aquáticas.Palavras-chave: perifíton, riqueza, composição específ...

Com este trabalho, objetivou-se investigar as espécies pertencentes às famílias Desmidiaceae, Gonatozygaceae e Mesotaeniaceae na comunidade perifítica de um reservatório, localizado no Sul do Brasil. As amostras foram coletadas durante os períodos de verão e inverno em distintas regiões ao longo do eixo rio-barragem do reservatório. Os substratos, coletados sempre na região litorânea, foram pecíolos de vegetação aquática. Foram identificados 45 táxons, distribuídos nos gêneros Actinotaenium (1 espécie), Cosmarium (17), Cylindrocystis (1), Euastrum (3), Gonatozygon (1),Hyalotheca (1), Micrasterias (7), Netrium (1), Pleurotaenium (1), Spondylosium (1), Staurastrum (9) e Staurodesmus (2). Maior riqueza de espécies ocorreu na região de transição para ambos os períodos de coleta. Euastrum denticulatum Gay e Hyalotheca dissiliens (Smith) Brébisson ex Ralfs apresentaram 100% de ocorrência, enquanto Cosmarium abbreviatum Raciborski var. minus (West & West) Krieger & Gerloff e Pleurotaenium ehrenbergii (Brébisson) De Bary ocorreram em 83% das amostras.

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