Reservoir longitudinal gradient promotes ordered losses on diversity and density of Ephemeroptera community / O gradiente longitudinal de um reservatório promove perdas ordenadas na diversidade e densidade da comunidade de Ephemeroptera

Abstract Reservoir operations alter, eliminate or restrain the natural hydrologic cycles. Biotic community has become subject to these non-cyclic events, responding by reducing the species diversity. Ephemeroptera species present distinct responses to environmental deterioration such that poses this assemblage between the most useful groups in biomonitoring programs. We hypothesized an alteration in beta diversity at the longitudinal species gradient, which will be influenced mainly by species losses between zones. Changes in temporal beta diversity is also expected, but the main drivers of such alterations will be the species turnover between the sampling period. Ephemeroptera community was monitored in nine sampling points from Itaipu Reservoir, where were installed three sets of substrates composed by a float and 2 wooden substrates. We took biological samples in triplicates monthly, from June-01 to August-02. Our initial hypothesis was partially supported and with significant variations only for spatial approach, between the Reservoir zones. The generated ordering from Non-Metric Dimensional Scale - NMDS - corroborated with spatial analyzes, with the formation of two groups along the gradient zonation of the reservoir. The temporal ordination showed no clear pattern. As expected, the contribution to beta diversity was different for our two approaches, such that the loss of species was more important along the spatial gradient and despite of no significant result, the species replacement was more important among months. The spatial results lead us to infer that differences in limnological characteristics between zones are important for determining differences in Ephemeroptera composition and can reflect the dependency degree of the species in relation to the lentic and sometimes-lotic conditions, mainly in the riverine zone of reservoirs. On the other hand, the absence of a temporal pattern can be result of chaotic variations in the physical and chemical attributes imposed by the reservoir operation, disrupting continuity of the biota and natural succession processes.

Resumo As operações de reservatórios alteram, eliminam ou restringem os ciclos hidrológicos naturais. A comunidade biótica torna-se sujeita a estes eventos não-cíclicos, respondendo com a redução da diversidade de espécies. As espécies de Ephemeroptera apresentam respostas distintas à deterioração ambiental, sendo o grupo muitousado em programas de biomonitoramento. Nós hipotetizamos uma alteração na diversidade beta das espécies no gradiente longitudinal, influenciada principalmente pelo componente aninhamento com a consequente perda de espécies entre as zonas do reservatório. Também são esperadas mudanças na diversidade beta entre os meses de amostragem, mas o principal fator dessas alterações será a substituição das espécies entre os períodos, em função dos rápidos ciclos de vida que o grupo apresenta. A comunidade Ephemeroptera foi monitorada em nove pontos amostrais do reservatório de Itaipu, onde foram instalados três conjuntos de substratos compostos por um flutuador e 2 substratos de madeira. Tomamos amostras biológicas em triplicatas mensalmente, de junho de 2001 a agosto de 2002. Nossa hipótese inicial foi parcialmente suportada, com variações significativas apenas na escala espacial. A ordenação gerada pelo Escalonamento Dimensional Não-Métrico - NMDS - corroborou com as análises espaciais, com a formação de dois grupos ao longo do gradiente de zonação do reservatório. A ordenação temporal não mostrou um padrão claro. Como esperado, a contribuição para a diversidade beta foi diferente para nossas duas abordagens, de modo que a perda de espécies foi mais importante ao longo do gradiente espacial e apesar de não haver resultado significativo, a substituição das espécies foi mais importante entre os meses de amostragem. Os resultados espaciais levam-nos a inferir que as diferenças nas características limnológicas entre as zonas são importantes para determinar as diferenças na composição de Ephemeroptera e podem refletir o grau de dependência das espécies em relação às condições lênticas e às vezes lóticas, principalmente na zona fluvial dos reservatórios. Por outro lado, a ausência de um padrão temporal pode ser resultado de variações caóticas nos atributos físicos e químicos impostos pela operação do reservatório, que interrompem a continuidade da biota e os processos de sucessão naturais.

Reservoir longitudinal gradient promotes ordered losses on diversity and density of Ephemeroptera community.

Reservoir operations alter, eliminate or restrain the natural hydrologic cycles. Biotic community has become subject to these non-cyclic events, responding by reducing the species diversity. Ephemeroptera species present distinct responses to environmental deterioration such that poses this assemblage between the most useful groups in biomonitoring programs. We hypothesized an alteration in beta diversity at the longitudinal species gradient, which will be influenced mainly by species losses between zones. Changes in temporal beta diversity is also expected, but the main drivers of such alterations will be the species turnover between the sampling period. Ephemeroptera community was monitored in nine sampling points from Itaipu Reservoir, where were installed three sets of substrates composed by a float and 2 wooden substrates. We took biological samples in triplicates monthly, from June-01 to August-02. Our initial hypothesis was partially supported and with significant variations only for spatial approach, between the Reservoir zones. The generated ordering from Non-Metric Dimensional Scale - NMDS - corroborated with spatial analyzes, with the formation of two groups along the gradient zonation of the reservoir. The temporal ordination showed no clear pattern. As expected, the contribution to beta diversity was different for our two approaches, such that the loss of species was more important along the spatial gradient and despite of no significant result, the species replacement was more important among months. The spatial results lead us to infer that differences in limnological characteristics between zones are important for determining differences in Ephemeroptera composition and can reflect the dependency degree of the species in relation to the lentic and sometimes-lotic conditions, mainly in the riverine zone of reservoirs. On the other hand, the absence of a temporal pattern can be result of chaotic variations in the physical and chemical attributes imposed by the reservoir operation, disrupting continuity of the biota and natural succession processes.

Diversity in migratory patterns among Neotropical fishes in a highly regulated river basin.

Migratory behaviour of selected fish species is described in the Paraná River, Brazil-Argentina-Paraguay, to search for patterns relevant to tropical regulated river systems. In a 10 year mark-recapture study, spanning a 1425 km section of the river, 32 867 fishes composed of 18 species were released and 1083 fishes were recaptured. The fishes recaptured were at liberty an average 166 days (maximum 1548 days) and travelled an average 35 km (range 0-625 km). Cluster analysis applied to variables descriptive of movement behaviour identified four general movement patterns. Cluster 1 included species that moved long distances (mean 164 km) upstream (54%) and downstream (40%) the mainstem river and showed high incidence (27%) of passage through dams; cluster 2 also exhibited high rate of movement along the mainstem (49% upstream, 13% downstream), but moved small distances (mean 10 km); cluster 3 included the most fishes moving laterally into tributaries (45%) or not moving at all (25%), but little downstream movement (8%); fishes in cluster 4 exhibited little upstream movement (13%) and farthest downstream movements (mean 41 km). Whereas species could be numerically clustered with statistical models, a species ordination showed ample spread, suggesting that species exhibit diverse movement patterns that cannot be easily classified into just a few classes. The cluster and ordination procedures also showed that adults and juveniles of the same species exhibit similar movement patterns. Conventional concepts about Neotropical migratory fishes portray them as travelling long distances upstream. The present results broaden these concepts suggesting that migratory movements are more diverse, could be long, short or at times absent, upriver, downriver or lateral, and the diversity of movements can vary within and among species. The intense lateral migrations exhibited by a diversity of species, especially to and from large tributaries (above reservoirs) and reservoir tributaries, illustrate the importance of these habitats for the fish species life cycle. Considering that the Paraná River is highly impounded, special attention should be given to the few remaining low-impact habitats as they continue to be targets of hydropower development that will probably intensify the effects on migratory fish stocks.