Abstract
The structure of the fish communities of a pool and a rapid in the ribeirão Santa Bárbara is described. This stream of 5th order is a direct tributary of the rio Tietê in the system of the upper rio Paraná. Thirty three species, from nine families and three orders, were referred in the two mesohabitats: the pool with 31 species, and the rapid with 18. Orders Characiformes, Siluriformes, and Perciformes presented the greatest number of species in the two mesohabitats. The families Characidae and Loricariidae were the most specious, followed by Cichlidae in the pool, and by Parodontidae in the rapid. Most species were accidental, 17 in the pool, and 10 in the rapid, and only six were constant in the two mesohabitats. The greatest diversity and evenness occurred in the pool. The seasonal variation for both assemblages was high, with the pool having a high turnover of species that could be due to the proximity with main channel of the rio Tietê.
Highlights
S A estrutura das comunidades de peixes de um poço e uma corredeira do ribeirão Santa Bárbara é descrita
A variação sazonal no poço e na corredeira foi alta, com o poço apresentando uma grande substituição de espécies, que pode ser devida à proximidade com o canal principal do rio Tietê
The ribeirão Santa Bárbara is a direct tributary of the rio Tietê right margin, in the Upper rio Paraná
Summary
In our analysis we have used the volume of rain, and have divided the studied period into high waters, from December to April (total precipitation of 874 mm), and low waters, from May to No-. To assess seasonal variation of the assemblages in each mesohabitat, we calculated the coefficient of variation (CV), using relative abundance of the species present in at least 50% of the collections (Grossman et al, 1990). We quantified the differences in the abundance and the composition of the ichthyofauna for both mesohabitats along the study period using non-metric multidimensional scaling analysis (MDS), a method for bidimensional arrangement which represents the association among samples in a similarity matrix; this analysis have been considered a robust technique for analyzing ecological data (Minchin, 1987). To quantify the similarity among months we used the Bray-Curtis distance measure applied to log(x+1) transformed data, in multivariate analyses software PRIMER 5 (Clarke and Gorley, 2001)
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