This study presents applied methodologies to better understand the dynamics of mechanisms characterizing a portion of the Xingu River, with respect to fish communities living in that environment. Through the study of the ichthyofauna it is aimed to verify various environmental standard patterns, in order to assess the current conservation state of a part of the Xingu River. Based on surveys of the local ichthyofauna conducted over seasonal variations, analyses were conducted at the specieS, population and trophic guild levels. With regards to the ecological population level, study of biological parameters such as individual growth rates, asymptotic body length, mortality rates and size at first maturity were good indicators for a better understanding of the life history of those fish groups. Therefore a trend was observed in which species of relatively small body size to followed a "r" type strategy, whilw species of larger body sizes would follow the "k" strategy tactics. From a functional point of view, it was verified that guild community structure is not only a good indicator of convergence patterns to similar ecosystems as like the Xingu River studied stretch, but also a tool to assess its conservation status. A steady- state ecosystem model for the medium Xingu River sector indicated that it is a system highly instable, and simultaneusly look like a mature seasonal system. An apparent seasonal restriction of food availability observed in the studied river section could imply optimum use efficiency and transfer of the trophic resources. A biogeographic study was undertaken based on species occurrence in order to conceptualise the River stretch comprised between the confluences of the Iriri and Xingu Rivers up to the vicinity of of the village Senador José Porfirio, in the Xingu basin. By means of this analysis, it was possible to demonstrate that the medium upstream of waterfalls) and lower (downstream) courses of the Xingu River are parts of two endemic areas. The low affinity of species composition observed in these two sectors is attributed to geographic variations in the landscape. Therefore, the boundaries of the waterfalls around the village of Belomonte and the influence of the Amazon River in the lower Xingu course could trigger differences in ichthyofaunal composition and species abundance when compared to the medium course of that river. Finally, the importance of maintaining all hydrologic connectivity is pointed out in order to maintan the unity of the system, from the headwaters to the mouth. Impacts on environmental processes and fish populations in the medium course of the Xingu River as a result of the eventual construction of the Belemonte hydroelectric dam are discussed.
|
