Influência da Sazonalidade na Densidade e uso do Ambiente por Podocnemis Unifilis Troschel, 1848 (Testudines, Podocnemididae) na Área de Influência da Usina Hidrelétrica de Belo Monte, Rio Xingu, Pará

Abstract

The habitat loss by environmental degradation and fragmentation due to human activities is the most relevant impact to the drastic reduction of biodiversity. However, to the populations of Amazonian chelonians, above all the animals of the genus Podocnemis, we must add the direct capture of eggs and adult individuals that are historically and culturally used as food by indigenous people since before the European colonization persisting on riverine populations to this day. Despite the increasing academic and conservationist, interest that lead to the growth scientific publications about these podocnemidideans in the Amazon, most of the studies have dealt with reproductive aspects in nesting sites in large Brazilian rivers. Rare are the studies that deal with density, environmental use, and how seasonal variations influence their thermoregulatory behavior in habitats highly pressured by anthropic pressure. The construction Belo Monte hydroelectric power plant, on the Xingu River, Pará, will cause relevant environmental changes either aquatic or terrestrial ecosystems. To know the ecological parameters of Podocnemis unifilis a priori of the river impoundment, it is extremely important to evaluate the responses to these environmental changes and to guide actions directed to minimize the negative effects of such alterations might represent to this species. In this study, we evaluated the different factors that, together with the seasonal variation, might influence on the population abundance and density of P. unifilis in this area of the Xingu River. During field works, we proceeded with visual count of specimens in thermoregulatory activity on the three sampling areas, during the four regional hydrological cycles, seeking out density, abundance and possible preferences of habitat use and its relationships with abiotic variables as air and water temperature and depth of the water body. As a result, we observed that the population density of P. unifilis is not uniform among the sampling areas, probably due the unequal human occupation of the study area. As to seasonality, there were evidences of a higher number of individuals sighted during the dry season of the Xingu River followed by the rainy season. The abundance difference between seasons was not statistically significant and the density presented the same pattern of variability along the season periods. As to habitat use it was not possible to statistically determine preferences as to the side (left or right) nor the kind of margin (island or riverbank) used by these animals. However, it was noted a uneven distribution on these environments which might also be related with the irregular anthropic occupation between both margins and to the known seasonal migratory movement of this species. Generally, when we evaluate the influence of water temperature and depth of the sighting spots, between hydrological cycles, we did not verify statistical differences with positive correlation. However, when the environmental variable analyzed is the air temperature we observed a strong statistical significance when compared to the population density in all hydrological cycles evaluated. We suggest that this environmental variable may better explain the density patterns when the method used to estimate abundance is the count of the number of specimens in thermoregulatory activities. The differences observed in the population density among sampling areas and hydrological cycles in this part of Xingu River demonstrate the importance of knowing the influence of the environmental characteristics in the process of habitat use facing the indiscriminate consumption of this species by the local community. Moreover, the data obtained will enable that comparative studies a posteriori of the Belo Monte hydroelectric power plant impoundment permit to know the real effect of these environmental changes on this important zoological category.