Diversidade de avifauna aquática nas represas do médio e baixo Rio Tietê (SP) e nos sistema de lagos do médio Rio Doce (MG) e sua relação com o estado trófico e a morfometria dos ecossistemas aquáticos.
Branco, Magno Botelho Castelo
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Relationships between aquatic birds and the trophic state of freshwaters are not well known in tropical systems. In the present work the influence of some limnological variables on the structure of the aquatic bird comunnity was investigated for two distinct freshwater systems: The cascade of reservoirs in the middle and low portions of Tietê River (SP) and in the lakes belonging to the Rio Doce Valley( MG). In the Tietê River 37 different species were recorded. In the Rio Doce Valley 39 species were recorded. Together they totalize 52 species belonging to 10 Orders and 21 Families. In the Rio Doce system species of the Order Anseriformes were the most abundant, regarding both, numerical abundance and biomass. The highest density of birds in the Rio Doce lakes was 2,676 ind.km−2, recorded in Lagoa Amarela, and the lowest of 5.23 ind.km−2, in Lake Dom Helvécio. In this system community variables were significantly influenced only by the area and the perimeter of lakes. There were no significant relationships with the trophic state index or with the concentration of nitrogen and phosphorus, isolately. In the reservoirs of the Tietê River, the highest abundances were observed for the orders Ciconiiformes and Pelecaniformes. The highest densities occurred in Nova Avanhandava reservoir (64 ind.km−1) and the lowest in Ibitinga (6.0 ind.km−1). In this system the higher abundance of piscivorous birds, when compared to those of Rio Doce lakes, is probably related to the higher fish productivity of Tietê River. Although the influence of the trophic state upon the structure of the aquatic bird communities has not been verified for each system alone, due to the fact that the range of variation of the IET is too narrow, it is notorious the higher density of birds (ind.km−1 e kg.km−1) in the Tietê reservoir system when compared to that of the Rio Doce lakes. Differences in the trophic state among both systems are great, allowing to see a general relationship between the trophic state of these two systems and the densities of aquatic birds on them.