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.
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2003-04-16Autor
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.