A trophic study of the sympatric Amazonian freshwater turtles Podocnemis unifilis and Podocnemis expansa (Testudines, Podocnemidae) using carbon and nitrogen stable isotope analyses - Lara, Neliton Ricardo Freitas; Marques, T.S; Montelo, K.M; Ataídes, Á.G. de; Verdade, Luciano Martins; Malvasio, Adriana; Camargo, Plinio Barbosa de (Canadian Journal of Zoology, 2012)