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A trophic study of the sympatric Amazonian freshwater turtles Podocnemis unifilis and Podocnemis expansa (Testudines, Podocnemidae) using carbon and nitrogen stable isotope analyses

Lara, N.R.F., Marques, T.S., Montelo, K.M., de Ataídes, Á.G., Verdade, L.M., Malvásio, A., de Camargo, P.B.
Canadian journal of zoology 2012 v.90 no.12 pp. 1394-1401
C3 plants, Podocnemis, basins, carbon, diet, intraspecific variation, nitrogen, rivers, stable isotopes, trophic relationships, turtles, Brazil
The Yellow-spotted River Turtle (Podocnemis unifilis Troschel, 1848) and the South American River Turtle (Podocnemis expansa (Schweigger, 1812)) are two turtles species that are widely distributed and have ecological, economic, and cultural importance in the Amazon basin. Although sympatric regarding most of their distribution, few studies have addressed the coexistence of these two species. To examine this, we analyzed the trophic level and the primary carbon source from the diets of both species in Baixo Araguaia, Tocantins, Brazil, using stable isotope analyses of carbon (δ¹³C) and nitrogen (δ¹⁵N). We also verified possible intraspecific variations (related to sex and body mass) in the trophic levels and primary carbon sources of their diets. Podocnemis unifilis had higher values of δ¹⁵N than P. expansa, averaging 7.59‰ and 5.06‰, respectively, a difference which may indicate a possible trophic change owing to exploiting different food resources. No differences were found between the two species in relation to δ¹³C (mean values of –26.2‰ and –26.1‰, respectively). The similarity between δ¹³C values suggests that the sources of their basal feeding are the same, consisting mainly of C₃ plants. There was no intraspecific variation in the values of δ¹³C and δ¹⁵N.