Stable isotopic composition of Bothrops atrox (common lancehead) in four distinct land covers in eastern Amazonia

Since consumers reflect the isotopic composition of an assimilated diet, stable isotopes can be a useful tool to address the feeding ecology of tropical snakes. This is the first study reporting carbon and nitrogen stable isotopic composition of Bothrops atrox (Linnaeus, 1758) living in different landscapes located in the lower Amazon river, encompassing four main natural landscapes of the Amazon: old-growth forests, várzeas (flooded forests), savannas, and pastures. Our null hypothesis is that the δ¹³C of forest specimens of B.atrox is more negative because forests are dominated by C₃ plants, while C₄ plants are common in the other landscapes. On the other hand, δ¹⁵N of forest specimens should be more positive, since the δ¹⁵N of old-growth forests are higher than plants of savanna, várzea, and pastures. Confirming our hypothesis, the δ¹³C of B. atrox scales of the Tapajós National Forest was approximate −25‰ to −24‰, increased to approximately −23.5‰ to −23.0‰ in the savanna and pasture, and to −21‰ in the várzea, showing an increased contribution of C₄-derived carbon. Some specimens of B. atrox had δ¹⁵N as high as 18‰, which is much higher than the average δ¹⁵N of the snake's prey (7‰), confirming the apex position of B. atrox in the Amazon region. The δ¹⁵N values of the forest specimens were 5‰ higher than the savanna specimens, and this difference decreased to 3‰ between the forest and the pasture, and the várzea specimens. Finally, there were not large differences between δ¹⁵N values of livers and scales in any of the landscapes, suggesting a constant diet through time, and reinforcing the possibility of the use of snake's scale as a less invasive and non-lethal tissue to analyze.

Abstract in Portuguese is available with online material.