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In the quest of isotope equilibrium for trophic discrimination estimation: diet–tissue dynamics in Nile crocodiles (<i>Crocodylus niloticus</i>)
Soto, David X Radloff, Frans GT Hobson, Keith A Leslie, Alison J
Soto, David X
Radloff, Frans GT
Hobson, Keith A
Leslie, Alison J
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2025-06-09
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Stable isotopes of carbon (<i>δ</i><sup>13</sup>C) and nitrogen (<i>δ</i><sup>15</sup>N) are increasingly employed to study the foraging ecology of ectothermic predators like crocodilians. However, accurate and precise estimations of trophic discrimination factors between diet and crocodile tissues (<i>Δ</i><sup>13</sup>C and <i>Δ</i><sup>15</sup>N) from captive experiments under controlled conditions are necessary to reliably quantify the contribution of different prey items make to their diet. The issue of an isotopically constant diet which leads to isotope equilibrium is an important factor influencing accurate estimations of diet-tissue discrimination factors. We raised Nile crocodiles (<i>Crocodylus niloticus</i>) under controlled experimental conditions feeding them with two isotopically distinct (but constant) diets until tissues reached isotopic equilibrium. We sampled blood (plasma and red blood cells, RBC), scute keratin and collagen, and nail tissues throughout the experiment to estimate diet-tissue discrimination factors. Overall, our estimations of average diet-tissue discrimination factors for <i>δ</i><sup>13</sup>C were +0.2 ‰ for plasma, +0.1 ‰ for RBC, +0.2 ‰ for keratin, +1.9 ‰ for collagen, and +1.2 ‰ for nail tissue, while for <i>δ</i><sup>15</sup>N values were -0.6 ‰ for plasma, +1.5 ‰ for RBC, +1.5 ‰ for keratin, +2.3 ‰ for collagen, and +1.8 ‰ for nail tissue. Body size did not have a significant effect on these tissue estimates, but plasma <i>Δ</i><sup>15</sup>N was influenced slightly. Understanding these differences in ectotherm isotope ecology is crucial for interpreting trophic relationships within food webs that include animals such as reptiles.
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Soto, D. X., Radloff, F. G. T., Bond, A. L., Hobson, K. A., & Leslie, A. J. (2025). In the quest of isotope equilibrium for trophic discrimination estimation: diet–tissue dynamics in Nile crocodiles (Crocodylus niloticus). Isotopes in Environmental and Health Studies, 1–20. https://doi.org/10.1080/10256016.2025.2535762
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1025-6016
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1477-2639