Gut content and stable isotope analyses provide complementary understanding of ontogenetic dietary shifts and trophic relationships among fishes in a tropical river
2012
DAVIS, AARON M. | BLANCHETTE, MELANIE L. | Pusey, Brad | JARDINE, TIM D. | PEARSON, RICHARD G.
1.âDespite widespread recognition of the role of body size in fish trophic ecology, little attention has been focused on this issue in isotopic studies, particularly in tropical systems. 2.âWe used analyses of stomach contents and stable isotopes to examine sizeârelated shifts in diet in a terapontid fish assemblage in the Australian wet–dry tropics. Stomach content analysis identified substantial ontogenetic dietary shifts in all species, corresponding to changes in body size–isotope trajectories for two species. Shifts away from relatively specialised diets of heavily 13Câdepleted insect larvae to consumption of a range of items across multiple basal carbon sources appeared to be the proximate cause of observed isotopic changes. 3.âAllochthonous organic matter in the form of C3 riparian vegetation was particularly important to smaller terapontids before larger fish shifted to a broad range of dietary items and similarly broad range of basal carbon sources. 4.âWhile there was general agreement between δ13C and stomach content analysis, there was minimal concurrence between the latter and δ15N isotopic derivation of estimates of trophic position. Due to factors such as omnivory, isotopically overlapping basal sources and uncertainties about rates of isotopic fractionation in both predator and prey species, stomach content analysis provides an essential complement to isotopic methodologies in tropical systems. 5.âGiven that basal sources supporting any individual species can change markedly with ontogeny, consideration of intraspecific, sizeârelated variation is necessary in isotopic studies of food web structure.
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