Stable isotopes indicate consistent trophic structures but marked spatial variation in isotopic values across contrasting high-altitude Andean salars

High-altitude Andean salars are poly-extreme wetlands that support communities dominated by microorganisms and important populations of flamingos. Much of the work on these systems has focused on microbial community composition and function, but little is known regarding their trophic ecology. We evaluated the use of stable isotopes to compare food web organisation and consumption pathways in three contrasting Andean salars. We analysed δ¹³C, δ¹⁵N and δ³⁴S of primary producers, aquatic invertebrates and flamingos (feathers and faeces) in Laguna Puilar (Salar de Atacama), Salar de Tara and Salar de Pujsa. We quantified the isotopic niche volume and overlap between trophic components and used Bayesian mixing models to estimate the relative contribution of putative prey resources to flamingo diet. The trophic organisation was quite similar among the salars, however, the relative size of community and consumer isotopic niches differed markedly. At Puilar and Tara, most invertebrate niches were narrow and largely nested within the isotopic space occupied by flamingos, suggesting restricted resource use and limited dispersion in three-isotope space. In contrast, Pujsa showed a broader and more heterogeneous occupation of isotopic space among consumer taxa. Mixing models indicated that one or two dominant groups of aquatic invertebrates, together with diatoms, contributed substantially to the flamingos' diet, consistent with previous studies. The isotopic values of the feathers showed high variability, consistent with integration between multiple wetlands and, potentially, multiple species of flamingos, rather than simple local trophic generalism. Despite limitations related to the inability to assign feathers to specific species and incomplete coverage of meiofauna, the triple isotope approaches provided robust information on dominant energy sources and revealed local 'trophic identities' among salars. Stable isotopes therefore offer a non-invasive and effective framework for monitoring trophic structure in remote and difficult to study Andean salars under increasing anthropogenic pressure.