Which trophic discrimination factors fit the best? A combined dietary study of a coastal seabird

  • PDF / 1,561,691 Bytes
  • 12 Pages / 595.276 x 790.866 pts Page_size
  • 65 Downloads / 167 Views

DOWNLOAD

REPORT


ORIGINAL ARTICLE

Which trophic discrimination factors fit the best? A combined dietary study of a coastal seabird Annick Morgenthaler1   · Ana Millones1   · Patricia Gandini1,2 · Esteban Frere1,2  Received: 18 June 2020 / Revised: 3 August 2020 / Accepted: 20 August 2020 © Deutsche Ornithologen-Gesellschaft e.V. 2020

Abstract The use of combined conventional and stable isotope analyses to study the diet of seabirds has become very frequent. Unfortunately species and tissue-specific Trophic Discrimination Factors (TDF), necessary to run stable isotope mixing models in the most performing way, are lacking for a wide number of seabird species. We assessed the process of inspecting and selecting the most adequate TDFs by running mixing region simulations with three different TDFs scenarios. This was carried out in a combined dietary study of a widespread but poorly studied seabird from the Americas: the Neotropic Cormorant (Phalacrocorax brasilianus), at a breeding colony from coastal Patagonia. The mixing models were run with the best fitting carbon and nitrogen TDFs (whole blood), which were those obtained with R package SIDER, a Bayesian inference-based model predicting the TDFs of consumers considering their ecology and phylogenetic relatedness. We found that cormorants fed on rather mobile fish of a fairly variable ecological spectrum, both benthic and pelagic, and showed low prey diversity. Our results coincide with the overall generalist and opportunistic piscivorous habit found at different coastal areas along its broad distribution range. Despite some differences found in the proportion estimates of the main prey between the two methods, their combination through the incorporation of prior information into the mixing models provides a comprehensive trophic profile. Finally, the use of SIDER, alongside the inspection and comparison of different potential TDF values, offered a simple and effective framework to calculate and select the most adequate specific TDFs to be employed in stable isotope mixing models. Keywords  Diet · Stable isotope mixing model · Trophic discrimination factor · SIDER · Phalacrocorax brasilianus · Neotropic cormorant Zusammenfassung Welche trophischen Unterscheidungsfaktoren passen am besten? Eine kombinierte Ernährungsstudie bei einem Küsten-Seevogel Bei Ernährungsuntersuchungen an Seevögeln wird immer häufiger eine Kombination von konventionellen Analysen mit solchen mit Stabilen Isotopen angewandt. Leider aber fehlen uns für eine große Anzahl von Seevogelarten die art- und Communicated by C. Barbraud. Electronic supplementary material  The online version of this article (https​://doi.org/10.1007/s1033​6-020-01813​-5) contains supplementary material, which is available to authorized users. * Annick Morgenthaler [email protected] 1



Centro de Investigaciones de Puerto Deseado, Universidad Nacional de la Patagonia Austral, Av. Prefectura s/n, 9050 Puerto Deseado, Santa Cruz, Argentina



Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Av. Prefectu