Abstract
Variation in the foraging strategies used among species is a key factor in determining the trophic structure of ecological communities. Moreover, foraging niche differentiation could be driven by inter-specific competition and/or variation within species due to seasonal, age, sex and/or individual factors. Using stable isotope analysis, we assessed inter- and intra-specific differences in the foraging niches of female Southern Rockhopper penguin (Eudyptes chrysocome; SRP) and male and female Magellanic penguins (Spheniscus magellanicus; MP) at Isla de los Estados, Argentina. We sampled whole blood and feathers from breeding adults, representing the breeding and pre-moult periods over two consecutive years (2012 and 2013). We also compared stable isotope values between tissue to test for consistency in individuals foraging niches and the potential for foraging niche specialisation and segregation within breeding pairs. We observed clear foraging niche segregation between species that persisted during both breeding and pre-moult periods. SRP foraged in more oceanic/pelagic waters (lower δ13C values) while MP used coastal/benthic foraging habitats (higher δ13C values). In addition, SRP fed on lower trophic level prey (low δ15N values) relative to MP during both time periods. The isotopic foraging niches of MP highly overlapped between sexes at the population level and there was little to no evidence of niche segregation within breeding pairs or individual consistency in the seasonal foraging niche of both species. The results suggest that inter-specific foraging niche segregation is likely a more important factor influencing the trophic ecology and foraging behaviours of these species, relative to intra-specific factors. Even so, the persistence of inter-specific foraging niche segregation outside the breeding season suggests that either the potential for competition for food resource or foraging habitats remain high during this time or that the ultimate factors responsible for foraging niche segregation among these two species may be unrelated to these proximate factors.
Zusammenfassung
Saisonal anhaltende Nischensegregation zwischen sympatrischen Felsenpinguin und Magellan-Pinguinen, die auf de Isla de los Estados in Argentinien brüten
Variabilität in den Futtersuchstrategien zwischen Arten ist ein Schlüsselfaktor für die Bestimmung der trophischen Struktur ökologischer Gemeinschaften. Differenzierung in der Nahrungssuche könnte zusätzlich durch interspezifische Konkurrenz und/oder innerartliche Variation aufgrund saisonaler, altersbedingter, geschlechtsspezifischer und/oder individueller Faktoren bestimmt sein. Durch die Analyse von Stabilen Isotopen untersuchten wir inter- und intraspezifische Unterschiede in der Nahrungssuche von weiblichen Felsenpinguinen (Eudyptes chrysocome; SRP) und männlichen und weiblichen Magellan-Pinguinen (Spheniscus magellanicus; MP) auf der Isla de los Estados in Argentinien. In zwei aufeinander folgenden Jahren (2012 und 2013) haben wir sowohl zur Brutzeit wie zur Mauserzeit Blut und Federn von brütenden Altvögeln gesammelt. Auch haben wir Stabile Isotopen zwischen Geweben verglichen, um die Konsistenz der individuellen Nahrungsnische sowie das Potenzial für die Spezialisierung und Segregation von Nahrungsnischen innerhalb von Brutpaaren zu testen. Wir beobachteten eine klare Segregation der Nahrungsnischen zwischen den Arten, die während der Brut- und der Mauserzeit fortbestanden. SRP suchten nach Futter vornehmlich in ozeanischeren/pelagischen Gewässern (niedrigere δ13C-Werte), MP dagegen in küstennahen/benthischen Nahrungslebensräumen (höhere δ13C-Werte). Außerdem ernährten sich SRP während beider Zeiträume von Beute mit niedrigerem trophischen Niveau (niedrige δ15N-Werte). Die über die Isotopenzusammensetzung ermittelten Nahrungsnischen von MP überlagerten sich auf Populationsebene stark zwischen Geschlechter, doch es fanden sich keine deutlichen Hinweise auf eine Nischentrennung innerhalb der Brutpaare oder auf individuelle Konsistenz in der saisonalen Nahrungsnische beider Arten. Die Ergebnisse deuten darauf hin, dass die interspezifische Nischensegregation bei der Nahrungssuche wahrscheinlich ein wichtigerer Faktor ist, im Vergleich zu intra-spezifischen Faktoren, der die trophische Ökologie und das Nahrungssuchverhalten dieser Arten beeinflusst. Das Fortbestehen einer interspezifischen Nischensegregation außerhalb der Brutzeit lässt darauf schließen, dass entweder das Konkurrenzpotenzial um Nahrungsressourcen oder Nahrungslebensräume während dieser Zeit hoch bleibt, oder dass die ultimten Faktoren, die für die Segregation der Nahrungsnischen der beiden Arten unabhängig von diesen proximaten Faktoren sind.
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Acknowledgements
This study was financially supported by the Agencia Nacional de Promoción Científica y Tecnológica (PICT 2010 No. 1520, 2012 No. 1832, 2014 No. 1870), Wildlife Conservation Society, Consejo Nacional de Investigaciones Científicas y Técnicas (Rosciano PhD fellowship) and the BEC.AR-Fulbright program, Argentine Presidential Fellowship in Science and Technology (Rosciano fellowship). The authors thank to R. Saenz Samaniego for logistic support and fieldwork assistance; Juan Romanelli, Sabrina Harris, Valeria Bruno and Mariel Guala for fieldwork assistance. Thank you to K. Duernberger, S. Emslie and C. Lane for helpful assistance with stable isotope analysis. Special thanks go to the Argentine Navy and Henk Boersma for transportation to Isla de los Estados. We are thankful to two anonymous reviewers that helped improve the manuscript with their comments and suggestions. Thank you to Tamara Zalewski for the abstract translation to German.
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Rosciano, N.G., Polito, M.J. & Raya Rey, A. Seasonally persistent foraging niche segregation between sympatric Southern Rockhopper and Magellanic penguins breeding at Isla de los Estados, Argentina. J Ornithol 161, 1093–1104 (2020). https://doi.org/10.1007/s10336-020-01800-w
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DOI: https://doi.org/10.1007/s10336-020-01800-w