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Ogilvy C, Constantine R, Bury SJ, Carroll EL. Diet variation in a critically endangered marine predator revealed with stable isotope analysis. ROYAL SOCIETY OPEN SCIENCE 2022; 9:220470. [PMID: 35991335 PMCID: PMC9382206 DOI: 10.1098/rsos.220470] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Accepted: 07/20/2022] [Indexed: 06/15/2023]
Abstract
Understanding the foraging ecology of animals gives insights into their trophic relationships and habitat use. We used stable isotope analysis to understand the foraging ecology of a critically endangered marine predator, the Māui dolphin. We analysed carbon and nitrogen isotope ratios of skin samples (n = 101) collected from 1993 to 2021 to investigate temporal changes in diet and niche space. Genetic monitoring associated each sample with a DNA profile which allowed us to assess individual and population level changes in diet. Potential prey and trophic level indicator samples were also collected (n = 166; 15 species) and incorporated in Bayesian mixing models to estimate importance of prey types to Māui dolphin diet. We found isotopic niche space had decreased over time, particularly since the 2008 implementation of a Marine Mammal Sanctuary. We observed a decreasing trend in ∂13C and ∂15N values, but this was not linear and several fluctuations in isotope values occurred over time. The largest variation in isotope values occurred during an El Niño event, suggesting that prey is influenced by climate-driven oceanographic variables. Mixing models indicated relative importance of prey remained constant since 2008. The isotopic variability observed here is not consistent with individual specialization, rather it occurs at the population level.
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Affiliation(s)
- Courtney Ogilvy
- School of Biological Sciences, University of Auckland, Auckland 1010, New Zealand
| | - Rochelle Constantine
- School of Biological Sciences, University of Auckland, Auckland 1010, New Zealand
- Institute of Marine Science, University of Auckland, Auckland 1010, New Zealand
| | - Sarah J. Bury
- National Institute of Water and Atmospheric Research, Greta Point, Wellington 6021, New Zealand
| | - Emma L. Carroll
- School of Biological Sciences, University of Auckland, Auckland 1010, New Zealand
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Schwarz JFL, DeRango EJ, Zenth F, Kalberer S, Hoffman JI, Mews S, Piedrahita P, Trillmich F, Páez-Rosas D, Thiboult A, Krüger O. A stable foraging polymorphism buffers Galápagos sea lions against environmental change. Curr Biol 2022; 32:1623-1628.e3. [PMID: 35240048 DOI: 10.1016/j.cub.2022.02.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 01/20/2022] [Accepted: 02/01/2022] [Indexed: 11/26/2022]
Abstract
Understanding the ability of animals to cope with a changing environment is critical in a world affected by anthropogenic disturbance.1 Individual foraging strategies may influence the coping ability of entire populations, as these strategies can be adapted to contrasting conditions, allowing populations with foraging polymorphisms to be more resilient toward environmental change.2,3 However, environmentally dependent fitness consequences of individual foraging strategies and their effects on population dynamics have not been conclusively documented.4,5 Here, we use biologging data from endangered Galápagos sea lion females (Zalophus wollebaeki) to show that benthically foraging individuals dig after sand-dwelling prey species while pelagic foragers hunt in more open waters. These specialized foraging behaviors result in distinct and temporally stable patterns of vibrissae abrasion. Using vibrissae length as a visual marker for the benthic versus pelagic foraging strategies, we furthermore uncovered an environment-dependent fitness trade-off between benthic and pelagic foragers, suggesting that the foraging polymorphism could help to buffer the population against the negative effects of climate change. However, demographic projections suggest that this buffering effect is unlikely to be sufficient to reverse the ongoing population decline of the past four decades.6 Our study shows how crucial a deeper understanding of behavioral polymorphisms can be for predicting how populations cope within a rapidly changing world. VIDEO ABSTRACT.
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Affiliation(s)
- Jonas F L Schwarz
- Department of Animal Behaviour, Bielefeld University, Bielefeld, NRW 33615, Germany.
| | - Eugene J DeRango
- Department of Animal Behaviour, Bielefeld University, Bielefeld, NRW 33615, Germany
| | - Friederike Zenth
- Chair of Wildlife Ecology and Management, Freiburg University, Freiburg, BW 79106, Germany
| | - Stephanie Kalberer
- Department of Animal Behaviour, Bielefeld University, Bielefeld, NRW 33615, Germany
| | - Joseph I Hoffman
- Department of Animal Behaviour, Bielefeld University, Bielefeld, NRW 33615, Germany
| | - Sina Mews
- Department of Business Administration and Economics, Bielefeld University, Bielefeld, NRW 33615, Germany
| | - Paolo Piedrahita
- Facultad de Ciencias de la Vida, Escuela Superior Politécnica del Litoral, Guayaquil, GP 090902, Ecuador
| | - Fritz Trillmich
- Department of Animal Behaviour, Bielefeld University, Bielefeld, NRW 33615, Germany
| | - Diego Páez-Rosas
- Universidad San Francisco de Quito, Galápagos Science Center, Isla San Cristobal, Islas Galápagos 200101, Ecuador
| | - Antoine Thiboult
- Department of Civil and Water Engineering, Université Laval, Québec, QC G1V 0A6, Canada
| | - Oliver Krüger
- Department of Animal Behaviour, Bielefeld University, Bielefeld, NRW 33615, Germany
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Jones KA, Ratcliffe N, Votier SC, Newton J, Forcada J, Dickens J, Stowasser G, Staniland IJ. Intra-specific Niche Partitioning in Antarctic Fur Seals, Arctocephalus gazella. Sci Rep 2020; 10:3238. [PMID: 32094418 PMCID: PMC7039921 DOI: 10.1038/s41598-020-59992-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Accepted: 01/31/2020] [Indexed: 11/10/2022] Open
Abstract
Competition for resources within a population can lead to niche partitioning between sexes, throughout ontogeny and among individuals, allowing con-specifics to co-exist. We aimed to quantify such partitioning in Antarctic fur seals, Arctocephalus gazella, breeding at South Georgia, which hosts ~95% of the world’s population. Whiskers were collected from 20 adult males and 20 adult females and stable isotope ratios were quantified every 5 mm along the length of each whisker. Nitrogen isotope ratios (δ15N) were used as proxies for trophic position and carbon isotope ratios (δ13C) indicated foraging habitat. Sexual segregation was evident: δ13C values were significantly lower in males than females, indicating males spent more time foraging south of the Polar Front in maritime Antarctica. In males δ13C values declined with age, suggesting males spent more time foraging south throughout ontogeny. In females δ13C values revealed two main foraging strategies: 70% of females spent most time foraging south of the Polar Front and had similar δ15N values to males, while 30% of females spent most time foraging north of the Polar Front and had significantly higher δ15N values. This niche partitioning may relax competition and ultimately elevate population carrying capacity with implications for ecology, evolution and conservation.
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Affiliation(s)
| | | | | | - Jason Newton
- Scottish Universities Environmental Research Centre, East Kilbride, Scotland
| | | | - John Dickens
- British Antarctic Survey, Cambridge, United Kingdom
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