Abstract
Individual specialization, which describes whether populations are comprised of dietary generalists or specialists, has profound ecological and evolutionary implications. However, few studies have quantified individual specialization within and between sympatric species that are functionally similar but have different foraging modes. We assessed the relationship between individual specialization, isotopic niche metrics and foraging behaviour of two marine predators with contrasting foraging modes: pelagic foraging female South American fur seals (Arctocephalus australis) and benthic foraging female southern sea lions (Otaria byronia). Stable isotope analysis of carbon and nitrogen was conducted along the length of adult female vibrissae to determine isotopic niche metrics and the degree of individual specialization. Vibrissae integrated time ranged between 1.1 and 5.5 years, depending on vibrissae length. We found limited overlap in dietary niche-space. Broader population niche sizes were associated with higher degrees of individual specialization, while narrower population niches with lower degrees of individual specialization. The degree of individual specialization was influenced by pelagic and benthic foraging modes. Specifically, South American fur seals, foraging in dynamic pelagic environments with abundant but similar prey, comprised specialist populations composed of generalist individuals. In contrast, benthic southern sea lions foraging in habitats with diverse but less abundant prey had more generalist populations composed of highly specialized individuals. We hypothesize that differences in specialization within and between populations were related to prey availability and habitat differences. Our study supports growing body of literature highlighting that individual specialization is a critical factor in shaping the ecological niche of higher marine predators.
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The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
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Acknowledgements
We thank R. Orben, N. Rendell, M. Tierney and L. Poncet for assisting with field work, as well as J. Newton for his help with laboratory work. AMMB received funding from the Shackleton Scholarship Fund (Centenary Award), Rufford Small Grants, Sea World and Busch Gardens Conservation Fund, Joint Nature Conservation Committee, National Geographic Society, Winifred Violet Scott, Falkland Islands Government Environmental Studies Budget, Darwin Initiative, Project AWARE, PADI Foundation, Falkland Islands Offshore Hydrocarbons Environmental Forum, and a Waitt ROC grant. KAJ received funding from the NERC Life Sciences Mass Spectrometry Facility and National Geographic Society. Financial support to SR through a co-funded scholarship of Macquarie University and Agencia Nacional de Investigación e Innovación, is deeply acknowledged.
Funding
This research was funded by Shackleton Scholarship Fund (Centenary Award), Rufford Small Grants, Sea World and Busch Gardens Conservation Fund, Joint Nature Conservation Committee, National Geographic Society, Winifred Violet Scott, Falkland Islands Government, Darwin Initiative, Project AWARE, Macquarie University and Agencia Nacional de Investigación e Innovación (2017654), PADI Foundation, and Waitt ROC grant. It was also funded by the NERC Life Sciences Mass Spectrometry Facility (EK280-03/17), and the National Geographic Society (Early Career Explorers Grant; WW-260ER-17).
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AMMB conceived the study. SR, AMMB, RGH, VR and DJS contributed to the study design. AMMB and KAJ conducted the fieldwork. AMMB and KAJ processed the samples and performed the laboratory analysis. SR analysed the data, created figures and wrote the manuscript. All co-authors revised the manuscript critically and provided feedback. All authors read and gave approval for publication to the final version of the manuscript.
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Riverón, S., Raoult, V., Baylis, A.M.M. et al. Pelagic and benthic ecosystems drive differences in population and individual specializations in marine predators. Oecologia 196, 891–904 (2021). https://doi.org/10.1007/s00442-021-04974-z
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DOI: https://doi.org/10.1007/s00442-021-04974-z