Abstract
Intra- and inter-specific resource partitioning within predator communities is a fundamental component of trophic ecology, and one proposed mechanism for how populations partition resources is through individual niche variation. The Niche Variation Hypothesis (NVH) predicts that inter-individual trait variation leads to functional trade-offs in foraging efficiency, resulting in populations composed of individual dietary specialists. The degree to which niche specialization persists within a population is plastic and responsive to fluctuating resource availability. We quantified niche overlap and tested the NVH within an Arctic raptor guild, focusing on three species that employ different foraging strategies: golden eagles (generalists); gyrfalcons (facultative specialists); and rough-legged hawks (specialists). Tundra ecosystems exhibit cyclic populations of arvicoline rodents (lemmings and voles), providing a unique system in which to examine predator diet in response to interannual fluctuations in resource availability. Using blood δ13C and δ15N values from 189 raptor nestlings on Alaska’s Seward Peninsula (2014–2019), we calculated isotopic niche width and used Bayesian stable isotope mixing models (BSIMMs) to characterize individual specialization and test the NVH. Nest-level specialization estimated from stable isotopes was strongly correlated with indices of specialization based on camera trap data. We observed a high degree of isotopic niche overlap between the three species and gyrfalcons displayed a positive relationship between individual specialization and population niche width on an interannual basis consistent with the NVH. Our findings suggest plasticity in niche specialization may reduce intra- and inter-specific resource competition under dynamic ecological conditions.
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Data archiving statement
Data (except nest locations) and code available from the Dryad digital repository (submission upon acceptance with a one-year embargo); no location data will be provided for raptors as specified by Alaska state law.
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Acknowledgements
Special thanks to Peter Bente, John Earthman, Bryce Robinson, Joe Eisaguirre, Tim Howe, and all field technicians that assisted in fieldwork. The following employees of the University of Alaska Museum of the North assisted with collection protocols and specimen identification: Link Olson, Aren Gunderson and Jack Withrow. We also thank PhD committee members Diane O’Brien and Greg Breed for providing feedback on the manuscript.
Funding
Funding was provided by The Peregrine Fund (Graduate Research Grant), the University of Alaska Fairbanks, the Alaska Department of Fish and Game (ADFG) State Wildlife Grant Program, the Calvin J. Lensink Graduate Fellowship in Wildlife Biology, and the Angus Gavin Migratory Bird Grant.
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DLJ and CTW conceived the manuscript and analyzed the data. DLJ, DLA, MTH, and TLB conducted fieldwork. DLJ wrote the manuscript; other authors provided editorial advice.
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All fieldwork conducted for this study was approved under the University of Alaska Fairbanks Institutional Animal Care and Use Committee (IACUC) protocols (#1187547; #1151727). Banding activities were conducted under USGS federal permit (#20499). Scientific collection activities were conducted under a USFWS Migratory Bird Collection Permit (#MB-75275-0) and ADFG Scientific Permit (#18-139; #19-139).
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Communicated by Seth Newsome.
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Johnson, D.L., Henderson, M.T., Anderson, D.L. et al. Isotopic niche partitioning and individual specialization in an Arctic raptor guild. Oecologia 198, 1073–1084 (2022). https://doi.org/10.1007/s00442-022-05154-3
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DOI: https://doi.org/10.1007/s00442-022-05154-3