DOI: 10.5061/dryad.b5mkkwhg3
title: Isotopic niche partitioning and individual specialization in an Arctic raptor guild

description: 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.
description: This dataset contains the following files:
 "CAM_MASTER_FULL.csv": Raw dietary data from Gyrfalcon
 feeding observations from nest cameras from 2014-2019.
 "CAM_MASTER_SIA.csv": Subset of CAM_MASTER_FULL.csv
 which only includes camera prey observations contemporaneous with stable
 isotope data (e.g., select nests from 2016-2019).
 "SIA_GYRF_CAM.csv": Stable isotope data from red blood
 cells for individual Gyrfalcons from 2016-2019, for the subset of the
 study which had contemporaneous camera and stable isotope data.
 "SIA_Nests.csv": Mean stable isotope values for each
 raptor nest included in this study.
 "SIA_Prey.csv": Stable isotope values for each prey
 specimen measured in this study and incorporated into prey
 categories. "SIA_RAPTORS.csv": Stable isotope
 data from red blood cells for individual raptors; 2016-2019.
 Further methodological details can be found in the article to
 which this dataset is supplement
 (https://doi.org/10.1007/s00442-022-05154-3).
description: Further details on this dataset and how it was used can be found
 in the attached RMarkdown document (JAE-2020-00518.Rmd). 
 *note*: the "RData" data folder contains a .RData
 object containing output from the Bayesian Stable Isotope Mixing Models we
 ran for this analysis. Due to the computational intensity of these mixing
 models, we included the code we used to generate said models, then import
 them into the RMarkdown document via a separate .RData file
 (CH3_MODELS.RData). *note*: Some plots were generated
 using a package we wrote: "SIAplotR". A tar.gz file for this
 package is included so figures can be recreated exactly as they appear in
 the manuscript using the RMarkdown file.