DOI: 10.5061/dryad.wwpzgmstq
title: Trophic discrimination of amino acid-specific nitrogen stable isotopes in raptor nestlings: implications for estimating trophic position

description: Bulk stable isotope analysis of carbon and nitrogen is commonly used to
 assess trophic relationships among organisms in a wide variety of
 ecosystems. However, compound-specific stable isotope analysis of
 individual amino acids may be a more accurate approach for resolving food
 web structure. We compared the applicability of bulk and compound specific
 methods in an Arctic tundra ecosystem. Specifically, we determined bulk
 δ13C and δ15N, as well as amino acid specific δ15N, in red blood cells
 from nestling raptors and muscle samples from common prey species. We
 subsequently estimated bulk and amino-acid specific trophic discrimination
 factors (TDFs) for nitrogen in gyrfalcons (Falco rusticolus) using
 high-precision diet estimates from nest cameras to compare against TDFs in
 the literature. Although bulk δ15N values of secondary consumers were
 enriched relative to primary consumers, overlap occurred across groups and
 greater separation was apparent using δ15N of amino acids. Comparing red
 blood cell δ15N values to prey muscle δ15N values, we found that bulk TDFs
 and compound-specific TDFs for trophic amino acids were lower than values
 from the literature that have typically been used to estimate trophic
 position. Our findings suggest that while δ15N values of amino acids have
 the potential to improve our assessment of trophic relationships, the
 assumption that amino acid specific TDFs remain constant across all
 consumers and diet types is violated for raptor nestlings, such that
 consumer-specific TDFs must be calculated to accurately estimate trophic
 position. Use of “universal” TDFGlu-Phe values will result in an
 underestimate of nestling trophic level. Diet estimates for nestlings
 based on stable isotope mixing models that use adult TDFs for will be
 inaccurate.  
description: ## Trophic discrimination of amino acid-specific nitrogen stable isotopes
 in raptor nestlings: implications for estimating trophic position
 [https://doi.org/10.5061/dryad.wwpzgmstq](https://doi.org/10.5061/dryad.wwpzgmstq) ## Description of the data and file structure These datasets include both bulk and compound-specific stable isotope values from a variety of species collected in the Seward Peninsula in Alaska in .csv format. ### Files and variables For the following CSV's, there are quite a few repeated variables and as such they are only defined in the data sheet they first appear in. Furthermore, some of the variable names are self-explanatory and as such are not defined. Finally, some column names were only used for record-keeping purposes and are not relevant to analysis. These column names are thus omitted to avoid confusion. **File: CSIA_Bulk.csv** **Description:** Dataset for compiled bulk and compound specific stable isotope values across all species.  ** Missing values denoted as NA in this datasheet **Variables** * UCD_ID: ID assigned by UC Davis * id:  * nest_id: * species:  * hatch_date: * year:  * category: A, M, P, S, T or R for Arctic Ground Squirrel, Microtine Rodents, Passerine, Shorebirds, Ptarmigan, or Raptors, respectively.  * Ala: Alanine (permil) * Asp: Aspartic Acid (permil) * Glu: Glutamine (permil) * Gly: Glycine (permil) * His: Histidine (permil) * Hyp: Hydroxyproline (permil) * Ile: Isoleucine (permil) * Leu: Leucine (permil) * Lys: Lysine (permil) * Met: Methionine (permil) * Phe: Phenylalanine (permil) * Pro: Proline (permil) * Ser: Serine (permil) * Thr: Threonine (permil) * Tyr: Tyrosine (permil) * Val: Valine (permil) * d15N: Delta 15 N (permil) * d13C: Delta 13 C in (permil) **File: CSIA_camdata.csv** **Description:** Data from camera traps nests describing prey type consumed at each nest. *Missing values are not present except for in the comments, where they are denoted with a "-". **Variables** * nest_id:  * year: * age_precise: Exact age as according to the hour * brood_size: * photo: photo number * species: * class: A, M, P, S, T or R for Arctic Ground Squirrel, Microtine Rodents, Passerine, Shorebirds, Ptarmigan, or Raptors, respectively.  * biomass_total_alt: Estimated biomass for each species of prey. * time: * sex: * consumed: Percentage of prey item that was consumed by nestling * corrected_biomass_alt: Percentage of prey item that was consumed by nestling * A: Binary 0/1 Arctic Ground Squirrel, * M: Binary 0/1 Microtine Rodents * O: Binary 0/1 Other * P: Binary 0/1 Passerine * S: Binary 0/1 Shorebirds * T: Binary 0/1 Ptarmigan * comments:  **File: preytab_CSIA.csv** **Description:** Summarized compound-specific data of amino acids across prey species grouped into one of five categories. **Variables** * category: A, M, P, S, T for Arctic Ground Squirrel, Microtine rRodents, Passerine, Shorebirds, Ptarmigan, or Raptors, respectively.  * n: number of individuals per category  *** SD stands for standard deviation. **File: RAPTOR_CSIA_GYRF.csv** **Description:** Compound specific data of amino acids across all juvenile raptors. **Variables** See above variables ## Code/software R (V 4.2.1) and RStudio (2024.04.2+764) were used to run the analysis. Base R, as well as the following packages were used. * ggplot2 * plyr * dplyr * lme4 * lmerTest * emmeans * car * agricolae * tidyr