Compound‐specific stable isotope analysis (
Ecological similarity between species can lead to interspecific trophic competition. However, when ecologically similar species coexist, they may differ in foraging strategies and habitat use, which can lead to niche partitioning. As the body tissues of consumers contain a stable isotope signature that reflects the isotopic composition of their diet, stable isotope analysis is a useful tool to study feeding behavior. We measured the isotopic niche width, which is a proxy for trophic niche width, of mantled (
Between 2008 and 2012, we collected hair samples from 200 subjects (113 black and 87 mantled howler monkeys) and used continuous flow isotope ratio mass spectrometry to estimate
In allopatry, isotopic niche width and isotopic variation were similar in both species. In sympatry, black howler monkeys had a significantly broader isotopic niche, which was mainly determined by high
The coexistence of these ecologically similar species may be linked to trophic niche adjustments by one species, although the particular features of such adjustments (e.g., dietary, spatial, or sensory partitioning) remain to be addressed.
- NSF-PAR ID:
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Physical Anthropology
- Page Range / eLocation ID:
- p. 438-446
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Compound‐specific stable isotope analysis (
CSIA) of amino acids ( AA) has rapidly become a powerful tool in studies of food web architecture, resource use, and biogeochemical cycling. However, applications to avian ecology have been limited because no controlled studies have examined the patterns in AAisotope fractionation in birds. We conducted a controlled CSIAfeeding experiment on an avian species, the gentoo penguin ( Pygoscelis papua), to examine patterns in individual AAcarbon and nitrogen stable isotope fractionation between diet (D) and consumer (C) (Δ13CC‐Dand Δ15NC‐D, respectively). We found that essential AA δ13C values and source AA δ15N values in feathers showed minimal trophic fractionation between diet and consumer, providing independent but complimentary archival proxies for primary producers and nitrogen sources respectively, at the base of food webs supporting penguins. Variations in nonessential AAΔ13CC‐Dvalues reflected differences in macromolecule sources used for biosynthesis (e.g., protein vs. lipids) and provided a metric to assess resource utilization. The avian‐specific nitrogen trophic discrimination factor ( TDFGlu‐Phe= 3.5 ± 0.4‰) that we calculated from the difference in trophic fractionation (Δ15 NC‐D) of glutamic acid and phenylalanine was significantly lower than the conventional literature value of 7.6‰. Trophic positions of five species of wild penguins calculated using a multi‐ TDFGlu‐Pheequation with the avian‐specific TDFGlu‐Phevalue from our experiment provided estimates that were more ecologically realistic than estimates using a single TDFGlu‐Pheof 7.6‰ from the previous literature. Our results provide a quantitative, mechanistic framework for the use of CSIAin nonlethal, archival feathers to study the movement and foraging ecology of avian consumers.
It is imperative to understand how chemical preservation alters tissue isotopic compositions before using historical samples in ecological studies. Specifically, although compound‐specific isotope analysis of amino acids (CSIA‐AA) is becoming a widely used tool, there is little information on how preservation techniques affect amino acid
δ15N values. Methods
We evaluated the effects of chemical preservatives on bulk tissue
δ13C and δ15N and amino acid δ15N values, measured by gas chromatography/isotope ratio mass spectrometry (GC/IRMS), of (a) tuna ( ) and squid ( Thunnus albacares ) muscle tissues that were fixed in formaldehyde and stored in ethanol for 2 years and (b) two copepod species, Dosidicus gigas and Calanus pacificus , which were preserved in formaldehyde for 24–25 years. Eucalanus californicus Results
Tissues in formaldehyde‐ethanol had higher bulk
δ15N values (+1.4, ; +1.6‰, D. gigas ), higher T. albacares δ13C values for (+0.5‰), and lower D. gigas δ13C values for (−0.8‰) than frozen samples. The bulk T. albacares δ15N values from copepods were not different those from frozen samples, although the δ13C values from both species were lower (−1.0‰ for and −2.2‰ for E. californicus ) than those from frozen samples. The mean amino acid C. pacificus δ15N values from chemically preserved tissues were largely within 1‰ of those of frozen tissues, but the phenylalanine δ15N values were altered to a larger extent (range: 0.5–4.5‰). Conclusions
The effects of preservation on bulk
δ13C values were variable, where the direction and magnitude of change varied among taxa. The changes in bulk δ15N values associated with chemical preservation were mostly minimal, suggesting that storage in formaldehyde or ethanol will not affect the interpretation of δ15N values used in ecological studies. The preservation effects on amino acid δ15N values were also mostly minimal, mirroring bulk δ15N trends, which is promising for future CSIA‐AA studies of archived specimens. However, there were substantial differences in phenylalanine and valine δ15N values, which we speculate resulted from interference in the chromatographic resolution of unknown compounds rather than alteration of tissue isotopic composition due to chemical preservation.
Plant lipid biomarkers, such as plant waxes and terpenoids, and the stable isotopic composition of bulk leaves are widely used in both modern and paleoclimate studies for tracking vegetation and climate. However, the effects of different drying methods on the preservation of plant lipid biomarkers and the stable isotopic compositions of leaves are less explored. Here, we investigated various drying methods for the measurement of plant lipid concentrations and bulk leaf isotopic compositions.
Leaves from four tree species (
, Acer rubrum , Pinus sylvestris , and Platanus occidentalis ) were collected and dried using air, an oven, a freeze‐dryer, and a microwave. We compared concentrations of leaf waxes and terpenoids and carbon (δ13C) and nitrogen (δ15N) isotopic compositions of leaves by different drying methods. Taxodium distichum Results
The air, oven, freeze‐dryer, and microwave drying methods did not affect lipid concentrations significantly, and only a few homologues differed (38.1% or 41.8 μg/g on average) possibly due to biological variations or enhanced extraction efficiencies. The δ13C values were not affected by drying methods, whereas the δ15N values in oven‐dried leaves in some species were higher by 0.2–0.7‰ than those obtained by other methods. Though small, we attribute these patterns to loss of leaf compounds with lower isotope ratios during oven‐drying.
Based on our results, each drying technique yielded equivalent results for all plant wax and terpenoid concentrations and bulk leaf δ13C values; however, oven‐drying modified the δ15N values.
The grey seal,
(GS), and the northern elephant seal, Halichoerus grypus (NES), come ashore for reproduction. This period involves intense physiological processes such as lactation in females and a developmental post‐weaning fast in juveniles. Previous studies have shown that Mirounga angustirostris δ13C and δ15N values are affected by starvation, but the precise effects of fasting associated with lactation and post‐weaning fast in seals remain poorly understood. Methods
To examine the effect of lactation and post‐weaning fast on stable isotope ratios in GS and NES, blood and hair were sampled from 21 GS mother‐pup pairs on the Isle of May and on 22 weaned NES pups at Año Nuevo State Reserve during their respective breeding seasons. Milk samples were also collected from GS mothers. Stable isotope measurements were performed with an isotope ratio mass spectrometer coupled to an N‐C elemental analyser.
Changes in stable isotope ratios in blood components during fasting were similar and weak between GS and NES mothers especially in blood cells (GS:
Δ15N = 0.05‰, Δ13C = 0.02‰; NES: Δ15N = 0.1‰, Δ13C = 0.1‰). GS showed a15N discrimination factor between maternal and pup blood cells and milk, but not for13C. The strongest relationship between the isotopic compositions of the mother and the pup was observed in the blood cells. Conclusions
Isotopic consequences of lactation, fasting, and growth seem limited in NES and GS, especially in medium‐term integrator tissues of feeding activity such as blood cells. Stable isotope ratios in the blood of pups and mothers are correlated. We observed a subtle mother‐to‐pup fractionation factor. Our results suggest that pup blood cells are mostly relevant for exploring the ecology of female seals.
Nitrogen stable isotope ratio (δ15N) processes are not well described in reptiles, which limits reliable inference of trophic and nutrient dynamics. In this study we detailed δ15N turnover and discrimination (Δ15N) in diverse tissues of two lizard species, and compared these results with previously published carbon data (δ13C) to inform estimates of reptilian foraging ecology and nutrient physiology.
We quantified15N incorporation and discrimination dynamics over 360 days in blood fractions, skin, muscle, and liver of
and Sceloporus undulatus that differed in body mass. Tissue samples were analyzed on a continuous flow isotope ratio mass spectrometer. Crotaphytus collaris Results
Δ15N for plasma and red blood cells (RBCs) ranged between +2.7 and +3.5‰; however, skin, muscle, and liver did not equilibrate, hindering estimates for these somatic tissues.15N turnover in plasma and RBCs ranged from 20.7 ± 4 to 303 ± 166 days among both species. Comparison with previously published δ13C results for these same samples showed that15N and13C incorporation patterns were uncoupled, especially during winter when hibernation physiology could have played a role.
Our results provide estimates of15N turnover rates and discrimination values that are essential to using and interpreting isotopes in studies of diet reconstruction, nutrient allocation, and trophic characterization in reptiles. These results also suggest that somatic tissues can be unreliable, while life history shifts in nutrient routing and metabolism potentially cause15N and13C dynamics to be decoupled.