An experimental study of carbon-isotope fractionation between diet, hair, and feces of mammalian herbivores

Abstract

The carbon-isotope composition of hair and feces offers a glimpse into the diets of mammalian herbivores. It is particularly useful for determining the relative consumption of browse and graze in tropical environments, as these foods have strongly divergent carbon-isotope compositions. Fecal δ13C values reflect the last few days consumption, whereas hair provides longer term dietary information. Previous studies have shown, however, that some fractionation occurs between dietary δ13C values and those of hair and feces. Accurate dietary reconstruction requires an understanding of these fractionations, but few controlled-feeding studies have been undertaken to investigate these fractionations in any mammalian taxa, fewer still in large mammalian herbivores. Here, we present data from the first study of carbon-isotope fractionation between diet, hair, and feces in multiple herbivore taxa. All taxa were fed pure alfalfa (Medicago sativa) diets for a minimum period of 6 months, at which point recently grown hair was shaved and analyzed for carbon isotopes. The mean observed diet–hair fractionation was +3.2‰, with a range of +2.7 to +3.5‰. We also examined diet–feces fractionation for herbivores on alfalfa and bermudagrass (Cynodon dactylon) feeds. The mean diet–feces fractionation for both diets was –0.8‰, with less fractionation for alfalfa (–0.6‰) than bermudagrass (–1.0‰). Fecal carbon turnover also varies greatly between taxa. When diets were switched, horse (Equus caballus) feces reflected the new diet within 60 h, but alpaca (Lama pacos) feces did not equilibrate with the new diet for nearly 200 h. Thus, fecal carbon isotopes provide far greater dietary resolution for hindgut-fermenting horses than foregut-fermenting alpacas.

Spatial and temporal expression of vegetation and atmospheric variability from stable carbon and nitrogen isotope analysis of bat guano in the southern United States

“…Both these studies concluded 15 N in chitin was depleted relative to source material, whereas we find values that are more positive. Organic matter d 15 N values in arid regions are often correlated with precipitation (e.g., Sealy et al, 1987), and d 15 N value of faecal material is known to be similar to diet and body tissues (e.g., Sponheimer et al, 2003). We found a large difference in d 15 N values amongst our modern spatial samples, but relatively little within our time-series, suggesting d 15 N to be more dependent on local soils.…”

Large regional-scale variation in C3/C4 distribution pattern of Inner Mongolia steppe is revealed by grazer wool carbon isotope composition

“…Yet, the present data indicated no preferential grazing of one photosynthetic type (C3 relative to C4, or vice versa). This was suggested by the fact that the observed vegetation-wool shift (+2.7‰) was similar to that of pure C3 or C4 diets (average shift: +2.6‰ ±0.6‰ SD for hairs of different animal species in the studies of Minson et al, 1975;Jones et al, 1981;Sponheimer et al, 2003a;Ayliffe et al, 2004;Schwertl et al, 2005). If animals had grazed preferentially one component of vegetation, then the apparent shift should deviate.…”

“…The constant 14.4‰ is the minimal reference 13 3 as reported by Wittmer et al (2008) for 1000 m a.s.l. In principle, recent P C4 can be estimated from wool considering the isotopic offset with respect to vegetation: in studies with pure or mixed C3 or C4 diets the δ 13 C of hair was 2 to 3‰ enriched with 13 C relative to diet (Jones et al, 1981;Sponheimer et al, 2003a;Männel et al, 2007). This offset is termed "vegetation-wool shift", S VW (S VW = δ 13 C wool -δ 13 C vegetation ), and results from 13 C fractionation during digestion or metabolism of animals (De Niro and Epstein, 1978).…”

Reconstruction of breastfeeding and weaning practices using stable isotope and trace element analyses: A review

“…The assessment of biological age is relatively straightforward in soft tissues because the potential time lags between actual weaning ages and elemental signals are relatively small. The turnover rates of most soft tissues, such as blood, hair, nail, and muscle, and excreta are relatively high and these reflect diet during relatively short time periods (as little as a few days to months) before sampling for most animal species (e.g., O'Connell and Hedges, 1999;Sponheimer et al, 2003;McCullagh et al, 2005;Codron et al, 2011;Braun et al, 2013;Bahar et al, 2014).…”