Nitrogen isotopes in mammalian herbivores: hair δ¹⁵N values from a controlled feeding study

Abstract

Nitrogen isotope analysis is a common technique for investigating dietary behaviour in modern and archaeological populations. One of its primary uses is to provide trophic level information. This application is possible because of a ∼3‰ enrichment in 15 N along each step in the food chain, resulting in carnivores having higher δ 15 N values than herbivores, which in turn have higher δ 15 N values than plants. Much variation has also been observed within a trophic level, although the reasons for this are poorly understood. Here we present the results of a controlled feeding study designed to test the effects of gut anatomy and dietary protein levels on hair δ 15 N values within a trophic level. The data reveal that mammalian herbivores eating identical diets can have hair δ 15 N values that differ by as much as 3.6‰. This is particularly striking as it suggests that interspecific physiological differences can lead to larger shifts in δ 15 N values than a shift in trophic level. We also found that diet-hair fractionation was 2.3‰ greater when herbivores were fed high-protein (19%) diets than when they were fed low-protein (9%) diets. The primary nitrogen losses in mammalian herbivores are 15 N-depleted urine and 15 N-enriched faeces. We reason that an increase in the ratio of urinary to faecal nitrogen efflux leads to greater diet-hair fractionation on the high-protein diet.

The effect of dietary water soluble carbohydrate to nitrogen ratio on nitrogen partitioning and isotopic fractionation of lactating goats offered a high-nitrogen diet

“…This is consistent with findings from Sponheimer et al (2003), who suggested that the main reason for the enrichment of 15 N in faeces is the presence of enriched endogenous material. The majority of N in milk and plasma exists as true protein, which has been reported to be enriched in 15 N (Sick et al, 1997;Cheng et al, 2010).…”

“…This may be related to an increased proportion of microbial protein synthesised from ammonia N and greater activity by hyper-ammonia-producing bacteria with high-urea diet (Maeng and Baldwin, 1976;Cherdthong and Wanapat, 2010). Although the enrichment and depletion effects were consistent with literature, the levels of enrichment in body N sinks were generally higher than previously observed (Koyama, 1985;Sponheimer et al, 2003;Cheng et al, 2011). Caution is needed to interpret the 15 N results from period 2, as there may be a carry-over effect from infusion 15 N-urea into blood at the end of period 1, which led to body N sinks in period 2 (excluding one replacement goat) being slightly enriched in 15 N compared with non-infused goats from period 1 (Figure 1).…”

San Pedro De Atacama Y La Cuestión Tiwanaku en El Norte De Chile: Impresiones a Partir De Un Clásico Estudio Cerámico Y La Evidencia Bioarqueológica Actual (400-1.000 D.C.)

“…Por lo tanto, es necesario considerar la influencia de otros factores que pudieran estar elevando los valores de nitrógeno en Coyo 3 como, por ejemplo, el consumo de carne de alpaca. Esta, según se ha demostrado, posee valores de δ 15 N más altos que otros herbívoros, incluyendo las llamas, debido a su particular fisiología intestinal (Sponheimer et al 2003). Complementariamente, análisis de isótopos estables en llamas y guanacos de Tulán 54, al sur de San Pedro, han evidenciado que sus valores de nitrógeno pueden ascender hasta 13‰ (López et al 2013), posiblemente debido a su adaptación a ambientes desérticos y al efecto de la aridez (Ambrose 1991).…”

History of Animals using Isotope Records (HAIR): A 6-year dietary history of one family of African elephants

“…This study builds on our long-term observations of elephants in northern Kenya (19)(20)(21)(22)(23)(24), on our interests in understanding isotope incorporation into animal tissues (12,(25)(26)(27)(28)(29)(30), and on our interests in applying those principles to wildlife ecology (14,15,16). Diet records are interpreted from multiple hair samples collected annually or subannually over the study interval.…”