Are elevated δ¹⁵N values in herbivores in hot and arid environments caused by diet or animal physiology?

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

“…15 N values in mammalian body tissues likely because of the excess 15 N-depleted urea excretion to increase urine osmolality (e.g., Ambrose and DeNiro, 1986;Heaton et al, 1986;Sealy et al, 1987;Schwarcz et al, 1999) though this relationship is also likely driven by foliar d 15 N (e.g., Murphy and Bowman, 2006;Hartman, 2011). A negative nitrogen balance during heavy nutritional stress also increases body tissue d…”

Refinement of reconstructed ancient food webs based on the nitrogen isotopic compositions of amino acids from bone collagen: A case study of archaeological herbivores from Tell Ain el-Kerkh, Syria

“…For example, at Geoktchik Depe, an Iron Age site in Turkmenistan, Bocherens et al (2005) reported that δ 15 N values in cattle were enriched by 5.0‰ relative to those in goats, a value which is greater than the ~3.4‰ difference attributed to isotopic discrimination between different trophic levels; thus, these isotopic data are not consistent with the fact that both cattle and goats are herbivores. This contradiction has generally been explained by the fact that bulk δ 15 N values reflect not only the trophic position, but also temporal and spatial variations in the isotopic composition of feed plants in the environment (Hartman, 2011) and physiological effects (e.g., the degree of nitrogen efflux to urine and feces) on 15 N-enrichment in each herbivore (Sponheimer et al, 2003). These issues generate ambiguity when interpreting the isotopic data.…”

Elevated δ15N values in mammoths: a comparison with modern elephants

“…Heaton et al 1986;Ambrose and DeNiro 1986) or difference in diet, e.g. due to different δ 15 N values in vegetation between dry and wet environments (Murphy and Bowman 2006;Hartman 2010); feeding on specific plant species or plant parts, e.g. grazing vs. browsing (Sealy et al 1987;Ambrose 1991) andcoprophagy (van Geel et al 2011;Clementz et al 2009) are often mentioned.…”