The effects of sex, tissue type, and dietary components on stable isotope discrimination factors (Δ 13 C and Δ 15 N) in mammalian omnivores

The Δ 13 C and Δ 15 N values ranged from 1.7–4.1 ‰ and 0.4–4.3 ‰, respectively. Females had higher Δ 15 N values than males because males grew larger, whereas Δ 13 C values did not differ between sexes.

Differences in Δ 13 C values among tissue types increased with increasing variability in dietary carbon sources. The Δ 15 N values increased with increasing dietary δ 15 N values for all tissues except liver and serum, which have fast stable isotope turnover times, and differences in Δ 15 N values among tissue types decreased with increasing dietary animal protein. Our results demonstrate that variability in dietary sources can affect Δ 13 C values, protein source affects Δ 15 N values even when protein quality and quantity are controlled, and the isotope turnover rate of a tissue can influence the degree to which diet affects Δ 15 N values.