1. Stable isotopes represent a unique approach to provide insights into
the ecology of organisms. δ13C and δ15N have specifically be used to
obtain information on the trophic ecology and food web interactions.
Trophic discrimination factors (TDF, Δ13C and Δ15N) describe the
isotopic fractionation occurring from diet to consumer tissue and these
factors are critical for obtaining precise estimates within any
application of δ13C and δ15N values. It is widely acknowledged that
metabolism influences TDF, being responsible for different TDF between
tissues of variable metabolic activity (e.g. liver vs. muscle tissue) or
species body size (small vs. large). However, the connection between the
variation of metabolism occurring within a single species during its
ontogeny and TDF has rarely been considered. 2. Here, we conducted a
9-month feeding experiment to report Δ13C and Δ15N of muscle and liver
tissue for several weight classes of Eurasian perch (Perca fluviatilis),
a widespread teleost often studied using stable isotopes, but without
established TDF for feeding on a natural diet. In addition, we assessed
the relationship between the standard metabolic rate (SMR) and TDF by
measuring their oxygen consumption of the individuals. 3. Our results
showed a significant negative relationship of SMR with Δ13C, and a
significant positive relationship of SMR with Δ15N of muscle tissue, but
not with TDF of liver tissue. SMR varies inversely with size, which
translated into a significantly different TDF of muscle tissue between
size classes. 4. In summary, our results emphasize the role of
metabolism in shaping specific TDF (i.e. Δ13C and Δ15N of muscle
tissue), and especially highlight the substantial differences between
individuals of different ontogenetic stages within a species. Our
findings thus have direct implications for the use of stable isotope
data and the applications of stable isotopes in food web studies.
Vibrissae growth rates and trophic discrimination factors in captive southern sea otters (Enhydra lutris nereis)