Negative exponential equations of the form y=ae−bx+c were
fitted to the data of the experiment for the isotopic fractionation,
where y is the δ13C or δ15N values of the tissue in question, x is the
growth ratio (=final weight/initial weight), a and b are constants,
and c is an asymptotic value (AV) of the tissue on the diet. The
best-fit curves were optimized using the software KyPlot (KyensLab).
The diet-tissue fractionation (DTF) was calculated as: DTF=AV−DV,
where DV is the diet value.