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Hertz E, Robinson JPW, Trudel M, Mazumder A, Baum JK
Estimation of predator–prey mass ratios using stable isotopes: sources of errors
Nitrogen stable isotopes (δ15N) are used to estimate predator–prey mass ratios (PPMR), a food web property that has been linked to aquatic ecosystem structure and stability. Previous approaches assume that the isotopic discrimination between diet and tissue δ15N is constant at 3.4‰. However, recent advances show that this relationship may be better described by a scaled approach, in which isotopic discrimination decreases with increasing diet δ15N. Hertz and co-workers estimate PPMR using the scaled approach for a simulated and real food web and show that the traditional approach yields incorrect PPMR estimates, with the extent of bias depending on baseline δ15N and trophic level sampled. Scaled estimates of PPMR thus allow for comparison across trophic levels and baseline δ15N values.