RATIONALE
Stable isotope analysis (SIA) is used widely for reconstructing trophic links of vertebrate and invertebrate animals. Soil macrofauna form a substantial food source for a range of predators including amphibians, reptiles, birds and mammals. SIA‐based estimations of their trophic niches require knowledge on the full range of isotopic signatures of potential preys. Considering the extremely high diversity of soil animals, this information is not easy to obtain.
METHODS
We estimated a typical range of the isotopic signatures of soil macrofauna by compiling published and original data on soil macroinvertebrates in 11 temperate forests. We examined whether the baseline correction (i.e. subtracting δ13C or δ15N values of local litter) would decrease the between‐site variability in the δ13C and δ15N values of soil animals. The dataset was subsequently used to estimate the frequency distribution of δ13C and δ15N values in saprophagous and predatory soil animals.
RESULTS
The baseline correction reduced the between‐site variability in δ15N, but not in δ13C values of soil animals. Over 95% of the taxa or individuals examined fell into an isotopic space with uncorrected δ13С values ranging from −27.9 to −22.5‰, and litter‐normalized δ15N values from 0.8 to 9.6‰. Saprophagous and predatory soil animals were on average enriched in 13C relative to plant litter by 3.5 and 2.7‰, respectively, which is likely to reflect the importance of saprotrophic microorganisms as the main energy source in soil food webs. The difference in δ15N values between saprophages and predators averaged 2.8‰, which fits the anticipated trophic enrichment per trophic level.
CONCLUSIONS
Our results indicate that the range of possible δ15N values of soil macrofauna in temperate forest ecosystems can roughly be predicted based on the δ15N values of plant litter. On the other hand, no site‐specific normalization is usually required when predicting the range of δ13C values of soil macroinvertebrates. Copyright © 2014 John Wiley & Sons, Ltd.