Variation in δ13C and δ15N trophic enrichment factors among Hyalella azteca amphipods from different lakes

Stable isotopes are a powerful tool used to study the diets of animals because they provide information on food assimilated over an extended period. However, trophic enrichment factors used to reconstruct diets sometimes vary substantially, even among animals from the same trophic level. The goal of this study was to verify if trophic enrichment factors vary among animals as similar as Hyalella azteca amphipods from different lakes. We compared the carbon and nitrogen isotopic compositions of amphipods from different lakes fed on leaf detritus and on periphyton. Amphipods showed significant differences in their trophic enrichment factors among treatments (about 3.0‰ for carbon and nitrogen). The trophic enrichment factor of carbon was more affected by the food type, whereas the trophic enrichment factor of nitrogen was more affected by lake of origin. We estimated that amphipods had a tissue turnover of 25 days for carbon and 34 days for nitrogen. Our study showed that animals from different lakes can exhibit substantial variation in their trophic enrichment factors. This strengthens the view that trophic enrichment factors specific to a study system should be used whenever possible to reconstruct the in situ diet of consumers.