Compound-specific stable isotope analysis in population and community ecology: Theory, development, and a call for more laboratory experiments

Background/Question/Methods

Compound-specific stable isotope analysis (CSIA) of individual amino acids has seen an explosion of publications in recent years across diverse fields of ecology, oceanography, and biogeochemistry. The power of the CSIA approach lies in the differential fractionation of individual amino acids during trophic transfer. As a result, CSIA provides the unique ability to disentangle the relative influences of variability at the base of the food web from trophic variability of consumers. This talk will provide an overview of the theory and development behind the recent expansion of CSIA research in population and community ecology, illustrated with a case study on food web architecture in coral reef seascapes.

Results/Conclusions

Diagnostic amino acid δ¹³C fingerprints of primary producers at the base of food webs are passed on to upper trophic level consumers virtually unmodified. These amino acid isotope fingerprints, when coupled with Bayesian stable isotope mixing models, have opened new doors for quantifying the flow of carbon through complex food webs. Stable nitrogen isotope analysis of individual amino acids provides independent but complimentary insight into trophic dynamics in food webs. In particular, the δ¹⁵N analysis of fractionating and non-fractionating amino acids provides a trophic position estimator that is internally normalized to variations in δ¹⁵N at the base of the food web. While still relatively new, CSIA has produced transformative data to address a wide range of questions about resource utilization and trophic dynamics, animal migration, and biogeochemical cycling. However, to realize the full potential of the CSIA approach, we must continue to investigate the underlying biochemical and physiological mechanisms generating variability in individual amino acid fractionation. For instance, there is still much progress to be made in developing non-essential amino acid carbon isotope fractionation as a metric of diet quality. Similarly, continued investigation into the sources and magnitude of variation in trophic discrimination factors, particularly of higher trophic level consumers, is crucial to accurately reconstructing consumer trophic dynamics with compound specific nitrogen isotope analysis.