Amino acid nitrogen and carbon isotope data: Potential and implications
for ecological studies
Abstract
Explaining food web dynamics, stability, and functioning depend
substantially on understanding of feeding relations within a community.
Bulk stable isotope ratios (SIRs) in natural abundance are
well-established tools to express direct and indirect feeding relations
as continuous variables across time and space. Along with bulk SIRs, the
SIRs of individual amino acids (AAs) are now emerging as a promising and
complementary method to characterize the flow and transformation of
resources across a diversity of organisms, from microbial domains to
macroscopic consumers. This significant AA-SIR capacity is based on
empirical evidence that a consumer’s SIR, specific to an individual AA,
reflects its diet SIR coupled with a certain degree of isotopic
differences between the consumer and its diet. However, many empirical
ecologists are still unfamiliar with the scope of applicability and the
interpretative power of AA-SIR. To fill these knowledge gaps, we here
describe a comprehensive approach to both carbon and nitrogen AA-SIR
assessment focusing on two key topics: pattern in AA-isotope composition
across spatial and temporal scales, and a certain variability of
AA-specific isotope differences between the diet and the consumer. On
this basis we review the versatile applicability of AA-SIR to improve
our understanding of physiological processes as well as food web
functioning, allowing us to reconstruct dominant basal dietary sources
and trace their trophic transfers at the specimen and community levels.
Given the insightful and opportunities of AA-SIR, we suggest future
applications for the dual use of carbon and nitrogen AA-SIR to study
more realistic food web structures and robust consumer niches, which are
often very difficult to explain in nature.