Martinez del Rio and S.A. Carleton. 2011. How fast and how faithful- the dynamics of isotopic incorporation into animal tissues. Journal of Mammology 93:353-359
Abstract
The interpretation of isotopic data gathered in the field often demands knowing the rate at which isotopes are
incorporated into different tissues and species, and the discrimination factor between tissues and diet. These 2
quantities are estimated in laboratory experiments on diet shifts in which results are interpreted using simple
mathematical models, which we describe here. The simplest of these models assumes that each tissue can
be represented as a well-mixed, single compartment that obeys 1st-order kinetics. Fitting this model to
experimental data allows estimating discrimination factors and the instantaneous rate of isotopic incorporation,
l (the reciprocal of l, 1/l, equals the average residence time, t, of an atom in the tissue). In 1-compartment
models the magnitude of l equals the sum of catabolic turnover and mass-specific growth rate. Examination of
available data suggests that the magnitude of l scales with body mass to an exponent equal to approximately
20.25, differs between endotherms and ectotherms, and could be a useful feature in isotopic incorporation
studies. We outline suggestions for the design and analysis of isotopic incorporation experiments and suggest
that an increased data set of species and tissues can allow field researchers to estimate rates of incorporation
from body size and growth rate data.