Should we use one‐, or multi‐compartment models to describe ¹³C incorporation into animal tissues?

Abstract

Understanding rates of isotopic incorporation and discrimination factors between tissues and diet is an important focus of ecologists seeking to use stable isotopes to track temporal changes in diet. We used a diet-shift experiment to measure differences among tissues in (13)C incorporation rates in house sparrows (Passer domesticus). We predicted faster incorporation rates in splanchnic than in structural tissues. We also assessed whether isotopic incorporation data were better supported by the one-compartment models most commonly used by ecologists or by multi-compartment models. We found large differences in the residence time of (13)C among tissues and, as predicted, splanchnic tissues had faster rates of isotopic incorporation and thus shorter retention times than structural tissues. We found that one-compartment models supported isotopic incorporation data better in breath, excreta, red blood cells, bone collagen, and claw tissues. However, data in plasma, intestine, liver, pectoralis muscle, gizzard, and intestine tissues supported two-compartment models. More importantly, the inferences that we derived from the two types of models differed. Two-compartment models estimated longer (13)C residence times, and smaller tissue to diet differences in isotopic composition, than one-compartment models. Our study highlights the importance of considering both one- and multi-compartment models when interpreting laboratory and field isotopic incorporation studies. It also emphasizes the opportunities that measuring several tissues with contrasting isotopic residence times offer to elucidate animal diets at different time scales.

An experimental exploration of the incorporation of hydrogen isotopes from dietary sources into avian tissues

“…Following Carleton et al (Carleton et al, 2008), we used small-sample Akaike's information theoretic criterion (AIC c ) to determine whether the data were best described by one-compartment or two-compartment models. We chose the model with the lowest AIC c value (Burnham and Anderson, 2002).…”

“…This need for a thorough understanding of the processes that influence the transfer of stable isotopes from the environment and resources to consumer tissues has motivated researchers to perform experiments and develop mathematical models to describe changes in the isotopic values of consumer tissues after a shift in dietary resources (Phillips and Gregg, 2001;Jardine et al, 2004;Carleton and Martínez del Rio, 2005;Martínez del Rio and Anderson-Sprecher, 2008). These investigations also examined the factors that determine variation in both incorporation rates, such as growth rate, temperature and protein turnover (Jardine et al, 2004;Carleton and Martínez del Rio, 2005;Carleton et al, 2008), and the discrimination between the isotopic values of resources and consumers (Caut et al, 2009).…”

“…protein turnover) will also have an effect on the incorporation of hydrogen. (Carleton et al, 2008;Caut et al, 2009). …”

Stable carbon and nitrogen incorporation in blood and fin tissue of the catfish Pterygoplichthys disjunctivus (Siluriformes, Loricariidae)

“…Because single compartment models can oversimplify the isotopic incorporation process in tissues, we also used two compartment models to analyze our isotopic incorporation data (Carleton et al 2008). We used the Akaike's Information Criterion (AIC) to analyze the support of the different models and evaluate which models more appropriately fit our data (Carleton et al 2008).…”

“…We used the Akaike's Information Criterion (AIC) to analyze the support of the different models and evaluate which models more appropriately fit our data (Carleton et al 2008). For plasma solutes and RBCs, the AIC values were lower for the one compartment models (34.73 to 46.41) than for the two compartment models (41.51 to 53.25), indicating that one compartment models were appropriate in our data analysis (Carleton et al 2008).…”