Abstract
Stable isotope mixing models are regularly used to provide probabilistic estimates of source contributions to dietary mixtures. Whilst Bayesian implementations of isotope mixing models have become prominent, the use of appropriate diet-tissue discrimination factors (DTDFs) remains as the least resolved aspect. The DTDFs are critical in providing accurate inferences from these models. Using both simulated and laboratory-based experimental data, this study provides conceptual and practical applications of isotope mixing models by exploring the role of DTDFs. The experimental study used Mozambique Tilapia Oreochromis mossambicus, a freshwater fish, to explore multi-tissue variations in isotopic incorporation patterns, and to evaluate isotope mixing model outputs based on the experiment- and literature-based DTDFs. Isotope incorporation patterns were variable for both muscle and fin tissues among the consumer groups that fed diet sources with different stable isotope values. Application of literature-based DTDFs in isotope mixing models consistently underestimated the dietary proportions of all single-source consumer groups. In contrast, application of diet-specific DTDFs provided better dietary estimates for single-source consumer groups. Variations in the proportional contributions of the individual sources were, nevertheless, observed for the mixed-source consumer group, which suggests that isotope assimilation of the individual food sources may have been influenced by other underlying physiological processes. This study provides evidence that stable isotope values from different diet sources exhibit large variations as they become incorporated into consumer tissues. This suggests that the application of isotope mixing models requires consideration of several aspects such as diet type and the associated biological processes that may influence DTDFs.
Highlights
Stable isotope mixing models are regularly used to provide probabilistic estimates of source contributions to dietary mixtures
Diet-tissue discrimination factors (DTDFs), represented as 13C for the carbon and 15N for the nitrogen stable isotopes reflect the amount of change in dietary stable isotope values when they become incorporated into consumer tissues[15]
Based on the deviance information criterion (DIC) values, isotopic incorporation was best explained by both one-compartment and two-compartment models (Table 3)
Summary
Stable isotope mixing models are regularly used to provide probabilistic estimates of source contributions to dietary mixtures. Bayesian inference-based isotope mixing models have risen to prominence in providing robust inferences on consumer diets by addressing challenges such as the occurrence of multiple prey sources in food w ebs[5,6], the uncertainties associated with measurement, source and mixture process errors[1,7,8], the incorporation of concentration d ependences[9] and the use of prior information for both sources and mixtures[10,11,12] Despite these significant improvements, the use of appropriate diet-tissue discrimination factors, which have a direct influence on the correct interpretation of mixing models outputs, remains a key c hallenge[8,13]. In fishes, studies have demonstrated interspecific differences in diet-to-tissue isotope assimilation due to differences in diet quality, feeding and excretion rates[35,36], and among different body tissues, with metabolically active tissues, such as blood, liver and fins, showing relatively faster turnover rates compared to less active and structural tissues, such as muscle, scales and o toliths[19,37,38]
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