Whole-animal metabolic rate is a repeatable trait: a meta-analysis

Repeatability studies are gaining considerable interest among physiological ecologists, particularly in traits affected by high environmental/residual variance, such as whole-animal metabolic rate (MR). The original definition of repeatability, known as the intraclass correlation coefficient, is computed from the components of variance obtained in a one-way ANOVA on several individuals from which two or more measurements are performed. An alternative estimation of repeatability, popular among physiological ecologists, is the Pearson product-moment correlation between two consecutive measurements. However, despite the more than 30 studies reporting repeatability of MR, so far there is not a definite synthesis indicating: (1) whether repeatability changes in different types of animals; (2) whether some kinds of metabolism are more repeatable than others; and most important, (3) whether metabolic rate is significantly repeatable. We performed a meta-analysis to address these questions, as well as to explore the historical trend in repeatability studies. Our results show that metabolic rate is significantly repeatable and its effect size is not statistically affected by any of the mentioned factors (i.e. repeatability of MR does not change in different species, type of metabolism, time between measurements, and number of individuals). The cumulative meta-analysis revealed that repeatability studies in MR have already reached an asymptotical effect size with no further change either in its magnitude and/or variance (i.e. additional studies will not contribute significantly to the estimator). There was no evidence of strong publication bias.