Commentary: Allometric analyses of data with outlying observations: The ontogenetic shift in metabolic allometry of American eels (Anguilla rostrata)

Authors of a recent report concluded that different patterns of metabolic allometry characterize juvenile and subadult stages in the life cycle of American eels (Anguilla rostrata). This conclusion was based on a comparison of straight lines fitted to logarithmic transformations of the original observations for metabolic rate and body mass, with the line fitted to transformations for 30 juveniles having a substantially lower slope than the line describing observations for 30 subadults. However, the authors failed to account for an influential outlier in the sample of juvenile eels, and this one outlier was determinative for the outcome of the analysis. When the outlier is removed from the combined data set for juveniles and subadults, the resulting sample of 59 observations is well described by a single straight line, which implies, in turn, that untransformed observations can be described by a two-parameter power equation with lognormal error. This supposition is confirmed by a graph of the two parameter equation against the backdrop of the untransformed data. Thus, no change in the pattern of metabolic allometry occurs during the ontogeny of American eels: the same pattern of allometric variation characterizes both juvenile and subadult animals.