Removing allometric effects of body size in morphological analysis

In the present paper, a normalization technique to scale data that exhibit an allometric growth is presented and the way it has to be used is described. It is shown how the method has been derived from the theoretical equations of allometric growth. Consequently, the method completely removes all the information related to size, not only scaling all individuals to the same size, but also adjusting their shape to that they would have in the new size according to allometry. In the particular case of isometry when the measures are of identical dimension, this normalization coincides with ratios (one of the most popular methods but only valid in this particular case). This procedure is a theoretical generalization of the technique used by Thorpe (1975, Biol. J. Linn. Soc.7, 27-43; 1976, Biol. Rev.51, 407-452) which was recorded as one of the most efficient methods in the empirical evaluation done by Reist (1985, Can. J. Zool.63, 1429-1439).