Response to ‘Allometry to evaluate Allen’s rule in climate warming’ by Santoro and Calzada

Abstract

Our recent review in TREE [ 1. Ryding S. et al. Shape-shifting: changing animal morphologies as a response to climatic warming. Trends Ecol. Evol. 2021; 36: 1036-1048 Abstract Full Text Full Text PDF Scopus (8) Google Scholar ] found that many species are responding to climate change by ‘shape-shifting’; increasing the size of appendages relative to body size, sensu Allen’s rule [ 2. Allen J.A. The influence of physical conditions in the genesis of species. Radical Rev. 1877; 1: 108-140 Google Scholar ]. This has been explained as an adaptation enabling animals to dissipate excess body heat more effectively as temperatures continue to rise, or the result of relaxed selection against larger appendages since losing body heat is less problematic as cold temperatures become rarer. Most of the studies that have identified increasing appendage size, either directly or indirectly, have done so in relation to a linear measure of body size (e.g., wing length in birds), with some studies using body mass. Santoro and Calzada [ 3. Santoro S. Calzada J. Allometry to evaluate Allen’s rule in climate warming. Trends Ecol. Evol. 2022; (Published online March 23, 2022)https://doi.org/10.1016/j.tree.2022.02.012 Abstract Full Text Full Text PDF Google Scholar ] point out the allometric implications of such an approach, and propose that a more detailed investigation is required. While we agree with the important implications that allometry may have in this space, we remain convinced that the standard practice approach, controlling for body size as a covariate in a multiple regression, is appropriate and effectively equivalent [ 4. Freckleton R.P. On the misuse of residuals in ecology: regression of residuals vs. multiple regression. J. Anim. Ecol. 2002; 71: 542-545 Crossref Scopus (336) Google Scholar ].