Phylogenetic comparisons of pedestrian locomotion costs: confirmations and new insights

The energetic costs for animals to locomote on land influence many aspects of their ecology. Size accounts for much of the among-species variation in terrestrial transport costs, but species of similar body size can still exhibit severalfold differences in energy expenditure. We compiled measurements of the (mass-specific) minimum cost of pedestrian transport (COT_min, mL/kg/m) for 201 species – by far the largest sample to date – and used phylogenetically informed comparative analyses to investigate possible eco-evolutionary differences in COT_min between various groupings of those species. We investigated number of legs, ectothermy and endothermy, waddling, and nocturnality specifically in lizards. Thus, our study primarily revisited previous theories about variations in COT_min between species, testing them with much more robust analyses. Having accounted for mass, while residual COT_min did not differ between bipedal and other species, specifically waddling bipeds were found to have relatively high COT_min. Furthermore, nocturnal lizards have relatively low COT_min although temperature does not appear to affect COT_min in ectotherms. Previous studies examining across-species variation in COT_min from a biomechanical perspective show that the differences between waddling birds and nonwaddling species, and between nocturnal lizards and other ecotherms, are likely to be attributable to differences in ground reaction forces, posture, and effective limb length.