Origins of interspecific variation in lizard sprint capacity

1. Data were compiled on maximal sprint speed, body mass and temperature in squamate lizards from the literature and from our own data on lacertid lizards. 2. Both traditional (i.e. non-phylogenetic) and phylogenetic statistical analyses showed that sprint speed is positively correlated with body mass ('bigger is better') and temperature ('hotter is better'). 3. Additionally, we tested whether sprint speed correlates with behavioural and ecological characteristics, i.e. foraging mode (sit-and-wait or active), activity (diurnal or nocturnal), microhabitat use (saxicolous, arboreal or terrestrial) and climate (Mediterranean, xeric, cool or temperate). Lizards from Mediterranean and xeric climates, diurnal lizards, sit- and wait predators and terrestrial species are expected to run the fastest. Traditional tests suggest that lizards from Mediterranean and desert areas are faster than lizards from cool and tropical regions; that diurnal species are faster than nocturnal species; and that saxicolous animals have higher sprint capacities than do arboreal and terrestrial species. No difference was found between sit-and-wait predators and actively foraging animals. 4. However, the effects of climate, activity period and microhabitat use were no longer significant when the data were analysed in a proper phylogenetic context. This seems to suggest that differences in sprint speed reflect phylogeny, rather than ecology. The discrepancy between the results of phylogenetic and traditional analyses forms a strong case for the use of phylogenetic information in comparative studies.