Effect of Ontogeny on Escape Response and Locomotor Performance in Sceloporus woodi

Predator prey interactions have the potential to shape patterns of natural selection. For prey, avoiding detection by predators is of primary importance; however prey species must often risk detection by movement. Most prey species also use secondary defenses when detected by a predator. Examples include threat displays and more commonly, flight. Flight initiation distance describes the distance between a prey item and a predator where the benefits of fleeing outweigh the benefits of remaining stationary. There are many factors that influence flight initiation distance including ontogenetic stage, ability to escape, and the degree of crypsis. Of these, ontogenetic affects on escape velocity and flight initiation distance are likely to be substantial. Younger animals typically have a lower absolute velocity than adults. If escape velocity is a key variable in survival then juveniles may be forced to tolerate shorter flight initiation distances than adults. As a result, they may be susceptible to greater predation than adults or may switch anti-predator tactics. Hence, flight initiation distance of juveniles may be optimized such that their decreased locomotor abilities and their use of immobility for concealment changes at a particular body size. We examined this hypothesis in Sceloporus woodi , a small terrestrial lizard. Field measurements or escape velocity were recorded of an ontogenetic series of lizards using high speed video. Maximal running velocity was also quantified on a raceway to examine if the speeds obtained by lizards in the field are reflective of maximal speeds, or if other variables are correlated with flight initiation distance and running performance.