Term of Award

Summer 2011

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Department

Department of Biology

Committee Chair

Lance D. McBrayer

Committee Member 1

C. Ray Chandler

Committee Member 2

David C. Rostal

Abstract

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 risk detection by movement. Other than crypsis, prey species also use secondary defenses when detected by a predator. The most common secondary defense is 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, the ontogenetic effects on escape velocity and flight initiation distance are likely to be substantial. Juvenile and hatchling 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 switch anti-predator tactics or be susceptible to higher predation risk than adults. Hence, flight initiation distance of juveniles may be optimized such that their decreased locomotor abilities and use of immobility for concealment changes at a particular body size. I examined this hypothesis in Sceloporus woodi, a small terrestrial lizard. Field measurements of escape velocity were recorded on an ontogenetic series of lizards using high speed video. Maximal running velocity was also quantified on a laboratory raceway to examine if the velocities used by lizards in the field are reflective of maximal velocities as measured in the lab, or if other variables, such as muscle size and limb size, are correlated with flight initiation distance and running performance. I found that hind limb morphology scales isometrically with body size. Maximum velocity in the lab increased with size, adults being fastest and hatchlings being slowest (F2, 97 = 12.6088, P = <0.0001). Escape velocity in the field did not vary between adults, juveniles, and hatchlings (F2, 24 = 2.39, P = 0.114). Flight initiation distance increased as body size increased (F2, 39 = 3.32, P = 0.047). Larger animals did not allow close approach of a human predator presumably escaping early and to avoid the need to use high sprint velocities to escape. Smaller lizards, due to slower sprint velocities, must use behavior to compensate for decreased sprint velocity. Small lizards remained immobile longer, allowing close approach of the predator, likely relying on crypsis to remain concealed. By remaining immobile longer, smaller lizards did not attract unnecessary attention of the predator and likely increase the probability of being required to use sprinting to escape predation. Isometric scaling coupled with the findings for sprint and escape velocity allow all classes to perform similarly thus optimizing hatchling and juvenile survival.

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