Abstract :
Antipredatory behaviour may be temperature dependent in ectotherms because locomotor capacity varies with temperature, affecting ability to escape. I studied thermal dependence of escape by the keeled earless lizard, Holbrookia propinqua. Distance to refuge and distance from an approaching predator at which escape was initiated (approach distance) increased with substrate temperature, but distance fled was unaffected by temperature. Approach distance in other species decreases with temperature increases, which has been explained by decreased risk due to greater speed for warmer lizards. However, H. propinqua maintains nearly constant mean body temperature from completion of post-emergence basking until it retires for the night. Increase in approach distance with substrate temperature in this species may reflect occupation of or flight to more open sites where the probability of being detected increases. Other risk factors that vary with temperature may affect escape decisions. The lizards used burrows of the Mexican ground squirrel Citellus mexicanus as refuges only at substrate temperatures < 31°C and > 50°C. Shortly after they emerge in the morning, lizards remaining closer to refuge may have a greater probability of escape when slowed by low body temperature. After warming to preferred body temperature, they refuse to enter burrows when chased until environmental temperatures become high enough to place them in danger of heat exhaustion. Effects of temperature on risk and escape costs, and consequent effects on optimal escape by ectotherms are discussed.
