Size-related activity patterns in an herbivorous lizard

A study of the pre-breeding season behavior of a colony (N=16) of Ctenosaura hemilopha revealed significant differences among the four size classes with respect to time of activity. Comparisons of lizard size classes showed that the smaller lizards emerged earlier, had earlier activity periods, and usually fed earlier than the larger lizards (all P<0.01). The two smaller sizes were also aggressive earlier in the day than the two larger classes (P<001). Members of all size classes ate the same food items, but food competition was absent. Thus, the differences in activity patterns among the size classes are not due to avoidance of food competition, an explanation which has been invoked for insectivorous lizards. These patterns probably result from the fact that thermal inertia increases with body size. Differences in activity patterns of insectivorous species can also originate from thermoregulatory constraints, and could provide the variation upon which selection for reduced competition may have acted to increase separation along the time axis of niche space.