Natural Selection on Behavioral Phenotypes of the Lizard Uta Stansburiana

Abstract

Behavioral differences of resource utilization between juvenile survivors and nonsurvivors of the desert side—blotched lizard Uta stansburiana stejnegeri were measured. Marked individuals were followed through time in enclosed field plots so disappearance indicated death. In the 1st yr of the study, one characterized by light selection pressure, survival was independent of most of the behavioral variables. In the 2nd yr of the study, one characterized by heavy selection pressure, oversummer survivors were active under conditions of clearer skies, warmer temperatures, later morning hours, earlier evening hours, and were associated with vegetation furnishing more shade and shelter than nonsurvivors. Two—way analysis of variance demonstrated behavioral differences between survivors and nonsurvivors, independent of age. Survivors were seen less frequently during the summer of heavy selection pressure, and were more specialized in their activity (smaller phenotypic breadth). The home ranges of survivors contained significantly greater densities of yucca and shelter holes, and lesser densities of Croton. The diversity of plants and other elements on the home ranges of survivors was significantly greater than on those of nonsurvivors. Older, larger juvenile lizards moved to the unmodified sector of an experimental plot in which vegetation was cut away. Those older juveniles which showed some activity on the modified sector experienced heavy mortality. No genetic basis for the behavioral differences between survivors and nonsurvivors was obtained. The behavioral variation in the population, if directly heritable, may be maintained by opposing, fluctuating selection pressures; or, if a consequence of microhabitat differences, by the limiting amount of superior habitat used somewhat exclusively by surviving lizards. The quality of the home range an individual inhabits probably influences his behavior and ultimately his survival. Aggressive behavior may influence the quality of home range in individual obtains.