The causes and consequences of natal dispersal in the side-blotched lizard (Uta stansburiana, Phrynosomatidae)

A release-recapture experiment was carried out on two populations of Uta stansburiana (Sauria: Phrynosomatidae) in the Coastal Range of California. Hatchlings were from size-manipulated eggs; miniaturized (42%), giganticized (8%), or control (50%). Over 1000 lizards were released at two sites: Del Puerto Canyon and the Los Banos Plains. Egg treatments had no effect on dispersal distances; therefore, all treatments were pooled in the analyses. Size at hatching only had an effect on dispersal for females released early at both sites, with larger females dispersing shorter distances. Because of the amount of scatter and small effect size of the early release female data and the nonsignificance of all other comparisons, these data were pooled in all other analyses. Del Puerto Canyon is a chapparal community characterized by high densities of lizards distributed throughout the area, as well as high plant and animal diversity. At Del Puerto Canyon hatchlings dispersed short distances (over 75% less than 50 m) and then remained there until the following spring. Males dispersed farther than females (males [median dispersal distance] = 33.5 m, females = 24 m) and there were no differences due to early or late releases. In contrast to Del Puerto Canyon, adults at the Los Banos Plains site occur almost entirely on rocky outcrops in the spring. Outcrops are separated from each other by large expanses of grassy fields and plant and animal diversity is low at this site. Here, most hatchlings dispersed long distances (up to 500 m) from these outcrops in the summer and established territories in mammal burrows in the surrounding fields. In the fall and winter juveniles returned to the outcrops and re-established territories. There were no dispersal differences in males due to time of release, but females released later in the summer dispersed farther than those released earlier in both years (1989: early = 116.5 m, late = 188 m,- 1990: early = 58 m, late = 119 m). Because there were no differences between early and late released males at Los Banos, these data were pooled and compared with early and late release females. There were significant differences between males and early release females, but there were no significant differences between males and late release females in both years. Genetic and somatic factors are both likely to influence dispersal in the side-blotched lizard. Males at both sites dispersed farther than females. This is predicted by the mate-defence theory of Greenwood: at least one sex should disperse to avoid inbreeding and in polygynous mating systems males should disperse to acquire territories and females. The male sex bias observed with side-blotched lizards is not as strong as that observed in mammals, and this may be due to the lack of female affiliative behavior in reptiles that is almost always present in mammals. Hatchlings released later at Del Puerto Canyon may have dispersed similar distances as early release hatchlings but likely resided in lower qualility home ranges. Late release females at the Los Banos Plains dispersed significantly farther than early release females due to a lack of unoccupied territories and thier relatively small body size. Thus somatic factors influenced females, but not males, at the Los Banos Plains.