Food resources affect female distribution and male mating opportunities in the iguanian lizard Uta palmeri

Abstract

Abstract. A previous study found that food of the San Pedro side-blotched iguanian lizard was more abundant around seabird nest-sites (blue-footed booby, Sula nebouxii, and brown booby, S. leucogaster), and that mating success of male lizards correlated with territory food quality, as measued by the cumulative number of booby chicks recorded in weekly censuses during the lizard breeding season. In the present study, descriptive data suggest that lizard density is correlated with the density of seabird nesting sites. Spatial distribution and social behaviour of adult male and female lizards differ, however. Females are not aggressive, lack territoriality and have highly overlapping home ranges, but males are aggressive, many are territorial, and male territories can contain several female home ranges. The number of females resident on a male's territory is a good index of mating success for the territorial male: 87% of matings observed involved a territorial male and a resident female. A food supplement experiment for half of the breeding season explored whether food distribution affects the placement of female home ranges. Experimental females shifted home ranges into supplemented areas, compared with control females, whose home ranges changed little. Females apparently responded to changes in food and not male distribution, because males did not alter territory locations during food addition. There was an increase in courtship rates for males in the food addition zone, suggesting that mating opportunities were affected by the food supplement. These results support the hypothesis, generated by a previous selection-gradient analysis, that variation in territory food quality contributes to variation in male mating success and indirect selection on male head size. In addition, contrasting these results with published information for Uta stansburiana supports the Emlen & Oring (1977, Science, 187, 215-223) hypothesis that ecological factors affecting the distribution of the limiting sex, and the ability of the other sex to monopolize mates are important mating system determinants.