Physiological and Environmental Sources of Variation in Reproduction: Prairie Lizards in a Food Rich Environment

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Abstract
Between-year variation in the reproduction of the iguanid lizards, Holbrookia maculata and Sceloporus undulatus, was studied in Nebraska [USA] during 1978 and 1981-1983. Reproduction of both species varied significantly between years but the nature of variation was different for the two species. Clutch frequency of H. maculata did not vary among years and clutch size varied only in older females (.gtoreq. 2 yr). Both clutch frequency and clutch size of S. undulatus varied among years. Clutch frequency varied from 1-3 for yearlings and 2-3 for older females. The size of the first clutch of older females varied significantly among years, but differences were not significant when adjusted for body length. Several physiological and environmental factors contributed to variation in reproduction. These factors included lipid storage prior to reproduction, body mass, body length, water stress, and environmental temperatures, but not food abundance during the reproductive season. The effect of each factor was dependent on the age and species of lizard as well as the stage within the reproductive cycle.