Variation in Reproductive Productivity of Range Margin Tree Lizards (Urosaurus ornatus)

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Abstract
Reproduction of U. ornatus was studied at the mesic eastern margin of its range during a 3 yr sequence (1971-1973) of increasing annual precipitation in central Texas [USA]. Lizards were in reproductive condition from March through mid-Aug. Females matured sexually at .apprx. 39 mm SVL [snout vent length]; nearly all females were reproductive by April. Ovulation began in late April or early May; 3-4 clutches/season were possible. Clutch size was correlated directly with body size. Clutch size decreased with time within individual seasons although body size did not vary. Body and clutch size were significantly larger in 1972 and 1973 than in 1971. Clutch weight/total body weight decreased during each breeding season but was similar in any given month of all 3 yr. Occurrence of follicular atrisia varied during the reproductive season; this variation probably was adaptive and may be useful in inferring life span. Seasonal and annual reproductive patterns correlate with long and short term trends in regional precipitation; an hypothesis is suggested to explain this correlation.