The Dynamics of a Utah Population of Sceloporus undulatus

Tinkle, Donald

A population study of Sceloporus undulatus near the western extreme of its range in Utah was carried out from 1969-1971, and the data were compared with those obtained from four other populations of this species. Most adults (90%) require 2 years to reach sexual maturity at which time they produce 3 clutches during each breeding season which average 6.3 eggs per clutch. Most females become postreproductive after mid-July. Mean clutch size increases by about one egg per year; few females live to reproduce more than 3 or 4 years and the mean generation time is about 2.4 years. Hatchlings first appear in late July at a size of about 25 mm SVL. This body length is doubled by the following June, and by August the lizards have reached a minimum mature size (60 mm SVL) and breed the following spring. About 20% of hatchlings survive to age 1 and about 50% of the yearling females and 40% of the yearling males survive to maturity. Average annual survivorship of adults is near 50% for females, 40% for males. A life table for this population indicates a replacement rate of .83. Average density (excluding hatchlings) was about 35 per hectare, the highest found in any previously studied population of this species, and is apparently associated with low predation levels. Biomass averaged nearly 250 g per hectare. Delayed maturity, small clutch size and rate of growth suggest greater resource limitation on individuals in this population than in those previously studied. It may be significant that there are more potential competitors at this site than at others previously investigated.

The Dynamics of a Utah Population of Sceloporus undulatus

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