Selective Basis for the Evolution of Variable Egg and Hatchling Size in Some Iguanid Lizards

• Published in: Herpetologica Vol. 38; no. 1; pp. 178 - 188
• Main Authors: Ferguson, Gary W., Kent L. Brown, DeMarco, Vincent G.
• Format: Journal Article
• Language: English
• Published: Herpetologists' League 01-01-1982
• Subjects: Clutch size; Ecological competition; Eggs; Evolution; Female animals; Herpetology; Lizards; Predation; Predators; Young animals
• ISSN: 0018-0831; 1938-5099

Experiments with Sceloporus undulatus in Kansas and Uta stansburiana in Texas tested the alternate hypotheses that food shortage, predator pressure, or a combination of the two are responsible for the previously observed, presumably adaptive, increase in size of hatchling-sized animals late in the season. Hatchling-sized Sceloporus undulatus in Kansas were subject to increasingly severe food competition as the hatching season progressed in 1978 and 1979. Larger juveniles previously had exhibited increased survivorship late in the season, but this advantage did not accompany the increase in competition in 1978 and 1979. Juvenile Uta stansburiana in Texas were subject to reduced food competition as the hatching season progressed in 1980. A survival advantage for larger juveniles decreased with the decrease in competition. Both supplemental feeding and predator-exclusion decreased the advantage of large size early in the hatching season.