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Annual Variation of Survival Advantage of Large Juvenile Side-Blotched Lizards, Uta stansburiana: Its Causes and Evolutionary Significance

Gary W. Ferguson and Stanley F. Fox
Evolution
Vol. 38, No. 2 (Mar., 1984), pp. 342-349
DOI: 10.2307/2408492
Stable URL: http://www.jstor.org/stable/2408492
Page Count: 8
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Annual Variation of Survival Advantage of Large Juvenile Side-Blotched Lizards, Uta stansburiana: Its Causes and Evolutionary Significance
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Abstract

Analysis of five generations of Uta stansburiana showed that larger hatchlings enjoyed increased survivorship over two weeks and to breeding age than smaller hatchlings. This advantage of large size was most apparent for survival to maturity and for lizards hatched during July 1-15, when most hatchlings appeared in the field. This period was also the time when food was often the most limiting. The degree of advantage varied among years. Results from experimental treatments on juveniles over two other years indicated that large juvenile advantage was observed only during conditions of food competition and predation. Removal of predators or supplementary feeding nullified the otherwise beneficial effect of large body size during the year when control populations with natural levels of food and predation showed significant differences in body size between survivors and nonsurvivors. These results support the hypothesis that levels of either predation or resource abundance define the degree of survival advantage of larger juveniles. Even small differences in size among very young juveniles is likely to affect their interactions with conspecifics during the acquisition of optimal home ranges. Quality of home ranges ultimately affects the probability of survival during strong selective conditions. If larger juvenile size is governed to some extent genetically, then selection for larger size could effect changes in time of hatching, growth of hatchlings, and size of hatchlings.

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