Density-dependent processes in the juvenile stage of the life cycle in the striped plateau lizard, Sceloporus virgatus

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Michael S. Gaines - Committee Chair


Elucidating where in the life cycle density dependence occurs as well as what effect density has on specific life-history traits and demographic components of population growth rate will advance our understanding of population dynamics. In this study I experimentally manipulated hatchling cohort density in the striped plateau lizard (Sceloporus virgatus) in order to investigate density dependence in the juvenile stage. Large-scale field enclosures (average 800 m2) constructed of drift fencing with pitfall traps were established in the preferred habitat of S. virgatus and treated with high and low densities of hatchlings. Enclosures were monitored over a ten month period (August 1997 to May 1998). The experiment was then replicated from August 1998 to May 1999.In chapter one, I focus on the influence density has on demographic variables and life-history traits. I found that enclosure densities converged by the end of the experiments; dispersal increased at high density; survivorship, growth rates, body lengths attained by May, and the proportion of yearlings attaining reproductive maturity by May decreased at high density.In chapter two, I focus on how density influences space use. I found that home range size and shape and core area size were reduced at high density, but no significant effects were detected for core area shape and overlap.In chapter three, I focus on how density influences behavior of juveniles. I found that the number of agonistic encounters, the duration of agonistic interactions, and the number of advertisement displays increased at high density whereas the number of feeding strike attempts decreased at high density.These results indicate that density has a significant influence during the juvenile stage. Agonistic behavior appears to be the mechanism driving these density-dependent effects. The density-dependent processes during the juvenile stage may interact with abiotic influences and play a key role in the life-history strategy of S. virgatus.


Biology, Ecology

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