All ETDs from UAB

Advisory Committee Chair

Daniel A Warner

Advisory Committee Members

Ken R Marion

Robert W Thacker

Document Type

Thesis

Date of Award

2015

Degree Name by School

Master of Science (MS) College of Arts and Sciences

Abstract

All organisms have specific habitat requirements that allow them to properly function in the environment. However, optimal habitats often differ across age classes, and accordingly, juveniles shift habitat choice as they age. Field observations of the brown anole lizard (Anolis sagrei) suggest that juveniles perch in open-canopy areas on low vegetation whereas adults reside in forest edges on higher vegetation. I hypothesized that this age-specific habitat variation is because adults force juveniles to less preferred habitat. To address these issues, I conducted a series of experiments to examine the role of inter-age class competition in driving variation in perch use behaviors. In Chapter 1, I provide a background of relevant literature and briefly discuss the justification and design of the experiments. In Chapter 2, I altered the density of adult males in mesh enclosures in the laboratory to examine the response of microhabitat choice by juveniles. I found that juveniles decreased perch height and had complex density-dependent effects on perch width and substrate use in the presence of adult males. In Chapter 3, I conducted two simultaneous field experiments. The first experiment examined how adult male and female (independently) density affect juvenile microhabitat choice and survival. The second experiment examined how juvenile presence influences adult microhabitat choice. I found that high adult male density reduced juvenile survival, yet juveniles did not vary microhabitat choice in response to either adult male or female density. In addition, adults did not select against juveniles in a way that would contribute to the observed age-class habitat variation. Neither adult male or female microhabitat choice was influenced by the presence of juveniles. Overall, we show that adults have a sex- and density-dependent effect on juvenile populations. In the lab, we found that juveniles modify microhabitat choice in response to adult males, but we find no evidence for this in the field. This inconsistency in laboratory versus field studies may be explained by the differences of juvenile body size used between experiments (i.e., juveniles in the field experiment were much smaller than those used in the laboratory experiment). Thus, I suggest that the selective pressure from adults and/or other predators is strong enough that hatchlings innately stay low to the ground, whereas larger juveniles are able to shift microhabitat choice plastically depending on environmental context. In addition, juvenile macrohabitat dispersal from areas of high adult male density may contribute to the variation in age-class habitat use.

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