Doctoral Dissertations

Date of Award

8-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Arthur C. Echternacht

Committee Members

Hamparsum Bozdogan, Gordon M. Burghardt, Susan E. Riechert, Daniel Simberloff

Abstract

Since its introduction to Florida, the brown anole, Anolis sagrei, has steadily expanded its range into that of its native congener in the southeastern United States, the green anole, A. carolinensis. Anolis sagrei achieves very high densities both in its native and invaded range and appears to impose population declines and shifts in the realized habitat niche of A. carolinensis. In order to investigate whether these effects arise prior to the adult age class in which they have previously been described, I studied the behavior of juvenile anoles at the individual, dyadic, and neighborhood levels. Contrary to some characterizations of adult microhabitat selection, distribution models of individual movement on laboratory thermal gradients indicate that juvenile A. carolinensis are likely to occupy warmer sites than A. sagrei, but with broad overlap in the full range of temperatures selected by these species. Staged dyadic encounters between socially naïve juveniles of these species, however, suggest that intrinsic individual characteristics influencing dominance and behavioral exclusion in the youngest juvenile anoles favor A. carolinensis over A. sagrei. To confirm these observations and explore their consequences under conditions representative of natural juvenile assemblages, I compared the behavior and habitat use of A. carolinensis juveniles in single-species field enclosures with A. carolinensis and A. sagrei juveniles in two-species enclosures and described changes in the partitioning of space over the first weeks of life. Within the first week, thermal microhabitat partitioning was apparent and juvenile A. carolinensis in the presence of A. sagrei juveniles exhibited an upward shift in mean perch height similar to that seen in reproductive males following experimental imposition of sympatry in adults of these species. Despite the shift in structural habitat use of A. carolinensis juveniles in the presence of A. sagrei, there was no observed consequence of syntopy on growth rate or survival. This study suggests no immediate role of juvenile interactions on numerical declines in A. carolinensis in sympatry with A. sagrei, but does indicate that a more ontogenetically comprehensive approach is warranted in the characterization of niche differences and habitat partitioning.

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