Date of Award:

8-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Charles T. Hanifin

Committee

Charles T. Hanifin

Committee

Karen Beard

Committee

Susannah French

Abstract

Lizards actively maintain a narrow range of body temperatures through behavioral thermoregulation and microhabitat selection. Body temperature plays a critical role in many physiological processes. As a result, there is a range of body temperatures at which a lizard’s reproductive success (fitness) is maximized, known as the lizard’s thermal niche. There is strong evidence linking the available temperatures, or thermal properties of a microhabitat, to success in maintaining body temperatures within a preferred set range. Microhabitats have differing thermal properties, and so have different relative quality. Because thermal properties are limited in space and time, competition for high quality microhabitat can occur. Reduction of competition for resources can increase overall resource exploitation, as well as the overall fitness of an organism. This can lead to the partitioning, or division, of resources that an organism utilizes. Resource partitioning can further lead to the differentiation of a lizard’s thermal niche. In my thesis, I report on a multi-year study comparing thermal niche and microhabitat selection in three lizard species found in a semi-arid desert in northeastern Utah: Sceloporus graciosus, Sceloporus tristichus, and Uta stansburiana. I compare microhabitat characteristics and thermal niche traits across species. I described and compared fundamental and realized thermal niche by measuring preferred body temperatures and field body temperatures. I compared habitat quality and efficiency of thermoregulation. Multinomial regression suggests differentiation in microhabitat selection. Preferred body temperatures show differentiation in the fundamental thermal niche of my study species. Field body temperatures show overlap in the realized thermal niche of my species. Specifically, field body temperatures show Sceloporus tristichus being warmer than preferred and Uta stansburiana being cooler than preferred. This shows strong evidence of thermal niche differentiation and possible partitioning. Efficiency of thermoregulation differs between species and between seasons. Taken together, this shows differentiation of thermal niche as well as microhabitat selection. Operative temperatures, temperatures experienced by non-thermoregulating organisms, suggest that, similar to tropical lizards, increasing temperatures may present physiological challenges for temperate desert species, rather than opportunities for increased activity.

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