Biology ETDs


Ian W. Murray

Publication Date



The physical environment has a profound influence over many aspects of animal ecology, such as governing the pace and timing of phenology and the patterns of activity across space and time. In extreme habitats such as deserts, the most important components of the physical environment are precipitation and temperature. Not only do these vary temporally and spatially, but this variation may influence the life history and ecology of species. My research examines how variance in temperature and precipitation influences the ecology of two species of desert dwelling consumers (desert woodrats and desert tortoises) over differing temporal scales. In Chapter 1, I describe how temperature constrains the daily activity of desert woodrats for much of the year. In the spring and summer, woodrats significantly reduce nocturnal activity outside of the den as environmental temperature increases. Indeed, during the warm summer months, nightly activity does not begin until temperature drops below the physiological lethal limit. This relationship is dependent upon gender and body mass. In Chapter 2, I estimate the tissue carbon incorporation rates and diet-to-tissue discrimination in desert tortoises. Characterizing these relationships in consumers is a critical part of being able to more accurately study how animal diet varies through the use of stable isotope analyses. However, our current understanding of the tissue isotope dynamics in terrestrial ectotherms such as tortoises is poorly developed. In Chapter 3, I examine how precipitation shapes the nutritional ecology of desert tortoises on a seasonal basis across a precipitation gradient. Due to differences in digestibility and nutritional content, foraging on C3 vs. C4/CAM plant resources has important fitness repercussions for the consumer. I use the variance in growth ring carbon isotope ratios to estimate the dietary integration of C3 and C4/CAM plant resources across tortoise populations. Individual tortoise dietary breadth, as estimated by carbon isotopic variances, becomes more generalized as local rainfall decreases. I find that juvenile desert tortoises have a more narrow dietary breadth relative to adults, and adult male tortoises have less specialized diets compared to adult female tortoises.

Project Sponsors

National Science Foundation, Arizona Game and Fish Department Heritage Fund Program, University of New Mexico Biology Department Graduate Research Allocation Committee, University of New Mexico Student Research Allocation Committee




stable isotope, carbon, desert woodrat, desert tortoise, Death Valley, thermal biology, Neotoma lepida, Gopherus agassizii, dietary breadth, carbon incorporation, growth ring

Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Committee Member (Chair)

Bedrick, Edward J.

Second Committee Member

Tracy, C. R.