Methods & Study Systems

My questions are general, but answering them takes a concrete study system and the right tools. These are the organisms I work with and the methods I use.

Study systems

Western fence lizards

My main field system is the western fence lizard (Sceloporus occidentalis) in the Great Basin Desert of northern Nevada. During my Ph.D. I followed two populations at contrasting elevations: one at 1,200 m, and one at 2,400 m, where conditions are cooler and more variable, food is more abundant and there are no competing lizard species. Over three years of mark–recapture we individually marked more than 900 lizards and recorded over 3,500 captures. This lets us follow each animal’s growth, survival and reproduction against the thermal environment it actually lived in.

Projects: The cost-of-living squeeze

Anolis lizards

At Georgia Tech I work on green anoles (Anolis carolinensis), a lineage of tropical origin that has spread far north into temperate North America. That makes it a natural test of whether behavior can let an ectotherm persist in climates its physiology alone should not allow.

Projects: Behavior beyond physiological limits

Other systems

Some questions are best answered across many species at once, or in theory. My work on the evolution of live birth asks why viviparity has evolved more than 70 times across lizards, and my theoretical work on thermal performance and plasticity applies across ectotherms. I also collaborate on projects in other systems, from alpine butterflies to woodrats.

Projects: The evolution of live birth in lizards · Evolutionary constraints on thermal performance · The paradox of plasticity

Methods

Thermal mapping

To understand how animals experience temperature, the environment has to be measured at their scale. With colleagues I developed two tools for this. 3D-printed operative temperature models are an accurate, inexpensive and reproducible way to record the temperature an animal would reach at a given spot. Combining these models with drone thermal imagery produces fine-scale (about 0.5 m²) thermal maps that are complete in both space and time; this approach is available as the R package throne.

Projects: The cost-of-living squeeze

Biophysical modeling

Biophysical models predict an animal’s body temperature, and with it its physiological performance, from the physics of heat exchange between the animal and its surroundings. I use them to translate environmental conditions into the conditions individual animals experience, and to ask how behaviors, such as choosing where and when to be active, change that experience.

Projects: Behavior beyond physiological limits · The evolution of live birth in lizards · The cost-of-living squeeze

Mark–recapture

Marking individual animals and recapturing them repeatedly lets us follow their survival, growth and reproduction through time in the wild. Combined with thermal maps, it links what each animal experienced to how it fared, which is how natural selection can be measured in the field.

Projects: The cost-of-living squeeze

Theoretical models

Mathematical and simulation models let me ask questions that are hard or impossible to answer in the field: how genetic correlations among thermal traits constrain adaptation to warmer and more variable climates, or when plasticity should be favored as climates become more variable.

Projects: Evolutionary constraints on thermal performance · The paradox of plasticity