I am generally interested in animal movement and trophic ecology.  I use biogeochemical tracers integrated within a geospatial framework to understand the ecology, behavior, physiology, and movement of organisms. My work addresses issues in ecological theory, conservation, and management.  Many of the tools I have used are applicable in a variety of environments and organisms.

Research themes

1) Geographic origin and spatial ecology

When large-scale gradients in isotope values lead to isotopic patterns across a wide geographic space, isotopic landscapes, or isoscapes, can be useful for tracking animal migration. I have used isoscapes to determine the origin of a variety of organisms.  Most recently, I am working with isotopic data from birds and bats killed at renewable energy facilities in California to determine the geographic extent of the impacts to their populations.  I have also developed and validated the use of marine isoscapes for determining the geographic origin of sea turtles in order to assess potential interactions of sea turtles with anthropogenic threats and characterize geospatial population trends.  Finally, I am currently contributing to an NSF-funded project ORIGIN (ORigin Inference from Geospatial Isotope Networks) to enhance the data and analytical resources for isotope-enabled migration research.

2) Physiological ecology

I have been investigating processes linking organisms to the isotopic signals in environmental water.  H and O isotopes of consumer tissues reflect not geographic origin only but also the behavioral and physiological traits of animals. I am currently examining how physiological and climatic parameters can affect the coupling or decoupling of these ratios using a mass balance modeling framework.

3) Resource use and individual specialization

I use stable isotopes to characterize the ecological niche of individuals.  For example, I found that loggerhead sea turtles are specialists in a generalist population and that they use a small portion of the available ecological niche. We have since demonstrated that individuals exhibit long-term fidelity to a foraging region, which can result in differences in reproductive output.

Besides determining how individuals vs. populations use the ecological niche, it is important to consider how consistent individuals are in their resource use through time.  I also have examined foraging consistency and degree of individual specialization in multiple life stages of green turtles and found that these patterns change through ontogeny.


4) Cross-ecosystem nutrient linkages

Stable isotopes can be useful tracers for denoting energy flow between ecosystems.  For example, sea turtles act as biological vectors to deposit marine-derived nutrients in the nutrient-poor beach ecosystem when they nest.  While much of the energy and nutrients return to the ocean in the form of hatchlings, I have demonstrated that a portion of these nutrients remain in the beach ecosystem and affect the plant community. In another project, I have been using hydrogen isotopes to trace energy flow pathways in aquatic systems and quantify the proportion of autochthonous vs. allochthonous inputs. I am investigating how nutrient inputs to the aquatic food web change along the reach of a montane stream from an undeveloped canyon to the highly urbanized Salt Lake Valley.  This work is part of a collaboration in the iUtah (innovative Urban Transitions and Aridregion Hydro-sustainability) NSF-EPSCoR program.