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Current projects
Climate change impacts on grazer dominated food chains
In pre-colonial times as much as 25% of the earth’s terrestrial habitats were grasslands. While a large percentage of this area has been converted to agriculture, grasslands still support much of the world’s large megafauna. Present day grassland ecosystems are particularly vulnerable to climate change, especially in northern and temperate latitudes where warming is occurring rapidly. A mechanistic understanding of how changes in climate impact species interactions will be crucial to predicting and mitigating changes in the distribution and abundance of species in these systems. To this end, I am working with NPS biologists to investigate how physical forcing by climate interacts with top-down control by wolves (Canis lupus) to influence the elk (Cervus elaphus) mediated food web in Yellowstone National Park.
Mountain lion physiology, ecology and conservation in the Santa Cruz Mountains
Large predators play a keystone role in structuring ecological communities by suppressing the abundance and altering the behavior of herbivores. In terrestrial systems, however, little is known about the energetic performance of large predators in killing prey, particularly by cryptic species such as felids. I am working with an animal physiologist (Terrie Williams) and electrical engineer (Matt Rutishauser) to develop telemetry collars for deployment on mountain lions that will collect continuous movement and location data from each animal. This novel technology will allow us to answer important physiological and ecological questions that have so far evaded science regarding the success rate, effort and community-level consequences of predation. The study will enhance our understanding of cougar habitat requirements as well as provide guidance on important movement corridors for lions within and between mountain ranges on the central coast of California.
Trophic mismatch and its consequences for the dynamics of an arctic herbivore
Trophic mismatch occurs when the timing of the peak of resource demand during offspring provisioning does not overlap with the peak of resource availability. In highly seasonal environments such as the Arctic, offspring production by vertebrates is timed to coincide closely with the annual peak of resource availability. For herbivores, this resource peak is represented by the annual onset and progression of the season of plant growth. As plant phenology advances in response to climatic warming, however, there is potential for development of a mismatch between the peak of resource demands by reproducing herbivores and the peak of resource availability. For migratory herbivores such as caribou, development of a trophic mismatch is particularly likely because the timing of their seasonal migration to summer ranges where calves are born is cued by changes in day length, while onset of the plant growing season on the same ranges is cued by local temperatures. The phenomenon of trophic mismatch may represent one of the most important climate change threats to the persistence of migratory vertebrates in the far north, yet its role in the dynamics of arctic populations has not been investigated. By continuing observations that collaborator and fearless leader Eric Post began in 1993, we are investigating changes in the timing of caribou calving in Greenland in relation to changes in plant phenology on their calving grounds, and the consequences of such changes for caribou calf production and population persistence.
Understanding ecosystem robustness
I am working with physicist Sitabhra Sinha to understand the basic properties of ecosystems that make them either vulnerable or resistant to species extinctions. Our research thus far has illustrated various ways in which community assembly, source-sink dynamics and network topology either increase or decrease the vulnerability of ecosystems to species losses. Our current work is focused on understanding how ecological networks respond to different types of perturbations associated with climate change.