Communities and disease
Although direct pathogen-host interactions are often well-described, my work in this area focuses on the comparatively less-studied effects of predation, competition, and resource availability on disease dynamics. I am currently studying the long-term implications of an aphid-vectored disease, barley yellow dwarf virus, on West Coast grassland community composition in collaboration with several researchers (Eric Seabloom - OSU, Sunny Power - Cornell, Charles Mitchell - UNC, Kevin Gross - NC State, Andy Dobson- Princeton, and Parviez Hosseini - Wildlife Trust). We are developing theory and empirically testing it to examine the indirect influence of the abiotic environment on host (grass), vector (aphid), and pathogen (BYDV) dynamics. We are using this work to generate predictions about other vectored diseases, such as malaria, Lyme disease, and West Nile virus.
Even though two of the most globally-pervasive human impacts are alteration of global budgets of the resources that limit primary production and changes in the abundance and identity of consumers, there have been no globally coordinated experiments to quantify the general impacts of these perturbations on ecological systems. I am collaborating with Eric Seabloom, John Orrock, Mendy Smith, Stan Harpole, and Peter Adler to develop and coordinate this grassroots research effort composed of more than 60 sites and 100 collaborators in 15 countries on 6 continents. These Nutrient Network, or NutNet, participants are performing coordinated, long-term experimental research to gain a general understanding of the extent to which multiple resource limitation and consumers influence community dynamics and ecosystem functioning.
Communities and stoichiometry
Fossil fuel combustion, agricultural runoff, and eradication of predators affect all ecological systems. Although my empirical research is in terrestrial systems, much of my work quantifies the impacts of altered nutrient availability (i.e. bottom-up effects) and consumers (i.e. top-down effects) among ecosystems, including lakes, grasslands, and kelp forests, by compiling and analyzing data from published ecological studies. I am involved in a variety of collaborative projects employing cross-system meta-analysis and development of general theory to examine the independent and interacting effects of these global changes in predator numbers and nutrient supply rates on community composition, interactions among species, and energy flow.
Other ongoing projects
My other ongoing projects include examining the role of intraguild predation in structuring communities, where and why trophic cascades occur, mechanisms of coexistence in biological control, and top-down and bottom-up effects in food webs, and the outcome of interactions among different types of consumers, like vertebrates and invertebrates (e.g. cows and caterpillars), in grasslands.
I have done quite a bit of work sorting apart the mechanisms of coexistence of two parasitoids: Aphytis melinus and Encarsia perniciosi. These are two parasitoid wasps involved in biological control of California red scale, an agricultural pest of citrus. Because the biology this system is well-studied by Bill Murdoch (UC Santa Barbara), Bob Luck (UC Riverside), and many others, and because it has only a few species, it provides a great field system for testing quantitative ecological theory in a real system.