Mitchell-Umbanhowar Lab

JAMES PATRICK CRONIN

Positions

Contact Information

RESEARCH INTERESTS

I take an experimental approach to ecology, testing hypotheses that attempt to explain general biodiversity and ecosystem function patterns. I am particularly interested in explaining why the relative importance of different species interactions (e.g., resource competition, herbivory, pathogens) varies spatially and temporally and how this subsequently determines the distributions, relative abundances, and productivity of organisms. To address these questions, I use terrestrial plant, insect herbivore, and plant pathogen communities as model systems.

PROJECTS

Postdoctoral Research in Disease Ecology (Univ. of North Carolina at Chapel Hill)

Global changes such as decreased biodiversity, nitrogen deposition, and drought are expected to change plant susceptibility and tolerance to insect herbivores and pathogens. Consequently, there is increasing demand to predict how human impacts on ecosystems alter the dynamics of emerging infectious diseases. To rigorously address this issue, we have formed research collaborations with Alison Power (Cornell), Andy Dobson (Princeton), Parviez Husseini (Princeton), Elizabeth Borer ( Oregon State), and Eric Seabloom ( Oregon State). We are developing and experimentally testing mathematical models that predict how changes in biodiversity and nutrient cycling determine the transmission and impact of barley yellow dwarf virus (BYDV). BYDV is an aphid-transmitted pathogen that attacks both wild and cultivated grasses worldwide.

As part of this collaboration, I am experimentally testing the following hypotheses:

• Plant phenotypes can be defined by a key set of general, covarying physiological plant traits (e.g., specific leaf area, leaf nitrogen concentration, photosynthetic rate).
• The interaction between these physiological traits and resource availability mechanistically explains shifts in an individual's ecological traits (e.g., competitive ability, tolerance to herbivores and pathogens), an individual's epidemiological traits (e.g., disease risk), and disease prevalence in host communities.

Ph.D. Research (Univ. of Pittsburgh): Explaining variation in insect herbivore control over plant communities.

Abstract (manuscript in preparation): Research repeatedly demonstrates that herbivores can control the distribution and abundance of plants. Thus, predicting herbivore control over plants is a central goal of ecology. The vegetation characteristics thought to influence herbivore control, however, are naturally correlated and typically confounded in experiments. This makes identifying the mechanisms responsible for changes in herbivore control extremely difficult. To address this problem, we define five conventional models that are based on different vegetation characteristics (i.e., host concentration, tissue quality, size, productivity, and tolerance). We then test each model against two experimental old-field studies. Our results clearly reject all prominent models of herbivore control except for a single parsimonious and general mechanism: plants with greater access to limiting resources are more tolerant to herbivory, regardless of where herbivore activity is greatest.

TraitNet (Core Participant)

A research coordination network and biological database designed to foster the systematic collection and dissemination of species trait data (http://www.columbia.edu/cu/traitnet/)

Nutrient Network

A global experiment investigating the effects of resources and consumption on ecosystem processes (http://www.science.oregonstate.edu/~seabloom/nutnet/)