Ragan Callaway ( edit )

B.S. Westmont College, 1978
M.S. University of Tennessee, 1983
Ph.D. University of California, Santa Barbara, 1990

The primary focus of the research in my lab is on interactions among plants.  These include direct interactions, such as competition for resources, allelopathy, and facilitation; and indirect interactions mediated by herbivores, soil microbes, and other plants.  Although I continue to pursue research on positive interactions in plant communities, mostly in collaboration with the international Alpine Pals research group, most of my current work is on interactions between exotic invaders and native species.  These invaders include Centaurea maculosa, C. diffusa, C. melitensis, C. solstitialis, Alliaria petiolata, Acroptilon repens, and Acer platanoides.  We have found that two of the world’s nastiest invaders, C. maculosa and C. diffusa, are much more allelopathic to species in invaded areas than species with which they coexist in Eurasia.  Our research has also demonstrated strong effects of soil microbes (primarily fungi) on Centaurea’s invasive capabilities, and that biogeographical differences in soil microbial communities play a large role in the benign effects of C. maculosa on native Eurasian communities, but the devastating effects of this species on invaded communities.  These biogeographical differences include significant negative feedbacks between soil microbes from Eurasia and Centaurea, but significant positive feedbacks between soil microbes from North America and Centaurea.  Considered as a whole, research in my lab indicates that that shared evolutionary trajectories may mediate coexistence in the original, natural, communities of invaders but collapse in the communities they invade.  Perhaps when humans introduce some plant species to new regions they force together species with different biochemically driven coevolutionary trajectories from different continents, providing instances of profound community disruption and an unparalleled opportunity to test long held ecological paradigms.