Document: RAG-3-38-15

Co-evolution in plant communities: Invaders interact differently with new neighbors than with old ones.

CALLAWAY, R.M.* ¹ and E.T.ASCHEHOUG ²

The University of Montana, Missoula, MT 59812, USA ¹
The Nature Conservancy, 201 Mission Street, San Francisco, CA 94105 ²

Abstract:
Little attention has been paid to the possibility that long-term associations among plants may promote co-evolution, and coexistence among interacting species in natural communities. In part the lack of interest in such co-evolved interactions is because plant communities are widely thought to be "individualistic", composed primarily of plant species that have similar adaptations to a particular physical environment. We compared the competitive effects of an invasive Eurasian forb in North America, Centaurea diffusa (diffuse knapweed), on three grass species that co-exist with C. diffusa in Eurasia to the effects of C. diffusa on three grass species from North America, each of which is closely related to one of the Eurasian grass species. We found that Centaurea diffusa had much stronger negative effects on grass species from North America than on closely related grass species from communities to which Centaurea is native. Centaurea's advantage against North American species appears to be due to differences in the effects of its root exudates and how these root exudates affect competition for resources. Our results suggest that natural plant communities may be more co-evolved entities than is generally thought, and may help to explain why exotic species so successfully invade them.

Keywords: exotic invasion, knapweed, allelopathy, competition

This abstract is being presented at: 12:00 PM in session:
Oral Session #72: Plant Competition.