PARENT SESSION
Organized Oral Session 16: Allelopathy: Biochemical interactions among plants affecting community structure, exotic invasions and evolutionary theory
Organizer(s): A Mallik and R Callaway
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 511 C, Level 5, Palais des congrès de Montréal
Centaurea maculosa from North America are better competitors and better defended than conspecifics from Europe.
Ridneour, Wendy*,1, Callaway, Ragan1, 1 Division of Biological Sciences, Missoula, Montana, USA
ABSTRACT- Several nonmutually exclusive hypotheses have been proposed for the dramatic transmogrification of some invasive plant species, including some with significant evolutionary implications. One of these, the enemy release hypothesis, posits that exotic invaders explode in abundance because they are no longer suppressed by the specialist herbivore consumers they evolved with. A current extension of the enemy release hypothesis is that release from natural enemies would allow plants to reallocate energy and resources from defensive weapons to growth; the evolution of increased competitive ability (EICA). Reallocation to growth is thought to make these new genotypes more competitive than their predecessors in their native range. We conducted experiments with Centaurea maculosa populations from Europe and North America and found that, on average, North American populations were larger, more fecund, and better competitors against North American grasses than European populations of C. maculosa. These results support the EICA hypothesis. However, we also found that North American C. maculosa were better defended against both specialist and generalist herbivores from Europe and North America. These results do not support EICA. Our preliminary results suggest that growth does not contribute strongly to the competitiveness of C. maculosa, but that the allelopathic effects of C. maculosa may be directly selected on in North American communities where (±)catechin, a phytoxic root exudate, is highly effective. Centaurea maculosa may have evolved in North America, but selection for competitive ability and defense does not appear to be driven by allocational tradeoffs, but by direct selection on specific biochemical traits.
Key words: allelopathy, invasion, evolution, herbivory