PARENT SESSION
Contributed Oral Session 3: Herbivory: Plant - Herbivore Interaction
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 513 E, Level 5, Palais des congrès de Montréal
Release from natural enemies and invasion success: An experimental test on goldenrod.
Auge, Harald*,1, Brandl, Roland2, Schaedler, Martin2, 1 UFZ Centre for Environmental Research, Halle, Germany2 Philipps University Marburg, Marburg, Germany
ABSTRACT- It is often argued that the lack of natural enemies in a new area is an important mechanism of plant invasions. Reduced levels of herbivore or pathogen attack on exotic plants should result in a competitive advantage over native species (enemy release hypothesis). This leads to the prediction that, if native competitors were also released from their enemies, population growth of invasive plants should decrease. We carried out an herbivore exclusion experiment on an old-field plant community in central Germany to test this prediction for goldenrod, Solidago canadensis, which is native to North America and invasive in Europe. We applied foliar insecticide, soil insecticide and molluscicide to 9 m2 plots using a fully factorial randomized block design. S. canadensis was the most frequent exotic species colonizing the abandoned field. We monitored its population growth during the first seven years of succession. Other studies showed that population dynamics of the closely related S. altissima was positively affected by insect exclusion in its native range. Our experiment, carried in the new range of goldenrod, revealed the opposite result: When removing above-ground or below-ground insects from the plant community on the experimental plots, colonization by S. canadensis was delayed compared with control plots. In the sixth year of succession, population density of S. canadensis leveled off, with lower values in the insecticide-treated plots. This effect was strongest when both insecticides were applied. In contrast, molluscicide application had a positive effect on population growth of goldenrod. Insecticides and molluscicide did not affect growth of goldenrod and other plant species in a greenhouse trial, indicating that the effect measured in the field was the result of the exclusion of herbivores. Hence, our field experiment indicates that release from insect herbivory contributes to the invasion dynamics of S. canadensis in its new range owing to a shift in the competitive relationships among plant species.
Key words: biological invasion, competition, insect herbivory, Solidago canadensis