Do Genetic Differences in Growth and Defense Contribute to the Success of an Invasive Plant Species? Experimental Tests

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Chinese Tallow Tree (Sapium sebiferum) is a major invader in the Gulf Coast thataggressively displaces native plants and forms monospecific stands. Experiments in Texas and Hawaii have shown that invasive ecotypes of Sapium have higher growth rates but lower defense abilities than Asian (native) ecotypes, and suffer higher damage from introduced Asian herbivores in Hawaii. We propose to use a series of experiments to answer the following questions: (1) How important is the combination of high growth, low defense and low herbivore attack for Sapium's invasion success? (2) How important are differences in its growth and defense in determining the severity of Sapium invasion in different conditions? (3) Are the same Sapium ecotypes that are invasive in North America also successful when grown in Asia in similar conditions? These experiments will be replicated across field sites that differ in Sapium status and insect herbivore assemblages. In Texas, Sapium is invasive and experiences low herbivore pressure with no documented specialists; in Hawaii, Sapium is a 'casual alien' that experiences very high generalist herbivore pressure with no documented specialists; and in China, where Sapium is native, it experiences high herbivore pressure from Sapium specialists. Our experiments will investigate the performance and competitive ability of native and invasive ecotypes of Sapium with resource manipulations, insect herbivore suppressions and density manipulations and simulated herbivore defoliation. These experiments represent a unique investigation into the interactions of invasive plants and herbivores that will elucidate the mechanisms by which exotic species successfully invade native communities. The broader impacts of the study are twofold. It will promote collaboration with Chinese scientists and train both Chinese and U.S. graduate students. It also will provide practical information for the prediction of future invasive species and help guide the management of current problem species.