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Thesis Abstract – Janes (2006)


The Effect of Herbivory on Native/Exotic Plant Competition

Author and college:

Kelly A. Janes, Scripps College


April 24, 2006


Bachelor of Arts in Environmental Science


Diane Thomson, Joint Science Department of Claremont McKenna, Pitzer, and Scripps Colleges


Invasion by exotic species is one of the major threats to biodiversity on a global scale. The Enemy Release Hypothesis (ERH), which states that the success of exotics in the introduced range is due to their release from co-evolved natural enemies such as herbivores, pathogens, and predators, is commonly used to explain how exotics become invasive. Few studies have experimentally tested the ERH, and most of these have looked at how rates of herbivore damage differ between native and exotic plants but not at the effects of herbivory on the outcome of competitive interactions. By conducting an enemy exclusion experiment, I tested the prediction of ERH that natives will compete better with exotics when herbivores are excluded. Specifically, I carried out an experiment testing whether competition between an invasive herbaceous plant (Brassica nigra) and a native competitor (Amsinckia spectabilis) differed in the presence of absence of herbivores. The goal of this work was to test whether the ERH might explain the success of this invasive plant and the inability of native forbs to re-invade areas that are dominated by Brassica. While Amsinckia showed a marginally significant negative effect of competition on plant size, there were no other significant results. This may be due to the short time period in which the experiment was performed and more data taken over a longer period of time may show more conclusive results. Basic research into the mechanisms of invasion such as this has helped to predict and control the spread of exotic invasives and conserve dwindling populations of native communities.

For more information:

Contact Diane Thomson – dthomson@kecksci.claremont.edu

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