Author's Department


Date Submitted

Spring 4-10-2015

Research Mentor and Department

Tiffany Knight, Department of Biology




Invasive species are widely considered to be a major threat to native biodiversity, however some studies suggest that exotic species seldom cause the extinction of native species, and may even increase biodiversity at some spatial scales. This leads to the question of whether exotic plant species that have naturalized to a new range are biologically distinct from their native counterparts. Here, we chose one common native and one common exotic plant species from each of five plant families, and evaluated their growth over one growing season for two proposed mechanisms of biological invasion. We evaluated the Enemy Release Hypothesis (ERH), which states that exotic species leave behind their predators and parasites in their introduced range, through an herbivore removal treatment. We addressed the Competitive Release Hypothesis (CRH), the idea that exotic species leave behind their specific competitors in their introduced range, through a competitor removal treatment. We hypothesized that if ERH and CRH are correct, then the herbivore removal and competitor removal treatments will benefit the native species more than the paired invasive species. However, we observed that our herbivore removal treatments did not affect most species’ growth, while the competitor removal treatment significantly improved the growth rate of several invasive species and only one native species. We also hypothesized that there would be a negative relationship between phylogenetic novelty and response to our treatments, with more novel species being less affected by absence of herbivores and competitors. However we did not observe any significant relationship between phylogenetic novelty and response to our treatments. The lack of difference between native and invasive species does not support ERH or CRH, and suggests that there is not a fundamental difference in these species’ reactions to competition and herbivory. The absence of significant relationship between phylogenetic novelty and response to our treatments may suggest that more species would be required to observe this pattern. After another season of data collection, we believe our treatments will have an increased effect over that increased period of time. Also, we will be able to more accurately assess the response of our focal species to treatment by constructing demographic models to evaluate the response of population growth rate to our treatments.