Changes in species interactions between native and introduced ranges of exotic species are important determinants of invasion success. Despite this, little is known about how predation and competition interact to affect the evolution of traits that increase the impacts of invasive species. Underlying predictions of plant invasiveness is the assumption that individuals tradeoff energy devoted to growth and defense, and that the effects of this tradeoff depend on the biotic environment. The goal of this research is to understand how variation in important species interactions contributes to invasive species success and to predict when certain traits that may influence invasiveness are likely to evolve. The project relies on multiple lines of a rapidly growing model plant that differ in lifetime intensity of competition and predation, will characterize differences in life history strategies among these lines, and will use a field invasion experiment to detect the effects of both historic and current biotic interactions on plant success.

Exotic species threaten global biodiversity by damaging native ecosystems and the services they provide. This project will increase understanding of the evolution in exotic species and bridges the gap between plant ecology and evolution. The project includes a collaboration with Chinese scientists. One of the investigators has considerable experience mentoring undergraduate students, and particularly those from under-represented groups, and plans to continue these training activities during the proposed project.

Project Report

The major experimental goals of this project were: 1) To examine the relative contributions of selection from herbivores and competitors in shaping plant allocation to defense against herbivores versus plant growth and reproduction, 2) To determine the impact of selection from specialist, generalist, or mixed herbivory on the evolution of plant tolerance of herbivores, 3) To use experimental evolution within a model species to infer ecological and evolutionary tradeoffs in natural and exotic, invasive plant populations. Additional goals include mentoring and training undergraduate students in the research process, especially those from underrepresented groups in STEM fields. Major activities include the training of a PhD student, the inclusion of the project work in a PhD dissertation (published in Dec. 2013) and the involvement of numerous undergraduates and recent graduates working on the project. We generated 140 independent experimental selection lines of Brassica rapa, starting in March 2012 and ending in July 2013. We selected the lines with either one of two generalist herbivores, one of two specialist herbivores, both specialist and generalist herbivores, no herbivores, or artificial herbivory, at high or low plant competition. Therefore, our lines varied in herbivore and competitive history. We then used the lines to ask how selection history influenced contemporary resistance to both specialist and generalist herbivory, tolerance to damage, and competitive ability in two follow-up experiments in fall 2013 and spring 2014. Fifteen undergraduates and recent graduates were involved with the project. Undergraduates were involved in most aspects of the project. Our research demonstrated that herbivore identity matters for the defensive response of plants, including resistance and tolerance to herbivores. However, although both historical herbivore selection and contemporary herbivore identity influenced plant resistance and tolerance, this was not predicted by the feeding breadth of the herbivore, i.e. specialist versus generalist. This research also demonstrated that the ability of a plant to accumulate biomass after damage and replace aboveground tissue loss is a good predictor of plant fitness.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Saran Twombly
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Rice University
United States
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