Date of Award

8-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Jennifer A. Schweitzer and Joseph K. Bailey

Committee Members

Alison Buchan, Aimee Classen, Richard Norby

Abstract

Interactions between intraspecific plant variation and the environment can create evolutionary and ecosystem feedbacks, but the contribution of these feedbacks to the success of invasive plant species has rarely been explored or quantified. To test whether evolution occurs during the process of plant invasion I conducted three major experiments and a meta-analysis to test various aspects of this central question. First, I conducted a meta-analysis of studies that tested the Evolution of Increased Competitive Ability (EICA) hypothesis. The meta-analysis did not support EICA’s prediction that release from herbivores leads to reduced defenses and higher performance, but it showed that evolutionary change occurs in these traits across plant invasions. To test whether soils act as selective agents for invasive plants, I grew 13 populations of the invasive tree Ailanthus altissima in a common garden. Phenotypic variation showed that genetic differentiation correlated with climate and soil factors has occurred among populations, indicative of rapid evolution in response to local conditions. To test how soils act as selective agents, I conducted a study in which seeds from 3 populations were reciprocally transplanted in soils from those populations. Genetic variation and positive feedbacks to plant performance were expressed in soils with biotic communities, but not in sterilized soils. This indicates that soil biotic communities may select for plant performance and genetic variation in future generations. To test whether intraspecific variation associated with plant nutrient availability could create ecosystem feedbacks, I conducted a decomposition experiment of leaf litter from elevated carbon dioxide and nitrogen fertilization experiments. There were feedbacks that led to faster mass loss at control sites and in the nitrogen fertilized sites, but a negative feedback led to slower mass loss in elevated carbon dioxide sites. Environmental conditions, including anthropogenic alterations to environment, can create ecosystem feedbacks between intraspecific plant variation and processes that regulate soil nutrient availability. Overall, this dissertation indicates that evolution is broadly important in invasive plant species, that it occurs in response to climatic, abiotic soil properties, and soil biotic communities and that plant-soil feedbacks to ecosystem properties vary by environment, with theoretical and applied implications for all results.

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