Date of Award

December 2018

Degree Type


Degree Name

Doctor of Philosophy (PhD)




Jason D. Fridley

Subject Categories

Life Sciences


Invasive species are a persistent threat to biodiversity and agriculture that cost countries millions of dollars each year. Despite the scale and impact of the problem of invasive species, it remains a mystery why some introduced species become invasive and others remain benign. Here, I examined the theory that invasive species possess key traits which make them successful invaders. Specifically, I investigated the hypotheses that 1) plasticity increases invasive species’ success compared to native species, 2) invaders evolve rapidly in their new ranges, 3) invasive species avoid tradeoffs apparent in natives related to growth, resource use, or defense. Using 30 species of native and invasive shade tolerant shrub species in a common garden, I tested whether invasive species had leaf traits that were more plastic to seasonal changes in light availability. I found that invasive species were more plastic, but I found no evidence that their plasticity contributed to increased carbon assimilation across the growing season. Next, I compared leaf traits of populations of five invasive species growing in forests from East Asia in their native range (Japan) and their invasive range (Eastern North America). I also compared these five invaders to three native co-occurring North American species. I selected individuals that occurred along a natural light gradient to assess leaf plasticity in response to light availability. I determined that plasticity in invaders partially arose in the native range, and that some plasticity evolved rapidly in the invaded range after introduction. I concluded that many North American species are less adapted for life in high light environments, such as along forest edges, than East Asian invaders; the ability to grow in both low and high-light conditions may give some forest invaders a competitive advantage. Finally, I quantified traits of annual, perennial, coastal salt tolerant perennials, and invasive populations of Mimulus guttatus in a greenhouse setting (22 total populations). I decomposed relative growth rates of each group into specific leaf area, photosynthetic rate, and leaf mass fraction to determine which trait contributed most to growth rate within each group of populations. Invasive populations did not have higher relative growth rates, contrary to our predictions, but they did have different ways of achieving high growth rates. I also examined whether tradeoffs associated with global trait patterns such as the leaf economics spectrum apply at the population level. I found that global patterns of plant functional traits may not be applicable when studying traits within species. I conclude that a variety of traits and evolutionary history contribute to the success of invasive species around the globe.


Open Access

Included in

Life Sciences Commons