Poison ivy (Toxicodendron radicans (L.) Kuntze) is a native perennial liana widely recognized for the production of urushiol, and the associated contact dermatitis it causes in humans. Poison ivy is predicted to become both more prevalent and more noxious in response to projected patterns of global change. Moreover, poison ivy is an important food source for avian species, and urushiol has numerous applications as a high-value engineering material. Thus, this curious weed has many avenues for future concern, and promise. Here, I address gaps in knowledge about poison ivy ecology and physiology so that we may better understand its weediness and utilize its benefits. I address three core areas: poison ivy establishment patterns; biotic interactions with multiple taxa; and the development of molecular tools for use in poison ivy. I found that the early life stage of seedling emergence is a critical linchpin in poison ivy establishment due largely to herbivore pressure from large grazers. I also describe the multifaceted relationship between poison ivy and avian frugivores that not only disperse the drupes of poison ivy but also aid in reduction of fungal endophytic phytopathogens. A survey of poison ivy urushiols yielded that while variation in urushiol congeners was high across individuals, relative congener levels were stable within individuals over a two month period. Lastly I demonstrate best practices for introducing and transiently expressing recombinant DNA in poison ivy as a step towards future reverse genetic procedures. / Doctor of Philosophy / Poison ivy is a native plant best known for its capacity to cause allergenic skin reactions in humans due to the chemical urushiol, which is found in all parts of the plant. While most people prefer to avoid this plant, poison ivy is an important food source for birds. In addition, urushiol has numerous applications as an engineered material. Despite these positive aspects, poison ivy is among those plants that are responding well to global change, such as increasing CO₂ levels and habitat fragmentation. Poison ivy has been shown to increase in size and produce more allergenic forms of urushiol under elevated CO₂ levels and there are concerns that poison ivy prefers the disturbed areas created by habitat fragmentation. These attributes suggest that poison ivy will become more prevalent and more noxious in the coming years. Thus, this curious weed has many avenues for both future concern and promise. To aid in our ability to manage poison ivy in the future, I used a combination of field, greenhouse, and laboratory studies to study the ecology of poison ivy. I investigated the early stages of the poison ivy life cycle, and the relationship between poison ivy and the animals that interact with it. I found that the earliest life stages of poison ivy are a critical linchpin for poison ivy survival due largely to large animals like deer eating the seedlings. I also describe the multifaceted relationship between poison ivy and birds, which not only disperse the seeds of poison ivy but also aid in reducing pathogens associated with the seeds. I surveyed the amounts and types of urushiols that poison ivy produces and found them to be highly variable from plant to plant, but relatively stable over time within a plant. Lastly, I demonstrate best practices for transient transgene expression in poison ivy leaves as a step towards future genetic studies. These studies help expand our understanding of a problematic weed, and pave the way for future studies in weed ecology and in the utilization of urushiol in positive applications, showing that even poison ivy can be of benefit to the environment and humans.

Urbanization is increasing at a dramatic rate as the human population increases. While it is well-known that urbanization tends to decrease species diversity (i.e., biotic homogenization), it is not known how urbanization affects the frequency and efficiency of species interactions. Seed dispersal is a plant-animal interaction that depends on disperser feeding rate, disperser diversity, probability of seed dispersal and germination. How these factors are affected by urbanization however is unknown. In this study, we evaluate how urbanization alters these factors. Urban sites had 2x higher feeding rate and 3x higher number of disperser species. The probability of seed dispersal however was the same between natural and urban sites. Moreover, the probability of germination after dispersal was 20% lower in urban sites, leading to overall negative effects of urbanization on T. radicans seed dispersal. In this study we demonstrated that urbanization can affect species diversity, as well as their ecological functions.

Urbanization is increasing at a rapid pace with negative consequences for native biodiversity. While it is well-known that urbanization can lead to biotic homogenization (dominance of a few competitive species), effects of urbanization on ecological functions that rely on the frequency and efficiency of species interactions are less understood. Seed dispersal success depends on seed disperser feeding rate and diversity, which can affect the probability of fruit removal (i.e. seed dispersal) and germination rates. However, how these factors are affected by urbanization is unknown. In this study, we evaluate the effects of urbanization on factors that contribute to seed dispersal success (seed disperser diversity, frequency, probability of fruit removal and germination rate using Toxicodendron radicans and its seed disperser community as a model system. We found that urban sites had three times more disperser species and two times higher feeding rate compared to natural sites. However, the probability of individual fruit removal did not differ between natural and urban sites. Moreover, germination rate after dispersal was 20% lower in urban sites, leading to overall negative effects of urbanization on T. radicans seed dispersal. We propose differences in seed germination rate are driven by changes in seed disperser species composition and their differences in seed gut transit time. This in turn affects disperser species’ ability to successfully scarify seeds. Overall, our results highlight the need to evaluate urbanization's effects on functional ecological processes, in addition to biotic homogenization effects, in order better understand and mitigate its negative impacts on biodiversity.