My research program is centered around the population and community ecology of weedy and invasive species. Within this broad field I currently have four main focus areas, which are described below.
1) What are the ecological implications of intraspecific diversity for colonization success? (supported by the National Science Foundation: DEB-1433886)
Increasing propagule pressure (i.e., more seeds) is known to increase colonization success, but the largest pools of propagules should also contain the greatest genetic and phenotypic diversity. Propagule pressure may therefore affect colonization success in part because of the effects of genetic or functional diversity within founding populations. To decouple these effects, I am using the weedy mustard Arabidopsis thaliana as a model invader in an ongoing field experiment near Houston, TX (on land owned by the Katy Prairie Conservancy). In addition to disentangling the effects of propagule pressure from those of population genetic diversity, this project is designed to assess relationships between genetic variation, functional trait variation and colonization success and test hypotheses about how increased genetic diversity will affect recruitment curves (which show how colonization success responds to increasing seed input).
Despite many compelling reasons to use A. thaliana for studying genetic diversity effects on colonization and invasion, I am also excited to address these questions in non-model systems where these basic concepts may have important real-world applications. For example, giant ragweed (Ambrosia trifida) is a serious agricultural and allergenic weed that has increased in geographic range and pest status within North America (where it is native). Giant ragweed populations are extremely variable morphologically, so we can hypothesize that its spread may have been aided through the increase of genetic and/or phenotypic variation in newly colonized populations. Together with colleagues in the Horticulture and Crop Science Department here at OSU, plus a crew of awesome OSU undergraduates, we have started quantifying how giant ragweed partitions its morphological variation within and among populations across the Midwest.
2) Does interspecific hybridization enhance invasiveness in plants, and if so how?
Hybrids may be better able to establish and spread into new regions than their parental taxa if they contain more variation or novel combinations of genes relative to their parental taxa. This hypothesis is widely cited but remains poorly tested, although data from a recent meta-analysis I conducted is consistent with this hybridization-invasion hypothesis. Some of my experimental work has also indicated that hybridization in radish (Raphanus sp.) enhances invasiveness in a novel region and that the critical traits leading to fitness gains in hybrids may differ among regions. Thus, not only can hybridization promote invasiveness, but it can apparently do so via an even greater diversity of pathways than previously imagined.
3) Does resource enrichment interact with herbivory to influence biological invasions?
Ecological theory predicts that introduced species will respond positively to release from their natural enemies and that nutrient enrichment may enhance this response. For my dissertation, I tested this hypothesis using two species that commonly dominate North American wetlands: the invasive purple loosestrife (Lythrum salicaria) and the native broad-leaved cattail (Typha latifolia). Data from a large-scale mesocosm experiment showed that loosestrife suppresses diversity far more than cattail, while also raising fundamental questions about our standard method for comparing competitive effects among species. In a complementary field study, I found that nutrient-enriched sites may be the least likely to experience successful biocontrol-based management of loosestrife populations, providing insights for invasive species management using biocontrol. These projects have led to many new questions and inspired plans for future work with loosestrife and other species that commonly dominate the plant communities in which they occur.
4) How can we use functional traits to predict invasive potential?
Interspecific variation in traits that can influence invasiveness has received a great deal of attention, not only because of basic questions regarding what makes a species invasive but also for the possibility that invasive potential could be predicted prior to a species’ introduction. My interests in functional trait variation and biological invasions led me to develop a novel approach that I tested using a suite of wetland plant species that vary widely in invasiveness.
More recently, I have also been looking at breeding systems as functional traits that contribute to colonization and early establishment success through my involvement in a NESCent working group organized to test the predictions of Baker’s Rule. Baker’s Rule states that species and populations colonizing islands should have an enhanced degree of uniparental reproduction (e.g., self-compatibility or vegetative reproduction), thus we might analogously expect that introduced species will be more self-compatible or capable of clonal reproduction than native species.