Research Areas:
Understanding rarity and invasiveness through congeneric comparisons and analyses of phylogenetic novelty


When examining the factors that cause rarity or invasiveness, biologists have generally focused on two disparate scales: the macro-evolutionary scale and the local-ecological scale. At the macro-scale, biologists have considered how traits and evolutionary lineages correlate with rarity or invasiveness. Rare plants tend to have poor dispersal, long generation times, specific habitat requirements and require pollinators for reproduction, whereas invasive plants tend to have the opposite traits. However, macro-scale studies neglect ecological mechanisms that determine a species' population growth and local abundance. Ecological studies at the local-scale involve collection of detailed demographic data and experimentation to determine the ecological factors that regulate critical vital rates (i.e., birth and death rates). These demographic studies are better predictors of the causes of rarity and invasiveness of individual species than macro-scale studies. However, because a single species is the focus of the study, these results can not be generalized to other rare or invasive species.

We are interested in understanding the causes of rarity and invasiveness by combining a comparative, macro-evolutionary approach with species-specific demography and manipulation of ecological factors. Many of the worst invasive species co-occur with non-invasive, native or even rare congeners. By comparing closely related species in the same habitat, we can control for the evolutionary history of the species and for the ecological environment. We are currently working on several different congeneric groups, examining the role of interspecific interactions such as competition, pollination, and herbivory. Our studies include exotic invasive, native common, and federally endangered species that coexist in a single habitat type, and are on Lespedeza' in the Midwestern U.S., and Cirsium's and Lupinus' in Northern California. We are also examining the role of interspecific interactions in determining the relative population growth rates of exotic and invasive plant species, and how their phylogenetic relationships with members of the native community ('phylogenetic novelty') mediate those effects.