In a general sense, I am interested in how species interactions influence plant distribution and abundance. Much of my research has involved large-scale field experiments to address how particular interactions influence the demography and population abundance of component species in a community. Below is a brief description of some of the research I have conducted.
- Exotic species are transported to new regions where the abiotic and biotic environment may be quite different from their native range. We are interested in how successful exotics adapt to these new ecological circumstances. In particular, we seek to understand the importance of rapid genetically-based evolutionary change in enabling exotics to persist in newly colonized areas.
To examine these issues, I have studied St. John's Wort, Hypericum perforatum, a perennial plant native to Europe, North Africa and Asia that has been introduced into my continents around the world. Read More
- Classic ecological theory has long predicted that native plant diversity plays a key role in promoting resistance to exotic invasion. A central reason this may be so is that diverse native assemblages usually contain species that vary in how they capture resources. That is, diverse assemblages contain mixes of species that vary in their rooting depth, phenology, photosynthetic rates, and other functional attributes. This increased functional diversity may enable diverse assemblages of plants to more efficiently capture resources than less diverse assemblages, thereby leaving less "free" resources available to colonizing exotics. Since resource availability may critically influence invasibility, one would predict that resource addition could influence the relationship between native diversity and invasibility. In collaboration with Marilyn Marler, we are exploring: 1) how resource availability interacts with native diversity to influence invasibility; 2) whether functional overlap between exotic and native plants influences invasibility; and 3) how native diversity, functional overlap between natives and exotics, and resource availability influence the impact that an invader has on a recipient community. We have initiated a large manipulative experiment where we are addressing these issues. Read More
Food Web Ecology
At the simplest level, food webs describe who eats who in a community. However, beyond this description, food webs can summarize the important ecological interactions that influence the population growth and abundance of species in a community. I am interested in how top predators, through their effects on consumers, influence plant distribution and abundance.
- Across the Aleutian Islands in Alaska, we have studied how introduced predators and spatial subsidies influence plant community composition and productivity on islands across the archipelago. Read More.
- In collaboration with Dr. Dean Pearson, I am conducting a large manipulative experiment to determine how mid-sized mammalian carnivores (weasel, fox, coyote, badger, mountain lion, etc.) and raptors, as a group, influence herbivorous and granivorous small mammal populations, and how small mammals, in-turn affect grassland productivity and diversity. Our goal is to test whether top predators have strong indirect cascading effects on terrestrial plant communities through their impacts on consumers. Read More
Plant - Consumer Interactions
We know from a growing number of studies that both invertebrate and vertebrate consumers can have strong impacts on plant performance and even plant fitness. Yet, quite surprisingly, we still have a very rudimentary understanding of when and where pervasive negative effects of consumers on plants actually translate to changes in plant abundance or distribution. That is, at the most fundamental level, we do not really know how commonly consumers limit plant abundance, alter plant population dynamics, or change plant distributions. As a result, predicting the conditions under which consumers have important population-level impacts on plants has proved difficult. I am interested in how variation in plant life history and environmental context interact to influence the population-level impacts of consumers on plants. Read More.
While the major thrust of my research centers on the issues discussed above, I have been involved in a variety of collaborative projects that span a diverse conceptual areas in plant ecology. These projects have explored how spatial processes influence insect outbreaks, the effects of plant mating system on inbreeding depression, the metapopulation dynamics of rare endemic plants confined to serpentine seeps, and the consequences of plant-plant communication on induced defense and plant fitness. The publications from these previous collaborations and a description of a current collaboration are shown here