Nature videos wouldn’t be complete without the classic predator-prey interaction scenes. Nevertheless, biologists have only begun to investigate the importance of top-down consumer-driven impacts on communities in the past 50-60 years. We are still working to develop a predictive understanding about when predation and consumption are likely to have strong impacts on ecosystems. Nevertheless, a predictive understanding of feeding interactions is particularly important at a time when many top predators are threatened with extinction, agriculture and urbanization are altering the distributions of species, and consumer species are regularly transported into novel environments.
Why do some introduced species have dramatic impacts on their communities while others are mostly benign? Why are some species generalists while others are specialists, and why are some species apparently so much better defended than others? These are some of the big questions that drive the ecological and evolutionary investigations of trophic interactions in my lab. It is my hope that what we learn will contribute to a predictive understanding of the impacts of consumption in communities.
Plants and insects provide a useful system for studying feeding interactions because they are accessible, easy to manipulate, and are important players in many terrestrial ecosystems, including agricultural settings. Most of my research focuses on interactions between milkweed plants and their associated insects. Milkweeds are well-known because they provide a toxic food source for monarch caterpillars. Monarchs sequester toxic compounds from plants in their bodies for their own defenses-making them unpalatable to birds and other predators. The phenomenon of sequestering toxic compounds is not limited to monarchs, however. It occurs in many consumer-resource interactions.
A variety of aphid species also consume milkweeds and presumably sequester its compounds, and we have been focusing on these insects because of their remarkably fast reproduction and their susceptibility to a variety of known predators, including lady beetles, lacewings, and parasitic wasps. One of the aphids is an introduced species. Aphids are fascinating because they reproduce both sexually and clonally (adults already have their daughters and even granddaughters developing inside of them), they exhibit phenotypic plasticity of wing formation, they harbor endosymbionts that confer interesting traits (like the ability to survive on low-protein high-sugar diets of phloem), and they are often “tended” or protected by ants that consume the aphids’ secretions of excess sugar. The plants and predators are interesting too!
I am also open to investigating new model systems.
Questions and Methods
Plant Tolerance. Previous research has shown that when predators consume aphids, plants grow better. However, the effects attenuate, that is, the effect of predators on aphids is greater than the effect on plant growth. Furthermore, the effects attenuate more on some species of milkweeds than others. I hypothesize that these effects are due to the different abilities of milkweeds to tolerate aphid herbivory. Initial projects will help to test this hypothesis. The methods in these projects will primarily involve growing plants, exposing them to different amounts or types of herbivory, and measuring their responses.
Plant Resistance. Many traits in milkweeds may help to reduce herbivory, but the production of toxic cardenolides is one of the best-studied resistance traits. We can also measure resistance by observing the growth rate of aphids on different plants. Evidence is mixed about whether cardenolides impact aphids, and it will be interesting to learn whether resistance and tolerance traits are correlated in milkweeds. Students and I have begun to work on implementing protocols for measuring cardenolides using liquid chromatography; work is ongoing.
Insect Behavior. Plants are known to produce a variety of cues that attract or repel insects. I am interested in understanding whether there are correlations between tolerance and resistance traits in plants and the behavioral responses of insects, including both herbivore and predator species. These methods will involve designing choice tests and measuring insect behavioral responses to volatile cues using an olfactometer.
Science Education. I am interested in developing ways to involve students and teachers in authentic research building upon models of citizen science. I am also interested in developing labs using our model system that help teachers teach standards and concepts that are otherwise difficult for students to explore in a classroom setting. Some ideas include phenotypic plasticity, predator-prey interactions, and competition.
Field Experiments. Although I am not immediately planning them, I am interested in conducting field experiments in the long term to investigate how local adaptation, landscape ecology, ecological complexity, and introduced species affect feeding interactions and their impacts on communities.
Scope of Projects. I look forward to working with students to develop projects relevant to these immediate questions or broader interests. I have ideas for some short term projects and long term projects. Please contact me if you are interested in discussing the possibilities.
We’re working on developing a new, distributed research and education project on milkweed adaptation that will hopefully be conducted simultaneously at many educationaly institutions. Read more about it here: http://erenweb.org/milkweed-adaptations/