Variation in tritrophic interactions due to climate change The primary goal of this research is to characterize variation in plant-herbivore-parasitoid interactions in natural and managed ecosystems distributed along temperature and precipitation gradients. We have initiated a long-term study (10 years), integrating research at multiple sites in North, Central, and South America that vary in temperature, precipitation and seasonality. The research along these natural gradients is enhanced by recently initiated macrocosm experiments designed to mimic storm surge and rising sea levels. We also utilize laboratory mesocosms and various modeling approaches to test questions about climate change and tritrophic interactions. With these correlative, experimental, and modeling approaches, we will determine how plant chemistry, leaf phenology, caterpillar densities, herbivory, parasitism, and caterpillar and parasitoid species diversity are affected by climate and how they react to extreme climatic events, such as El Niños, floods, droughts, or hurricanes. This work is currently funded by the National Science Foundation, the National Institute for Climate Change Research, Earthwatch Institute, and Tulane University.
Diversity A major component of global change biology is the loss of diversity. We study many aspects of diversity, how it is changing, how it is maintained, and how it can be studied. For example, we are documenting diversity of interactions at 4 distinct ecosystems in Louisiana, Arizona, Costa Rica, and Ecuador and comparing our results with those of other research groups. Documenting diversity of interactions is a novel way to study diversity and is relevant to major issues in global change, such as loss of predators from forests due to fragmentation and loss of keystone species from biotic communities.
Chemical ecology We are examining the effects of plant allelochemicals on interactions between plants and arthropods in natural and managed ecosystems in Costa Rica and Colorado. Results from our previous work indicated that specific amides and imides (plant secondary metabolites) in understory shrubs (Piper spp.) play important roles in determining the diversity of arthropods associated with these shrubs and their interactions. We are conducting long-term experiments, synthesis of secondary compounds, quantification of compounds, and field/laboratory assays to elucidate the ecological roles of these chemicals. Similarly, to test the roles of saponins in trophic relationships between alfalfa and associated arthropods, we are conducting trophic cascades research in alfalfa fields in Colorado, Arizona, and Louisiana.
Conservation and applied ecology The primary conservation and applied interests in this laboratory are: 1) the role of ecological theory in managed ecosystems, 2) conservation of plant and insect diversity in tropical ecosystems, and 3) monitoring and protecting rare and threatened species in the United States. In addition to the research in our laboratory relevant to these 3 issues, we have initiated a new project (2004) examining effects of various land management policies on trophic interactions in the Southwestern United States.
Use of ecological theory to guide biological control Current advances in ecology could provide useful guidelines for management of agricultural systems, plantations, and natural reserves. We use results from our research on tritrophic interactions to construct predictive models that can be used as guidelines for choosing appropriate natural enemies in biocontrol. We also test predictions with empirical data from our work in banana plantations and alfalfa fields.
Parasitoid Diversity in Tropical Rainforests Over half of the described species of organisms in the world are directly involved in plant-herbivore-parasitoid interactions, yet very little is known about the actual diversity of parasitoids in tropical ecosystems. Similarly, little is known about how land management and human disturbances affect parasitoid diversity and population dynamics or how parasitoids affect ecosystem functions. We are examining parasitoid and herbivore diversity in rain forests in Costa Rica and Ecuador. Through an exhaustive collecting and rearing program, we will uncover patterns of parasitoid diversity that will help us answer basic and applied questions about parasitoids and herbivores on different host plants and in different plant communities. Basic natural history data and keys to immatures are continually entered into an online database (http://www.caterpillars.org). This project is part of major conservation and biodiversity inventory efforts in Ecuador.
Evolution of ant-plant associations in a diverse tropical plant genus Ecological specialization is often thought to be a result of coevolutionary interactions between animals and plants. Shrubs in the tropical genus, Piper, sometimes house mutualist ants in their petioles and constitute a useful system for examining specific questions about the evolution of specialized plant and ant adaptations. We are constructing phylogenies for species of Piper based on molecular data and stem anatomy. We can map plant chemistry, presence of ant mutualists, and other ecological data onto these phylogenies to answer questions about the evolution of chemical defenses versus specialized ant attractants in Piper spp.
Antiparasitoid mechanisms in caterpillars and discovery of novel plant secondary compounds Research in our laboratory contributes to closing the gap between the assumed function of larval traits and the demonstration that they are actually effective against natural enemies. We examine morphological, behavioral, and chemical defenses that caterpillars deploy against parasitoids and use various experimental approaches to test their effectiveness. For the chemical defenses, we have developed assays to detect active compounds in plants and caterpillars; once we have detected these defenses, we examine the effects of sequestered compounds on parasitoids. This work has led to the discovery of novel plant compounds, which could possibly have pharmaceutical value.
Quantitative ecology Our laboratory and collaborators are interested in using mathematical modeling to complement our experimental and correlative research. For example, a collaborator is developing a model in the Piper ant plant system that examines population dynamics of herbivores, ants, and ant predators. Our correlative and experimental work provides parameter estimates for this model, and the model helps us put our results into a larger theoretical context. We are also very interested in statistical methods and experimental design in evolutionary biology and ecology. We will continue to study and utilize new multivariate methods, categorical data analyses, structural equation modeling, and meta-analysis. All graduate students in the laboratory are required to do a meta-analysis as the first chapter of their dissertation.

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For more information, contact Lee Dyer: ldyer@tulane.edu