DISSERTATION RESEARCH: A mechanistic test of the keystone mutualism hypothesis

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This project will investigate how ecological interactions among caterpillars, treehoppers, and ants determine the health trees. Caterpillars damage forest trees by eating leaves and treehoppers feed on trees by sucking sap. An important consequence of sap-feeding by treehoppers is their excretion of a sugary solution called honeydew. Some forest-dwelling ants depend on the honeydew for food. This relationship is called a food-for-protection mutualism because ants receive carbohydrate-rich food, while treehoppers receive protection from predators by the ants. In this project, investigators will study how this interaction between ants and treehoppers affects all participants, and how the outcome impacts forest health.Societal benefits of this project are several-fold. First, results from the research will contribute to the scientific understanding of pest control in forests. Second, the project will contribute to education about forest ecology and entomology through the training of undergraduate research assistants, as well as through broader educational benefits to college students, public school teachers, and members of the public. Third, the investigators will partner with the Connecticut Forest and Park Association (CFPA), which offers outdoor education programs for teachers and members of the public. More specifically, this research will experimentally test several hypothesized mechanisms for top-down trophic effects of ant-sap-feeder mutualisms in a temperate forest community. This system contains multiple species of predatory ants interacting with sap-feeding insects (mainly Membracidae). Ant-sap-feeder mutualisms may trigger top-down trophic effects on caterpillars and plants via increases in total ant abundance (the "density increase hypothesis"), changes in the behavior of individual ants (the "behavioral modification hypothesis"), or changes in ant community structure (the "community shift hypothesis"). Experiments will be used to distinguish among these hypotheses. The community scope of this study system, which currently lacks an invasive ant species, is novel and important because it offers an opportunity to test ant-community mechanisms for keystone mutualism effects as well as ant density- and ant trait-related mechanisms in a relatively intact ecosystem.