RUI: Plant-Herbivore Dynamics in an Herbivore-Protection Mutualism

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Many mutualisms involve the exchange of a resource reward by one partner for some service by the other. Such interactions can influence the structure of ecological communities as well as the functioning of ecosystems. For example, in ant-protection mutualisms, ants protect plants or herbivores in exchange for a nectar reward. Ant mutualisms are hypothesized to have large effects on plant and herbivore species diversity and abundance. This project combines modeling and field work to explore the long-term consequences of a mutualism involving ant-protected herbivores. Understanding the feedbacks among plants, mutualistic herbivores and ants across multiple growing seasons will advance ecology by highlighting the potentially destabilizing effects of mutualisms on terrestrial ecosystems. This project brings together two researchers at a primarily undergraduate institution with a strong record of undergraduate training and incorporation of underrepresented groups in science. The proposed work will employ honors undergraduate research as its primary vehicle for outreach and training, including integrative empirical and theoretical approaches. By definition, the short-term effect of mutualism is to increase population densities. In herbivore-protection mutualisms, this increase in population density may lead to over-exploitation of host plants in the long-term with corresponding negative consequences for protected herbivores. Preliminary results show that herbivory by the ant-protected herbivore, Publilia concava, reduces the attractiveness of its perennial host-plant, tall goldenrod, to subsequent generations. Using a two-way factorial design experiment (presence/absence of herbivores and presence/absence of ants) in two tall goldenrod field sites, this project will experimentally evaluate the consequences of the delayed herbivore effect on host-plants for host-plant selection and performance of Publilia concava. Repeated censuses of plants, herbivores, and ants over two years will document if herbivory mediates plant responses that influence herbivore performance and future host plant selection. These data will also be used to test a generalized spatial model of herbivore-protection mutualisms linking host choice behavior, induced plant resistance, and herbivore population dynamics. Results from the proposal will increase understanding of the potentially destabilizing effects of mutualism and the effect of host-choice behavior by herbivores on herbivore-plant dynamics following delayed effects of herbivory.