Mechanisms of Plant-Herbivore Interactions

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The P.I.'s intend to explore the mechanisms of interaction among terrestrial plants and their herbivores, including both direct interactions (e.g. herbivores consume plants) and indirect interactions (e.g. herbivores may affect the outcome of plant competition by increasing soil nutrient concentration). previous studies of old field grasses and herbs and their major herbivores, grasshoppers, at their study site in central Minnesota indicate that (1) plants are limited by and compete for soil nitrogen, (2) grasshopper reduce plant abundance and affect plant species composition, and (3) grasshoppers are limited by and compete for plant food. Based on these studies, the investigators propose three experiments to show how these interactions link together: (1) garden experiments in which the effects of different plants on soil nitrogen, plants on other plants, grasshoppers on plants, grasshoppers on nitrogen, and grasshoppers on other grasshoppers will be measured separately and in combination on plots where soil nutrients, plant species composition, and grasshopper densities will be controlled, (2) field experiments in which densities of six grasshopper species will be manipulated to look at these same potential effects in a natural community, and (3) laboratory feeding experiments in which grasshoppers will be fed different plant species and their preference and physiological responses measured. These experiments will measure the mechanisms and strength of direct and indirect plant - herbivore interactions under controlled conditions, determine the role of herbivore diet selection in these interactions, and determine the importance of these interactions in a real community containing the same plant and grasshopper species. This study may be the first to address all three goals in a single, relatively simple, system. The results will provide a foundation for predicting the outcome of these interactions and consequently, the structure of plant and herbivore communities. //