REU: Effects of Bison Herbivory on Two Tallgrass Prairie Species: The Influence of Fire, Neighbors, and Pattern of Defoliation on Plant Response

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Herbivores can strongly influence plant fitness, population dynamics, and community structure. Plant responses to herbivory vary along a continuum depending on the spatial/temporal patterns of defoliation and the competitive neighborhood or physical environment of the defoliated plant. The proposed research will 1) assess the consequences of bison herbivory on tiller growth, reproduction, clonal spread, and survivorship of tallgrasses (Panicum virgatum and Andropogon gerardii) and 2) determine the interacting effects of competitors, spatial and temporal patterns of defoliation, and fire on plant responses to bison herbivory on a prairie. The studies will test the hypothesis that the effects of fire and biotic neighborhood variation alter responses to grazing and that the relative grazing tolerances of different species change under different fire regimes. Vegetative growth, seed reproduction, and clonal growth performance, and plant responses over two growing seasons will be measured to determine long-term effects of herbivory on individuals and populations and whether a single herbivore may have opposite or congruent effects on different plant life history stages. These experiments will examine proximal consequences of herbivory on herbaceous plants and plant growth form and how abiotic and biotic interactions influence plant responses to herbivory. They will also provide insight into the interactions of grazing and fire effects on tallgrass prairie perennials, and its consequences for individual clone success and species relative abundances. This proposed project is part of a longer-term research program that will more fully address patterns of variation in responses to herbivory among species and among years.