Dissertation Research: Interspecific Interactions in Stage Structured Population Models: The Effects of Herbivores and Pollinators on Trillium grandiflorum

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Proposal 0105000DIG: Interspecific interactions in stage structured population models: The effects of herbivores and pollinators on Trillium grandiflorumSusan Kalisz , Tiffany KnightThe growth rate of a plant population depends on the strength of its interactions with herbivores and pollinators, as well as the stage in the plant life-cycle in which these interactions take place. Thus, variation in the magnitude of interactions with herbivores and pollinators among plant populations can cause variation in the rates of growth among natural plant populations. If populations that have a high density of flowering plants are more attractive to both herbivores and pollinators, then the magnitude of their interactions with both herbivores and pollinators may be expected to change deterministically as plant populations grow or decline in time. I have collected preliminary data on 12 populations of Trillium grandiflorum, a perennial forest herb. The magnitude of its interactions with its mammalian herbivore, white tailed deer, and insect pollinator, bumblebees, vary highly among these populations, and these interactions primarily influence the reproductive stage in the plant life-cycle. In a pilot experiment that manipulated plant density, significant changes in the magnitude of both plant-herbivore and plant-pollinator interactions were found. In this proposed work, I will quantify the amount variation among populations that is caused by variation in herbivore and pollinator interactions. In addition, among several populations, I will experimentally manipulate the plant density to more fully quantify the density-dependent influences of herbivores and pollinators on Trillium survival, growth and fecundity. I will use a modeling framework to synthesize all of this information and assess the effects of changes in interspecific interactions on the growth rate of plant populations.