Speaker:William F. Fagan ,
University of Maryland

Title:Dynamical Consequences of Growth Rate Variation: Lessons from Mount St. Helens and Beyond

Abstract:Variation among individual organisms is often abstracted out in models for mathematical ecology. I will discuss two ecological cases in which individual variation uniquely contributes to dynamics. In the first case, growth rates systematically vary among individuals based on spatial position. I will outline a long-studied field system at Mount St Helens that has been used to parameterize a theoretical model of plant-herbivore invasion dynamics. Aspects of plant population growth and the intensity of herbivory under low-density conditions (at the front "edge" of the invading plant population) can determine whether the plant population spreads across a landscape or is prevented from doing so by the herbivore. In the second case, growth rates vary among individuals leading to asynchronous development. I discuss how stochastic variation in maturation rates may result in individuals being reproductively isolated in time, generating an Allee effect. This phenomenon has implications for the conservation of small populations.