Carol Horvitz

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  Stochastic Demography of Tropical and Subtropical Plan
  Carol Horvitz

  Perennial tropical and subtropical plants inhabit inherently variable environments, where both abiotic and biotic features vary from place to place and during the life times of individuals. To address ecological, evolutionary and applied demographic questions, we employ structured models (matrix projection and integral projection) using a framework that includes stage (sometimes age) structure and environmental variability. Projection models are used in two ways, to track population dynamics and to generate sample paths of individuals across the life cycle. The former concerns ecological dynamics and evolutionary demography where fitness is measured as the (stochastic) population growth rate. The latter concerns life histories, life expectancies and the timing of other key events (such as age of first reproduction). In some systems we also address rate of spread across the landscape. Issues we address quantitatively by these methods include: the effect of hurricanes on the impact of native seed predators ; integrating selection on quantitative traits across the life cycle when selection gradients vary over time; trade-offs due to the cost of reproduction; how harvest regime of non-timber forest products affects longevity of trees; life expectancy of pioneer vs shade-tolerant tropical trees; the impact of rarely occurring long distance dispersal vectors to invasion speed; effectiveness of bio-control agents on invasive trees and shrubs; and others. As models are applied to different problems, new issues and new models arise through collaborations.