Date of Award

Spring 5-7-2014

Document Type

Thesis

Degree Name

Bachelor of Arts

Department

Biology

First Advisor

Andrew Kerkhoff

Abstract

The inverse relationship between body mass and abundance is a well-documented pattern in plant and animal communities that holds true across many diverse ecosystems. In plants, this process is driven by the balance between growth and mortality rates of individual plants within the community, and alternative assumptions about growth and mortality result in different probability distributions of individual size. Traditionally, studies of plant size distributions have focused on forests, but here we also examine the size distributions of diverse herbaceous and shrub-dominated communities including wetland, prairie, desert, and alpine meadow sites. In particular, we focus on the metabolic scaling theory vs. the demographic equilibrium theory and their respective size distribution model predictions in plant communities. Metabolic scaling theory predicts that plant size distributions follow a power-law or Pareto distribution. In contrast, the assumptions of demographic equilibrium theory result in a Weibull distribution for plant size. We also test a combined Pareto-Weibull distribution model based on a size dependent transition in mortality rate. In all thirteen of our study sites the Weibull distribution provided the best fit to the data, followed by the combined model, then the Pareto distribution. The fact that one model could provide the best fit for this wide variety of diverse ecosystems shows support for underlying ecological mechanisms that govern plant community structure whether forest or non-forest.

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