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Citation. Klausmeier, C. 200. The role of spatial heterogeneity in ecological communities. Ph.D. Thesis, University of Minnesota. 

Abstract. All ecological systems are spatially heterogeneous. The goal of this thesis is to investigate the causes of spatial hetereogeneity and its effects on the dynamics and structure of ecological communities. Chapters 1 and 2 use patch models to study the effects of habitat destruction on the structure of competitive communities. In Chapter 1, I extend Tilman et al.'s model of strong competition in two ways: by deriving exact conditions for species to go extinct in order of competitive ability as habitat destruction is increased and by analyzing an explicitly spatial analog. I complement these results in Chapter 2, where I derive a metapopulation model of weak competition or facultative mutualism. I find that locally poor competitors are often regionally rare and most prone to extinction and that pairs of mutualists can face catastrophic extinction. In Chapter 3, I develop a simple model of water and plant dynamics which can explain regular and irregular patterns found in semiarid vegetation. The regular patterns arise from a diffusive-advective instability; the irregular patterns result from the amplification of variation in microtopography. In Chapter 4, I use a game theoretical approach to analyze the vertical distribution of phytoplankton in stratified water columns. The model reproduces many features of actual distributions, including deep chlorophyll maxima in deep oligotrophic lakes, benthic mats in shallow oligotrophic lakes, and surface scums in shallow eutrophic lakes. In chapter 5, I expand the patch model of chapter 1 to include heterogeneity in the underlying environment. This allows coexistence of competing species that differ in their optimal patch type. There is no evolutionary limit to similarity when there is an absolute competitive hierarchy in each patch type, but a relaxed competitive hierarchy produces a finite limit to how similar competing species may be.

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