Plant interactions (e.g., competition, facilitation) are critical drivers in community development and structure. The Stress Gradient Hypothesis (SGH) provides a predictive framework for how plant species interactions vary inversely across an environmental stress gradient, predicting that facilitation is stronger with increasing levels of stress. The SGH has been supported in numerous ecosystems and across a variety of stress gradients, but recent research has demonstrated contradictory results. These discrepancies have led to SGH revisions that expand its conceptual framework by incorporating additional factors, such as other stressor types and variations in species life history strategies. In this dissertation, I examine a further modification of the SGH by proposing and testing a Multiple Stress Gradient Hypothesis (MSGH) that considers how plant interactions vary along a continuous gradient of two co-occurring stressors using mangrove and salt marsh communities as a case study. In Chapter 1, I outline the predictive framework of a MSGH, by creating a series of predictions of species interactions. The components of the MSGH predict that stressors of similar types (e.g., resource and nonresource) will have similar effects and be additive. On the other hand, varying species life history strategies and life stages will lead to extremes of plant interactions. In Chapter 2, I performed a series of experiments to test the various components of the MSGH. In Chapter 3, I performed a large-scale observational study to test whether multiple co-occurring stressors altered the cumulative effects on plant interactions, and if these stressors should be grouped (e.g., resource and non-resource, abiotic and biotic, etc.) to enhance predictability. From a series of studies conducted herein, I concluded that co-occurring stressors are important factors that control complex species interactions as shown in my MSGH modeling approach. Further, future theories need to incorporate species-specific and stressor specific grouping when modeling how species interactions shape communities. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2013.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2002. / Vita. Includes bibliographical references (leaves 153-161).

Thesis (Ph. D.)--University of California, San Diego, 2000. / Vita. Includes bibliographical references.

No description available.

Thesis (M.S.)--University of Delaware, 2008. / Principal faculty advisor: W. G. Shriver, Dept. of Entomology & Wildlife Ecology. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 1992. / Typescript (photocopy). Includes bibliographical references (leaves 105-112). Also available via the World Wide Web.

Thesis (M.A.)--San Francisco State University, 1979. / "December, 1979." Includes bibliographical references (leaves 149-153).

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 100-108). Also available on the World Wide Web.

Thesis (doctoral)--Tartu University, 1999. / Curriculum vitae. Includes bibliographical references.

"A thesis submitted to the Graduate Faculty of Georgia Southern University in partial fulfillment of the requirements for the degree Master of Science." Title from PDF of title page (Georgia Southern University, viewed on April 5, 2010). Stephen P. Vives, major professor; Sophie B. George, Risa A. Cohen, committee members. Electronic version approved: December 2009. Includes bibliographical references (p. 37-40).