| Summary: | Individuals within a species vary in a host of morphological, physiological, and phenological traits, and this trait variation, particularly within dominant species, can have a strong influence on community structure and function. Salt marshes in the southeastern United States are dominated in the low and mid intertidal by the foundation plant, Spartina alterniflora, which exhibits high levels of genetic and phenotypic variation across small spatial scales within natural marshes. However, relatively little is known about the ecological consequences of Spartina intraspecific variation for marsh communities. I have examined whether a) phenotypic variation of Spartina across tidal elevation results in trait trade-offs that confer a fitness advantage in local habitats; b) Spartina genotypic identity and associated traits influence a plant-plant-herbivore interaction; and c) the relative importance of Spartina genotypic diversity on population- and community-level responses varies across an abiotic gradient. In this dissertation, I demonstrate that intraspecific variation in Spartina alterniflora can be important both between and within populations, and that differential response among Spartina individuals to abiotic (e.g., tidal elevation and nutrient availability) and biotic (e.g., plant and animal community) factors may contribute to the maintenance of high levels of Spartina genetic diversity observed in natural marshes.
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