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Date Permissions Signed
Date of Award
Master of Science (MS)
Hooper, David U., 1961-
Miner, Benjamin G., 1972-
McLaughlin, John F.
DeChaine, Eric G.
The theory of resource use pre-emption suggests that diverse communities may be more resistant to invasion than simple communities due to lack of niche space for invaders. Studies examining the relationship of native species richness to exotic success have provided mixed support for this idea. To test this theory, I measured plant diversity and cover across topographic gradients differing in resource availability in a California serpentine grassland, and measured exotic success as either species richness, absolute cover, or dominance of exotic species. I then evaluated models predicting these different measures of exotic success, using either native richness alone or in conjunction with environmental variables as predictors. Species richness was a poor index of exotic success, as it was relatively weakly related to more direct measures of exotic success, exotic cover and dominance, and varied differently along environmental gradients from those two variables. Native richness was a significant negative predictor of exotic success whether environmental variables were included or excluded, although the relationship was stronger when using exotic cover or dominance than exotic richness. My results contrast with observational studies that have found positive relationships between native and exotic richness, in part because environmental conditions favoring native richness at the site (low Ca:Mg) were opposite to those favoring exotics, and in part because exotics likely out-competed natives in more fertile habitats. Using cover or dominance as an index of exotic success and incorporating underlying environmental gradients provided a more realistic assessment of the factors controlling native and exotic success than simple models correlating native and exotic richness.
Western Washington University
Copying of this thesis in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Slakey, Daniel, "The relationship between native richness and exotic success depends on the index of exotic success and environmental gradients" (2010). WWU Masters Thesis Collection. 94.