Award Date


Degree Type


Degree Name

Master of Science (MS)


Life Sciences

First Committee Member

Dale Devitt

Second Committee Member

Lloyd Stark

Third Committee Member

David Charlet

Fourth Committee Member

Christie Batson

Number of Pages



Impending threats to shrubland ecosystems, posed by climate change, necessitate niche modeling efforts to project vegetation range shifts. However, efforts often remain unguided by individual-scale interspecific plant interactions. The stress gradient hypothesis posits that facilitation should increase in areas of high abiotic stress, only if the individuals are able to ameliorate the surrounding area via functional traits. The Sheep Range of Nevada was used to assess the role of functional traits as predictors of plant association. Larrea tridentata, Coleogyne ramosissima, and Artemisia nova were selected as shrubs with variable life history strategies and ranges in order to identify general patterns between canopy level traits concerning morphology and physiology to intensity of interactions. Over the observed gradient there was a predominance of competition, defined by reduced undershrub abundance in comparison to adjacent spaces. However, data suggest that interaction may not be driven specifically by macroclimate but by microclimate modulating traits, as observed net effects of facilitation or competition were more greatly impacted by composites of traits, as opposed to singular traits. Composite traits that parsed canopy morphology and physiology, defining plants by canopy size, leaf nutritional value, and resource-use efficiency were significant predictors of relative interaction intensity (RII) (Adj. R2 = 0.49--0.7, p < 0.01). δ15N, was the only singular trait positively associated with RII when accounting for other aspects of climate and plant physiology and morphology (Adj. R2 = 0.64, p < 0.001). Contrary to the stress gradient hypothesis, climate what not a significant predictor of RII when accounting for plant morphology and physiology. Over time as the macroclimate continues to fluctuate, above and beyond ameliorative ability, these facilitative interactions may shift to competition. As such, further identification of patterns of association and trait characteristics will be imperative to provide suitable assessments of potential community dynamics shifts.


climate change; Functional traits; Nurse plant; Plant ecology; relative interaction


Biology | Botany | Environmental Sciences | Terrestrial and Aquatic Ecology

File Format


File Size

2.2 MB

Degree Grantor

University of Nevada, Las Vegas




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