Biology and Biomedical Sciences: Evolution, Ecology and Population Biology
Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
This dissertation documents the relationship between stress-adaptation and reproductive specialization in three endemic plant species: Delphinium treleasei, Echinacea paradoxa, and Scutellaria bushii) that are locally abundant but restricted to stressful habitats and their closely-related congeners: D. carolinianum, E. pallida, S. ovata, and S. parvula) that have broader habitat use, including hot, xeric habitats. In Chapter Two, I test two hypotheses concerning reproductive specialization in endemic plants and their common congeners: CC). I quantify morphological traits that are associated with stress-adaptation and reproductive specialization, pollinator behavior, and reproductive specialization. The locally abundant, habitat specialist: LAHS) species were significantly different from their CCs in vegetative traits but the direction of the differences was not consistent among genera. On the other hand, two of the three LAHS taxa had larger flowers and fewer dominant pollinators than their CCs. In Chapter 3, I examine the responses of the LAHS and CC plants to drought and high heat conditions in order to explicitly test the prediction that the LAHS species are more resistant to high-stress environments. The LAHS species were more resistant to stress, and the CC species were not. Moreover, the LAHS species had fewer, higher-quality offspring, whereas the CC species have more seeds of lower quality. In Chapter 4, I test the hypothesis that two LAHS species are poorer competitors for pollinators, as predicted by traditional theory of reproduction in rare species. The congeneric pairs did not compete for pollinators but varied in their morphological traits and reproductive success across sites. Finally, the research in Chapter 5 explores the response of two LAHS species and their CCs to regional climate change. Using herbarium specimens, I test the prediction that LAHS species that specialize on stressful habitats are less responsive to climate change in comparison to their CC. The LAHS species are responding to climate change by flowering earlier, but none of the widespread species exhibited a change in phenology with climate change. This dissertation supports a more nuanced theory of the relationship between reproductive specialization and rarity that addresses additional factors influencing rare taxa, such as stress-adaptation, and that has important implications for species' responses to climate change.
Miller-Struttmann, Nicole, "Causes of rarity in glade-endemic plants: Implications for responses to climate change" (2011). All Theses and Dissertations (ETDs). 617.