Introduction: Polyploidy is the doubling of a genome. Autopolyploidy and allopolyploidy are two different modes of genome duplication. These events are common in angiosperms and usually involve diploids and tetraploids, a resulting polyploid species. Both cytotypes exhibit competitive exclusion and environmental adaptation according to their spatial distributions. My research focuses on how abiotic environmental factors affect the range and the amount of range overlap of the taxon within the Callisia graminea and Allium canadense systems over time. Niche modeling determines whether there is substantial niche overlap between the Callisia graminea diploid and tetraploid, whether range shifts occur between the Callisia graminea cytotypes or Allium canadense varieties, and whether there is substantial range overlap between the Allium canadense parental and hybrid varieties.

Methods: The environmental layers from 1929 and 2011 were used for building the niche models and were downloaded from PRISM (http://www.prism.oregonstate.edu/recent/). The layers were clipped to encompass the range that each system occupies. The niche models were constructed using MaxEnt and assessed for robustness. Area under the receiver operating characteristic curve values were utilized to evaluate the accuracy of each model. The model-based methods used to evaluate niche overlap were Schoener’s D and the I Similarity tests and permutation tests. The other statistic used to evaluate niche overlap was Principal Component Analysis (PCA).

Key Results: For the Callisia graminea system, the range overlap of the diploids and tetraploids increased when comparing the 1929 models to the 2011 models. Surprisingly, diploid range increased, while the tetraploid range decreased. For the Allium canadense system, the range of variety lavendulare increased in 2011. Though the range of hybrid varieties had decreased in 2011, it was larger compared to the range of the parental varieties of the same year. The parentals’ range increased when comparing the 1929 model to the 2011 model.

Conclusions: The increase in niche overlap over time between the Callisia graminea cytotypes indicates that the two cytotypes are not diverging ecologically, but actually appear to be converging ecologically instead. The Callisia graminea tetraploids and the Allium canadense hybrids have experienced its boundary of accommodating environmental conditions and may not be capable of expanding further, whereas the Callisia graminea diploids and the Allium canadense parentals have not. The variety lavendulare has successfully expanded by encountering favorable abiotic conditions.

Date of publication

Fall 11-27-2017

Document Type




Persistent identifier


Committee members

Dr. Kate Hertweck, Dr. Joshua Banta, Dr. Katrin Kellner, Dr. Lance Williams


Masters of Science in Biology

Included in

Biology Commons