Committee Chair

Boyd, Jennifer N.

Committee Member

Klug, Hope; Cruse-Sanders, Jennifer M.


Dept. of Biological and Environmental Sciences


College of Arts and Sciences


University of Tennessee at Chattanooga

Place of Publication

Chattanooga (Tenn.)


Human activity worsens global biodiversity loss, particularly for vulnerable rare species. Plant species can respond to environmental changes via adaptation and/or acclimation or migration, yet limited genetic diversity and fitness in rare species can hinder these processes. Changes in light availability from human activities impact the growth and fitness of broadleaf species like sunflowers (Helianthus spp.). In a garden experiment, we compared the phenotypic plasticity of five Helianthus species representing different geographic ranges. Locally restricted H. longifolius and H. verticillatus showed less plasticity in growth and allocation traits than widespread H. angustifolius and H. maximiliani. Rare species with narrower ranges also displayed less population-level plasticity compared to common species. Geographically restricted rare species may struggle to acclimate to changes in light availability caused by human activities, which could increase extinction vulnerability. Conservation efforts should target limiting invasive and woody species to mitigate reduced light availability in their native habitats.


I’d first like to thank my advisor, Dr. Jennifer Boyd, for the years of mentorship as both an undergraduate and graduate student. You fostered my passion for conservation through years of opportunities in research, professional development, and travel, and I am extremely grateful. Thank you also to Dr. Hope Klug for the years of support through advisement. You broadened my horizons in research and helped me discover new interests outside of plant science. Thank you to Dr. Jennifer Cruse-Sanders for your support of my research with the State Botanical Garden of Georgia and for your unwavering encouragement. The resources you provided and the time I spent working with you in Georgia were invaluable to me. A special thank you to Will Rogers who has been instrumental in every stage of my research. Not only have you been a huge inspiration to me, but you are also a constant source of motivation and joy. Thank you also to Dr. Jill Anderson and Dr. Lisa Donovan for your help in conceptualizing this project and to Mike Boyd for the resources you graciously provided. This research would not have been possible without the hard work of many undergraduate students, including Annabree Corlew, Noura Elsaeed, Cora Fleming, Jessica Anchanattu, Uma Plambeck, and Leslie Eselgroth. A special thank you to Jared Odell and Holly Seiler Odell for your continued friendship and advice. Thank you also to Cooper Breeden of the Southeastern Grasslands Initiative and the many iNaturalist users who were instrumental in the collection of wild sunflowers across the United States. Lastly, I’d like to thank my family for their commitment to my success from the beginning.


M. S.; A thesis submitted to the faculty of the University of Tennessee at Chattanooga in partial fulfillment of the requirements of the degree of Master of Science.




Sunflowers--Effect of light on; Phenotypic plasticity


sunflower; rarity; plasticity; light; range size

Document Type

Masters theses




ix, 44 leaves





Date Available