Date of Award

12-9-2019

Semester of Degree

December

Document Type

Open Access Dissertation

Degree Name

Ph.D. in Environmental and Forest Biology

Department

Environmental and Forest Biology

Major Professor

Donald Leopold

Steering Committee Member

Jannice Friedman

Steering Committee Member

Mark Lomolino

Steering Committee Member

Sean Robinson

Steering Committee Member

Danilo Fernando

Steering Committee Member

John Stella

Abstract

Amid the current global biodiversity crisis spurred by anthropogenic environmental changes, determining conservation priorities and the extinction vulnerability of rare taxa are tasks of critical importance. Organisms can avoid environmental change-induced extinction through three possible response modes: evolutionary adaptation, migration (range shift), and tolerance through phenotypic plasticity. In this dissertation, I leveraged transplant experiments and population genomics to assess the ability of rare alpine rattlesnake-roots (Nabalus spp.) to adapt, migrate, and/or tolerate environmental change. I also employed these same techniques to define conservation units and priorities within two endemic alpine taxa (Nabalus boottii and Nabalus trifoliolatus var. nanus) and widespread non-alpine Nabalus trifoliolatus. Finally, I used

this study system to investigate more fundamental ecological questions: (1) the niche breadth- range size hypothesis; and (2) the factors contributing to historical persistence of Nabalus taxa in

small, isolated mountaintop populations. Overall, my results supported probable resilience to environmental change in alpine Nabalus taxa, which harbor moderate to high levels of genetic diversity (especially N. boottii), show evidence of historic and recent migration among summits, and are highly plastic for several functional traits linked to climate change response. However, alpine Nabalus taxa may suffer from reduced seed recruitment under ongoing climate change, and I therefore recommend

continued population monitoring. My results further indicated that both N. boottii and broad- sense N. trifoliolatus should be managed at the species level. I did not find evidence for multiple

evolutionary significant units or highly distinct individual populations within N. boottii, and morphological and genomic evidence suggested that alpine N. trifoliolatus var. nanus is not distinct from widespread non-alpine N. trifoliolatus. Regarding the more fundamental ecological questions, I found tentative support for the niche breadth-range size hypothesis in the focal Nabalus spp., but not for phenotypic plasticity as the driving mechanism. Finally, the ability of small populations of Nabalus taxa to maintain genetic diversity (likely via tetraploidy for N. boottii) and migrate between summits helps explain their historical persistence on isolated mountaintops of the northeastern United States.

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