Date of Award

Summer 8-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

First Committee Advisor

Brian McGill

Second Committee Member

Jacquelyn Gill

Third Committee Member

Jose Eduardo (Dudu) Meireles

Additional Committee Members

Shawn Fraver

Abstract

The sister disciplines of ecology and biogeography have a shared interest in understanding where, when, and why biodiversity is distributed as it is, has been, and might be. Emerging from this interest in cataloging the present, understanding the past, and forecasting the future are the related concepts of the geographic range and the ecological niche that have been developed and widely applied to understand species’ distributions and tolerances. The range represents a species’ distribution at a given point in time. Importantly, ranges are dynamic in time and space. Increasingly available geographic occurrence data from various sources presents opportunities to estimate geographic ranges across broad timescales using diverse methods and tools. When paired with environmental data to characterize sites, occurrence data encodes information about how species relate to their environments and enables the estimation of the species’ niche. Both the geographic range and the ecological niche are, therefore, measurable units that can be estimated and applied to understand changes in species’ geographic distributions and/or environmental tolerances. Specific assumptions about how ranges and niches are structured often influence or underpin efforts to estimate, explain, and/or predict this change, despite lacking empirical support.

In this dissertation, I take an empirical, data-driven approach to quantifying continental-scale geographic range and realized climatic niche shifts for trees in North America using methods that do not rely on pre-determined assumptions about the underlying structure of the range or niche. In Chapter 1, I quantitatively summarize contemporary geographic range shifts using tree life stage as a proxy for time. In Chapter 2, I extend this analysis into environmental space, estimating and comparing the realized climatic niche of trees as juveniles and adults. In Chapter 3, I present a guide to working with the dataset underlying the analyses in Chapters 1 and 2. In Chapter 4, I extend Chapter 1’s analysis across broader timescales, quantitatively summarizing patterns of historic tree range shifts over the last 21,000 years. By analyzing large spatial, temporal, and taxonomic scales and utilizing diverse data sources in each of my studies, I quantify and summarize general patterns of distributional change through time.

Download

Share