Publication Date
8-2025
Date of Final Oral Examination (Defense)
5-21-2025
Type of Culminating Activity
Dissertation
Degree Title
Doctor of Philosophy in Ecology, Evolution, and Behavior
Department
Biological Sciences
Supervisory Committee Chair
Kelly A. Hopping, Ph.D.
Supervisory Committee Member
Marie-Anne de Graaff, Ph.D.
Supervisory Committee Member
Nancy F. Glenn, Ph.D.
Supervisory Committee Member
Matthew A. Williamson, Ph.D.
Abstract
Global plant diversity is declining at a rate unprecedented in human history. Rare endemic species are especially vulnerable due to their small geographic ranges, often coupled with limited dispersal capacity and narrow ecological requirements. Yet these plants make outsized contributions to regional floristic diversity and can fulfill irreplaceable ecological roles. Conservation efforts, however, are frequently constrained by basic knowledge gaps and a lack of tools and resources to address species declines. Informed decision-making depends on a clear understanding of species’ ecological needs, interdependencies, and threats, particularly under conditions of limited capacity and mounting environmental pressures. In this dissertation, I examine rare plant conservation through multiple, complementary lenses, focusing on the case of Astragalus mulfordiae, a rare and threatened species endemic to the western Snake River Plain. Across three chapters, I explore key facets of its ecology and community context that can guide conservation priorities in the face of ongoing ecological threats.
A critical piece of missing information for many rare species is their reproductive biology. My first chapter investigates A. mulfordiae’s reproductive strategy using a pollinator exclusion experiment. I show that A. mulfordiae is highly dependent on pollinators—primarily solitary, cavity-nesting bees. I then show how a trait-based analysis of its pollinator cohort can help identify critical populations for maintaining habitat connectivity.
Rare plants are embedded within broader ecological communities, yet their interdependencies and ecological roles are often poorly understood. In my second chapter I situate A. mulfordiae within its plant-pollinator community using bipartite network analysis. I show that despite its rarity, A. mulfordiae plays an important role in its networks, supporting pollinators that might otherwise be weakly tied to the community and contributing to network stability. I also show that the introduced plant Sisymbrium altissimum plays a central structural role in these networks. These findings add nuance to understandings of rarity and introduced status and emphasize the importance of evaluating species’ functional roles when setting conservation priorities.
Finally, in Chapter 3, I examine anthropogenic pressures affecting A. mulfordiae, with a focus on motorized recreation. Using high-resolution aerial imagery, I show how widespread and shifting networks of informal trails intersect A. mulfordiae habitat. Although I found no clear link between these trails and A. mulfordiae population trends, this study underscores how the increasing availability of high-resolution imagery can support the detection and monitoring of diffuse and episodic disturbances such as motorized activity.
Together, these chapters demonstrate how even basic ecological information, such as reproductive strategy and ecological associations, and increasingly available tools like high-resolution imagery can be leveraged to clarify the contributions and vulnerabilities of rare plant species and to identify strategic, scalable conservation priorities. Such approaches become more vital given the scale of global plant biodiversity loss and the practical constraints that shape conservation decision-making. By applying these methods in a focused case study, this work highlights their broader relevance and potential for conserving other rare and understudied species.
DOI
10.18122/td.2397.boisestate
Recommended Citation
Buchholtz, Clara, "Reproductive Ecology, Pollinator Networks, and Anthropogenic Disturbance Inform Rare Plant Conservation: Insights From Astragalus Mulfordiae" (2025). Boise State University Theses and Dissertations. 2397.
10.18122/td.2397.boisestate