Congratulations to Dr. Benjamin R. Shipley (Georgia Institute of Technology, United States) recipient of the International Biogeography Society’s 2024 Dissertation Award!
Dissertation committee members:
Jenny McGuire, Lin Jiang, Joseph Mendelson, Joel Kostka, and Brody Sandel.
Chaired by Israel Borokini, IBS Student-at-large.
The Geography, Ecology, and Evolution of Mammalian Endemism
Synopsis
Understanding how and why species ranges vary across the Earth is a defining question in biogeography. Abiotic and biotic factors influence species range sizes in myriad ways; however, their effects on small-ranged and endemic species are still understudied. In this dissertation, I contribute to uncovering the drivers of mammalian endemism, employing and innovating a wide variety of analytical tools to describe the spatial patterns of endemism and the ecology of endemic mammals from multiple perspectives. Levels of endemism form the basis of many conservation prioritization schemes, including some of the most used definitions of biodiversity hotspots. However, there are many different definitions of endemism, each with their own interpretations, assumptions, and biases. In my first chapter (Shipley & McGuire 2022. Biological Conservation) I reviewed these definitions and applied them to a case study of Mesoamerican mammals, demonstrating that the definition of endemism and the resolution of spatial units used profoundly influence the interpretation of endemism hotspots, and I propose a new scheme that integrates multiple endemism definitions, adding nuance into endemism-based conservation. After reviewing how endemism is defined across discipline, in Chapter 2 (Shipley & McGuire 2023. Global Change Biology) I evaluated how patterns in global mammalian endemism are driven by landscape factors like topography and long-term climate stability, trends in species richness, and the climatic specialization (niche breadth) of the species. I developed a novel null-model technique that employs spatial randomization to remove ecological factors. Overall, these methods demonstrated that mammalian endemism patterns mirror those of species richness, but endemism is exceptionally high in topographically diverse regions that have had stable climates through time. I next expanded my analyses from the abiotic to the biotic factors influencing endemism, evaluating the ecological and evolutionary distinctiveness of highly endemic mammalian communities. I found that species living in areas of high endemism tend to have small body sizes, short lifespans, and few offspring per year, indicating they may have been unable to expand their ranges after habitat fluctuations. Furthermore, highly endemic mammalian communities have greater redundancy and lower diversity of traits than communities without many endemic species (Chapter 3, in review). The high clustering of these species in functional space indicates that abiotic trait filtering from stable climates is a stronger influence than biotic interactions in structuring endemic communities. In fact, I found little evidence that climatic niche breadth structures continental patterns of small-ranged species. To explore this result further, I narrowed my focus from global endemism to island-endemic mammals, using the controlled situation of island biogeography to ask whether the climatic niches of these species diverge from their closest relatives (Chapter 4, in prep). Using metrics of niche overlap and divergence, I evaluated how phylogenetic relatedness, phenotypic evolution, and geography influence the evolution of climatic niches on islands. I found that geography was by far the most influential driver of niche evolution in island mammals, and that neither relatedness nor phenotype influenced niche shifts. Overall, my results clearly demonstrate that understanding geographical patterns is vital for preserving unique species, communities, and ecosystems.
Statement of significance:
This dissertation significantly expands on our current knowledge of the ecology of range-limited vertebrates and contributes to our understanding of how topography, climate, trait evolution, and phylogenetics interact to structure and maintain global patterns of diversity and endemism. It introduces novel methods for disentangling these interactions, including a niche-based null model of global mammalian endemism. In addition, this research comprises important contributions to the study of endemism as a baseline for conservation. It evaluates the use of varying endemism metrics in the literature, providing recommendations for researchers studying the biogeographical characteristics of endemism and introducing a new method of characterizing endemism-based conservation prioritization. The results of this research demonstrate the paramount importance of geography, historical climate trends, and tectonics in structuring biodiversity patterns, and characterizes the influence those factors have on both the distribution of a species and its functional characteristics on the individual and community level. This research contributes one small step towards uncovering the dynamic factors influencing the distribution and maintenance of biodiversity in mammals, opening up new avenues of inquiry into the origins and future of spatial patterns and the biogeographic processes that create them.
Links to Dissertation Chapters:
Complete Dissertation: On ResearchGate at: https://www.researchgate.net/publication/374374006_The_Geography_Ecology_and_Evolution_of_Mammalian_Endemism
Chapter 1: Shipley, B.R., McGuire, J. L. 2022. Interpreting and integrating multiple endemism metrics to identify hotspots for conservation priorities. Biological Conservation, 109403. https://doi.org/10.1016/j.biocon.2021.109403
Chapter 2: Shipley, B.R., McGuire, J. L. 2023. Disentangling the drivers of continental mammalian endemism. Global Change Biology. https://doi.org/10.1111/gcb.16628.
Chapter 3: Shipley, B.R., McGuire, J. L. The stable environmental conditions of endemism hotspots shape the functional traits of mammalian assemblages. Proceedings of the Royal Society B. In review. See pages 74-92 in the complete dissertation.
Chapter 4: Shipley, B.R., McGuire, J.L. Relatedness, trait evolution, and climatic niche divergence in mammalian island endemics. In prep. See pages 93-126 in the complete dissertation provided.
Additionally, we recognize two runners up to the Dissertation award:
Evelyn M Beaury
Dissertation: The spatial distribution of invasive plant presence, abundance, and impact
Graduated: February 1, 2022, at University of Massachusetts, Amherst
Twitter: @evecologist
Laura Jiménez Jiménez
Dissertation: Estimation of the fundamental niche of a species using presence data, physiological tolerances, and accessible areas, and the evaluation of niche and species distribution models
Graduated: January 27, 2021, at University of Kansas, Lawrence
Twitter: @LauVioletaMx
