Date of Award

Spring 5-15-2019

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Evolution, Ecology & Population Biology)

Degree Name

Doctor of Philosophy (PhD)

Degree Type



Human activities are profoundly altering biodiversity at all spatial scales by disturbing local interaction networks, homogenizing regional biotas, and causing global extinctions. These changes in biodiversity can in turn influence the provisioning and stability of vital ecosystem functions (biomass production, biogeochemical cycling, pollination services, etc.). Therefore, a priority for ecology and global-change biology is to provide predictions for how biodiversity will respond to environmental changes. Inconveniently, biodiversity often responds unpredictably even when disturbances or environmental conditions are similar. Such contingencies have prevented the development of a general theory for ecological communities, undermining explanatory power and causing some to challenge the relevance of community ecology.

This contingency may in part result from a pattern-first focus on single dimensions of biodiversity. Biodiversity is multi-dimensional, but most hypotheses to explain it have focused on the number of species (richness) or mean measures of diversity at local or regional scales (α-diversity and γ-diversity, respectively). Meanwhile, some of the largest changes in biodiversity worldwide are occurring through changes to the spatial variation in species composition (β-diversity). As a scaler that links patterns at local and regional scales, β-diversity can provide key insights into multi-scale mechanisms through which environmental change influences community assembly, biotic homogenization, and ecosystem stability. Recent conceptual frameworks suggest that four fundamental, high-level processes – speciation, dispersal, niche-selection, and ecological drift – may provide a path towards a general theory of ecological communities. However, it is unknown whether this approach will reconcile much of the contingency currently plaguing community ecology or provide useful predictions necessary to anticipate and mitigate undesired changes in biodiversity.

There are two primary goals of my dissertation: 1) to understand the factors that mediate the importance of fundamental community assembly processes that cause β-diversity patterns; and 2) to determine how spatial processes that alter β-diversity contribute to, or undermine, the stability of large regional ecosystems. In Chapter 2, I address why the relative importance of selection and drift varies across natural communities for structuring herbaceous plant species and trait β-diversity. I find that drift plays an underappreciated role in causing biodiversity patterns in environmentally structured landscapes. This study highlights that understanding the scale-dependent mechanisms driving trait filtering and community size can reveal why the importance of selection and drift varies across communities and scales. In Chapter 3, I synthesize experiments to understand how and why dispersal alters the importance of drift and selection during community response to disturbance. I find that contingent assembly outcomes that cause variation in β-diversity following disturbance can be explained by dispersal that alters community size and the strength of selection. In Chapter 4, I ask how and why bird biodiversity across scales influences that stability of regional ecosystems in North America. I find that bird species β-diversity and climate heterogeneity generate asynchronous dynamics among local communities that stabilize total bird biomass at regional scales.

By integrating concepts from community assembly theory, spatial ecology, and functional ecology my dissertation provides novel perspectives on the processes that influence variation in biodiversity and their consequences for ecosystem stability across scales. These insights have broad implications for both general theory and the potential to aid development of more comprehensive strategies for biodiversity conservation, ecosystem management, and landscape restoration.


English (en)

Chair and Committee

Jonathan A. Myers

Committee Members

Carlos Botero, Scott Mangan, Rachel Penczykowski, Sebastian Tello,


Permanent URL: https://doi.org/10.7936/55m4-8g42

Available for download on Monday, May 15, 2119