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In partial fulfillment of the requirements for the degree of
Doctor of Philosophy in Biology
in the
School of Biological Sciences
Xian Yang
will defend her dissertation
Ecological Community Assembly in the Face of Anthropogenic Environmental Changes
Thursday, October 31, 2019
9:30 AM
Marcus Nanotechnology Building
Conference Room 1116
Thesis Advisor:
Dr. Lin Jiang
School of Biological Sciences
Georgia Institute of Technology
Committee Members:
Dr. Mark E. Hay
School of Biological Sciences
Georgia Institute of Technology
Dr. Marc J. Weissburg
School of Biological Sciences
Georgia Institute of Technology
Dr. Linda E. Green
Department of Biology
Georgetown University
Dr. Nathan J. Sanders
Rubenstein School of Environment and Natural Resources
University of Vermont
Abstract
Anthropogenic environmental changes, such as increased nitrogen (N) deposition, changes in precipitation regimes, and habitat loss and fragmentation, are known to affect Earth’s ecosystems. Understanding mechanisms regulating the assembly of ecological communities in the face of anthropogenic environmental changes is one of the primary goals of contemporary ecology. In this dissertation, I present four studies addressing questions on community assembly under anthropogenic environmental changes. First, I conducted an experiment in a semi-arid grassland to examine how anthropogenic environmental changes, in the form of resource addition, influence phylogenetic alpha- and beta-diversity of the communities. I found N and water addition influenced different aspects of the grassland community structure. N addition altered plant community phylogenetic structure, driving communities towards phylogenetic overdispersion; water addition promoted phylogenetic convergence, driving communities to converge towards a more similar phylogenetic structure over time. Next, I used bacterivorous ciliated protists as model organisms to explore how the loss of a keystone local community affects metacommunity biodiversity and ecosystem functions. I found that local communities with distinct environmental conditions supported endemic species, and had greater impact on regional-scale diversity than other local communities, therefore qualifying them as keystone communities. These keystone communities also had significant impacts on ecosystem functions, including biomass production and particulate organic matter decomposition. Finally, I investigated the drivers of variation in the phyllosphere microbial community composition in a fragmented subtropical forest on the islands of the Thousand-Island Lake, China. I found that stochastic processes, rather than deterministic processes, played a prominent role in shaping phyllosphere bacterial and fungal communities in the context of habitat fragmentation. Taken together, these findings further our understanding of community assembly processes in the face of anthropogenic environmental changes.
