PhD Defense by Qianna Xu

Event Details
  • Date/Time:
    • Monday November 28, 2022
      8:00 am - 11:00 am
  • Location: EBB Children’s Healthcare of Atlanta (CHOA) Seminar Room
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Summary Sentence: Ecological Determinants of Ecosystem Stability

Full Summary: No summary paragraph submitted.

In partial fulfillment of the requirements for the degree of


Doctor of Philosophy in Biology

In the

School of Biological Sciences


Qianna Xu


Will defend her dissertation


Ecological Determinants of Ecosystem Stability


Monday, 28th November 2022



In-person: EBB Children’s Healthcare of Atlanta (CHOA) Seminar Room

Via Zoom:


 Thesis Advisor:

Lin Jiang, Ph.D.

School of Biological Sciences

Georgia Institute of Technology


Committee Members:

Mark Hay, Ph.D.

School of Biological Sciences

Georgia Institute of Technology


Marc Weissburg, Ph.D.

School of Biological Sciences

Georgia Institute of Technology


Joel Kostka, Ph.D.

School of Biological Sciences

Georgia Institute of Technology


Yann Hautier, Ph.D.

Department of Biology

Utrecht University



Understanding the mechanisms underpinning the stability of ecological systems has been a central goal of community ecology. This dissertation presents studies examining the roles of several important ecological factors, including species diversity, nutrient enrichment, and interspecific competition, in regulating ecological stability. First, I conducted comprehensive quantitative meta-analyses that synthesized the findings of existing empirical studies of the relationships between species diversity and temporal stability of ecosystem properties. The meta-analysis revealed a general, consistently positive relationship between species diversity and ecosystem temporal stability, a robust finding that holds even after accounting for the confounding effects of environmental covariates. This study also identified species compensatory dynamics as an important mechanism underlying the observed positive diversity-ecosystem stability relationships. Second, I investigated the effects of nutrient enrichment on multiple dimensions of compositional and functional stability, using semi-arid grasslands as the study system. I found that nitrogen enrichment reduced grassland functional and compositional temporal stability, resistance, and recovery, but increased grassland functional and compositional resilience. Importantly, nitrogen enrichment influenced most functional stability dimensions by altering their corresponding compositional stability dimensions, whereas reduced species diversity under nitrogen enrichment contributed little to observed changes in grassland stability. Lastly, using laboratory microcosms containing assemblages of freshwater bacterivorous protozoans as model systems, I examined the effects of interspecific competition and determinants of competitive outcomes (species niche and fitness differences) on ecosystem temporal stability. I found that the presence of competition increased species asynchrony but not population stability, resulting in more stable ecosystem dynamics. Species niche differences increased species asynchrony, whereas species fitness differences decreased population stability, leading to changes in ecosystem temporal stability. These results demonstrate the linkage between species coexistence mechanisms and ecological stability, providing a mechanistic understanding of competition effects on population and ecosystem stability. Altogether, this dissertation contributes novel knowledge to the field of ecological stability, with important implications for the stable provisioning of ecosystem products and services under ongoing global environmental change.

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Phd Defense
  • Created By: Tatianna Richardson
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  • Created On: Nov 14, 2022 - 12:54pm
  • Last Updated: Nov 14, 2022 - 12:54pm