Influences of Natural Enemies and Resource Availability in Biological Invasions by Plants Public Deposited

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  • March 19, 2019
Creator
  • Heckman, Robert
    • Affiliation: College of Arts and Sciences, Department of Biology
Abstract
  • Biological invasions—the establishment and spread of species outside their historical native ranges—has implications for basic ecology as well as conservation and human well-being. As such, identifying the mechanisms that promote invasions is crucial for both applied and basic ecology. While most major invasion hypotheses focus on a single causal mechanism (e.g., nutrient availability, traits of the invasive species), my research examines whether trade-offs between resource allocation to growth of new tissue and defense of tissue against disease and herbivory can explain why some non-native species become invasive in their new range and others do not. Specifically, I tested whether exotic species benefit more from enemy release relative to native competitors in high resource environments. To that end, I conducted a series of field experiments at the level of individual plants and plant communities. This research represents the first thorough test of the assumptions and key predictions of a hypothesis which integrates information about invasive species, invaded communities, and the environment in which invasion occurs to explain invasion success more broadly than previously possible (the Resource-Enemy Release Hypothesis, R-ERH). I tested this hypothesis in grassland communities and with individuals of several grass species. At the community level, exotics were less damaged than natives, especially in fertilized communities. Moreover, fertilization increased foliar damage on native species. Finally, fertilization increased exotic dominance only in communities exposed to vertebrate herbivores, and excluding insect herbivores and fungal pathogens reduced exotic dominance regardless of fertilization. At the individual level, species benefitting most from fertilization also benefitted most from exclusion of fungal pathogens and insect herbivores; this relationship was similar for natives and exotics. Within assembled native communities, fertilization increased, and enemy exclusion reduced, exotic dominance. Furthermore, fertilization and enemy exclusion each reduced native colonization of exotic-dominated communities. Together, these results provided partial support for R-ERH. Importantly, they also show that invasions can be driven by multiple independent, not interacting, factors.
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  • In Copyright
Advisor
  • Wright, Justin
  • Mitchell, Charles
  • Umbanhowar, James
  • Bruno, John
  • Peet, Robert K.
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2017
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