Fluctuating Resources: A General Theory of Invasibility

1. Fluctuating Resources: A General Theory of Invasibility By: Megan Murphy, Sarah Brodeur, Lauren Bettino, Jenna Del Buono, and Keith Green

2. Original Paper Fluctuating resources in plant communities: a general theory of invasibility By: Mark A. Davis, J. Philip Grime and Ken Thompson Published In Journal of Ecology, 2000

3. The Theory Communities are more prone to invasion as a direct result of the presence of excess unused resources.

4. The Theory • Invasibility increases when there exists a difference between gross resource supply and total resource uptake • Resource supply/availability can increase due to: • A pulse in resource supply • A decline in resource uptake • A combination of both

5. Background • Invasions are influenced by three general factors: • Propagule pressure • Invasive species characteristics • Invasibility of new environment → Considerations: competitive abilities of resident species, presence (or absence) of herbivores, pathogens, and/or mutualists, facilitative effects of resident vegetation, and disturbance regimes

6. Background • Resources that may contribute to susceptibility: • Phosphorus and nitrogen levels • Precipitation levels • Global environmental changes (CO2) • Pronounced fluctuations of resource supplies • Factors that DO NOT contribute to susceptibility: • Community diversity • Average community productivity

7. Background • Designed experiment: controlled grassland plots • Tested: effects of varying disturbance and fertility gradients on invasions • Results: • Increased disturbance = increased invasions • Increased fertilizer = increased invasions

8. Literature Review / Methods • Keyword search using Web of Science and Google Scholar • Found 1192 papers, reviewed 43 • Looked specifically at: • The invasive species, taxonomic group, type of invaded ecosystem, and whether or not the results of the article matched our hypothesis

9. Does the literature support the fluctuating resources hypothesis? n=32 n=11

10. Taxonomic groups that follow the fluctuating resources hypothesis

11. P. arundinacea; Reed canary grass Kercher & Zedler: Phalaris arundinacea L. • Designed experiment: controlled mesocosms • Tested: effects of light availability, nutrients levels, flooding (disturbance) on invasions • Results: • Increased nutrients = increased P. arundinacea • Increased light = increased P. arundinacea • Most rapid invasion during max levels of both nutrients and light at once • Increased flooding = increased P. arundinacea

12. Discussion • Hypothesis IS well supported • Bias/point of error: different number of articles reviewed for each taxonomic group • Terrestrial plants support hypothesis 71% of the time • Aquatic plants support hypothesis 83% of the time • Pathogens and insects support hypothesis 100% of the time • NO mammals included • Article states how invasions affect wide range of habitats - matches our data • Many references to the importance of disturbance when considering the invasibility of habitats

13. References Davis, Mark A., J. Philip Grime, and Ken Thompson. “Fluctuating resources in plant communities: A general theory of invasibility.” Journal of Ecology 88.3 (2000): 528-34. Web. Kercher, Suzanne M., Zedler, Joy B. “Multiple disturbances accelerate invasion of reed canary grass (Phalaris arundinacea L.) in a mesocosm study.” Oecologia Volume 138, Issue 3 (2004): 455-64. Web.