Fluctuating Resources: A General Theory of Invasibility

By: Megan Murphy, Sarah Brodeur, Lauren Bettino, Jenna Del Buono, and Keith Green

Original Paper

Fluctuating resources in plant communities: a general theory of invasibilityBy:Mark A. Davis, J. Philip Grime and Ken ThompsonPublished In Journal of Ecology, 2000

The Theory

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

The Theory● Invasibility increases when

there exists a difference between gross resource supply and total resource uptake

● Resource supply/availability can increase due to:1. A pulse in resource supply2. A decline in resource uptake3. A combination of both

Background

● Invasions are influenced by three general factors:1. Propagule pressure2. Invasive species characteristics3. 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

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

Background

● Designed experiment: controlled grassland plotso Tested: effects of varying disturbance and

fertility gradients on invasions● Results:

o Increased disturbance = increased invasions

o Increased fertilizer = increased invasions

Literature Review / Methods

● Keyword search using Web of Science and Google Scholar

● Found 1192 papers, reviewed 43● Looked specifically at:

o The invasive species, taxonomic group, type of invaded ecosystem, and whether or not the results of the article matched our hypothesis

Does the literature support the fluctuating resources hypothesis?

n=32

n=11

Taxonomic groups that follow the fluctuating resources hypothesis

Kercher & Zedler: Phalaris arundinacea L.

● Designed experiment: controlled mesocosmso Tested: effects of light availability, nutrients

levels, flooding (disturbance) on invasions● Results:

o Increased nutrients = increased P. arundinaceao Increased light = increased P. arundinaceao Most rapid invasion during max levels of both

nutrients and light at once

○ Increased flooding = increased P. arundinacea

P. arundinacea; Reed canary grass

Discussion● Hypothesis IS well supported● Bias/point of error: different number of articles reviewed for each

taxonomic groupo Terrestrial plants support hypothesis 71% of the timeo Aquatic plants support hypothesis 83% of the timeo Pathogens and insects support hypothesis 100% of the timeo 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

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.