Fluctuating Resources: A General Theory of Invasibility

advertisement

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 invasibility

By:

Mark A. Davis, J. Philip Grime and Ken Thompson

Published 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 supply

2. A decline in resource uptake

3. A combination of both

Background

● Invasions are influenced by three general factors:

1. Propagule pressure

2. Invasive species characteristics

3. 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 plots o 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 mesocosms o Tested: effects of light availability, nutrients levels, flooding (disturbance) on invasions

● Results: o Increased nutrients = increased P. arundinacea o Increased light = increased P. arundinacea o 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 group o Terrestrial plants support hypothesis 71% of the time o Aquatic plants support hypothesis 83% of the time o Pathogens and insects support hypothesis 100% of the time o 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.

Download