Download Fluctuating Resources: A General Theory of Invasibility

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.