Experimental Studies of Competitive Interactoins

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Experimental Studies of Competitive Interactoins
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Commonly Used Designs
Partial Additive
Replacement Series
Additive
Complete Additive
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The Replacement Series Design

• Density is fixed
• Ratio of two species systematically altered

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The Replacement Series Design
Treatment 3
Treatment 2
Treatment 1
Treatment 6
Treatment 5
Treatment 4
Species 1
Density 5
Species 2
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A Non-Additive Example
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Predicting the Outcome of Competition
Log (Output1/Output 2)
Before competition
Log (Input1/Input 2)
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Predicting the Outcome of Competition
After competition
Log (Output1/Output 2)
Log (Input1/Input 2)
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Predicting the Outcome of Competition
yx
Log (Output1/Output 2)
Log (Input1/Input 2)
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Predicting the Outcome of Competition
New Input Ratio
Log (Output1/Output 2)
Log (Input1/Input 2)
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Predicting the Outcome of Competition
etc.
This is a process called cobwebbing.
Log (Output1/Output 2)
Log (Input1/Input 2)
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Predicting the Outcome of Competition
Coexistence
Extinction of Glycine
Log (OPanicum/OGlycine)
Log (IPanicum/IGlycine)
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Replacement Series Experiment
Monoculture treatment
Competitiontreatment
Problem?
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Extending the Replacement Series Approach
Inclusion of more densities provides more
information
In this example competitive effects on A. fatua
increase as overall density increases
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Extending the Replacement Series Approach
The outcome of competition changes with density.
Not an ideal technique for predicting the outcome
of competition
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Commonly Used Designs
Partial Additive
Replacement Series
Additive
Complete Additive
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The Complete Additive Design
replacement series design
partial additive design

• Provides information across a range of
  densities
• Contains other more restrictive designs
• Can be used to develop predictive models
  across a range of scales

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Experimental Outcome
Vulpia
Phleum
log(Vulpia density)
log(Phleum density)
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Experimental Outcome
monculture treatments
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Building a Predictive Model
Phleum
Incorporating the Effects of a Second Species
Vulpia
Our old friend the yield-density Equation
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Building a Predictive Model
Phleum
Incorporating the Effects of a Second Species
Vulpia
Our old friend the yield-density Equation
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Building a Predictive Model
Phleum
Incorporating the Effects of a Second Species
Vulpia
Our old friend the yield-density Equation
Species 2
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Building a Predictive Model
Phleum
Incorporating the Effects of a Second Species
Vulpia
Our old friend the yield-density Equation
Species 2 Density
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Building a Predictive Model
Phleum
Incorporating the Effects of a Second Species
Vulpia
Our old friend the yield-density Equation
Species 2s competitive effectrelative to
species 1s effect on itself
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Building a Predictive Model
Phleum
Incorporating the Effects of a Second Species
Vulpia
Our old friend the yield-density Equation
Species 2s competitive effectrelative to
species 1s effect on itself
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Building a Predictive Model
Phleum
Incorporating the Effects of a Second Species
Vulpia
Our old friend the yield-density Equation
Species 2s competitive effectrelative to
species 1s effect on itself
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Building a Predictive Model
Phleum
Incorporating the Effects of a Second Species
Vulpia
Our old friend the yield-density Equation
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Building a Predictive Model
Phleum
Incorporating the Effects of a Second Species
Vulpia
Our old friend the yield-density Equation
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Building a Predictive Model
Phleum
Parametrize the Models from the Results of the
Experiment
Vulpia
Vulpia
Phleum
Response surfaces
log(Vulpia density)
log(Phleum density)
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Predicting Change over Time
Phleum
Vulpia
Seed yield for Phleum
Seed yield for Vulpia
log(Vulpia density)
Input densities
log(Phleum density)
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Predicting Change over Time
Phleum
Vulpia
Seed yield for Phleum
Seed yield for Vulpia
log(Vulpia density)
New input densities
log(Phleum density)
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Vulpia Density
Phleum Density
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Phase Space Plot
Zero Net Growth Isocline for Vulpia
Vulpia Density
Phleum Density
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Phase Space Plot
Zero Net Growth Isocline for Vulpia
V
Vulpia Density
V
Phleum Density
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Phase Space Plot
Zero Net Growth Isocline for Phleum
P
Vulpia Density
P
Phleum Density
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Phase Space Plot
P
V
Vulpia Density
P
V
P
V
Phleum Density
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Phase Space Plot
P
V
Vulpia Density
P
V
P
V
Phleum Density
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Phase Space Plot
Endpoint of competition
Vulpia Density
Phleum Density
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Limitations of the Complete Additive Design

• Quite difficult to conduct
• Requires lots of resources
• Only easily used with short lived herbs

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General Outcomes of Competition
Species 1
Intraspecific gt Interspecific
Intraspecific lt Interspecific
Intraspecific gt Interspecific
Species 2
Intraspecific lt Interspecific
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General Outcomes of Competition
Species 1
Intraspecific gt Interspecific
Intraspecific lt Interspecific
Intraspecific gt Interspecific
Species 2
Intraspecific lt Interspecific
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General Outcomes of Competition
Species 1
Intraspecific gt Interspecific
Intraspecific lt Interspecific
Intraspecific gt Interspecific
Species 2
Intraspecific lt Interspecific
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General Outcomes of Competition
Species 1
Intraspecific gt Interspecific
Intraspecific lt Interspecific
Intraspecific gt Interspecific
Species 1 wins
Species 2
Intraspecific lt Interspecific
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General Outcomes of Competition
Species 1
Intraspecific gt Interspecific
Intraspecific lt Interspecific
Intraspecific gt Interspecific
Species 1 wins
Species 2
Intraspecific lt Interspecific
Species 2 wins
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General Outcomes of Competition
Species 1
Intraspecific gt Interspecific
Intraspecific lt Interspecific
Intraspecific gt Interspecific
Species 1 wins
Coexistence
Species 2
Intraspecific lt Interspecific
Species 2 wins
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General Outcomes of Competition
Species 1
Intraspecific gt Interspecific
Intraspecific lt Interspecific
Intraspecific gt Interspecific
Species 1 wins
Coexistence
Species 2
Unstable Equilibrium
Intraspecific lt Interspecific
Species 2 wins
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General Outcomes of Competition
Species 1
Intraspecific gt Interspecific
Intraspecific lt Interspecific
Intraspecific gt Interspecific
Species 1 wins
Coexistence
Species 2
Unstable Equilibrium
Intraspecific lt Interspecific
Species 2 wins
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General Outcomes of Competition
Species 1
Intraspecific gt Interspecific
Intraspecific lt Interspecific
Competitive Exclusion predicted in 3 out of 4
cases
Intraspecific gt Interspecific
Species 1 wins
Coexistence
Species 2
Unstable Equilibrium
Intraspecific lt Interspecific
Species 2 wins
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Coexistence is a Special Case
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Coexistence is a Special Case
Species must differ enough to not have a
big impact on one another
Limiting Simliarity
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The Paradox between Theory and Observation

• Lots of evidence for competition
• High degree of similarity in resource use by
  plants
• Appears to be less competitive exclusion than
  theory predicts

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End of Material for Next Exam!
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Developing a Mechanistic Model of Competition for
Plants
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Tilmans Resource Ratio Hypothesis
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Relationship between resource availability and
diversity
competition
stress
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Change over TimeThe Rothamsted Experiment
Diversity decreases over time with increased
nutrients