Terrestrial Ecology

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Terrestrial Ecology

• Introduction to ecology
• Competitive interactions_1
• Competitive interactions_2
• Predator-prey interactions
• Plant-herbivore interactions_1
• Plant-herbivore interactions_2
• More complicated ecological interactions

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Ecology
1. Studying interactions
2. Within between
3. At various levels
4. To understand (explain)
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1st How do we define (classify) ecological
interactions?
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Direct ecological interactions

• Defined by mechanisms
• Competition (- -)
• Predation ( -)
• Herbivory ( -, o?, ?)
• Parasitism ( -)
• Disease ( -)
• Mutualism ( )
• Others (? ?)

• Defined by effects
• - - Competition
• - Contramensalism
• Mutualism
• - o Amensalism
• o Commensalism
• o o No interaction

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Direct ecological interactions

• Defined by mechanisms
• Competition (- -)
• Predation ( -)
• Herbivory ( -, o?, ?)
• Parasitism ( -)
• Disease ( -)
• Mutualism ( )
• Others (? ?)

• Defined by effects
• - - Competition
• - Contramensalism
• Mutualism
• - o Amensalism
• o Commensalism
• o o No interaction

• All interspecific
• Some intraspecific
• e.g. ??

Competition Mutualism Parasitism?

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Interactions by mechanisms

• Competition (- -)
• Predation (? -?)
• Herbivory ( -, o?, ?)
• etc

• You know what youre studying
• predation is obvious!
• May not know effect until after studying it
• Focus what are the effects?

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Interactions by effects on populations

• - - Competition
• - Contramensalism
• Mutualism
• etc

• Helps think clearly about outcome
• effect on population
• gt1 mechanism ? 1 effect
• mechanism not important
• Useful modelling communities
• But unknown until after studying system?

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Which classification do you prefer?

• Depends on your questions
• I like defining by mechanismsChris likes
  defining by effects
• Why?
• Me how do these interactions work?
  (details, often between individuals)
• Chris what are the effects of the interactions
  on communities?

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back to Competition

• What is it?
• What types?
• Predicting outcomes of competition?
• How does it affect populations (ecology)?
• How can you detect it?
• How does it affect species (evolution)?

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What is Competition?

• ? 2 species or individualseither (1) use the
  same limited resourceor (2) seek the same
  resourcewith detrimental effect on both

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Types of competition?

• Resource competition
• Scramble or Exploitative competition
• Resource in common is limited
• Interference competition
• Context competition
• Resource in common not necessarily limited
• But individuals harm each other getting it

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Predicting outcomes of competition?
Wildebeest hartebeest feeding on same resource
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Modelling competitive outcomes

• If
• 2 species live together
• use the same resource(s)
• what happens to their populations?
• Mathematical models for predicting outcomes
  include
• Lotka Volterra (1925, 1926)NOT their
  predator-prey models
• Tilman (1977)

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Lotka-Volterra Competition Model

• See Krebs 2001 for details
• Based on
• carrying capacity (K)
• Logistic growth curve

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Lotka-Volterra Competition Model
Where for Species 1 N1 population size t
time r1 intrinsic capacity for ? K1 carrying
capacity
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Lotka-Volterra Model Step 1
Step 1 describe population change for both
species
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Lotka-Volterra Model Step 2
Step 2 describe one species in terms of the
other
How many (?) hartebeest 1 wildebeest ?
?N2 N1 individuals
How many (?) wildebeest 1 hartebeest ?
? N1 N2 individuals
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Lotka-Volterra Model Step 3
Step 3a define competition equation for
Wildebeest
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Lotka-Volterra Model Step 3
Step 3b plot line of population
equilibrium for Wildebeest
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Lotka-Volterra Model Step 4
Step 4a define competition equation for
Hartebeest
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Lotka-Volterra Model Step 4
Step 4b plot line of population
equilibrium for Hartebeest
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Lotka-Volterra Model Step 5
4 possible outcomes
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2 possible outcomes
Outcome 1 N1 outcompetes N2
Outcome 2 N2 outcompetes N1
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2 more possible outcomes
Outcome 3 N1 N2 stable equilibrium
Outcome 4 N1 N2, N1 or N2unstable equilibrium
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Lotka-Volterra Model - summary

• No overlap of isoclines?
• one species can ? in zone where other ?
• one species must outcompete the other
• Overlap of isoclines?
• 2 possibilities
• Stable OR Unstable equilibrium
• Depends on vector directions
• Competition described by results
• i.e. end populations of 2 species
• No mechanism specified

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Modelling competitive outcomes

• If
• 2 species live together
• use the same resource(s)
• what happens to their populations?
• Mathematical models for predicting outcomes
  include
• Lotka Volterra (1925, 1926)NOT their
  predator-prey models
• Tilman (1977) - NEXT