Competition revisited

1
Competition (re-visited)

• Asymmetric
• Un-equal division of resources among competing
  species or individuals
• why might this occur?
• differences in body size, growth efficiency,
  physiology, behaviour
• Apparent
• Indirect competition between two species that
  dont share resources (usually through enemies)

2
Largemouth bass
minnow
crayfish
3
Largemouth bass
minnow
crayfish
4
Largemouth bass
minnow
crayfish
5
Competition (re-visited)

• Asymmetric
• Un-equal division of resources among competing
  species or individuals
• why might this occur?
• differences in body size, growth efficiency,
  physiology, behaviour
• Apparent
• Indirect competition between two species that
  dont share resources (usually through enemies)
• can look like resource competition
• Another reason to understand the mechanism of
  competition (experimentally)

6
Grimes plant life histories

• Competitive Large, fast potential growth rate,
  early reproduction, vegetative spread
• Ruderals (weedy) high potential growth rate,
  early reproduction, production is largely seeds,
  seed bank/ easily spread seeds
• Stress tolerators slow growth rate, late
  reproduction, little energy to seeds

7
Trade-offs in plant species life-histories
Species best able to compete for abundant
resources (light, water, nutrients)
Competitors

• Boreal forests The pine and spruce survive
  stressful climatic conditions where other plants
  dont, regardless of their competitive ability

• Native prairie grasses hundreds of species in
  grasslands-maintained by disturbance

Ruderals (weeds)
Stress tolerators
8
Does competition drive species to use different
resources when together?
This process is called character displacement
9
Darwin and competition among related species
10
Character displacement
11
Diet composition of two ant species
Do they compete?
How could you know?
12

• How would you design an experiment to determine
• Whether two species were competing with each
  other?
• 2) What the strength of the competitive effects
  are?

13
Positive interactions

• Positive indirect effects
• trophic cascade
• Commensalism /0
• Mutualism /
• Mechanisms
• Coevolution

14

• Positive indirect effects
• trophic cascade
• every other trophic level benefits

15

• Commensalism /0
• Species pairs where one benefits and the other is
  not affected (neutral)
• Not well-studied
• Assumption of neutral effects for one species may
  not always be correct
• Hydrodynamic consequences of banacles/remoras?

16

• Mutualism /
• Species pairs where both benefit
• Trophic complimentary ways organisms obtain
  energy and nutrients
• Often highly specialized
• Defensive one species receives food/shelter in
  return for defense
• Often highly specialized
• Dispersive one species receives food in return
  for dispersal (pollen, seeds, fruit)
• Not usually highly specialized

17
Trophic Mutualism
Mycorrhizal fungi and plants
Cow gut bacteria
18
Defensive Mutualism
Clown anenomefish anenome nematocysts
Amphiprion percula
Pseudomyrmex ferruginea
Ant-Acacia
Acacia collinsii
19
Dispersive Mutualism
Pollinators and flowers
Fruit and frugivores
20

• Co-evolution as likely mechanism
• Originally proposed based on observations of
  butterflies and plants (flowers) they pollinate
• Definition Evolutionary change in a trait of
  species A in response to a trait in species B
• Driven by interactions between species
• Antagonistic (negative)
• Mutualistic (positive)

Ehrlich and Raven (1964) provided the
ecological context for coevolution