Speciation along Environmental Gradients

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Speciation along Environmental Gradients

• Michael Doebeli and Ulf Dieckmann

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Resource Competition
resource distribution k(s)
competition function a(s-s0)
resource gradient s
s0
Dynamics of population sizes ni of strategy si
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Resultant Pairwise Invasibility Plots

• With k k0 N(0,sk) and a N(0,sa) we obtain
• for sa gt sk
  for sa lt sk

Mutant trait s
Mutant trait s


Resident trait s
Resident trait s
? Evolutionary Stability
? Evolutionary Branching
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Evolutionary Branching
Branching point
Convergence to disruptive selection
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Sexual Cohesion Can Prevent Branching
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Mating Character
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Sexual Evolutionary Branching
Assortative Mating
Random Mating
Disassortative Mating
Evolutionary Branching Point
This mechanism also works when assortative mating
is based on a marker characterand when
evolutionary branching is driven by interspecific
interactions.
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Spatial Gradient

• Maximum of carrying capacity varies with location

Trait value at maximum
Spatial location
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Spatial Evolutionary Branching
Assortative Mating
Random Mating
Disassortative Mating
Evolutionary Branching Point
Spatial Gradient (vertical direction is
ecologically neutral)
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Spatial Evolutionary Branching
Trait value
Time
Spatial location
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Spatial Gradient Facilitates Branching
Branching range for non-spatial model
Extra branching range due to gradient
Migration scale
sa / sk
1
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Intermediate Slopes Are Most Speciation-Prone
sa ?
No branching expected for non-spatial model
Extra branching range due to gradient
Migration scale
g ss / sk
1
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Full Characterization
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Summary

• Spatial gradients can greatly facilitate
  branching
• Sympatric speciation processes may lead to
  patterns of species abutment
• The responsible mechanism is not isolation by
  distance but instead local adaptation leading to
  frequency-dependent disruptive selection
• Intermediate slopes appear to be most
  speciation-prone
• Sympatric speciation processes may lead to
  patterns of peripheral speciation

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Peripheral Speciation?
Species range