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Speciation along Environmental Gradients. Michael Doebeli and Ulf Dieckmann. Resource Competition. resource distribution k(s). competition function a(s-s 0 ). resource gradient s. s 0. Dynamics of population sizes n i of strategy s i. Resultant Pairwise Invasibility Plots.

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speciation along environmental gradients

Speciation along Environmental Gradients

Michael Doebeli and Ulf Dieckmann

resource competition
Resource Competition

resource

distribution k(s)

competition

function a(s-s0)

resource

gradient s

s0

Dynamics of population sizes ni of strategy si

resultant pairwise invasibility plots
Resultant Pairwise Invasibility Plots
  • With k = k0 N(0,σk) and a = N(0,σa) we obtain

for σa > σk for σa < σk

+

+

+

+

Mutant trait s‘

Mutant trait s‘

Resident trait s

Resident trait s

 Evolutionary Stability

 Evolutionary Branching

evolutionary branching
Evolutionary Branching

Branching point

Convergence to disruptive selection

sexual evolutionary branching
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.

spatial gradient
Spatial Gradient

Maximum of carrying capacity varies with location

Trait value at maximum

Spatial location

spatial evolutionary branching
Spatial Evolutionary Branching

Assortative

Mating

Random

Mating

Disassortative

Mating

Spatial Gradient

(vertical direction is ecologically neutral)

Evolutionary Branching Point

spatial evolutionary branching10
Spatial Evolutionary Branching

Trait value

Time

Spatial location

spatial gradient facilitates branching
Spatial Gradient Facilitates Branching

Branching range for non-spatial model

Extra branching range due to gradient

Migration scale

σa / σk

1

intermediate slopes are most speciation prone
Intermediate Slopes Are Most Speciation-Prone

σa = 

No branching expected for non-spatial model

Extra branching range due to gradient

Migration scale

g σs / σk

1

summary
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
peripheral speciation

Optimal

phenotype

Expected speciation zone?

Peripheral Speciation?

Species

range