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Speciation along Environmental Gradients

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

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  1. Speciation along Environmental Gradients Michael Doebeli and Ulf Dieckmann

  2. Resource Competition resource distribution k(s) competition function a(s-s0) resource gradient s s0 Dynamics of population sizes ni of strategy si

  3. 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

  4. Evolutionary Branching Branching point Convergence to disruptive selection

  5. Sexual Cohesion Can Prevent Branching

  6. Mating Character

  7. 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.

  8. Spatial Gradient Maximum of carrying capacity varies with location Trait value at maximum Spatial location

  9. Spatial Evolutionary Branching Assortative Mating Random Mating Disassortative Mating Spatial Gradient (vertical direction is ecologically neutral) Evolutionary Branching Point

  10. Spatial Evolutionary Branching Trait value Time Spatial location

  11. Spatial Gradient Facilitates Branching Branching range for non-spatial model Extra branching range due to gradient Migration scale σa / σk 1

  12. 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

  13. Full Characterization

  14. 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

  15. Optimal phenotype Expected speciation zone? Peripheral Speciation? Species range

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