1. Natural Selection & Evolutionary Patterning

3. Natural Selection Natural Selection acts on VARIATIONS
Stabilizing Selection: conditions favor intermediate variants rather than extremes
Directional Selection: conditions favor individuals at one extreme
Disruptive Selection: conditions favor individuals at both extremes

5. Which of these modes represents which type of selection?
What conditions might account for the observed types of selection among mouse populations?

6. Sexual Selection: Intrasexual vs. Intersexual Selection

7. Intrasexual – competition among individual within one of the sexes (same sex competes for mates of the opposite sex) Ex: male-male competition among elk for access to females Intersexual – selection between the sexes (mate choice) Ex: female choice (peahens ) for most vibrant & “showy” males (peacocks)

8. Evolutionary Patterns
Adaptive Radiation: common ancestral species evolves into many different species as populations move into new/ different habitats and have adaptations provide a “best-fit” with environment
Example: Darwin’s finches – certain beak types proved more advantageous for procuring food within a particular habitat

9. Evolutionary Patterns
Divergent Evolution: species that were once similar to ancestral species become increasingly more diversified; results in homologous structures

10. Evolutionary Patterns
Convergent Evolution: unrelated species evolve similar traits because they occupy similar environments in different parts of the world
Similar environmental pressures result in analogous structures (Ex: aquatic habitat favors streamlined body plan and flipper-like appendages)

12. Evolutionary Patterns
Coevolution – evolution of one species affects the evolution of another species due to a close ecological relationship between the two species
Ex: mutualism – many plants have evolved to produce fruits that are consumed by certain organisms so that seeds can be dispersed
A parasitic relationship is known as “coevolutionary arms race” – plants evolve a chemical defense against pests and pests in turn evolve to resist the defense

13. Rates of Speciation Speciation can occur quickly or slowly
Gradualism: species originate through a gradual change of adaptations over very long periods of time; many transitional species between ancient ancestor and modern-day species
Punctuated Equilibrium: speciation occurs relatively quickly, in rapid bursts, with long periods of genetic equilibrium in between