1. horse
donkey
Speciation
mule

2. Speciation Defined: evolution of a new species
Species: group of organisms that can interbreed and produce fertile offspring
Factors that lead to evolution
Natural Selection
Gene flow
Mutations
Sexual selection
Genetic drift

3. Gene Flow Defined: Movement of alleles from 1 population to another
Increases variations in a population
Keeps differing populations similar
If gene flow prevented
No variations exchanged
Populations isolated
Organisms adapt to their own environment

4. Genetic Drift
Defined: Changes in gene pool due to chance (not natural selection)
More likely in smaller populations
Ex: Forest fire destroys 90% of a forest
Survival unrelated to adaptations
Pre-forest fire (left picture): Blue is more advantageous
Post-forest fire (right picture): Due to more red survivors, red has the advantage to reproduce in this new environment

5. Geographic Isolation
Mountains, rivers, canyons, oceans may separate a population
Natural selection allows favorable organisms to survive in different environments
Each population adapts to its isolated environment
Because isolated, no gene flow

6. Kaibab Squirrel (Grand Canyon)

7. Founder Effect: 14 Species of Galapagos FinchesB B A D D C C

8. Behavioral Isolation
Although not geographically separated, reproduction is prevented
1) Different mating rituals
2) Use of pheromones
No gene flow: differing populations unable to reproduce

9. Temporal Isolation
Although not geographically separated, reproduction is prevented
1) Mate at different seasons
2) Some nocturnal
No gene flow: differing populations unable to reproduce

10. End Result: Reproductive Isolation
Created as a result of behavioral, geographical, & temporal isolation
No mating between populations (no gene flow)
Two groups unable to reproduce
Sex organs don’t match, rituals don’t attract, physically separated
Species: group of organisms that can interbreed and produce fertile offspring

11. Quick Review
New species are created (speciation) when populations become isolated
A changing or new environment greatly affects natural selection
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