1. The Process of Speciation
Section 16-3
The Process of Speciation

2. How does speciation occur?
A genetic change in one individual can spread through the population as reproduction occurs
If the change increases fitness it will increase in the population

3. How does speciation occur?
For new species to form, gene pools must be separated
As new species evolve, reproductive isolation occurs

4. Reproductive isolation can develop through:
Behavioral isolation
Geographic isolation
Temporal isolation

5. Behavioral Isolation
Differences in reproductive behaviors prevent interbreeding
Example: Birds that
use different songs
to attract mates won't
interbreed

6. Geographic Isolation
Populations are separated by geographical barriers
If barrier is removed (ex. lakes connect during a flood) and populations can still interbreed, it's still one species
Barriers may not separate all organisms (a river doesn't separate bird populations)‏

7. Temporal Isolation
Species reproduce at different times
Example: Plants that
flower at different
times

8. Darwin's Finches
Darwin's Hypothesis: Natural selection shaped the beaks of different finch populations

9. Peter and Rosemary Grant
The Grants researched
two testable
assumptions that
Darwin's theory was
based on

10. Testable Assumptions:
Enough heritable variation in beak size and shape for natural selection to act upon
Different beaks cause different fitnesses (allowing natural selection to occur)‏

11. Variation
They measured and banded individual birds on one of the Galapagos islands
Data showed great variation of heritable traits

12. Natural selection
Birds with different-sized beaks had different fitnesses during drought
Finches with large beaks could crack large seeds that others couldn't
Over time the average beak size of the population increased

13. Steps of speciation in Darwin's Finches
Founding of new populations
Geographic isolation
Changes in the gene pool
Reproductive isolation
Ecological competition

14. How we think it happened: Founders Arrive
Long ago, a few finches from the South American mainland flew or were blown to one of the Galapagos islands (SPECIES A)‏

15. How we think it happened:
Geographic isolation
Some birds from species A crossed to another island
The two populations were isolated (finches do not normally fly over open water)‏

16. How we think it happened:
Changes in gene pool
Natural selection caused the populations to evolve different beaks depending on available food sources

17. Reproductive Isolation
How we think it happened:
Reproductive Isolation
Finches mate with birds with the same-sized beaks as they have (behavioral isolation)‏
The populations are now separate species (species A on first island, Species B on second island)‏

18. Ecological Competition
How we think it happened:
Ecological Competition
If species B returns to the first island, A and B must compete for food
Differences increase
Species B evolves into species C

19. How we think it happened:
Continued evolution
Repeated isolation on a island, genetic change and reproductive isolation produced 13
species of
finches

20. Studying Evolution Since Darwin
New data from genetics, physics and biochemistry have supported evolution
New discoveries have led to new hypotheses that refine and expand Darwin's original theory
Many questions remain presently unanswered