1. Speciation and Population Evolution
Leopard Frog
Pickerel Frog

2. What is a species?

3. But what is a species?
An individual belonging to a group of organisms, having common characteristics, and are capable of mating with one another in nature.
A species is given a two-part name:
the generic name
specific name (or specific epithet).
Allium cepa (commonly known as onion)
Homo sapien (commonly known as us!)

4. Speciation is a lineage-splitting event that produces two or more separate species.

5. How do Species Form—Speciation!
Remember: natural selection favors changes that increase reproductive success.
The accumulation of differences between groups is called divergence.
Divergence leads to the formation of a new species.
Speciation is the process by which new species form.
Divergent evolution

6. Speciation—A Story of Lost Love…
The scene: a population of wild fruit flies minding its own business on several bunches of rotting bananas, cheerfully laying their eggs in the mushy fruit...

7. Disaster strikes: A hurricane washes the bananas and the immature fruit flies they contain out to sea. The banana bunch eventually washes up on an island off the coast of the mainland. The fruit flies mature and emerge from their slimy nursery onto the lonely island. The two portions of the population, mainland and island, are now too far apart for gene flow to unite them. At this point, speciation has not occurred — any fruit flies that got back to the mainland could mate and produce healthy offspring with the mainland flies.

8. The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves under different selective pressures and experiences different random events than the mainland population does. Morphology, food preferences, and courtship displays change over the course of many generations of natural selection.

9. So we meet again: When another storm reintroduces the island flies to the mainland, they will not readily mate with the mainland flies since they've evolved different courtship behaviors. The few that do mate with the mainland flies, produce inviable (unable to survive or develop normally ) eggs because of other genetic differences between the two populations. The lineage has split now that genes cannot flow between the populations.

10. Which is the Transitional Species?
Ensatina eschscholtzi –subspecies on the way to becoming new species
Which is the Transitional Species?

11. Speciation cont.
Separate populations of a single species often live in several different environments and become reproductively isolated.
If the environments are different enough, separate populations of the same population can become very dissimilar.
Albert Squirrel
Kaibab Squirrel

14. Maintaining New Species
There are several kinds of barriers that prevent different groups from breeding with one another:
Temporal isolation (seasonal)
Geographic isolation
Behavioral .
For example, organisms may be geographically isolated from one another or may reproduce at different times.
Geographic isolation

16. Different mating times prevents the Pickerel frog and the Leopard frog from mating.
Reproductive Isolation

17. The differences shown in the beaks of the ten species of Galapagos finches in the chart are most likely the result of –
a. a genetic equilibrium of the finch population
b. beak changes acquired during the life of the finch
c. natural selection due to competition for food
d. parasitic relationships among the finch species