1. Isolation
17.3 Speciation

2. State Standards:
8d. Students know reproductive or geographic isolation affects speciation.

3. Objectives:
What is reproductive isolation? What is geographic isolation? How can either of these lead to speciation?

4. Defining Species
Biological Context: A member of a group of populations that can interbreed to produce fertile offspring.

5. Forming New Species Populations of species live in different places.
Natural selection will act on the population resulting in offspring better suited to the particular environment.
If the environments differ, the adaptations may differ.
This is called divergence.

6. Speciation
The process of forming new species by evolution from preexisting species.
Occurs over many generations
When the population has developed such unique adaptations that it is reproductively isolated, speciation has occurred.

7. Reproductive Isolation
The state in which two populations can no longer interbreed to produce future fertile offspring.
This leads to continued tendency to diverge.
Divergence and Speciation can happen in many ways.

8. Mechanisms of Isolation
These are things that can contribute to a populations’ divergence, possibly leading to speciation.
Geography – a physical barrier arises between the populations.
Ecological Niche – members of the population occupy different niches
Can cause an increase in divergence

9. Mechanisms of Isolation
Mating Behaviors and Timing – differences form in the patterns or sounds that attract mates, or the specific timing of mating seasons.
Polyploidy – organism received duplicate copies of chromosomes by accident.
May now reproduce by vegetative growth, self-fertilization, or a polyploid mate.
Mostly found in plants.

10. Mechanisms of Isolation
Hybridization – closely related species (that already diverged) may come back together to mate. Their offspring are called hybrids.
Resulting hybrids:
If sufficiently diverged, offspring may be sterile. (Horse + Donkey = Mule)
Hybrid may not be suited to environment of either parent.

11. Extinction When a species fails to produce any more descendants.
Scientists estimate over 99% of all the species that have ever lived on Earth are now extinct!
Species that exist at any time are the net result of both speciation and extinction.
Mostly a result of environmental change.

12. Speciation and Extinction
If speciation is the branching of a tree, extinction is when one of the branches falls off!

13. Objectives: What is reproductive isolation?
Isolation of a species based on mating behaviors or differences
What is geographic isolation?
How can either of these lead to speciation?
The populations are separated for so long, all the while adapting to own environment, genes no longer will create offspring when fertilization occurs.