1. Biogeography
Chapter 23
Section 3

2. Biogeography
Different species live in different parts of the world. The study of where organisms live is called biogeography.

3. Continental Drift
One factor that has affected how species are distributed is the motion of Earth’s continents.
Continents are huge blocks of solid rock floating on a layer of hot, dense liquid.
The very slow motion of the continents is called continental drift.

4. Continental Drift
225 million years ago, all of today’s continents were part of one large land mass called Pangaea.

5. Continental Drift
Slowly our continents are moving away from each other.

6. Continental Drift
65 million years ago

7. Continental Drift
Present day

8. Dispersal
The movement of organisms from one place to another is called dispersal.
Dispersal can be caused by wind, water, or living things, including humans.

9. Wind and Water
Many animals move into new areas by simply walking, swimming, or flying.
Some plants and small organisms need assistance to move from place to place.
Wind provides a means of dispersal for seeds, spores of fungi, tiny spiders, and many other light organisms.
Water transports objects that float, such as coconuts and leaves.
Insects and other small animals may get a free ride to a new home on top of these floating rafts.

10. Wind and Water

11. Dispersal by Other living things
Organisms may also be dispersed by other living things.
Example, goldfinch may eat seeds in one area and deposit them elsewhere in its wastes.
A duck may carry algae or fish eggs on its feet from pond to pond.
Cats and dogs may come home with sticky plant burs.
People take plants, animals, and other organisms with them around the globe when they move from place to place.

12. Native Species
Species that have naturally evolved in an area are referred to as native species.

13. Exotic Species
When an organism is carried into a new location by people, it is referred to as an exotic species.

14. Limits on Dispersal Three factors limit dispersal of a species.
Physical barriers
Competition
Climate

15. Physical barriers

16. Competition

17. Climate