1. One Type Has a Very Large Effect!!
Keystone Species- a species whose impact on its community is much larger than its biomass or abundance would indicate.
Name comes from the wedge-shaped stone at the top of an arch that the other stones depend on to stay in place.
Keystone
absent

2. Studying Keystone Species
When scientists study the role of a keystone species they compare the amount of diversity present when the species is absent and present.
The presence of a keystone species usually raises the level of biodiversity.
Keystone species could be used in efforts to restore a damaged ecosystem.

3. Examples of Keystone Species
Beavers- Provide homes for other species by building dams.
African Elephants- eat small trees and prevent grasslands from becoming forests.
Fig Trees- provide food to animals year round when food sources are limited.
Coral- provide shelter and food for over 300 organisms.

4. What if the Keystone Species is a Predator?
Unlike the beaver, many keystone species are predators.
Feeding on their prey keeps the prey population from taking over the ecosystem.
The explosion of the prey population would decrease the amount of biodiversity in the ecosystem.

5. Example: Sea Stars
The Sea Star (genus Piaster) live in the intertidal zones where the ocean meets the land.
Mainly feed on mussels in the genus Mytilus which keeps the population from exploding.
Mussles can outcompete many other species.

6. How Keystone Species Affect Their Community and Trophic Cascades
Watch the video about Keystone Species and Trophic Cascades.
Try and answer questions as you hear them come up, but make sure you are paying attention.
Mr. Barker will stop the video and give you time to answer questions on that section.