2. ECOLOGICAL SUCCESSION Ecosystems tend to change with time until a stable system is formed. The stable system that will form depends on climatic limitations.

3. Ecological Succession The replacement of one community by another until a stable stage is reached is called ecological succession.

4. Primary Succession Primary succession occurs where there was no previous community, such as on bare rock or sand. Primary succession begins with pioneer organisms.

5. Pioneer Organisms Pioneer organisms can tolerate extreme conditions: hot and cold; dry and wet. Moss, dune grass, and lichens are pioneer organisms.

6. Lichens Lichens are algae and fungus growing together in a mutualistic relationship. Algae make the food; fungus anchor and capture water. Do not require soil. Colorful, flaky patches. Composed of two species, a fungi and an algae. The algae photosynthesize and the fungi absorbs nutrients from rocks and holds water. Over time, they break down the rock.

7. As the rocks breaks apart, water freezes and thaws on the cracks, which breaks up the rocks further. When the lichens die, they accumulate in the cracks. Then mosses begin to grow and die, leading to the creation of fertile soil. Fertile soil is made up of the broken rocks, decayed organisms, water, and air.

8. Secondary Succession When a community is disrupted and succession occurs again, it is called secondary succession. disturbed or disrupted by humans, animals, or by natural processes such as storms, floods, earthquakes, and volcanoes

9. Erupted in 1980. 44,460 acres were burned and flattened. After the eruption, plants began to colonize the volcanic debris. Pioneer species: the first organism to colonize any newly available area and begin the process of ecological succession.

10.  Over time, the pioneer species makes the area habitable by other species.  Today, Mt. St. Helens in the process of secondary succession.  Plants, flowers, new trees and shrubs have started to grow.  If this continues, over time they will form a climax community.

11. Succession occurs BECAUSE Each community changes the conditions so that they are more favorable to other organisms that replace them. For example, some types of trees need a lot of sun and their saplings cannot grow under the shade of their own species. They will be replaced by the types of trees whose saplings can grow in shade of other trees.

12. Climax community: the final and stable community. Climax community will continue to change in small ways, but left undisturbed, it will remain the same through time.

13. Ecological Succession Summary Succession Creates new ecosystem Restores previous ecosystem Example: New land created by volcanic eruption Example: An area destroyed by fire PrimarySecondary

14. Summary Questions How are primary and secondary succession different? What is a pioneer species? Give two examples of natural disturbances and two examples of human disturbances that can result in secondary succession. Grass poking through the cracks in a sidewalk is an example of succession. Is this primary or secondary succession? Explain.

15. Primary Succession

16. Secondary Succession