Chapter 15: Our Living Planet

1. Chapter 15:Our Living Planet Section 15-2: Environments and Life

2. Life Affects Environments • Think about a grassland or forest . . . • Organisms affect the environment • 3 billion years ago when photosynthetic bacteria began releasing oxygen into the atmosphere

3. Life Affects Environments • At first, oxygen was toxic, but over time aerobic organisms evolved (ones that need oxygen) to use the gas for energy production, changing the course of life on Earth • Ecosystems can respond to changes from the interactions of abiotic and biotic environmental factors

4. Changes in Ecosystems • Ecosystems are constantly changing • Ecological succession is the process by which an existing ecosystem is gradually and progressively replaced by another ecosystem. • Caused by biotic and abiotic factors

5. Ecological Succession Example • Rakata Island in Indonesia was formed as a result of a volcanic eruption • At first, only the hardiest organisms like mosses, fungi, and some grasses survived on the lava rock • Over time, these organisms broke down the rocks into a thin layer of soil, eventually allowing other plants to grow

6. Ecological Succession Example • As the plant community expanded and the soil changed further, trees began to grow • Animals from nearby islands began to migrate to Rakata • Within 100 years, Rakata Island was transformed into a tropical rain forest

7. Ecological Succession Example • Ecological succession can also occur as a result of human influence • If a field is cleared and left abandoned, resulting in the eventual return of grasses, wildflowers, and small animals

8. Climax Community • Ecological succession proceeds until the climax community is reached. • A climax community is a relatively stable state is reached in the interaction between organisms and their environment • This does not mean that the community never changes

9. Ecological Succession • When a small area in an ecosystem is disturbed or disappears, ecological succession will begin and continue toward another climax • Do not think of natural disaster as always being harmful to a community • Ecological succession occurs slowly because organisms change their environments, which usually happens little by little (humans are the exception!)