2. Chapter 19 Ecosystems

3. How Ecosystems Change Ecological succession that begins in a place that does not have soil is called primary succession. The first community of organisms to move into a new environment is called the pioneer community.

4. Pioneer Community

5. Life on a bare rock begins with a pioneer community of lichens. These hardy organisms produce acids that help break down the rock. The acids release chemicals and nutrients from the rock that can be absorbed by the lichens. The decaying bodies of dead lichens contribute to soil formation

6. Mosses and ferns gradually replace the lichens. These plants can grow even in extremely poor, thin soil. As they die, their decomposed bodies add humus to the soil. Insects and other small animals appear Insects and small animals appear

7. As the soil layer thickens, its ability to absorb and hold water improves. Grasses, wildflowers, and other plants that require richer, more moist soil begin to take over. Butterflies, bees, and caterpillars come to feed on the leaves and flowers. When these plants die, they also enrich the soil, which will become home to earthworm’s and other large soil organisms.

8. Thicker, richer soil supports the growth of shrubs and trees. More insects, birds, mammals, and reptiles move into the area. After hundreds or thousands of years of gradual change, what was once bare rock has become a forest

9. Primary Succession to Climax Community

12. Mount St. Helens Before and After

13. Secondary Succession Succession that begins in a place that already has soil and was once the home of living organisms is called secondary succession. Examples: After a forest fire, or when a building is torn down

14. Secondary Succession

18. Climax Communities When a community has reached the final stage of ecological succession, it is called a climax community. Climax communities are complex, they may contain hundreds of thousands of species, and feeding relationships usually involve complex food webs.

19. Land Environments: Factors that Determine Climate Temperature: The sun supplies life on Earth not only with light energy for photosynthesis, but also heat energy for warmth. The temperature of a region is regulated primarily by the amount of sunlight that reaches it. The amount of sunlight is determined by an area’s latitude and elevation.

20. Latitude Not all parts of Earth receive the same amount of energy from the sun. The nearer a region is to the north or south pole, the higher its latitude, the smaller the amount of energy it receives from the sun, and the colder its climate. Because Earth is tilted on its axis, the angle of the suns rays changes as Earth moves through its yearly orbit.

21. Earth’s Rotation Video Segment

22. Precipitation Precipitation is the amount of water that condenses and falls in the form of rain, snow, sleet, hail, and fog. Hot air is pushed upward whenever cold air sinks. Cold air is more dense than hot air, so it tends to move toward the ground

23. In warm tropical regions near the equator, the air, land, and oceans are constantly being heated by the direct rays of the sun. As the cooler air sinks, the warm air is pushed upward into the atmosphere. This warm air carries with it large amounts of water vapor from the oceans. When the air reaches a high enough altitude in the atmosphere, the water vapor it contains cools and condenses as rain. While the air rises, it also moves slowly toward either the north or south pole. The air loses virtually all of its moisture by the time it reaches a latitude of about 30º. Deserts are common at latitudes near 30º. Latitudes between 0º and 22º receive much larger amounts of rain.

24. The Rain Shadow Effect The presence of mountain ranges also has an effect on rainfall patterns. Air that is moving toward a mountain range is forced upward by the shape of the land. As warm air is forced upward, it cools, condensing the water vapor it contains and creating rain or snow. By the time it passes over the mountains, it loses its moisture. The opposite side of the mountain receives very little rain.

25. Rain Shadow Effect