Chapter 3

1. Chapter 3 Ecosystems: What Are They and How Do They Work?

2. ENERGY FLOW IN ECOSYSTEMS • Food chains and webs show how eaters, the eaten, and the decomposed are connected to one another in an ecosystem. Figure 3-17

3. Food Webs • A food web shows the connections of all organisms within an ecosystem. Figure 3-18

4. Food chains rarely have more than 4 steps or 3 trophic levels. Why?

5. Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs • In accordance with the 2nd law of thermodynamics, there is a decrease in the amount of energy available to each succeeding organism in a food chain or web. • Cellular respiration - the breakdown of glucose to release energy – is only 38% efficient • Energy is lost as heat • Energy is also used for growth, reproduction, movement

6. Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs • Ecological efficiency: percentage of useable energy transferred as biomass from one trophic level to the next. Figure 3-19

7. Roughly 90% of energy is lost from one trophic level to the next • Biological Magnification/Amplification - pollutants or toxins are magnified from one trophic level to the next

8. Productivity of Producers: The Rate Is Crucial • Gross primary production (GPP) • Rate at which an ecosystem’s producers convert solar energy into chemical energy (photosynthesis) as biomass. Figure 3-20

9. Productivity of Producers: The Rate Is Crucial • Net Primary Production (NPP) • NPP = GPP – R • Rate at which producers use photosynthesis to store energy minus the rate at which they use some of this energy through respiration (R). Figure 3-21

10. What are nature’s most productive and least productive systems? Figure 3-22

11. Info from notes handout