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Chapter 3. Ecosystems: What Are They and How Do They Work?. 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. Food Webs.
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Chapter 3 Ecosystems: What Are They and How Do They Work?
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
Food Webs • A food web shows the connections of all organisms within an ecosystem. Figure 3-18
Food chains rarely have more than 4 steps or 3 trophic levels. Why?
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
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
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
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
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
What are nature’s most productive and least productive systems? Figure 3-22