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Chapter 55: Ecosystems and Restoration Ecology Overview: 1. What is an ecosystem? An ecosystem is the sum of all the organisms living in a given area and the abiotic factors with which they interact. 2. Where does energy enter most ecosystems? How is it converted to chemical energy and then passed through the ecosystem? How is it lost? Remember this: Energy cannot be recycled. Energy enters most ecosystems as sunlight. It is converted to chemical energy by autotrophs, passed to heterotrophs in the organic compounds of food, and dissipated as heat. 3. Besides the energy flow that you described in question 2, chemicals such as carbon and nitrogen cycle through ecosystems. So energy flows through an ecosystem and matter cycles within and through them. Concept 55.1 Physical laws govern energy flow and chemical cycling in ecosystems 4. Both energy and matter can be neither created nor destroyed.

5. We can measure the efficiency of energy conversion in an ecosystem, as well as whether a given nutrient is being gained or lost from an ecosystem. Let us take a second look at trophic levels. What trophic level supports all others? Autotrophs or primary producers 6. List three groups of organisms that are photosynthetic autotrophs. Plants, algae, and photosynthetic prokaryotes 7. What are the primary producers of the deep-sea vents? Chemosynthetic prokaryotes 8. This concept reviews trophic relationships. Know all terms in your textbook that are bolded. What are trophic levels? What is always at the first trophic level? Trophic levels are feeding levels. Autotrophs are always at the first tropic level.

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9. What are detritivores? What is their importance in chemical cycling? Give some examples of detritivores. Detritivores are decomposers that eat nonliving organic material. Detritivores play a critical role in recycling chemical elements back to primary producers. Detritivores convert organic material from all trophic levels to inorganic compounds usable by primary producers, closing the loop of an ecosystem’s chemical cycling. Two important groups of detritivores are prokaryotes and fungi. 10. State the trophic level of each of the following:

cow: primary consumer grass: primary producer man: secondary consumer mushroom: detritivore

Concept 55.2 Energy and other limiting factors control primary production in ecosystems 11. What is primary production? Distinguish between gross primary production and net primary production. Primary production is the amount of light energy converted into chemical energy—in the form of organic compounds—by autotrophs during a given time period. Gross primary production (GPP) is the total primary production in an ecosystem—the amount of energy from light (or chemicals, in chemoautotrophic systems) converted to the chemical energy of organic molecules per unit of time. Not all of this production is stored as organic material in the primary producers because they use some of the molecules as fuel in their own cellular respiration. Net primary production (NPP) is equal to gross primary production minus the energy used by the primary producers for their “autotrophic respiration.” 12. Write an equation here that shows the relationship between gross and net primary production. NPP = GPP – Ra 13. You may recall from Chapter 54 that biomass is the total mass of all individuals in a trophic level. Another way of defining net primary production is as the amount of new biomass added in a given period of time. Why is net primary production, or the amount of new biomass/unit of time, the key measurement to ecologists? To ecologists, net primary production is the key measurement because it represents the storage of chemical energy that will be available to consumers in the ecosystem. 14. Which ecosystem would tend to have a greater biomass/unit area, a prairie or a tropical rain forest? Explain. The tropical rain forest will have the greater biomass/unit area. The rate of photosynthesis will be higher due to more light and available water.

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15. Describe a technique for measuring net primary production in an aquatic environment. (We will use this technique for AP Lab 12, Dissolved Oxygen and Aquatic Primary Productivity.) Primary productivity in an aquatic environment is often measured using dissolved oxygen tests. If samples are taken and placed in the light, and others are taken and placed in the dark for 24 hours, the difference in the amount of oxygen in the two sample groups would represent the amount of respiration in the system. If this is subtracted from the amount of oxygen produced in the light bottle, inferences can be made about net productivity. 16. What are some factors that limit primary productivity in aquatic ecosystems? Light limitation and nutrient limitation are factors that limit primary productivity in aquatic ecosystems. 17. What is a limiting nutrient? What is the limiting nutrient off the shore of Long Island, New York? In the Sargasso Sea? A limiting nutrient is an element that must be added for production to increase. The limiting nutrient off the shore of Long Island, New York, is nitrogen. The limiting unit in the Sargasso Sea is the micronutrient iron. 18. Phytoplankton growth can be increased by additional nitrates and phosphates. What are common sources of each of these? Sewage and fertilizer runoff from farms and lawns are a common source of additional nutrients. 19. What is eutrophication? What are factors that contribute to eutrophication? Eutrophication is where a body of water receives excess nutrients that enhance algal and bacterial growth. Although the algae, for example, are photosynthesizing and putting oxygen into the water, they are also respiring, and as they die, the process of decomposition also results in reduced oxygen. This ultimately reduces the oxygen content and clarity of the water. Sewage and fertilizer runoff from farms and laws contribute to eutrophication. Concept 55.3 Energy transfer between trophic levels is typically only 10% efficient 20. What is trophic efficiency? Trophic efficiency is the percentage of production transferred from one trophic level to the next. 21. Generally, what percentage of energy available at one trophic level is available at the next? 10%

This is important! Remember it.

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22. Consider a food chain with 1,000 joules (an energy unit) available at the producer level. If this food chain is grass grasshopper lizard crow, how much energy is found at the level of the crow? (See answer at the end of this Reading Guide chapter.) Show your work here. Grass (1,000 J) grasshopper (100 J) lizard (10 J) crow (1 J) 23. Notice that most biomass pyramids have greatest biomass on the bottom of the pyramid. Label the trophic levels on both figures below. Explain why the second pyramid of biomass is inverted. See page 1226 of your text for the labeled figure. The second pyramid of biomass is inverted because certain aquatic ecosystems have inverted biomass pyramids: Primary consumers outweigh the producers. Such inverted biomass pyramids occur because the producers—phytoplankton—grow, reproduce, and are consumed so quickly by the zooplankton that they never develop a large population size, or standing crop. In other words, the phytoplankton have a short turnover time, which means they have a small standing crop compared to their production. Because the phytoplankton continually replace their biomass at such a rapid rate, they can support a biomass of zooplankton bigger than their own biomass. Nevertheless, because phytoplankton have much higher production than zooplankton, the pyramid of production for this ecosystem is still bottom- heavy. 24. Why do people who have limited diets in overpopulated parts of the world eat low on the food chain? When humans consume rice and beans, for example, they are primary consumers, and about 10% of available energy is transferred to them. When humans consume meat, they are secondary consumers, and only about 1% of available energy is transferred to them. Consider the production of 100 hectares—if people eat the plant material rather than meat, there will be 10 times more energy (calories) available. Concept 55.4 Biological and geochemical processes cycle nutrients and water in ecosystems Pay particular attention to the nutrient cycles in Figure 55.14. Note the key processes in each cycle. 25. Use the following figure to describe the water cycle. Specify the roles of evaporation, transpiration, and rainfall. See page 1228 of your text for the labeled figure.

The main processes driving the water cycle are evaporation of liquid water by solar energy, condensation of water vapor into clouds, and precipitation. Transpiration by terrestrial plants also moves large volumes of water into the atmosphere. Surface and groundwater flow can return water to the oceans, completing the water cycle.

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26. Use this figure to describe the carbon cycle. In doing so, explain how carbon enters the living system and how it leaves, indicate the role of microorganisms in the cycle, and identify the reservoir for carbon.

See page 1228 of your text for the labeled figure. Photosynthesis by plants and phytoplankton removes substantial amounts of atmospheric CO2 each year. This quantity is approximately equaled by CO2 added to the atmosphere through cellular respiration by producers and consumers. The burning of fossil fuels and wood is adding significant amounts of additional CO2 to the atmosphere. Over geologic time, volcanoes are also a substantial source of CO2. Write the equation for photosynthesis here: 6 CO2 + 6 H2O C6H12O6 + 6 O2

Write the equation for cellular respiration here: C6H12O6 + 6 O2 6 CO2 + 6 H2O + ATP

27. Use the following diagram to describe the nitrogen cycle. In doing so, indicate the role of microorganisms in nitrogen fixation, nitrification, and denitrification See page 1229 of your text for the labeled figure.

The major pathway for nitrogen to enter an ecosystem is via nitrogen fixation, the conversion of N2 to forms that can be used to synthesize organic nitrogen compounds. Certain bacteria, as well as lightning, fix nitrogen naturally. Nitrogen inputs from human activities now outpace natural inputs on land. Two major contributors are industrially produced fertilizers and legume crops that fix nitrogen via bacteria in their root nodules. Other bacteria in soil convert nitrogen to different forms (see also Figure 37.9). Some bacteria carry out denitrification, the reduction of nitrate to nitrogen gases. Human activities also release large quantities of reactive nitrogen gases, such as nitrogen oxides, to the atmosphere. 28. Review the Case Study: Nutrient Cycling in the Hubbard Brook Experimental Forest. What effect has deforestation been shown to have on chemical cycling? Experimental deforestation of a watershed dramatically increased the flow of water and minerals leaving the watershed. The Hubbard Brook deforestation study showed that the amount of nutrients leaving an intact forest ecosystem is controlled mainly by the plants. Large amounts of calcium, nitrates, and potassium were washed into the creeks below the deforested areas. Retaining nutrients in ecosystems helps to maintain the productivity of the systems and, in some cases, to avoid problems cause by excess nutrient runoff. Concept 55.5 Restoration ecologists help return degraded ecosystems to a more natural state

29. What is the goal of restoration ecology?

Restoration ecologists seek to initiate or speed up the recovery of degraded ecosystems. 30. Restoration ecology uses two key strategies. Explain how each strategy works:

bioremediation: Using organisms—usually prokaryotes, fungi, or plant—to detoxify polluted ecosystems is known as bioremediation (see Chapter 27). Some plants and lichens adapted to soils containing heavy metals can accumulate high concentrations of potentially toxic metals such as

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zinc, nickel, lead, and cadmium in their tissues. Restoration ecologists can introduce such species to sites polluted by mining and other human activities and then harvest these organisms to remove the metals from the ecosystem.

biological augmentation: In contrast to bioremediation, which is a strategy for removing harmful substances from an ecosystem, biological augmentation uses organisms to add essential materials to a degraded ecosystem. To augment ecosystem processes, restoration ecologists need to determine which factors, such as chemical nutrients, have been lost from a system and are limiting its recovery.

Test Your Understanding Answers Now you should be ready to test your knowledge. Place your answers here: 1. c 2. b 3. d 4. d 5. c 6. e 7. a 8. e Solution to Question 22: Grass (1,000 J) grasshopper (100 J) lizard (10 J) crow (1 J)