ࡱ> vxu` ;bjbj 7V3::::::: ;HHH8FH<H, ;B\HHHHHIII[[[[[[[$^hh` [:3OII3O3O[::HH[1R1R1R3OX:H:H[1R3O[1R1RX::ZHH pjfzPHO-Z,[\0B\YZ,aPaXZa:ZId K1RLL`III[[QXIIIB\3O3O3O3O ; ; ; H ; ; ;H ; ; ;:::::: Chapter 23 Global ecology and human interferences LEARNING Objectives Define the terms ecosystem and biosphere. [23.1, p. 493] Give examples of the various terrestrial ecosystems or biomes and describe their temperature and rainfall. [23.1, p.493] Give examples of the various aquatic ecosystems. [23.1, p.493] Define each of the following terms as it relates to community: niche, autotrophs, producers, heterotrophs, consumers, herbivores, carnivores, omnivores, and detritus feeders. [23.1, p.494, Fig. 23.3] Explain the concepts of energy flow and chemical cycling in an ecosystem. [23.1, p.495, Figs. 23.4, 23.5] Differentiate between a grazing food web and a detrital food web. [23.2, pp.496497, Fig. 23.6] Explain how organisms can be assigned to trophic levels. [23.2, p.497] Describe an ecological pyramid and its relationship to trophic structure. [23.2, pp.497498, Fig. 23.7] Draw a generalized biogeochemical cycle. [23.3, pp.498499, Fig. 23.8] Diagram the hydrologic (water) cycle and explain its importance to life. [23.3, p.499, Fig. 23.9] Explain how humans interfere with the water cycle. [23.3, p.499] Describe the carbon cycle, carbon reservoirs, and the role of carbon dioxide in global warming and the greenhouse effect. [23.3, pp.500501, Figs. 23.10, 23.11] Describe the nitrogen cycle, the importance of bacteria in the cycle, and the manner in which humans affect the cycle. [23.3, pp.502503, Figs. 23.12, 23.13, 23.14] Know the basics of the phosphorus cycle and how human activities have caused water pollution. [23.3, pp.504505, Fig. 23.16] Understand and use the bold-faced and italicized terms included in this chapter. [Understanding Key Terms, p. 509] Extended Lecture Outline 23.1 The Nature of Ecosystems The biosphere is where organisms are found on planet Earth, from the atmosphere above to the depths of the oceans below and everything in between. An ecosystem is a place where organisms interact among themselves and with the physical and chemical environment. Ecosystems Scientists recognize several distinctive major types of terrestrial ecosystems, also called biomes. Temperature and rainfall define the biomes. Aquatic ecosystems are divided into those composed of freshwater and those composed of salt water (marine ecosystems). Biotic Components of an Ecosystem The abiotic components of an ecosystem are the nonliving components. The living things, or biotic components, are categorized according to their food source. Autotrophs Autotrophs require only inorganic nutrients and an outside energy source to produce organic nutrients for their own use and for all the other members of a community. They are producers. Heterotrophs Heterotrophs need a source of organic nutrients. They are the consumers. Herbivores are animals that graze directly on plants or algae. Carnivores feed on other animals. Omnivores feed both on plants and animals. Detritus feeders are organisms that feed on decomposing particles of organic matter. Niche A niche is the role of an organism in an ecosystem: how it gets its food and what eats it, and how it interacts with other populations in the same community. Energy Flow and Chemical Cycling Every ecosystem is characterized by two phenomena: energy flow and chemical cycling. Energy flow begins when producers absorb solar energy, and chemical cycling begins when producers take in inorganic nutrients from the physical environment. Chemicals cycle when inorganic nutrients are returned to the producers from the atmosphere or soil. 23.2 Energy Flow Food webs are diagrams that describe the trophic or feeding relationships in an ecosystem. Trophic Levels Diagrams that show a single path of energy flow are called food chains. A trophic level is composed of all the organisms that feed at a particular link in a food chain. Generally, the first level is producers, the second level is the primary consumers, and the next levels are the secondary consumers. Ecological Pyramids The shortness of food chains can be attributed to the loss of energy between trophic levels. Only about 10% of the energy of one trophic level is available to the next trophic level. The flow of energy with large losses between successive trophic levels is sometimes depicted as an ecological pyramid with each trophic level stacked on top of the other like building blocks. Pyramids of biomass eliminate size as a factor in the trophic level energy losses. Biomass is the number of organisms multiplied by the weight of organic matter within one organism. 23.3 Global Biogeochemical Cycles Biogeochemical cycles contain reservoirs, components of ecosystems like fossil fuels, sediments, and rocks that contain elements available on a limited basis to living things. Exchange pools are components of ecosystems like the atmosphere, soil, and waterwhich are ready sources of nutrients for living things. Nutrients cycle among the members of the biotic community of an ecosystem. Biogeochemical cycles may be gaseous or sedimentary. Human activities remove chemicals from reservoirs and exchange pools and make them available to the biotic community. The Water Cycle In the water cycle, evaporation over the ocean and cloud movement results in rainfall over the land. Evaporation from terrestrial ecosystems includes transpiration from plants. Precipitation over land results in bodies of fresh water plus groundwater, including aquifers. Eventually all water returns to the oceans. Human Activities Humans interfere with the water cycle in three ways: they withdraw water from aquifers, they clear vegetation from land and build roads and buildings that increase runoff, and they interfere with the natural processes that purify water and instead add pollutants to water. In certain areas of the country, withdrawals from aquifers exceed the ability of the aquifer to recharge. This is called groundwater mining. Water is a renewable resource but it is possible to run out of fresh water. The Carbon Cycle In the carbon cycle, organisms add as much carbon dioxide to the atmosphere as they remove. Plants take up carbon dioxide during photosynthesis. Consumers acquire carbon along with other nutrients. In aquatic ecosystems, the exchange of carbon dioxide with the atmosphere is indirect. Reservoirs Hold Carbon Living and dead organisms contain organic carbon and serve as one of the reservoirs for the carbon cycle. In the history of the Earth, some 300 MYA, plant and animal remains were transformed into fossil fuels. Human Activities More carbon dioxide is being deposited in the atmosphere than is being removed, mostly due to the burning of fossil fuels and the destruction of forests. CO2 and Global Warming Carbon dioxide and other gases such as nitrous oxide and methane are known as greenhouse gases. These gases are contributing to an overall rise in the Earths ambient temperature because of their greenhouse effect. This phenomenon is called global warming. Global warming will bring about major changes in ecosystems. The Nitrogen Cycle Nitrogen gas makes up about 78% of the atmosphere but plants cannot make use of nitrogen gas. Ammonium (NH4+) Formation and Use Nitrogen fixation occurs when nitrogen gas is converted to ammonium, a form plants can use. Some bacteria are also able to fix atmospheric nitrogen. Nitrate (NO3-) Formation and Use Plants can also use nitrates as a source of nitrogen. The production of nitrates during the nitrogen cycle is called nitrification and occurs in several ways. Formation of Nitrogen Gas from Nitrate Denitrification is the conversion of nitrate back to nitrogen gas, which enters the atmosphere. Denitrifying bacteria live in anaerobic mud environments. Human Activities Human activities significantly alter the transfer rates in the nitrogen cycle by producing fertilizers from nitrogen gas. Fertilizer contributes to cultural eutrophication which causes massive fish kills. Acid deposition occurs because nitrogen oxides and sulfur dioxide enter the atmosphere from the burning of fossil fuels. Nitrogen oxides and hydrocarbons from the burning of fossil fuels react with one another in the presence of sunlight to produce smog which contains dangerous pollutants. The Phosphorus Cycle In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and only limited quantities are made available by the weathering of rocks. Phosphorus and Water Pollution Human beings boost the supply of phosphate by mining phosphate ores for fertilizer and detergent production. Runoff of phosphate from various sources results in cultural eutrophication of waterways. Synthetic organic compounds, and inorganic chemicals and minerals pollute the water from various sources. Biological magnification occurs as they pass along a food chain and become more and more concentrated because they remain in the body and are not excreted. In the last 50 years, humans have polluted the seas and exploited their resources to the point that many species are at the brink of extinction. Student Activities Global Warming 1. Have your students research global warming on the Internet. Ask them to discover how much the temperature has increased. Since when were measurements taken? What effect does this rise in temperature have on sea level and various island nations? What is the Kyoto Protocol? Ask them to write a onetwo paragraph summary of their findings. Finally, ask students whether they were already concerned, are beginning to be concerned, or do not worry about the future of the environment. Personal Niches 2. Ask several volunteers from your class to describe their personal ecological niche (what they eat, how much carbon dioxide they contribute to the atmosphere by driving, interactions with other people, their jobs, and so forth). Include presumed interactions with living organisms (stepping on insects, receiving mosquito bites). List these items on the chalkboard, and ask other students to add to the list. Ask if you have anyone who enjoys fishing or hunting. Does that person function as a predator in his or her ecosystem? From this exercise, students should gain some appreciation for the fact that even though we are human, we still function as animals in the ecosystems to which we belong. Water Purification Plant 3. Arrange a field trip for your students to your local water purification plant. Take a tour of the facilities and allow time for the students to ask questions. Find out what pollutants your community tests for and obtain a copy of the annual water quality report. Nitrogen Fixing Bacteria 4. Obtain a sample of a legume such as a bean or pea plant along with the roots. Scientific supply houses do sell these, although it is preferable to have a fresh sample from a field if you can obtain one from a neighborhood garden. Have students examine the nodules that occur in the roots and research the relationship between the nitrogen fixing bacteria and the plant. What do the bacteria provide for the plant? What does the plant provide for the bacteria? How is this relationship classified? Acid Rain 5. Have students bring in photographs from the Internet or newspapers/magazines of damage caused by acid rain. Photographs could include forests, statues and buildings, lakes, etc. Discuss the problems associated with fossil fuel burning and pollution of the atmosphere. Who is responsible for protecting the air over our forests? Who is responsible for the pollution? What should be done if the pollution from one country is destroying the forests in another country? CLASSROOM DISCUSSION TOPICS 1. Students should read the Bioethical Focus, Oil Drilling in the Arctic before coming to class. Discuss the answers to the questions at the end of the reading. Discuss the uniqueness of the Arctic National Wildlife Refuge and the original intent of establishing such sites as preserved areas. Ask students whether it is important to continue to preserve such areas for all time or whether drilling for oil is a fair tradeoff. Include in your discussion ideas about alternative fuels to lessen the long-term need for fossil fuels. Discuss the political climates that favor drilling or preservation. 2. Students should read the Science Focus Ozone Shield Depletion before coming to class. Discuss the problems with the ozone shield and CFCs. What actual effect will a depletion of the ozone shield have on each one of them? Is this a good example of science and politics working to improve life on Earth? What other environmental concerns should be tackled? 3. Have students research the depletion of the aquifer under the central United States. They might want to do a search on the water problems in Phoenix, Arizona. Discuss the depletion of the aquifer, the restrictions placed on water usage in certain cities, and the problems associated with maintaining large cities in essentially desert land. Who owns the rights to the water under the ground? Who is responsible for protecting it? Who can use it?     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