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Ecosystems: What Are They and How Do They Work

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1 Ecosystems: What Are They and How Do They Work
Chapter 3 (Miller and Spoolman, 2010)

2 Core Case Study: Tropical Rain Forests Are Disappearing
Cover about 2% of the earth’s land surface Contain about 50% of the world’s known plant and animal species At least half have been destroyed. W/o strong conservation measures, most will be gone or severely degraded in your lifetime. Disruption will have three major harmful effects Reduce biodiversity Accelerate global warming Change regional weather patterns Once a tipping point is reached, tropical rainforests will become less diverse tropical grasslands

3 Figure 3-1 Natural capital degradation: satellite image of the loss of tropical rainforest, cleared for farming, cattle grazing, and settlements, near the Bolivian city of Santa Cruz between June 1975 (left) and May 2003 (right).

4 3-1 What Is Ecology? Concept 3-1 Ecology is the study of how organisms interact with one another and with their physical environment of matter and energy.

5 Cells Are the Basic Units of Life
Cell – smallest and most fundamental structural units of life. Cell Theory Eukaryotic cell Prokaryotic cell

6 Figure 3.2 Natural capital: (a) generalized structure of a eukaryotic cell and (b) prokaryotic cell. Note that a prokaryotic cell lacks a distinct nucleus and generalized structure of a eukaryotic cell.

7 Species Make Up the Encyclopedia of Life
For a groups of sexually reproducing organisms, a species is a set of individuals that can mate and produce fertile offspring. 1.8 Million species identified Insects make up most of the known species Perhaps 10–14 million species not yet identified Scientists have developed a distinctive system for classifying and naming each species.

8 Ecologists Study Connections in Nature
Ecology – derived from the Greek oikos and logos, is the study of how organisms interact with their living (biotic) environment and their nonliving environment (abiotic). Levels of organization Population (Figure 3-4) Genetic diversity (Figure 3-5) Habitat Community Ecosystem Biosphere

9 Figure 3. 3 Some levels of organization of matter in nature
Figure 3.3 Some levels of organization of matter in nature. Ecology focuses on the top five of these levels.

10 Figure 3-4 Population (school) of glassfish in a cave in the Red Sea.

11 Figure 3-5 Genetic diversity among individuals in a population of a species of Caribbean snail is reflected in the variations in shell color and banding patterns. Genetic diversity can also include other variations such as slight differences in chemical makeup, sensitivity to various chemicals, and behavior.

12 Science Focus: Have You Thanked the Insects Today? (1)

13 Science Focus: Have You Thanked the Insects Today? (2)
Pollinators Eat other insects Loosen and renew soil Reproduce rapidly, and can rapidly develop new traits Very resistant to extinction According to E.O. Wilson, if all insects disappeared, parts of the life support systems for us and other species would be greatly disrupted.

14 3-2 What Keeps Us and Other Organisms Alive?
Concept 3-2 Life is sustained by the flow of energy from the sun through the biosphere, the cycling of nutrients within the biosphere, and gravity.

15 The Earth’s Life-Support System Has Four Major Components (1)
Atmosphere – envelope of gas that surrounds the earth. Troposphere, extends to 17 km (11 mi) at tropics, 7 km (4 mi) at poles. 78 % N2, 21 % O2, and 1 % water vapor, CO2 and CH4 Stratosphere, from km (11-31 mi) Lower portion contains ozone (O3) Hydrosphere – all water on or near the earth’s surface. Most in oceans which cover 71 % of the globe. Liquid, ice, and water vapor

16 The Earth’s Life-Support System Has Four Major Components (2)
Geosphere Intensely hot core, a thick mantle, and thin outer crust. Upper portion contains nonrenewable fossil fuels and minerals that we use as well as renewable soil. Biosphere – parts of the atmosphere, hydrosphere and geosphere where life exists. From about 9 km (6 mi) above surface to bottom of the oceans.

17 Figure 3.6 Natural capital: general structure of the earth showing that it consists of a land sphere, air sphere, water sphere, and life sphere.

18 Life Exists on Land and in Water
Biomes – large regions such as forests, deserts, and grasslands with distinct climates and certain species (especially vegetation) adapted to them. Aquatic life zones – divisions of the watery parts of the biosphere each containing numerous ecosystems. Freshwater life zones Lakes and streams Marine life zones Coral reefs Estuaries Deep ocean

19 Figure 3.7 Major biomes found along the 39th parallel across the United States. The differences reflect changes in climate, mainly differences in average annual precipitation and temperature.

20 Three Factors Sustain Life on Earth
One-way flow of high-quality energy beginning with the sun Cycling of matter or nutrients Gravity Holds on to the atmosphere and enables the movement and cycling of chemicals through the air, water, soil, and organisms.

21 What Happens to Solar Energy Reaching the Earth?
UV, visible, and IR energy Much is reflected by the atmosphere, only 1 % reaches surface Lights the earth during the day, warms the air, evaporates and cycles water through the biosphere. 1 % generates the wind, and only 0.1 % is harnessed by photosynthetic organisms. Radiation Absorbed by ozone , including 95 % of harmful UV Absorbed by the earth Reflected by the earth Radiated by the atmosphere as heat Natural greenhouse effect Carbon dioxide, methane (CH4), nitrous oxide (N2O), and ozone (O3) Human activities are increasing these gases.

22 Figure 3.8 Solar capital: flow of energy to and from the earth.

23 3-3 What Are the Major Components of an Ecosystem?
Concept 3-3A Ecosystems contain living (biotic) and nonliving (abiotic) components. Concept 3-3B Some organisms produce the nutrients they need, others get their nutrients by consuming other organisms, and some recycle nutrients back to producers by decomposing the wastes and remains of organisms.

24 Ecosystems Have Living and Nonliving Components (1)
Abiotic Water Air Nutrients Rocks Heat Solar energy Biotic Living and once living biological components—plants animals and microbes. Dead organisms, dead part of organisms, and waste products of organisms.

25 Figure 3.9 Major living (biotic) and nonliving (abiotic) components of an ecosystem in a field.

26 Ecosystems Have Living and Nonliving Components(2)
Different species AND their populations thrive under different physical and chemical conditions. Some need bright light, or warmer temperatures, or higher humidity or pH, for example, than others. Each population in an ecosystem has a range of tolerance to variations in the physical and chemical environment. Likewise individuals in population can vary in their tolerance to environmental factors because of small differences in genetic makeup(i.e. genetic variation).

27 Figure 3.10 Range of tolerance for a population of organisms, such as fish, to an abiotic environmental factor—in this case, temperature. These restrictions keep particular species from taking over an ecosystem by keeping their population size in check. Question: Which scientific principle of sustainability (see back cover) is related to the range of tolerance concept?

28 Several Abiotic Factors Can Limit Population Growth
Limiting factor – specific factor(s) important in regulating the growth of a population. Terrestrial ecosytems: precipitation, soil nutrients, temperature Aquatic ecosystems: temperature, sunlight, nutrients, DO, and salinity. Limiting factor principle Too much or too little of any abiotic factor can limit or prevent growth of a population, even if all other factors are at or near the optimal range of tolerance One way in which population control (one of the scientific principles of sustainability) is achieved

29 Producers and Consumers Are the Living Components of Ecosystems (1)
Trophic level Producers, or autotrophs Photoautotrophs: plants, algae, aquatic plants, and phytoplankton, Photosynthesis Chemoautotrophs: mostly specialized bacteria Chemosynthesis (see p. 59 for details) Consumers, or heterotrophs Primary Secondary Third and higher level Omnivores Decomposers Primarily bacteria and fungi Detritus feeders, or detritivores Mites, earthworms, some insects, catfish, and larger scavengers like vultures.

30 Figure 3.11 Various detritivores and decomposers (mostly fungi and bacteria) can “feed on” or digest parts of a log and eventually convert its complex organic chemicals into simpler inorganic nutrients that can be taken up by producers.

31 Producers and Consumers Are the Living Components of Ecosystems (2)
Organisms use the chemical energy stored in glucose and other organic compounds to fuel their life processes. In most cells, energy released by aerobic respiration. Though the steps differ, the net chemical rxn is essentially the opposite of that for photosynthesis. Anaerobic respiration, or fermentation End products include CH4, ethyl alcohol (C2H6O), acetic acid (C2H4O2), or hydrogen sulfide (H2S).

32 Energy Flow and Nutrient Cycling Sustain Ecosystems and the Biosphere
Ecosystems and the biosphere are sustained through a combination of one-way energy flow from the sun through these systems and nutrient cycling of key materials within them. These two principles of sustainability (see back cover of textbook) arise from Structure and function of natural ecosystems Law of conservation of matter, and Two law of thermodynamics.

33 Figure 3.12 Natural capital: the main structural components of an ecosystem (energy, chemicals, and organisms). Nutrient cycling and the flow of energy—first from the sun, then through organisms, and finally into the environment as low-quality heat—link these components.

34 Science Focus: Many of the World’s Most Important Species Are Invisible to Us
Microorganisms, or microbes, are a vital part of earth’s natural capital. Explain. Bacteria Protozoa Fungi Phytoplankton

35 3-4 What Happens to Energy in an Ecosystem?
Concept 3-4A Energy flows through ecosystems in food chains and webs. Concept 3-4B As energy flows through ecosystems in food chains and webs, the amount of chemical energy available to organisms at each succeeding feeding level decreases.

36 Energy Flows Through Ecosystems in Food Chains and Food Webs
Chemical energy stored as nutrients in the bodies and wastes of organisms flows through ecosystems from one trophic level (feeding level) to another. Food chain – a sequence of organisms, each of which serves as a source of food or energy for the next. Primarily through photosynthesis, feeding and decomposition. Food web – complex network of interconnected food chains.

37 Figure 3.13 A food chain. The arrows show how chemical energy in nutrients flows through various trophic levels in energy transfers; most of the energy is degraded to heat, in accordance with the second law of thermodynamics. Question: Think about what you ate for breakfast. At what level or levels on a food chain were you eating?

38 Figure 3. 14 Greatly simplified food web in the Antarctic
Figure 3.14 Greatly simplified food web in the Antarctic. Many more participants in the web, including an array of decomposer and detritus feeder organisms, are not depicted here. Question: Can you imagine a food web of which you are a part? Try drawing a simple diagram of it.

39 Usable Energy Decreases with Each Link in a Food Chain or Web
Biomass – the dry weight of all organic matter contained in its organisms. Chemical energy stored in biomass is transferred up the food web. Inefficient. Decrease in energy available at each succeeding trophic level. Ecological efficiency – percentage of usable chemical energy transferred as biomass from one trophic level to the next. Ranges from 2 to 40 %, but 10 % is average. Using the idea of ecological efficiency, explain why can support more people if they ate a lower tropic levels. About 2/3 of world’s people survive on wheat, rice, and corn (1st trophic level) because they cannot afford meat. Again, using the idea of ecological efficiency, explain why food chains and food webs rarely support more than four or Five trophic levels.

40 Figure 3.15 Generalized pyramid of energy flow showing the decrease in usable chemical energy available at each succeeding trophic level in a food chain or web. In nature, ecological efficiency varies from 2% to 40%, with 10% efficiency being common. This model assumes a 10% ecological efficiency (90% loss of usable energy to the environment, in the form of low-quality heat) with each transfer from one trophic level to another. Question: Why is a vegetarian diet more energy efficient than a meat-based diet?

41 Some Ecosystems Produce Plant Matter Faster Than Others Do (1)
Ultimately, the biomass of an ecosystem depends on the amount of energy captured and stored by producers. Gross primary productivity (GPP) – the rate at which an ecosystems producers convert solar energy into chemical energy. Usually measured in energy production per unit area per unit time, e.g. kcal/m2/yr. To stay alive producers must use some of this stored chemical energy for their own respiration.

42 Some Ecosystems Produce Plant Matter Faster Than Others Do (2)
Net primary productivity – rate at which producers use photosynthesis to produce and store energy minus the rate at which they use this stored energy for aerobic respiration. Ecosystems and aquatic life zones differ in their NPP (Fig. 3-16). Decreases from equator to pole. Estuaries are high Upwellings (water moving up from depths to surface) Open ocean, low NPP, but high absolute amount. Why?

43 Figure 3.16 Estimated annual average net primary productivity in major life zones and ecosystems, expressed as kilocalories of energy produced per square meter per year (kcal/m2/yr). Question: What are nature’s three most productive and three least productive systems? (Data from R. H. Whittaker, Communities and Ecosystems, 2nd ed., New York: Macmillan, 1975)

44 Some Ecosystems Produce Plant Matter Faster Than Others Do (3)
Should be clear that the planet’s NPP ultimately limits the number of consumers (including humans) that can survive on the earth. Ecologists estimated that humans use, waste, or destroy about 20-32% of the earth’s total potential NPP. Remarkable considering that humans make up on 1% of the total biomass of all of the earth’s consumers.

45 3-5 What Happens to Matter in an Ecosystem?
Concept 3-5 Matter, in the form of nutrients, cycles within and among ecosystems and the biosphere, and human activities are altering these chemical cycles.

46 Nutrients Cycle in the Biosphere
Biogeochemical cycles, or nutrient cycles – the cycling of elements and compounds through air, water, soil, rock, and living organisms in ecosystems and in the biosphere. Driven directly and indirectly by the sun and gravity. Human activities are altering them. Include: Hydrologic, Carbon, Nitrogen, Phosphorus, and Sulfur Cycles. Atoms and compounds moving in this cycle may accumulate in one portion of the cycle indefinitely. These atmospheric, oceanic, and underground deposits are called reservoirs. Connect past, present , and future forms of life

47 Water Cycles through the Biosphere
The hydrologic cycle, or water cycle, collects, purifies, and distributes the earth’s fixed supply of water. Powered by energy from the sun, involves three major processes: Evaporation 84% of water in atmosphere comes from the ocean. Precipitation Surface runoff, infiltration, and percolation to aquifers Transpiration On land, 90% of water reaches atmosphere from plants. Alteration of the hydrologic cycle by humans Withdrawal of large amounts of freshwater at rates faster than nature can replace it Clearing vegetation Increased flooding when wetlands are drained

48 Figure 3.17 Natural capital: simplified model of the hydrologic cycle with major harmful impacts of human activities shown in red. See an animation based on this figure at CengageNOW. Question: What are three ways in which your lifestyle directly or indirectly affects the hydrologic cycle?

49 Science Focus: Water’s Unique Properties
Properties of water due to hydrogen bonds between water molecules: Exists as a liquid over a large range of temperature Changes temperature slowly (High heat capacity) High boiling point: 100˚C Takes lots of energy to evaporate (High heat of vaporization) Adhesion and cohesion Expands as it freezes Solvent Filters out harmful UV

50 Carbon Cycle Depends on Photosynthesis and Respiration
Carbon cycle – carbon circulates through the biosphere, the atmosphere, and parts of the hydrosphere. Based on CO2, which make up 0.038% of atmosphere. Link between photosynthesis in producers and aerobic respiration in producers, consumers, and decomposers. Key component of earth’s thermostat (a GHG). Additional CO2 added to the atmosphere Tree clearing Burning of fossil fuels Computer models suggest that it is very likely (90-99% probability) that human activities are enhancing the green house effect.

51 Figure 3.18 Natural capital: simplified model of the global carbon cycle, with major harmful impacts of human activities shown by red arrows. See an animation based on this figure at CengageNOW. Question: What are three ways in which you directly or indirectly affect the carbon cycle?

52 Nitrogen Cycles through the Biosphere: Bacteria in Action (1)
Major reservoir, the atmosphere; N2 makes up 78% Nitrogen is a crucial component of proteins, vitamins and nucleic acids. Two processes convert N2 to more usable forms: Electrical charges, such as lightning. Nitrogen-fixing bacteria; process called nitrogen fixation. Special bacteria in soil and blue-green algae (cyanobacteria) Combine N2 and H2 to make ammonia (NH3)  to NH4+ that can be used by plants. Nitrification – ammonia is converted by other bacteria to nitrate ions (NO3-). Ammoniafication – specialized decomposers convert detritus into simpler nitrogen-containing compounds like NH3 and NH4+. Denitrification – specialize bacteria in waterlogged soils and sediments of aquatic ecosystems convert ammonia and ammonium ions back into nitrite and nitrate ions and then into N2 and N2O.

53 Figure 3.19 Natural capital: simplified model of the nitrogen cycle with major harmful human impacts shown by red arrows. See an animation based on this figure at CengageNOW. Question: What are three ways in which you directly or indirectly affect the nitrogen cycle?

54 Nitrogen Cycles through the Biosphere: Bacteria in Action (2)
Human intervention in the nitrogen cycle: Burn fuels at high temperatures, creates nitric oxide (NO)  nitrogen dioxide (NO2)  nitric acid vapor (HNO3)  acid deposition, or acid rain. Anaerobic bacteria action on livestock waste and commercial inorganic fertilizer  nitrous oxide (N2O)  ghg forces warming and can destroy stratospheric ozone (O3) Destruction of forest, grasslands, and wetlands  releases large quantities of nitrogen as gaseous compounds. Add excess nitrates to bodies of water from agricultural runoff and municipal sewage systems  cultural eutrophication. Deplete nitrogen from topsoil when we harvest nitrogen-rich crops, irrigate crops and burn and clear grasslands and forests.

55 Figure 3.20 Global trends in the annual inputs of nitrogen into the environment from human activities, with projections to (Data from 2005 Millennium Ecosystem Assessment)

56 Phosphorus Cycles through the Biosphere
Phosphorus circulates through water, the earth’s crust, and living organisms; does not include the atmosphere. Component of nucleic acids and energy molecules, ATP. Major reservoir, phosphorus salts containing (phosphate ions, PO4-3) in terrestrial rock formations and ocean sediments. Limiting factor for plant growth in terrestrial and aquatic systems. Impact of human activities Clearing forests Removing large amounts of phosphate from the earth to make fertilizers Runoff from land can lead to further cultural eutrophication of lakes and coastal areas.

57 Figure 3.21 Natural capital: simplified model of the phosphorus cycle, with major harmful human impacts shown by red arrows. Question: What are three ways in which you directly or indirectly affect the phosphorus cycle?

58 Sulfur Cycles through the Biosphere
Sulfur is stored in rocks and minerals and ocean sediments. H2S released from volcanoes and anaerobic bacteria decomposition in flooded swamps, bogs and tidal flats. SO2 released from volcanoes and processing and burning fossil fuels. Sulfate (SO4-2) salts from sea spray, dust storms, and forest fires. Certain marine algae produce DMS, serves as nuclei for condensation for water into droplets found in clouds. DMS in atmosphere  SO2  SO3 and H2SO4  acid deposition. Human activities affect the sulfur cycle mostly by release of SO2. Burn sulfur-containing coal and oil Refine sulfur-containing petroleum Convert sulfur-containing metallic mineral ores

59 Figure 3.22 Natural capital: simplified model of the sulfur cycle, with major harmful impacts of human activities shown by red arrows. See an animation based on this figure at CengageNOW. Question: What are three ways in which your lifestyle directly or indirectly affects the sulfur cycle?

60 3-6 How Do Scientists Study Ecosystems?
Concept 3-6 Scientists use field research, laboratory research, and mathematical and other models to learn about ecosystems.

61 Some Scientists Study Nature Directly
Field research: “muddy-boots biology” New technologies available Remote sensors Geographic information system (GIS) software Digital satellite imaging 2005, Global Earth Observation System of Systems (GEOSS)

62 Some Scientists Study Ecosystems in the Laboratory
Simplified systems carried out in Culture tubes and bottles Aquaria tanks Greenhouses Indoor and outdoor chambers Supported by field research

63 Some Scientists Use Models to Simulate Ecosystems
Computer simulations and projections Field and laboratory research needed for baseline data

64 We Need to Learn More about the Health of the World’s Ecosystems
Determine condition of the world’s ecosystems More baseline data needed Doctor-patient analogy

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