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Ecosystems: What Are They and How Do They Work?
Chapter 3
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Figure 3.1 Natural capital degradation: satellite image of the loss of tropical rain forest, cleared for farming, cattle grazing, and settlements, near the Bolivian city of Santa Cruz between June 1975 (left) and May 2003 (right). Fig. 3-1a, p. 50
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Figure 3.1 Natural capital degradation: satellite image of the loss of tropical rain forest, cleared for farming, cattle grazing, and settlements, near the Bolivian city of Santa Cruz between June 1975 (left) and May 2003 (right). Fig. 3-1b, p. 50
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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 Disruption will have three major harmful effects Reduce biodiversity Accelerate global warming Change regional weather patterns
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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.
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Cells Are the Basic Units of Life
Cell Theory Eukaryotic cell Prokaryotic cell
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Protein construction and energy conversion occur without specialized
Cell membrane (a) Eukaryotic Cell Nucleus (DNA) Protein construction Energy conversion Protein construction and energy conversion occur without specialized internal structures (b) Prokaryotic Cell DNA (no nucleus) Cell membrane 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. Stepped Art Fig. 3-2, p. 52
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Species Make Up the Encyclopedia of Life
1.75 Million species identified Insects make up most of the known species Perhaps 10–14 million species not yet identified
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Ecologists Study Connections in Nature
Ecology Levels of organization Population Genetic diversity Community Ecosystem Biosphere
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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. Fig. 3-5, p. 53
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Biosphere Ecosystem Community Population Organism Cell Molecule Atom
Parts of the earth's air, water, and soil where life is found A community of different species interacting with one another and with their nonliving environment of matter and energy Ecosystem Community Populations of different species living in a particular place, and potentially interacting with each other Population A group of individuals of the same species living in a particular place Organism An individual living being The fundamental structural and functional unit of life Figure 3.3 Some levels of organization of matter in nature. Ecology focuses on the top five of these levels. See an animation based on this figure at CengageNOW. Cell Chemical combination of two or more atoms of the same or different elements Molecule Smallest unit of a chemical element that exhibits its chemical properties Atom Fig. 3-3, p. 52
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Science Focus: Have You Thanked the Insects Today?
Pollinators Eat other insects Loosen and renew soil Reproduce rapidly Very resistant to extinction
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Figure 3.A Importance of insects: The monarch butterfly, which feeds on pollen in a flower (left), and other insects pollinate flowering plants that serve as food for many plant eaters. The praying mantis, which is eating a house cricket (right), and many other insect species help to control the populations of most of the insect species we classify as pests. Fig. 3-A (1), p. 54
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Figure 3.A Importance of insects: The monarch butterfly, which feeds on pollen in a flower (left), and other insects pollinate flowering plants that serve as food for many plant eaters. The praying mantis, which is eating a house cricket (right), and many other insect species help to control the populations of most of the insect species we classify as pests. Fig. 3-A (2), p. 54
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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.
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Vegetation and animals Biosphere Crust Lithosphere Mantle Biosphere
Atmosphere Biosphere Soil Rock Crust Lithosphere Mantle Biosphere (living organisms) Atmosphere (air) 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. Core Mantle Crust (soil and rock) Geosphere (crust, mantle, core) Hydrosphere (water) Fig. 3-6, p. 55
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The Earth’s Life-Support System Has Four Major Components
Atmosphere Troposphere Stratosphere Hydrosphere Geosphere Biosphere
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Average annual precipitation
100–125 cm (40–50 in.) 75–100 cm (30–40 in.) 50–75 cm (20–30 in.) 25–50 cm (10–20 in.) below 25 cm (0–10 in.) Denver Baltimore San Francisco St. Louis Coastal mountain ranges Sierra Nevada Great American Desert Rocky Mountains Great Plains Mississippi River Valley Appalachian Mountains 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. Coastal chaparral and scrub Coniferous forest Desert Coniferous forest Prairie grassland Deciduous forest Fig. 3-7, p. 55
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Life Exists on Land and in Water
Biomes Aquatic life zones Freshwater life zones Lakes and streams Marine life zones Coral reefs Estuaries Deep ocean
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Three Factors Sustain Life on Earth
One-way flow of high-quality energy beginning with the sun Cycling of matter or nutrients Gravity
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What Happens to Solar Energy Reaching the Earth?
UV, visible, and IR energy Radiation Absorbed by ozone Absorbed by the earth Reflected by the earth Radiated by the atmosphere as heat Natural greenhouse effect
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Solar radiation Lower Stratosphere (ozone layer) Greenhouse effect
Reflected by atmosphere Radiated by atmosphere as heat UV radiation Lower Stratosphere (ozone layer) Most absorbed by ozone Troposphere Visible light Heat radiated by the earth Figure 3.8 Solar capital: flow of energy to and from the earth. See an animation based on this figure at CengageNOW. Heat Absorbed by the earth Greenhouse effect Fig. 3-8, p. 56
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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.
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Ecosystems Have Living and Nonliving Components
Abiotic Water Air Nutrients Rocks Heat Solar energy Biotic Living and once living
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Oxygen (O2) Precipitation Carbon dioxide (CO2) Producer Secondary
consumer (fox) Primary consumer (rabbit) Figure 3.9 Major living (biotic) and nonliving (abiotic) components of an ecosystem in a field. See an animation based on this figure at CengageNOW. Producers Decomposers Water Soluble mineral nutrients Fig. 3-9, p. 57
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Several Abiotic Factors Can Limit Population Growth
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
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Abundance of organisms
Lower limit of tolerance Higher limit of tolerance No organisms Few organisms Few organisms No organisms Abundance of organisms Population size 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? Zone of intolerance Zone of physiological stress Optimum range Zone of physiological stress Zone of intolerance Low Temperature High Fig. 3-10, p. 58
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Producers and Consumers Are the Living Components of Ecosystems (1)
Producers, autotrophs Photosynthesis Chemosynthesis Consumers, heterotrophs Primary Secondary Third and higher level Decomposers
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Producers and Consumers Are the Living Components of Ecosystems (2)
Detritivores Aerobic respiration Anaerobic respiration, fermentation
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Energy Flow and Nutrient Cycling Sustain Ecosystems and the Biosphere
One-way energy flow Nutrient cycling of key materials
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Many of the World’s Most Important Species Are Invisible to Us
Microorganisms Bacteria Protozoa Fungi
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decomposers into plant nutrients in soil
Detritus feeders Decomposers Carpenter ant galleries Termite and carpenter ant work Bark beetle engraving Dry rot fungus Long-horned beetle holes Wood reduced to powder 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. Mushroom Time progression Powder broken down by decomposers into plant nutrients in soil Fig. 3-11, p. 60
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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.
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Energy Flows Through Ecosystems in Food Chains and Food Webs
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Usable Energy Decreases with Each Link in a Food Chain or Web
Biomass Ecological efficiency Pyramid of energy flow
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Solar energy Abiotic chemicals (carbon dioxide, oxygen, nitrogen,
minerals) Heat Heat Heat Decomposers (bacteria, fungi) Producers (plants) 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. See an animation based on this figure at CengageNOW. Consumers (herbivores, carnivores) Heat Heat Fig. 3-12, p. 60
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Decomposers and detritus feeders
First Trophic Level Second Trophic Level Third Trophic Level Fourth Trophic Level Producers (plants) Primary consumers (herbivores) Secondary consumers (carnivores) Tertiary consumers (top carnivores) Heat Heat Heat Heat Solar energy Heat 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. See an animation based on this figure at CengageNOW. Question: Think about what you ate for breakfast. At what level or levels on a food chain were you eating? Heat Heat Decomposers and detritus feeders Fig. 3-13, p. 62
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Humans Blue whale Sperm whale Elephant seal Crabeater seal Killer whale Leopard seal Adelie penguin Emperor penguin Squid Petrel 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. Fish Carnivorous plankton Herbivorous zooplankton Krill Phytoplankton Fig. 3-14, p. 63
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Usable energy available
10 Heat Tertiary consumers (human) Usable energy available at each trophic level (in kilocalories) Heat Decomposers Heat Secondary consumers (perch) 100 Heat Primary consumers (zooplankton) 1,000 Heat Producers (phytoplankton) 10,000 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? Stepped Art Fig. 3-15, p. 63
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Some Ecosystems Produce Plant Matter Faster Than Others Do
Gross primary productivity (GPP) Net primary productivity (NPP) Ecosystems and life zones differ in their NPP
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Terrestrial Ecosystems
Swamps and marshes Tropical rain forest Temperate forest Northern coniferous forest Savanna Agricultural land Woodland and shrubland Temperate grassland Tundra (arctic and alpine) Desert scrub Extreme desert Aquatic Ecosystems Estuaries 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) Lakes and streams Continental shelf Open ocean 800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,600 Average net primary productivity (kcal/m2/yr) Fig. 3-16, p. 64
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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.
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Nutrients Cycle in the Biosphere
Biogeochemical cycles, nutrient cycles Hydrologic Carbon Nitrogen Phosphorus Sulfur Connect past, present , and future forms of life
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Water Cycles through the Biosphere
Natural renewal of water quality: three major processes Evaporation Precipitation Transpiration 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
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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 boiling point: 100˚C Adhesion and cohesion Expands as it freezes Solvent Filters out harmful UV
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Global warming Condensation Ice and snow Condensation Evaporation from land Evaporation from ocean Precipitation to land Transpiration from plants Surface runoff Increased flooding from wetland destruction Precipitation to ocean Runoff Lakes and reservoirs Reduced recharge of aquifers and flooding from covering land with crops and buildings Point source pollution Infiltration and percolation into aquifer Surface runoff Groundwater movement (slow) Ocean Aquifer depletion from overpumping 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? Processes Processes affected by humans Reservoir Pathway affected by humans Natural pathway Fig. 3-17, p. 66
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Carbon Cycle Depends on Photosynthesis and Respiration
Link between photosynthesis in producers and respiration in producers, consumers, and decomposers Additional CO2 added to the atmosphere Tree clearing Burning of fossil fuels
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Carbon dioxide in atmosphere Respiration Photosynthesis Burning fossil fuels Forest fires Diffusion Animals (consumers) Deforestation Plants (producers) Carbon in plants (producers) Transportation Respiration Carbon in animals (consumers) Carbon dioxide dissolved in ocean Decomposition Carbon in fossil fuels Marine food webs Producers, consumers, decomposers 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? Carbon in limestone or dolomite sediments Compaction Processes Reservoir Pathway affected by humans Natural pathway Fig. 3-18, p. 68
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Nitrogen Cycles through the Biosphere: Bacteria in Action (1)
Nitrogen fixed Lightning Nitrogen-fixing bacteria Nitrification Denitrification
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Nitrogen Cycles through the Biosphere: Bacteria in Action (2)
Human intervention in the nitrogen cycle Additional NO and N2O Destruction of forest, grasslands, and wetlands Add excess nitrates to bodies of water Remove nitrogen from topsoil
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Processes Nitrogen in atmosphere Reservoir Pathway affected by humans Natural pathway Denitrification by bacteria Electrical storms Nitrogen oxides from burning fuel and using inorganic fertilizers Nitrogen in animals (consumers) Volcanic activity Nitrification by bacteria Nitrogen in plants (producers) Nitrates from fertilizer runoff and decomposition Decomposition Uptake by plants 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? Nitrate in soil Nitrogen loss to deep ocean sediments Nitrogen in ocean sediments Bacteria Ammonia in soil Fig. 3-19, p. 69
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Nitrogen input (teragrams per year)
300 Projected human input 250 200 Total human input 150 Nitrogen input (teragrams per year) Fertilizer and industrial use 100 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) 50 Nitrogen fixation in agroecosystems Fossil fuels 1900 1920 1940 1960 1980 2000 2050 Year Fig. 3-20, p. 70
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Phosphorus Cycles through the Biosphere
Cycles through water, the earth’s crust, and living organisms May be limiting factor for plant growth Impact of human activities Clearing forests Removing large amounts of phosphate from the earth to make fertilizers
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Processes Reservoir Pathway affected by humans Natural pathway Phosphates in sewage Phosphates in fertilizer Plate tectonics Phosphates in mining waste Runoff Runoff Sea birds Runoff Phosphate in rock (fossil bones, guano) Erosion Ocean food webs Animals (consumers) Phosphate dissolved in water Phosphate in shallow ocean sediments Phosphate in deep ocean sediments 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? Plants (producers) Bacteria Fig. 3-21, p. 71
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Sulfur Cycles through the Biosphere
Sulfur found in organisms, ocean sediments, soil, rocks, and fossil fuels SO2 in the atmosphere H2SO4 and SO4- Human activities affect the sulfur cycle Burn sulfur-containing coal and oil Refine sulfur-containing petroleum Convert sulfur-containing metallic mineral ores
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Sulfur dioxide in atmosphere Sulfuric acid and Sulfate deposited as acid rain Smelting Burning coal Refining fossil fuels Sulfur in animals (consumers) Dimethyl sulfide a bacteria byproduct Sulfur in plants (producers) Mining and extraction Uptake by plants Decay Sulfur in ocean sediments 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? Decay Processes Sulfur in soil, rock and fossil fuels Reservoir Pathway affected by humans Natural pathway Fig. 3-22, p. 72
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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.
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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)
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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
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Some Scientists Use Models to Simulate Ecosystems
Computer simulations and projections Field and laboratory research needed for baseline data
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We Need to Learn More about the Health of the World’s Ecosystems
Determine condition of the world’s ecosystems More baseline data needed
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