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ENVIRONMENTAL SCIENCE
CHAPTER 3: Ecosystems: What Are They and How Do They Work?
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Rainforest
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Core Case Study In class assignment
Tropical Rainforests are Disappearing Where are tropical rainforests found? How much of the earth’s land surface do they cover? Studies indicate they contain up to ______ of the world’s known terrestrial plant and animal species Define ecosystems About ________ of these forests have been destroyed by humans
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Core Case Study: Tropical Rainforests Are Disappearing (2)
Consequences of disappearing tropical rainforests __________ as species become extinct ______________: fewer trees to remove carbon dioxide from the atmosphere _______________: can lead to increase in tropical grasslands
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Define Ecological Tipping Point-
What is the ecological tipping point for this case study?
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Satellite image of the loss of tropical rain forest near the Bolivian City of Santa Cruz. Why is this an example of Natural Capital degradation? June 1975 May 2003 Fig. 3-1, p. 39
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3-1 What Keeps Us and Other Organisms Alive?
Concept 3-1A The four major components of the earth’s life-support system are the atmosphere (air), the hydrosphere (water), the geosphere (rock, soil, sediment), and the biosphere (living things). Concept 3-1B 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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Earth Has Four Major Life-Support Components
Atmosphere Hydrosphere Geosphere Biosphere
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Vegetation and animals Atmosphere Biosphere Soil Rock Crust Lithosphere Mantle Biosphere (living organisms) Figure 3.2: Natural capital: general structure of the earth showing that it consists of a land sphere (geosphere), air sphere (atmosphere), water sphere (hydrosphere), and life sphere (biosphere) (Concept 3-1A). . Core Atmosphere (air) Mantle Crust (soil and rock) Geosphere (crust, mantle, core) Hydrosphere (water) Fig. 3-2, p. 41
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Three Factors Sustain Life on Earth
1) One-way flow of high-quality energy from the sun 2) Cycling of matter or nutrients through parts of the biosphere 3) Gravity
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Solar Energy Reaching the Earth
Electromagnetic waves Visible light UV radiation Heat Natural greenhouse effect Energy in = energy out Human-enhanced global warming
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on this figure at CengageNOW.
Solar radiation Reflected by atmosphere UV radiation Radiated by atmosphere as heat Lower Stratosphere (ozone layer) Most absorbed by ozone Visible light Troposphere Heat radiated by the earth Heat Active Figure 3.3: Solar energy: flow of energy to and from the earth. About one-third of the incoming solar radiation is reflected back into space by clouds, particles in the atmosphere, and the earth’s surface. Another fifth of the incoming radiation is absorbed by ozone in the lower stratosphere (mostly UV radiation) and clouds and water vapor in the troposphere. Most of the remaining half of incoming solar radiation is absorbed by land and water on the earth’s surface. Carbon dioxide and other gases in the troposphere lead to a warming of the troposphere known as the natural greenhouse effect (Science Focus, p. 27). See an animation based on this figure at CengageNOW. Absorbed by the earth Greenhouse effect Fig. 3-3, p. 41
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Greenhouse Effect Animation
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3-2 What Are the Major Components of an Ecosystem?
Concept 3-2 Some organisms produce the nutrients they need, others get the nutrients they need by consuming other organisms, and some recycle nutrients back to producers by decomposing the wastes and remains of organisms.
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Ecology How organisms interact with biotic (pertaining to life) and abiotic environment (non-living) Focuses on specific levels of matter: Organisms Populations Communities Ecosystems Biosphere
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See an animation based on this figure at ThomsonNOW.
Biosphere Parts of the earth's air,water, and soil where life is found Which 5 levels does ecology focus on? Ecosystem A community of different species interacting with one another and with their nonliving environment of matter and energy 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 _______________________________ Cell The fundamental structural and functional unit of life Figure 3.3: Some levels of organization of matter in nature. Ecology focuses on five of these levels. See an animation based on this figure at ThomsonNOW. Molecule Chemical combination of two or more atoms of the same or different elements Smallest unit of a chemical element that exhibits its chemical properties Atom Stepped Art Fig. 3-4, p. 42
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Living and Nonliving Components (1)
Abiotic Water Air Nutrients Solar energy Rocks Heat
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Living and Nonliving Components (2)
Biotic Plants Animals Microbes Dead organisms Waste products of dead organisms
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animation based on this figure at CengageNOW.
Oxygen (O2) Precipitation Carbon dioxide (CO2) Producer Secondary consumer (fox) Primary consumer (rabbit) Active Figure 3.5 Major living (biotic) and non living (abiotic) components of an ecosystem in a field. See an animation based on this figure at CengageNOW. Producers Water Decomposers Soluble mineral nutrients Fig. 3-5, p. 43
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Trophic Levels (feeding levels) (1)
Producers – autotrophs Photosynthesis Consumers – heterotrophs Primary - herbivores Secondary - carnivores Third-level (tertiary) quartenary Omnivores
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Trophic Levels (2) Decomposers (ex. bacteria and fungi)
Release nutrients from the dead bodies of plants and animals Detrivores (ex. earthworms, some insects, vultures) Feed on the waste or dead bodies of organisms
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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 3.6: Various detritus feeders 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. 3-6, p. 44
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Production and Consumption of Energy
Photosynthesis Carbon dioxide + water + solar energy glucose + oxygen 6CO2 + 6H2O + solar E C6H12O6 + 6O2 Aerobic respiration (opposite) Glucose + oxygen carbon dioxide + water + energy
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Energy Flow and Nutrient Recycling
Ecosystems sustained through: One-way energy flow from the sun Nutrient recycling
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Main components of an ecosystem Solar energy Abiotic chemicals
(carbon dioxide, oxygen, nitrogen, minerals) Heat Heat Heat Decomposers (bacteria, fungi) Producers (plants) Active Figure 3.7: 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. 3-7, p. 45
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3-3 What Happens to Energy in an Ecosystem?
Concept 3-3 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 Flow in Ecosystems
Trophic levels Food chain Sequence of organisms, each of which serves as a source of food for the next Food web Network of interconnected food chains More complex than a food chain
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Food chain 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 Active Figure 3.8: 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 thermo dynamics (Concept 2-3B, p. 34). 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. 3-8, p. 46
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Humans Antarctic Food Web Sperm whale Blue whale Elephant seal Crabeater seal Killer whale Leopard seal Adelie penguin Emperor penguin Squid Petrel Active Figure 3.9 ; 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. See an animation based on this figure at CengageNOW. Question: Can you imagine a food web of which you are a part? Try drawing a simple diagram of it. Fish Carnivorous plankton Krill Herbivorous zooplankton Phytoplankton Fig. 3-9, p. 46
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Usable Energy by Trophic Level
Energy flow follows the second law of thermodynamics – energy lost as heat Biomass decreases with increasing trophic level Ecological efficiency – typically 10% Pyramid of energy flow
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Usable energy available
at each trophic level (in kilocalories) Heat Tertiary consumers (human) 10 Heat Secondary consumers (perch) 100 Heat Decomposers Heat Primary consumers (zooplankton) 1,000 Active Figure 3.10: Generalized pyramid of energy flow showing the decrease in usable chemical energy available at each succeeding trophic level in a food chain or web. This model assumes that with each transfer from one trophic level to another there is a 90% loss in usable energy to the environment in the form of low-quality heat. See an animation based on this figure at CengageNOW. Question: Why is a vegetarian diet more energy efficient than a meat-based diet? Heat 10,000 Producers (phytoplankton) What happens to amount of usable energy as you go up each level? Fig. 3-10, p. 47
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Two Kinds of Primary Productivity
Gross primary productivity (GPP): the rate at which an ecosystems producers convert solar E into chemical E in the form of biomass found in their tissues Net primary productivity (NPP)- rate at which producer’s use photosynthesis to produce and store chemical E minus the rate at which they use some of this stored E thru aerobic respiration Planet’s NPP limits number of consumers Humans use, waste, or destroy 10-55% of earth’s total potential NPP Human population is less than 1% of total biomass of earth’s consumers
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Terrestrial Ecosystems
Swamps and marshes Tropical rain forest Temperate forest Northern coniferous forest (taiga) Savanna Agricultural land Woodland and shrubland Temperate grassland Tundra (arctic and alpine) Desert scrub Extreme desert Aquatic Ecosystems Estuaries Figure 3.11: 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 ,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. 3-11, p. 48
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3-4 What Happens to Matter in an Ecosystem?
Concept 3-4 Matter, in the form of nutrients, cycles within and among ecosystems and in the biosphere, and human activities are altering these chemical cycles.
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Biogeochemical Cycles
Nutrient cycles Reservoirs- temporary storage sites for nutrients Connect all organisms through time
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Hydrologic Cycle Water cycle is powered by the sun
Evaporation Precipitation Transpiration - evaporates from plant surfaces Water vapor in the atmosphere comes from the oceans – 84% Over land, most of water reaching the atmosphere comes from transpiration
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Climate change Ice and snow Condensation Condensation Precipitation to land Transpiration from plants Evaporation from land Evaporation from ocean Surface runoff Increased flooding from wetland destruction Runoff Precipitation to ocean 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 Ocean Groundwater movement (slow) Figure 3.12: Natural capital: simplified model of the water or hydrologic cycle with major harmful impacts of human activities shown by red arrows and boxes. 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? Aquifer depletion from overpumping Processes Processes affected by humans Reservoir Pathway affected by humans Natural pathway Fig. 3-12, p. 49
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Science Focus: Water’s Unique Properties (1)
Holds water molecules together – hydrogen bonding Liquid over a wide temperature range Changes temperature slowly Requires large amounts of energy to evaporate
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Science Focus: Water’s Unique Properties (2)
Dissolves a variety of compounds Filters out UV light from the sun Adheres to a solid surface – allows capillary action in plants Expands as it freezes
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Carbon Cycle Based on carbon dioxide (CO2)
CO2 makes up 0.038% of atmosphere volume Major cycle processes Aerobic respiration Photosynthesis Fossil fuel combustion and deforestation Fossil fuels add CO2 to the atmosphere and contribute to global warming
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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 Marine food webs Producers, consumers, decomposers Decomposition Carbon in fossil fuels Figure 3.13: 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. 3-13, p. 51
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Nitrogen Cycle Multicellular plants and animals cannot utilize atmospheric nitrogen (N2) Nitrogen fixation Nitrification Ammonification Denitrification
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Processes Reservoir Pathway affected by humans Natural pathway Nitrogen in atmosphere Denitrification by bacteria Electrical storms Nitrogen in animals (consumers) Nitrogen oxides from burning fuel Volcanic activity Nitrification by bacteria Nitrogen in plants (producers) Nitrates from fertilizer runoff and decomposition Decomposition Uptake by plants Figure 3.14: Natural capital: simplified model of the nitrogen cycle in a terrestrial ecosystem, 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. 3-14, p. 52
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Phosphorus Cycle Does not cycle through the atmosphere
Obtained from terrestrial rock formations Limiting factor on land and in freshwater ecosystems Biologically important for producers and consumers
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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 chain Animals (consumers) Phosphate dissolved in water Phosphate in shallow ocean sediments Phosphate in deep ocean sediments Figure 3.15: 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. 3-15, p. 53
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Sulfur Cycle Most sulfur stored in rocks and minerals
Enters atmosphere through: Volcanic eruptions and processes Anaerobic decomposition in swamps, bogs, and tidal flats Sea spray Dust storms Forest fires
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Sulfur dioxide in atmosphere Sulfuric acid and Sulfate deposited as acid rain Burning coal Refining fossil fuels Smelting Sulfur in animals (consumers) Dimethyl sulfide a bacteria byproduct Sulfur in plants (producers) Mining and extraction Uptake by plants Sulfur in ocean sediments Figure 3.16: 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? Decay Decay Processes Sulfur in soil, rock and fossil fuels Reservoir Pathway affected by humans Natural pathway Fig. 3-16, p. 54
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3-5 How Do Scientists Study Ecosystems?
Concept 3-5 Scientists use field research, laboratory research, and mathematical and other models to learn about ecosystems.
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Field Research Collecting data in the field by scientists
Remote sensing devices Geographic information systems (GIS)
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Laboratory Research Simplified model ecosystems
Culture tubes Bottles Aquariums Greenhouses Chambers with controllable abiotic factors How well do lab experiments correspond with the greater complexity of real ecosystems?
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Scientific Studies of Ecosystems
Models Mathematical Computer simulations Models need to be fed real data collected in the field- baseline data Models must determine relationships among key variables
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Baseline Data to Measure Earth’s Health
Needed to measure changes over time Lacking for many ecosystems Call for massive program to develop baseline data
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Core Case Study In class assignment
Tropical Rainforests are Disappearing Where are tropical rainforests found? Near equator How much of the earth’s land surface do they cover? No more than 6% Studies indicate they contain up to _50%__ of the world’s known terrestrial plant and animal species Define ecosystems: communities of organisms interacting with one another and with the physical environment of matter and energy in which they live About _half__ of these forests have been destroyed by humans
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Core Case Study: Tropical Rainforests Are Disappearing (2)
Consequences of disappearing tropical rainforests Decreased biodiversity as species become extinct Accelerated global warming: fewer trees to remove carbon dioxide from the atmosphere Changes regional weather patterns: can lead to increase in tropical grasslands
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Ecological tipping point- Point in development of an environmental problem where a threshold level is reached, causing an irreversible shift in the behavior of a natural system. What is the ecological tipping point for this case study? Once the tropical rain forests are cleared, local weather patterns change so that rainforests can no longer be supported; areas become much less diverse tropical grasslands
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