Transcript Chapter 3
Chapter 3 Ecosystems: What are they and how do they work? Ecology “Study of how organisms interact with one another and with their nonliving environment” “Connections in nature” Ecology focuses on: organisms, populations, communities, ecosystems, and biosphere Perspective Small scale Organism: any form of life Multi-celled and single-celled Species: “groups of organisms that resemble one another in appearance, behavior, chemistry, and genetic makeup” 1.4 million named/identified species Probably 4-100 million total species Large scale Population: “a group of interacting individuals of the same species occupying a specific area” Community: all populations of different species in the same area Ecosystem: where populations interact with their living and non-living environment Genetic diversity – variations in genetic makeup Habitat – where the population lives Distribution / range: area the species covers Natural or artificial Biosphere: all of earth’s ecosystems (all life on earth) THE EARTH’S LIFE SUPPORT SYSTEMS The biosphere consists of several physical layers that contain: Air Water Soil Minerals Life Figure 3-6 Earth’s spheres Atmosphere: air around earth Hydrosphere: all of earth’s water Troposphere: inner layer of atmosphere – most air is here (78% nitrogen, 21% oxygen) Stratosphere: upper layer of atmosphere – contains ozone Liquid water Ice Water vapor Lithosphere: earth’s crust and upper mantle Biosphere: all life on earth Life sustaining processes Flow of energy Sun and other organisms (feeding) go in as highquality energy Continue flow as low-quality energy Back to space as heat Cycling of matter: C, N, P cycles Gravity The sun! Sun earth (through electromagnetic waves) Plants/bacteria take in energy to make food other organisms eat photosynthetic organisms Energy from the sun drives other systems on earth, like weather and water 1/1x109 of the sun’s energy makes it to earth Most of the E is reflected back 80% warms troposphere and cycles water 1% generates wind <0.1% is used for photosynthesis What Happens to Solar Energy Reaching the Earth? Solar energy flowing through the biosphere warms the atmosphere, evaporates and recycles water, generates winds and supports plant growth. Figure 3-8 Greenhouse gasses H2O, CO2, CH4, N2O, O3 Larger-wavelength light waves are absorbed and re-emitted by these molecules, heating them up Natural greenhouse effect keeps us warm (moon is 107 C in the day, -153 C at night) Ozone keeps some harmful UV rays away Human-produced greenhouse gasses add to the effect Biomes and aquatic life zones Biomes: “large regions… with distinct climates and specific species (especially vegetation) adapted to them” Forests, deserts, grasslands, tundra, etc Aquatic life zones: watery parts of the biosphere Freshwater life zones Ocean/marine life zones Components of ecosystems Abiotic: nonliving components – air, water, nutrients, solar E Biotic: consists of living components Producers: photosynthetic plants and bacteria Consumers: eat producers/other consumers Decomposers: break down dead organisms Range of tolerance: extremities of the conditions that a population can live Members within a population will have variation in range of tolerance Limits to population growth Limiting factor: what is holding something back 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 optimum range of tolerance” Precipitation Nutrients Temperature Factors That Limit Population Growth Availability of matter and energy resources can limit the number of organisms in a population. Figure 3-11 Producers! Producers = autotrophs Photoautotroph Chemoautotroph Make their own food Land = plants (mostly) Water = phytoplankton (mostly) Photosynthesis: CO2 + H2O C6H12O6 + O2 Chemosynthesis: make food from chemical E (bacteria near hydrothermal vents use H2S) Photosynthesis: A Closer Look Chlorophyll molecules in the chloroplasts of plant cells absorb solar energy. This initiates a complex series of chemical reactions in which carbon dioxide and water are converted to sugars and oxygen. Figure 3-A Consumers Heterotrophs: get energy from other organisms Primary: herbivores; directly eat producers Secondary: eat primary consumers Third and further level: eat secondary or higher consumers Omnivores: eat plants and animals Decomposers Passively “eat” dead organic matter Dentritivores: “insects and other scavengers that feed on the wastes or dead bodies of other organisms” Very important to our ecosystem Examples: Bacteria Fungi Worms Aerobic and anaerobic respiration Aerobic respiration: oxygen burns organic nutrients into CO2 and H2O C6H12O6 + 6O2 6CO2 + 6H2O + E Anaerobic respiration: breaking down organic compounds without oxygen; fermentation Instead of CO2 and H2O, end results are methane, ethyl alcohol, acetic acid, and hydrogen sulfide Two Secrets of Survival: Energy Flow and Matter Recycle An ecosystem survives by a combination of energy flow and matter recycling. Figure 3-14 Biodiversity Biodiversity: “renewable resource” Four components: Functional diversity – bio and chem processes Ecological diversity – variety of ecosystems Genetic diversity – variety of genetic material in a species/population Species diversity – variety of species in different habitats Biodiversity loss HIPPO!!! Habitat destruction and degradation Invasive species Pollution Population growth (human) Overexploitation (overhunting, overconsumption) Why care? Two approaches: Ecosystem approach – protect populations of species in their natural habitats Species approach – protect species from premature exticntion The Ecosystem Approach Goal Protect populations of species in their natural habitats Strategy Preserve sufficient areas of habitats in different biomes and aquatic systems Tactics •Protect habitat areas through private purchase or government action •Eliminate or reduce populations of nonnative species from protected areas •Manage protected areas to sustain native species •Restore degraded ecosystems The Species Approach Goal Protect species from premature extinction Strategies •Identify endangered species •Protect their critical habitats Tactics •Legally protect endangered species •Manage habitat •Propagate endangered species in captivity •Reintroduce species into suitable habitats Fig. 3-16, p. 63 Energy flow in ecosystems Little matter is wasted in ecosystems Food chain – energy and nutrients move through an ecosystem Trophic level: where a species falls on a food web Food web – shows more connections than chain, relations between species First Trophic Level Second Trophic Level Third Trophic Level Producers (plants) Primary consumers (herbivores) Secondary consumers (carnivores) Heat Heat Fourth Trophic Level Tertiary consumers (top carnivores) Heat Solar energy Heat Heat Heat Heat Heat Detritivores (decomposers and detritus feeders) Fig. 3-17, p. 64 Humans Blue whale Sperm whale Crabeater seal Elephant seal Killer whale Leopard seal Adelie penguins Emperor penguin Petrel Fish Squid Carnivorous plankton Krill Phytoplankton Herbivorous plankton Fig. 3-18, p. 65 Energy flow Biomass – dry weight of all organic matter in organisms of a food chain/web Each time E is transferred, heat energy is lost Ecologic efficiency – usually about 10%, can be between 2% and 40% Heat Tertiary consumers (human) Heat Decomposers Heat 10 Secondary consumers (perch) Heat 100 1,000 Primary consumers (zooplankton) Heat 10,000 Producers Usable energy (phytoplankton) Available at Each tropic level (in kilocalories) Fig. 3-19, p. 66 Productivity Gross primary productivity (GPP) – “the rate at which an ecosystem’s producers convert solar energy into chemical energy” Net primary productivity (NPP) – “the rate at which producers use photosynthesis to store energy minus the rate at which they use some of this stored energy” NPP = GPP – R (energy used in respiration) NPP limits number of consumers Humans use/waste/destroy 27% of earth’s potential NPP Humans, pets, and livestock make up 98% of earth’s vertebrate biomass Gross primary productivity (grams of carbon per square meter) Fig. 3-20, p. 66 Sun Respiration Gross primary production Growth and reproduction Energy lost and unavailable to consumers Net primary production (energy available to consumers) Fig. 3-21, p. 66 What are nature’s three most productive and three least productive systems? Figure 3-22 Soil Soil – eroded rock, mineral nutrients, decaying organic matter, water, air, and organisms Weathering – rock breaking down into fragments and particles by physical, chemical, and biological processes Support for plants and other life, filters water, and helps remove CO2 Humans have accelerated natural soil erosion 1/3 to 1/2 of world’s croplands are losing topsoil faster than it’s being renewed naturally Soil layers “Soil horizons” Soil profile O horizon – organic material A horizon – “humus” = partially decomposed plants and animals B and C horizon – inorganic material Pores contain air and water Infiltration – water moving down through the soil Leaching – water dissolves minerals and organic matter and seeps down in the soil Oak tree Fern O horizon Leaf litter Wood sorrel Lords and ladies Dog violet Grasses and small shrubs Earthworm Millipede Honey fungus Mole Organic debris builds up Rock fragments Moss and lichen A horizon Topsoil B horizon Subsoil Bedrock Immature soil Regolith Young soil Pseudoscorpion C horizon Mite Parent material Nematode Root system Mature soil Red Earth Mite Springtail Actinomycetes Fungus Bacteria Fig. 3-23, p. 68 Some Soil Properties Soils vary in the size of the particles they contain, the amount of space between these particles, and how rapidly water flows through them. Figure 3-25 Soil properties Soil texture Clay particles = small Silt particles = medium Sand particles = large Loam = mix of all three, best for growing plants Soil Profiles of the Principal Terrestrial Soil Types Figure 3-24 Matter cycling Nutrients – “elements and compounds that organisms need to live, grow, and reproduce” Biogeochemical cycles aka nutrient cycles Driven by solar E and gravity Water cycle AKA hydrologic cycle Powered by gravity and E from sun About 84% water vapor from oceans Where does the water go? Glaciers Aquifers Surface runoff – streams lakes oceans Runoff causes natural erosion Carries nutrients in/between ecosystems Water is naturally purified in the water cycle Cycle of natural renewal of water quality Water’ Unique Properties There are strong forces of attraction between molecules of water. Water exists as a liquid over a wide temperature range. Liquid water changes temperature slowly. It takes a large amount of energy for water to evaporate. Liquid water can dissolve a variety of compounds. Water expands when it freezes. Effects of humans on the water cycle Withdraw large amounts of freshwater from rivers, lakes, and underground, sometimes faster than it is replaced Clearing land / destroying wetland Increases runoff – more chemicals and erosion Reduces ability to refill groundwater supplies Increases potential to flood Adding nutrients and pollutants Warmer climate (global warming) is causing the water cycle to speed up Change weather patterns Intensify global warming Carbon cycle Based on CO2 CO2 helps regulate temperature on earth Producers remove CO2, consumers put it back into the cycle Long-term carbon sinks Oil deposits Marine shells Human effects Clear more vegetation than can grow back, which reduces the CO2 taken out of the atmosphere Burn oil/wood which puts more CO2 into the atmosphere Effects of Human Activities on Carbon Cycle We alter the carbon cycle by adding excess CO2 to the atmosphere through: Burning fossil fuels. Clearing vegetation faster than it is replaced. Figure 3-28 Nitrogen cycle N is an important element to some organic molecules (nucleic acids and amino acids) Nitrogen is “fixed” by bacteria (or lightning), turning N2 into NH3 (plants can take up NH4+) NH3 can be turned into NO2- (harmful to plants) into NO3- (helpful to plants) by other bacteria Decomposers convert N in organic compounds back into NH3 Yet more bacteria can turn NH3 back into N2 or N2 O Effects of humans on the nitrogen cycle Add large amounts of NO into atmosphere when we burn fuels at high temps, which can turn into NO2, which can turn into HNO3 (acidic) Livestock and fertilizer adds N2O to the atmosphere (bacteria breaking down waste) which can deplete ozone or warm atmosphere NO3- from fertilizers can contaminate ground water Destroying plants releases more N into the atmosphere Agricultural and sewage runoff changes nitrate levels in aquatic ecosystems Harvesting or irrigating N-rich crops remove N from soil Phosphorus cycle Phosphorus needed in DNA and ATP Slow cycle, little P circulates in atmosphere, flows mostly from land into oceans P is typically found in salts (with PO43-) in rocks PO43- from rocks wash into oceans, get deposited as sediment, and will show up millions of years later as rocks shift back to surface Plants get PO43- from soil (usually a limiting growth factor) and we get P from plants, and waste P leaves us in urine PO43--salts are not very soluble in water, so aquatic plant life is limited by P levels Effect of humans on phosphorus cycle Mining for PO43- for fertilizers removes large quantities in a short period Destruction of tropical forests decreases amount of PO43- available in tropical soil PO43- runoff from fertilizers, livestock, and sewage disrupts aquatic systems Sulfur cycle A lot of sulfur is in rocks underground or in (SO42-) salts under ocean sediments H2S (toxic) released form volcanoes (as is SO2) and some organic matter broken down by decomposers SO42- can enter the atmosphere from sea spray, dust storms, and forest fires Plants absorb SO42- from the soil to use for some proteins Some marine algae produce CH3SCH3 which can form the starting points for cloud condensation SO2 and SO3 in the air can make H2SO4 (acidic) In anaerobic environments, SO42- can be converted to S2where it can react with metals to be deposited as rock Effects of humans on the sulfur cycle 3 ways we release sulfur into the atmosphere Burning coal and oil that contains sulfur Refining petroleum containing sulfur Converting metallic mineral ores that contain sulfur into free metal Gaia hypothesis The earth is very complex, with many different systems working together in intricate ways Does earth behave like a living thing? Strong Gaia hypothesis – life controls the earth’s life-sustaining processes Not widely supported Weak Gaia hypothesis – life influences the earth’s life-sustaining processes Widely supported HOW DO ECOLOGISTS LEARN ABOUT ECOSYSTEMS? Ecologist go into ecosystems to observe, but also use remote sensors on aircraft and satellites to collect data and analyze geographic data in large databases. Geographic Information Systems Remote Sensing Ecologists also use controlled indoor and outdoor chambers to study ecosystems Geographic Information Systems (GIS) A GIS organizes, stores, and analyzes complex data collected over broad geographic areas. Allows the simultaneous overlay of many layers of data. Figure 3-33 Systems Analysis Ecologists develop mathematical and other models to simulate the behavior of ecosystems. Figure 3-34 Importance of Baseline Ecological Data We need baseline data on the world’s ecosystems so we can see how they are changing and develop effective strategies for preventing or slowing their degradation. Scientists have less than half of the basic ecological data needed to evaluate the status of ecosystems in the United Sates (Heinz Foundation 2002; Millennium Assessment 2005).