Chapter 3Ecosystems: What AreThey and How Do They Work?
Chapter Overview Questions What is ecology? What basic processes keep us and other organisms alive? What are the major components of an ecosystem? What happens to energy in an ecosystem? What are soils and how are they formed? What happens to matter in an ecosystem? How do scientists study ecosystems?
Updates Online The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. InfoTrac: Rescuers race to save Central American frogs. Blade (Toledo, OH), August 6, 2006. InfoTrac: Climate change puts national parks at risk. Philadelphia Inquirer, July 13, 2006. InfoTrac: Deep-Spied Fish: Atlantic Expeditions Uncover Secret Sex Life of Deep-Sea Nomads. Ascribe Higher Education News Service, Feb 21, 2006. Environmental Tipping Points NatureServe: Ecosystem Mapping U.S. Bureau of Land Management: Soil Biological Communities
Core Case Study: Have You Thanked the Insects Today? Many plant species depend on insects for pollination. Insect can control other pest insects by eating them Figure 3-1
Core Case Study: Have You Thanked the Insects Today? …ifall insects disappeared, humanity probably could not last more than a few months [E.O. Wilson, Biodiversity expert]. Insect’s role in nature is part of the larger biological community in which they live.
THE NATURE OF ECOLOGY Ecologyis a study of connections in nature. How organisms interact with one another and with their nonliving environment. Figure 3-2
Universe Galaxies Solar systems Biosphere Planets Earth Biosphere Ecosystems Ecosystems Communities Populations Organisms Realm of ecology Communities Organ systems Organs Tissues Cells Protoplasm Populations Molecules Atoms OrganismsSubatomic Particles Fig. 3-2, p. 51
Organisms and Species Organisms, the different forms of life on earth, can be classified into different species based on certain characteristics. Figure 3-3
Other animalsKnown species 281,0001,412,000Insects751,000 Fungi 69,000 Prokaryotes 4,800 Plants 248,400 Protists 57,700 Fig. 3-3, p. 52
Case Study: Which Species Run the World? Multitudes of tiny microbes such as bacteria, protozoa, fungi, and yeast help keep us alive. Harmful microbes are the minority. Soil bacteria convert nitrogen gas to a usable form for plants. They help produce foods (bread, cheese, yogurt, beer, wine). 90% of all living mass. Helps purify water, provide oxygen, breakdown waste. Lives beneficially in your body (intestines, nose).
Populations, Communities, and Ecosystems Members of a species interact in groups called populations. Populations of different species living and interacting in an area form a community. A community interacting with its physical environment of matter and energy is an ecosystem.
Populations A population is a group of interacting individuals of the same species occupying a specific area. The space an individual or population normally occupies is its habitat. Figure 3-4
Populations Genetic diversity In most natural populations individuals vary slightly in their genetic makeup. Figure 3-5
THE EARTH’S LIFE SUPPORT SYSTEMS Thebiosphere consists of several physical layers that contain: Air Water Soil Minerals Life Figure 3-6
Oceanic Continental Crust Crust AtmosphereVegetation Biosphereand animals Lithosphere Soil Upper mantle Rock Crust Asthenosphere Lower mantle Core Mantle Crust (soil and rock) Biosphere Hydrosphere (living and dead (water) organisms) Lithosphere Atmosphere (crust, top of upper mantle) (air) Fig. 3-6, p. 54
Biosphere Atmosphere Membrane of air around the planet. Stratosphere Lower portion contains ozone to filter out most of the sun’s harmful UV radiation. Hydrosphere All the earth’s water: liquid, ice, water vapor Lithosphere The earth’s crust and upper mantle.
What Sustains Life on Earth? Solar energy, the cycling of matter, and gravity sustain the earth’s life. Figure 3-7
BiosphereCarbon Phosphorus Nitrogen Water Oxygen cycle cycle cycle cycle cycle Heat in the environment Heat Heat Heat Fig. 3-7, p. 55
What Happens to Solar Energy Reaching the Earth? Solarenergy flowing through the biosphere warms the atmosphere, eva porates and recycles water, generates winds and supports plant growth. Figure 3-8
Solar radiation Energy in = Energy out Reflected by atmosphere (34% ) Radiated byUV radiation atmosphere as heat (66%) Lower Stratosphere Absorbed (ozone layer) by ozone Visible Troposphere Greenhouse Light effect Heat Absorbed by the Heat radiated earth by the earth Fig. 3-8, p. 55
ECOSYSTEM COMPONENTS Lifeexists on land systems called biomes and in freshwater and ocean aquatic life zones. Figure 3-9
Average annual precipitation 100–125 cm (40–50 in.) 75–100 cm (30–40 in.) 50–75 cm (20–30 in.)4,600 m (15,000 ft.) 25–50 cm (10–20 in.)3,000 m (10,000 ft.) below 25 cm (0–10 in.) 1,500 m (5,000 ft.) Coastal Sierra Great Rocky Great Mississippi Appalachian mountain Nevada American Mountains Plains River Valley Mountains ranges Mountains DesertCoastal chaparral Coniferous Desert Coniferous Prairie Deciduousand scrub forest forest grassland forest Fig. 3-9, p. 56
Nonliving and Living Components of Ecosystems Ecosystems consist of nonliving (abiotic) and living (biotic) components. Figure 3-10
Oxygen Sun (O2) Producer Carbon dioxide (CO2) Secondary consumer Primary (fox) consumer (rabbit)Precipitation Producers Falling leaves and twigs Soil decomposers Water Fig. 3-10, p. 57
Factors That Limit Population Growth Availabilityof matter and energy resources can limit the number of organisms in a population. Figure 3-11
Lower limit of Upper limit of tolerance tolerance No Few Abundance of organisms Few Noorganisms organisms organisms organismsPopulation size Zone of Zone of Optimum range Zone of Zone ofintolerance physiological physiological intolerance stress stress Low Temperature High Fig. 3-11, p. 58
Factors That Limit Population Growth The physical conditions of the environment can limit the distribution of a species. Figure 3-12
Producers: Basic Source of All Food Mostproducers capture sunlight to produce carbohydrates by photosynthesis:
Producers: Basic Source of All Food Chemosynthesis: Some organisms such as deep ocean bacteria draw energy from hydrothermal vents and produce carbohydrates from hydrogen sulfide (H2S) gas .
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
Sun Chloroplast in leaf cell Chlorophyll H2O Light-dependent O2 Reaction Energy storage and release (ATP/ADP) Light- Glucose CO2 independent reaction6CO2 + 6 H2O Sunlight C6H12O6 + 6 Fig. 3-A, p. 59
Consumers: Eating and Recycling to Survive Consumers (heterotrophs) get their food by eating or breaking down all or parts of other organisms or their remains. Herbivores • Primary consumers that eat producers Carnivores • Primary consumers eat primary consumers • Third and higher level consumers: carnivores that eat carnivores. Omnivores • Feed on both plant and animals.
Decomposers and Detrivores Decomposers: Recycle nutrients in ecosystems. Detrivores: Insects or other scavengers that feed on wastes or dead bodies. Figure 3-13
Scavengers Decomposers Termite Bark beetle Carpenter and engraving ant carpenterLong-horned galleries ant work Dry rot fungusbeetleholes Wood reduced to Mushroom powderTime Powder broken down by decomposersprogression into plant nutrients in soil Fig. 3-13, p. 61
Aerobic and Anaerobic Respiration: Getting Energy for Survival Organisms break down carbohydrates and other organic compounds in their cells to obtain the energy they need. This is usually done through aerobic respiration. The opposite of photosynthesis
Aerobic and Anaerobic Respiration: Getting Energy for Survival Anaerobic respiration or fermentation: Some decomposers get energy by breaking down glucose (or other organic compounds) in the absence of oxygen. The end products vary based on the chemical reaction: • Methane gas • Ethyl alcohol • Acetic acid • 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
Abiotic chemicals Heat Heat (carbon dioxide, Solar oxygen, nitrogen, energy minerals) Heat Decomposers Producers(bacteria, fungi) (plants) Consumers (herbivores, Heat Heat carnivores) Fig. 3-14, p. 61
Biodiversity Loss and Species Extinction: Remember HIPPOH for habitat destruction and degradation I for invasive species P for pollution P for human population growth O for overexploitation
Why Should We Care About Biodiversity? Biodiversity provides us with: Natural Resources (food water, wood, energy, and medicines) Natural Services (air and water purification, soil fertility, waste disposal, pest control) Aesthetic pleasure
Solutions Goals,strategies and tactics for protecting biodiversity. Figure 3-16
The Ecosystem Approach The Species Approach Goal Goal Protect populations Protect species of species in their from premature natural habitats extinction Strategy Strategies Preserve sufficient •Identify endangered areas of habitats in species different biomes and •Protect their critical aquatic systems habitats Tactics Tactics •Protect habitat areas •Legally protect through private endangered species purchase or government action •Manage habitat •Eliminate or reduce populations of nonnative species •Propagate from protected areas endangered •Manage protected species in captivity areas to sustain native species •Reintroduce •Restore degraded species into ecosystems suitable habitats Fig. 3-16, p. 63
ENERGY FLOW IN ECOSYSTEMS Foodchains and webs show how eaters, the eaten, and the decomposed are connected to one another in an ecosystem. Figure 3-17
First Trophic Second Trophic Third Trophic Fourth Trophic Level Level Level Level Producers Primary Secondary Tertiary (plants) consumers consumers consumers (herbivores) (carnivores) (top carnivores) Heat Heat Heat Solarenergy Heat Heat Heat Heat Detritivores Heat (decomposers and detritus feeders) Fig. 3-17, p. 64
Food Webs Trophic levels are interconnected within a more complicated food web. Figure 3-18
Blue whale Humans Sperm whale Crabeater Elephant seal seal Killer whale Leopard sealAdeliepenguins Emperor penguin Squid Petrel Fish Carnivorous plankton Krill Herbivorous plankton Phytoplankton Fig. 3-18, p. 65
Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs Inaccordance with the 2nd law of thermodynamics, there is a decrease in the amount of energy available to each succeeding organism in a food chain or web.
Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs Ecological efficiency: percentage of useable energy transferred as biomass from one trophic level to the next. Figure 3-19
Productivity of Producers: The Rate Is Crucial Gross primary production (GPP) Rate at which an ecosystem’s producers convert solar energy into chemical energy as biomass. Figure 3-20
Gross primary productivity(grams of carbon per square meter) Fig. 3-20, p. 66
Net Primary Production (NPP) NPP = GPP – R Rate at which producers use photosynthesis to store energy minus the rate at which they use some of this energy through respiration (R). Figure 3-21
Sun Energy lost Respiration and unavailable to consumersGross primaryproduction Net primary production Growth and reproduction (energy available to consumers) Fig. 3-21, p. 66
What are nature’s three most productive and three least productive systems? Figure 3-22
Terrestrial Ecosystems Swamps and marshes Tropical rain forest Temperate forest North. coniferous forest Savanna Agricultural landWoodland and shrubland Temperate grasslandTundra (arctic and alpine) Desert scrub Extreme desert Aquatic Ecosystems Estuaries Lakes and streams Continental shelf Open ocean Average net primary productivity (kcal/m2 /yr) Fig. 3-22, p. 67
Stratigraphy Background Study of rock (ohhh, exciting) A grouping exercise Rock layers provide a quick look at regional climates and geological events throughout history Windows into climate conditions during specific times Ex. Of sedimentary rock layer: Grand Canyon (pre-cambian and Paleozoic) Rock-stratigraphic unit or rock unit Individual band with its own specific characteristics and position Formation: rock units stacked up vertically; composed of many rock units grouped into a section with same physical properties (takes thousands to millions of years to create) Lithology Visual study of rock’s physical characteristics using a handheld magnifying glass or low- power microscope Three Main rock type: Igneous, sedimentary, metamorphic Rock formations can be matched by their physical characteristics: Grain size and shape Grain orientation Mineral content Sedimentary structure Color weathering
Igneous Rock Rock formed by the cooling and hardening of molten rock (magma), deep in the Earth, blasted out during an eruption; 95% of the first 10 mi of crust six minerals: quartz, feldspar, pyroxene, olivine, amphibole, and mica (Si, Ca, Na, K, Mg, Fe, Al, H, O) Two type: • Felsic: affected by heat (magma rising or friction b/t plates); lots of Si minerals (quartz and granite) • Mafic: high levels of Mg and Fe containing minerals Sedimentary Rock Formed from rocks and soils from other locations compressed with the remains of dead organisms Fine-grained texture b/c they are layered or settled by water or wind Lithification: process that makes lithified soil (made of silt, sand, and organic compounds) by compaction and cementation Diagenesis: process that lithifies sediments; controlled by temperature (200’C); unstable minerals recrystallize into more stable matrix form or are chemically changed, like organic matter, into coal or hydrocarbons. • 1. Compaction, 2. cementation, 3. recrystallization, 4. chemical changes (ex oxidation and reduction) Detritus: any type of rock that has been moved from its original location Metamorphic Rock Formed when rocks (igneous or sedimentary) originally of one type change into a different type by heat and/or pressure 3 main causes/forces: internal heat of earth, weight of overlying rock, and horizontal pressures from previously changed rock Example: MARBLE and SLATE
SOIL: A RENEWABLE RESOURCE Soilis a slowly renewed resource that provides most of the nutrients needed for plant growth and also helps purify water. Soil formation begins when bedrock is broken down by physical, chemical and biological processes called weathering. Mature soils, or soils that have developed over a long time are arranged in a series of horizontal layers called soil horizons.
Soil Basics Renewable but very slowly (climate is factor) 1 cm of soil can take 15-100 years to form Mixture of six components 1) Eroded rock 2) Mineral nutrients 3) Decaying organic matter 4) Water 5) Air 6) Living organisms (microscopic decomp) 3 major roles of soil Provides Nutrients Filters water Stores water
3 Soil Horizons (Horizon 0) Surface litter layer Freshly fallen/partially decomposed (leaves, twigs, crop wastes, animal waste) Brown or black color Horizon A Topsoil Porous mix of partially decomposed organic matter (HUMUS) Horizon B Horizon C
Wood Oak tree sorrel Lords and Dog violet Organic debris ladies Grasses and builds up Rock small shrubs fragments Earthworm Fern Millipede Moss and Honey fungus lichenO horizon MoleLeaf litterA horizonTopsoilB horizon BedrockSubsoil Immature soil RegolithC horizon Young soil PseudoscorpionParent Mitematerial Nematode Root system Actinomycetes Red Earth Mite Fungus Mature soil Bacteria Springtail Fig. 3-23, p. 68
Layers in Mature Soils Infiltration: the downward movement of water through soil. Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower layers. The soil type determines the degree of infiltration and leaching.
Soil Profiles of thePrincipal Terrestrial Soil Types Figure 3-24
Mosaic of closely packed pebbles, boul ders Weak humus- mineral mixture Alkaline, dark, Dry, brown to and rich reddish-brown in humus with variable accumulations Clay, calciu of clay, calcium m and compounds carbonate, and Desert Soil Grassland Soil soluble salts(hot, dry climate) semiarid climate) Fig. 3-24a, p. 69
Acidic light-colored humus Iron and aluminum compounds mixed with clayTropical Rain Forest Soil(humid, tropical climate) Fig. 3-24b, p. 69
Forest litter leaf mold Humus-mineral mixture Light, grayish- brown, silt loam Dark brown firm clayDeciduous Forest Soil(humid, mild climate) Fig. 3-24b, p. 69
Acid litter and humus Light-colored and acidic Humus and iron and aluminum compoundsConiferous Forest Soil (humid, cold climate) Fig. 3-24b, p. 69
Some Soil Properties Soilsvary 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
Sand Silt Clay0.05–2 mm 0.002–0.05 mm less than 0.002 mm diameter diameter Diameter Water Water High permeability Low permeability Fig. 3-25, p. 70
MATTER CYCLING IN ECOSYSTEMS Nutrient Cycles: Global Recycling Global Cycles recycle nutrients through the earth’s air, land, water, and living organisms. Nutrients are the elements and compounds that organisms need to live, grow, and reproduce. Biogeochemical cycles move these substances through air, water, soil, rock and living organisms.
Rain clouds Condensation Transpiration Evaporation Precipitation Transpiration to land from plantsPrecipitation Precipitation Evaporation Surface runoff from land Evaporation Runoff from ocean Precipitation (rapid) to oceanInfiltration and SurfacePercolation runoff (rapid) Groundwater movement (slow) Ocean storage Fig. 3-26, p. 72
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 Human Activities on Water Cycle We alter the water cycle by: Withdrawing large amounts of freshwater. Clearing vegetation and eroding soils. Polluting surface and underground water. Contributing to climate change.
The Carbon Cycle:Part of Nature’s Thermostat Figure 3-27
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
CO2 emissions from fossil fuels (billion metric tons of carbon equivalent) Year Low projection High projectionFig. 3-28, p. 74
The Nitrogen Cycle: Bacteria in Action Figure 3-29
Gaseous nitrogen (N2) in atmosphere Food webs on landNitrogen fixation Fertilizers Uptake by Loss by Uptake by autotrophs Excretion, death, autotrophs denitrification decomposition Ammonia, ammonium in soil Nitrogen-rich wastes, Nitrate in soil remains in soil Nitrification Ammonification Loss by Loss by leaching leaching Nitrite in soil Nitrification Fig. 3-29, p. 75
Effects of Human Activities on the Nitrogen Cycle We alter the nitrogen cycle by: Adding gases that contribute to acid rain. Adding nitrous oxide to the atmosphere through farming practices which can warm the atmosphere and deplete ozone. Contaminating ground water from nitrate ions in inorganic fertilizers. Releasing nitrogen into the troposphere through deforestation.
Effects of Human Activities on the Nitrogen Cycle Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined. Figure 3-30
Global nitrogen (N) fixation (trillion grams) Nitrogen fixation by natural processes Year Fig. 3-30, p. 76
mining Fertilizerexcretion Guano agriculture uptake by weathering uptake by autotrophs autotrophs Marine Dissolved leaching, runoff Dissolved Land Food in Ocean in Soil Water, Food Webs Water Lakes, Rivers Webs death, death, decomposition decompositionsedimentation settling out weathering uplifting over geologic time Marine Sediments Rocks Fig. 3-31, p. 77
Effects of Human Activities on the Phosphorous Cycle We remove large amounts of phosphate from the earth to make fertilizer. We reduce phosphorous in tropical soils by clearing forests. We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers.
Sulfur Water Acidic fog and Sulfuric acid precipitation trioxide Ammonia Ammonium Oxygen sulfateSulfur dioxide Hydrogen sulfide Plants Dimethyl Volcano sulfide Industries AnimalsOcean Sulfate salts Metallic Decaying matter Sulfur sulfide deposits Hydrogen sulfide Fig. 3-32, p. 78
Effects of Human Activities on the Sulfur Cycle We add sulfur dioxide to the atmosphere by: Burning coal and oil Refining sulfur containing petroleum. Convert sulfur-containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment.
The Gaia Hypothesis: Is the Earth Alive? Some have proposed that the earth’s various forms of life control or at least influence its chemical cycles and other earth-sustaining processes. The strong Gaia hypothesis: life controls the earth’s life-sustaining processes. The weak Gaia hypothesis: life influences the earth’s life-sustaining processes.
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, an d analyzes complex data collected over broad geographic areas. Allows the simultaneous overlay of many layers of data. Figure 3-33
Critical nesting site locations USDA Forest Service USDA Private Forest Service owner 1 Private owner 2 Topography Habitat type ForestWetland Lake Grassland Real world Fig. 3-33, p. 79
Systems Analysis Ecologists develop mathematical and other models to simulate the behavior of ecosystems. Figure 3-34
Define objectives Systems Identify and inventory variablesMeasurement Obtain baseline data on variables Make statistical analysis of Data relationships among variables Analysis Determine significant interactions System Objectives Construct mathematical model Modeling describing interactions among variables System Run the model on a computer, Simulation with values entered for different Variables System Evaluate best ways to achieveOptimization objectives Fig. 3-34, p. 80
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).