Ecosystems: What Are They and How Do They Work

Ecosystems: What Are They and How Do They WorkChapter 3 (Miller and Spoolman, 2010)Core Case Study: Tropical Rain Forests Are DisappearingCover about 2% of the earths land surfaceContain about 50% of the worlds known plant and animal speciesAt 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 effectsReduce biodiversityAccelerate global warmingChange regional weather patternsOnce a tipping point is reached, tropical rainforests will become less diverse tropical grasslandsFigure 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).

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.Cells Are the Basic Units of LifeCell smallest and most fundamental structural units of life.

Cell Theory

Eukaryotic cell

Prokaryotic cell

Figure 3.2Natural 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.

Species Make Up the Encyclopedia of LifeFor a groups of sexually reproducing organisms, a species is a set of individuals that can mate and produce fertile offspring.1.8 Million species identifiedInsects make up most of the known speciesPerhaps 1014 million species not yet identifiedScientists have developed a distinctive system for classifying and naming each species.Ecologists Study Connections in NatureEcology 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 organizationPopulation (Figure 3-4)Genetic diversity (Figure 3-5)HabitatCommunityEcosystemBiosphere

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

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

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.

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

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.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. The Earths 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 CH4Stratosphere, from 17-50 km (11-31 mi)Lower portion contains ozone (O3)

Hydrosphere all water on or near the earths surface.Most in oceans which cover 71 % of the globe.Liquid, ice, and water vapor

The Earths Life-Support System Has Four Major Components (2)GeosphereIntensely 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.

Figure 3.6Natural capital: general structure of the earth showing that it consists of a land sphere, air sphere, water sphere, and life sphere.Life Exists on Land and in WaterBiomes 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 zonesLakes and streams

Marine life zonesCoral reefsEstuariesDeep ocean

Figure 3.7Major biomes found along the 39th parallel across the United States. The differences reflect changes in climate, mainly differences in average annual precipitation and temperature.Three Factors Sustain Life on EarthOne-way flow of high-quality energy beginning with the sun

Cycling of matter or nutrients

GravityHolds on to the atmosphere and enables the movement and cycling of chemicals through the air, water, soil, and organisms.What Happens to Solar Energy Reaching the Earth?UV, visible, and IR energyMuch is reflected by the atmosphere, only 1 % reaches surfaceLights 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 UVAbsorbed by the earthReflected by the earthRadiated by the atmosphere as heatNatural greenhouse effectCarbon dioxide, methane (CH4), nitrous oxide (N2O), and ozone (O3)Human activities are increasing these gases.Figure 3.8Solar capital: flow of energy to and from the earth.

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.

Ecosystems Have Living and Nonliving Components (1)AbioticWaterAirNutrientsRocksHeatSolar energy

BioticLiving and once living biological componentsplants animals and microbes.Dead organisms, dead part of organisms, and waste products of organisms.

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

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).Figure 3.10Range of tolerance for a population of organisms, such as fish, to an abiotic environmental factorin 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?

Several Abiotic Factors Can Limit Population GrowthLimiting factor specific factor(s) important in regulating the growth of a population.Terrestrial ecosytems: precipitation, soil nutrients, temperatureAquatic ecosystems: temperature, sunlight, nutrients, DO, and salinity.Limiting factor principleToo 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 toleranceOne way in which population control (one of the scientific principles of sustainability) is achieved

Producers and Consumers Are the Living Components of Ecosystems (1)Trophic levelProducers, or autotrophsPhotoautotrophs: plants, algae, aquatic plants, and phytoplankton,PhotosynthesisChemoautotrophs: mostly specialized bacteriaChemosynthesis (see p. 59 for details)Consumers, or heterotrophsPrimarySecondaryThird and higher levelOmnivoresDecomposersPrimarily bacteria and fungiDetritus feeders, or detritivoresMites, earthworms, some insects, catfish, and larger scavengers like vultures.

Figure 3.11Various 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.

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 fermentationEnd products include CH4, ethyl alcohol (C2H6O), acetic acid (C2H4O2), or hydrogen sulfide (H2S).Energy Flow and Nutrient Cycling Sustain Ecosystems and the BiosphereEcosystems 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 fromStructure and function of natural ecosystemsLaw of conservation of matter, andTwo law of thermodynamics.Figure 3.12Natural capital: the main structural components of an ecosystem (energy, chemicals, and organisms). Nutrient cycling and the flow of energyfirst from the sun, then through organisms, and finally into the environment as low-quality heatlink these components.

Science Focus: Many of the Worlds Most Important Species Are Invisible to UsMicroorganisms, or microbes, are a vital part of earths natural capital. Explain.BacteriaProtozoaFungiPhytoplankton3-4 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.Energy Flows Through Ecosystems in Food Chains and Food WebsChemical 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.Figure 3.13A 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?

Figure 3.14Greatly 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.

Usable Energy Decreases with Each Link in a Food Chain or WebBiomass 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 worlds 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.

39Figure 3.15Generalized 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?

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.

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 highUpwellings (water moving up from depths to surface)Open ocean, low NPP, but high absolute amount. Why?

Figure 3.16Estimated 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 natures three most productive and three least productive systems? (Data from R. H. Whittaker, Communities and Ecosystems, 2nd ed., New York: Macmillan, 1975)

Some Ecosystems Produce Plant Matter Faster Than Others Do (3)Should be clear that the planets 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 earths total potential NPP.Remarkable considering that humans make up on 1% of the total biomass of all of the earths consumers.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.

Nutrients Cycle in the BiosphereBiogeochemical 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 lifeWater Cycles through the BiosphereThe hydrologic cycle, or water cycle, collects, purifies, and distributes the earths fixed supply of water.Powered by energy from the sun, involves three major processes:Evaporation84% of water in atmosphere comes from the ocean.PrecipitationSurface runoff, infiltration, and percolation to aquifersTranspiration On land, 90% of water reaches atmosphere from plants.Alteration of the hydrologic cycle by humansWithdrawal of large amounts of freshwater at rates faster than nature can replace itClearing vegetationIncreased flooding when wetlands are drainedFigure 3.17Natural 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?

Science Focus: Waters Unique PropertiesProperties of water due to hydrogen bonds between water molecules:Exists as a liquid over a large range of temperatureChanges temperature slowly (High heat capacity)High boiling point: 100CTakes lots of energy to evaporate (High heat of vaporization)Adhesion and cohesionExpands as it freezes SolventFilters out harmful UV

Carbon Cycle Depends on Photosynthesis and RespirationCarbon 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 earths thermostat (a GHG).

Additional CO2 added to the atmosphereTree clearingBurning of fossil fuelsComputer models suggest that it is very likely (90-99% probability) that human activities are enhancing the green house effect.Figure 3.18Natural 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?

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.Figure 3.19Natural 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?

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.

Figure 3.20Global trends in the annual inputs of nitrogen into the environment from human activities, with projections to 2050. (Data from 2005 Millennium Ecosystem Assessment)

Phosphorus Cycles through the BiospherePhosphorus circulates through water, the earths 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 activitiesClearing forestsRemoving large amounts of phosphate from the earth to make fertilizersRunoff from land can lead to further cultural eutrophication of lakes and coastal areas.Figure 3.21Natural 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?

Sulfur Cycles through the BiosphereSulfur 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 oilRefine sulfur-containing petroleumConvert sulfur-containing metallic mineral oresFigure 3.22Natural 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?

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.

Some Scientists Study Nature DirectlyField research: muddy-boots biology

New technologies availableRemote sensorsGeographic information system (GIS) softwareDigital satellite imaging

2005, Global Earth Observation System of Systems (GEOSS)

Some Scientists Study Ecosystems in the LaboratorySimplified systems carried out inCulture tubes and bottlesAquaria tanksGreenhousesIndoor and outdoor chambers

Supported by field researchSome Scientists Use Models to Simulate EcosystemsComputer simulations and projections

Field and laboratory research needed for baseline dataWe Need to Learn More about the Health of the Worlds EcosystemsDetermine condition of the worlds ecosystems

More baseline data needed

Doctor-patient analogy