how ecosystems work apbio

Chapter 28Chapter 28

How Do Ecosystems How Do Ecosystems Work?Work?

Chapter 28 2

Energy and Nutrient PathwaysEnergy and Nutrient Pathways

Energy moves in a one-way flow through Energy moves in a one-way flow through communities within ecosystemscommunities within ecosystems

• The energy to drive life’s activities comes The energy to drive life’s activities comes from the sun from the sun

• It is used and transformed in the chemical It is used and transformed in the chemical reactions that power lifereactions that power life

• It is ultimately converted to heat that It is ultimately converted to heat that radiates back into space radiates back into space

Chapter 28 3

Energy Flow, Energy Flow, NutrientNutrientCycling, & Cycling, & Feeding Feeding RelationshipsRelationshipsNutrientsNutrients (purple) (purple) neither enter nor neither enter nor leave cycleleave cycle

Energy (yellow) is Energy (yellow) is not recyclednot recycled•Captured by Captured by producersproducers

•Transferred through Transferred through consumers (red)consumers (red)

•Each transfer loses Each transfer loses energy (orange)energy (orange)

Chapter 28 4

Energy Entry Via PhotosynthesisEnergy Entry Via Photosynthesis

Electromagnetic waves carry energy from Electromagnetic waves carry energy from the sun to the Earth the sun to the Earth

• Most solar energy reaching Earth is Most solar energy reaching Earth is reflected or absorbed reflected or absorbed

• Only about 1% of total energy is available Only about 1% of total energy is available for photosynthesisfor photosynthesis

• Photosynthetic organisms capture only Photosynthetic organisms capture only about 3% of this amount about 3% of this amount

Chapter 28 5

Primary Productivity: PhotosynthesisPrimary Productivity: Photosynthesis

Life uses < 0.03% of Life uses < 0.03% of the sun's energythe sun's energy

Most is lost as heat Most is lost as heat from respirationfrom respiration

Chapter 28 6

Energy Entry via PhotosynthesisEnergy Entry via Photosynthesis

Net primary productivityNet primary productivity is energy that is energy that photosynthetic organisms store and make photosynthetic organisms store and make available to the community over timeavailable to the community over time

• Determines how much life an ecosystem Determines how much life an ecosystem can support can support

• Can be measured as the amount of energy Can be measured as the amount of energy ((caloriescalories) or ) or biomassbiomass (dry weight of organic (dry weight of organic material) stored or added to the ecosystem material) stored or added to the ecosystem per unit area over timeper unit area over time

Chapter 28 7

Energy Entry via PhotosynthesisEnergy Entry via Photosynthesis

Productivity of an ecosystem is influenced Productivity of an ecosystem is influenced byby

• The availability of nutrients and sunlight to The availability of nutrients and sunlight to producersproducers

• The availability of waterThe availability of water• TemperatureTemperature

Chapter 28 8

Ecosystem Productivity ComparedEcosystem Productivity ComparedAverage net primary productivity, in grams of Average net primary productivity, in grams of

organic material per square meter per yearorganic material per square meter per year

openopenoceanocean(125)(125)

continentalcontinentalshelfshelf(360)(360)

estuaryestuary(1500)(1500)

tropicaltropicalrainforestrainforest

(2200)(2200)

tundratundra(140)(140) coniferousconiferous

forestforest(800)(800) temperatetemperate

deciduous forestdeciduous forest(1200)(1200)grasslandgrassland

(600)(600)

desertdesert(90)(90)

Chapter 28 9

Energy Flow Among Trophic Levels Energy Flow Among Trophic Levels

Energy flows through a series of Energy flows through a series of trophic levelstrophic levels (“feeding levels”) in a community (“feeding levels”) in a community

• The The producersproducers form the first trophic level, form the first trophic level, obtaining their energy directly from sunlight obtaining their energy directly from sunlight

• Those that feed directly on producers are called Those that feed directly on producers are called herbivoresherbivores or or primaryprimary consumersconsumers

• Those that feed on primary consumers are called Those that feed on primary consumers are called carnivorescarnivores or or secondary consumerssecondary consumers

• Some carnivores eat other carnivores, acting as Some carnivores eat other carnivores, acting as tertiary consumerstertiary consumers

Chapter 28 10

Energy Flow Among Trophic LevelsEnergy Flow Among Trophic Levels

Some animals are Some animals are omnivoresomnivores, acting as , acting as primary, secondary, and occasionally primary, secondary, and occasionally tertiary consumers at different timestertiary consumers at different times

• Example: humans Example: humans

Chapter 28 11

Food Chains Food Chains

A A food chainfood chain is a linear feeding relationship is a linear feeding relationship with just one representative at each with just one representative at each trophic level trophic level

• Different ecosystems have radically Different ecosystems have radically different food chainsdifferent food chains

• Natural communities rarely contain well-Natural communities rarely contain well-defined groups of primary, secondary, and defined groups of primary, secondary, and tertiary consumers tertiary consumers

Chapter 28 12

Food ChainsFood Chains

(a) A simple (a) A simple terrestrial food terrestrial food chain.chain.

(b) A simple marine (b) A simple marine food chain.food chain.

10% law determines10% law determinesthe population sizethe population sizeof each trophic levelof each trophic level

More organisms at More organisms at lower trophic levelslower trophic levels

Chapter 28 13

Food Webs Food Webs

A A food webfood web shows the actual feeding shows the actual feeding relationships in a community, including its relationships in a community, including its many interconnecting food chains many interconnecting food chains

Chapter 28 14

A Food WebA Food Web

Simple food web on Simple food web on a short-grass a short-grass prairieprairie

Numbers represent Numbers represent trophic levelstrophic levels

11

1122

22

22

2222

22

2222

33

33

33

33

3333 44

44

44

Chapter 28 15

Detritus Feeders and DecomposersDetritus Feeders and Decomposers

Detritus feedersDetritus feeders and and decomposersdecomposers release release nutrients for reusenutrients for reuse

• Detritus feedersDetritus feeders live on dead organic matter, live on dead organic matter, including the bodies of other organisms, including the bodies of other organisms, fallen leaves, and wastesfallen leaves, and wastes

• Examples: earthworms, protists, pillbugs, Examples: earthworms, protists, pillbugs, and vulturesand vultures

• Detritus feeders excrete consumed material Detritus feeders excrete consumed material in a decomposed state in a decomposed state

• Their excretory products are food for other Their excretory products are food for other detritus feeders and detritus feeders and decomposersdecomposers

Chapter 28 16

Detritus Feeders and DecomposersDetritus Feeders and Decomposers

DecomposersDecomposers digest food outside their bodies by digest food outside their bodies by secreting digestive enzymessecreting digestive enzymes

• Are primarily fungi and bacteria Are primarily fungi and bacteria • They absorb only needed nutrients; the rest are They absorb only needed nutrients; the rest are

available for other organisms available for other organisms Detritus feeders and decomposers convert the Detritus feeders and decomposers convert the

bodies of dead organisms into simple bodies of dead organisms into simple molecules molecules

• They recycle nutrients, making them available They recycle nutrients, making them available again for primary producersagain for primary producers

• If absent, primary productivity stops for lack of If absent, primary productivity stops for lack of nutrients and the community collapsesnutrients and the community collapses

Chapter 28 17

Energy Transfer Is InefficientEnergy Transfer Is Inefficient

Energy transfer through the trophic levels is Energy transfer through the trophic levels is inefficientinefficient

A small percentage of available energy A small percentage of available energy transfers to the next trophic level becausetransfers to the next trophic level because

• Energy conversion always involves losses Energy conversion always involves losses as low-grade heatas low-grade heat

• Some of the molecules in organisms Some of the molecules in organisms cannot be digested or absorbedcannot be digested or absorbed

Chapter 28 18

Energy Transfer Is InefficientEnergy Transfer Is Inefficient

A small percentage of available energy A small percentage of available energy transfers to the next trophic level becausetransfers to the next trophic level because

• Some energy is used by each trophic level Some energy is used by each trophic level for maintenance, repair, movement, etc. for maintenance, repair, movement, etc.

• Some organisms at each level die without Some organisms at each level die without being eaten and pass energy to detritus being eaten and pass energy to detritus feeders and decomposersfeeders and decomposers

Chapter 28 19

Energy Transfer and LossEnergy Transfer and LossHeatHeat

HeatHeat

ProducerProducer

PrimaryPrimaryConsumerConsumer

SecondarySecondaryConsumerConsumer

DetritusDetritusFeedersFeeders

HeatHeatHeatHeat

ChemicalsChemicalsChemicalsChemicals

Chapter 28 20

Energy Pyramids Energy Pyramids

Energy pyramidsEnergy pyramids illustrate energy transfer illustrate energy transfer between trophic levelsbetween trophic levels

The net energy transfer between trophic The net energy transfer between trophic levels is roughly 10% efficient levels is roughly 10% efficient

• An An energy pyramid energy pyramid represents this, with represents this, with primary producers on the bottom and primary producers on the bottom and higher trophic levels stacked on tophigher trophic levels stacked on top

Chapter 28 21

An Energy Pyramid for aAn Energy Pyramid for aPrairie Ecosystem: The 10% LawPrairie Ecosystem: The 10% Law

Chapter 28 22

The Carbon CycleThe Carbon Cycle

ReservoirsReservoirs

Processes/Processes/LocationsLocations

TrophicTrophicLevels/Levels/

OrganismsOrganisms

COCO22 in inatmosphereatmosphere(reservoir)(reservoir)

ProducersProducersConsumersConsumers

Wastes,Wastes,Dead bodiesDead bodiesSoil bacteria &Soil bacteria &

detritus feedersdetritus feeders


ConsumersConsumers







RespitationRespitation


Burning ofBurning offossil fuelsfossil fuels


FireFire


COCO22 dissolved dissolvedin oceanin ocean

(reservoir)(reservoir)


Chapter 28 23

Energy Pyramids Energy Pyramids

Sometimes biomass is used as a measure of Sometimes biomass is used as a measure of the energy stored at each trophic levelthe energy stored at each trophic level

• A similar A similar biomass pyramidbiomass pyramid can be can be constructed constructed

This pattern of energy transfer has some This pattern of energy transfer has some important ramificationsimportant ramifications

• Plants dominate most communities because Plants dominate most communities because they have the most energy available to them, they have the most energy available to them, followed by herbivores and carnivores followed by herbivores and carnivores

• We can feed more people directly on grain We can feed more people directly on grain than on meat from animals fed on grainthan on meat from animals fed on grain

Chapter 28 24

Nutrient CyclingNutrient Cycling

Same pool of nutrients supports all life—past, Same pool of nutrients supports all life—past, present, and futurepresent, and future

Cycle moves nutrients:Cycle moves nutrients:• From nonliving to livingFrom nonliving to living• From environmental to organismsFrom environmental to organisms

MacronutrientsMacronutrients are required by organisms in are required by organisms in large quantitieslarge quantities• Examples: water, carbon, hydrogen, oxygenExamples: water, carbon, hydrogen, oxygen

MicronutrientsMicronutrients are required only in trace are required only in trace quantities quantities • Examples: zinc, molybdenum, iron, seleniumExamples: zinc, molybdenum, iron, selenium

Chapter 28 25

Nutrient CyclesNutrient Cycles

Nutrient cyclesNutrient cycles (or (or biogeochemical cyclesbiogeochemical cycles) ) describe the pathways nutrients follow describe the pathways nutrients follow between communities and the nonliving between communities and the nonliving portions of ecosystems portions of ecosystems

• ReservoirsReservoirs are sources and storage sites of are sources and storage sites of nutrients nutrients

• Major reservoirs are usually in the abiotic Major reservoirs are usually in the abiotic environment environment

Chapter 28 26

Atmospheric Cycles (C & N)Atmospheric Cycles (C & N)

Majority of nutrient found in the atmosphereMajority of nutrient found in the atmosphere

Atmospheric nutrients get incorporated into Atmospheric nutrients get incorporated into living organismsliving organisms• Carbon—photosynthesisCarbon—photosynthesis

• Nitrogen—nitrogen fixationNitrogen—nitrogen fixation

Nutrients are returned to the environmentNutrients are returned to the environment• C—respiration (all organisms, detritus feeders, C—respiration (all organisms, detritus feeders,

decomposers)decomposers)

• N—decomposers and denitrifying bacteriaN—decomposers and denitrifying bacteria

Chapter 28 27

Nitrogen inNitrogen inAtmosphereAtmosphere

ReservoirReservoir


ReservoirReservoir

The Nitrogen CycleThe Nitrogen Cycle

Electrical stormsElectrical stormsproduce nitrateproduce nitrate

AmmoniaAmmonia& nitrate& nitrate

Nitrogen-fixingNitrogen-fixingbacteria inbacteria in

legume rootslegume rootsand soiland soilAmmoniaAmmonia

& nitrate& nitrate

UptakeUptakebyby

plantsplants

ProducersProducers ConsumersConsumers

Wastes,Wastes,Dead bodiesDead bodies

Soil bacteria andSoil bacteria anddetritus feedersdetritus feeders

AmmoniaAmmonia& nitrate& nitrate

DentitrifyingDentitrifyingbacteriabacteria


ReservoirReservoir



TrophicTrophicLevels/Levels/

OrganismsOrganisms

Chapter 28 28

The Phosphorous CycleThe Phosphorous Cycle

Phosphorus is a crucial component of ATP and NADP, Phosphorus is a crucial component of ATP and NADP, nucleic acids, and phospholipids of cell membranes nucleic acids, and phospholipids of cell membranes

The major reservoir of the phosphorus cycle is in rock The major reservoir of the phosphorus cycle is in rock bound to oxygen as phosphatebound to oxygen as phosphate

• Phosphate in exposed rock can be dissolved by Phosphate in exposed rock can be dissolved by rainwaterrainwater

• It is absorbed by autotrophs, where it is incorporated It is absorbed by autotrophs, where it is incorporated into biological molecules that pass through food websinto biological molecules that pass through food webs

• At each level, excess phosphorus is excreted and At each level, excess phosphorus is excreted and decomposers release phosphatedecomposers release phosphate

• Phosphate may be reabsorbed by autotrophs or Phosphate may be reabsorbed by autotrophs or reincorporated into rockreincorporated into rock

Chapter 28 29

Chapter 28 30

The Hydrologic CycleThe Hydrologic Cycle

Water molecules remain chemically Water molecules remain chemically unchanged during the unchanged during the hydrologic cyclehydrologic cycle

The major reservoir of water is the oceanThe major reservoir of water is the ocean• Contains more than 97% of Earth’s waterContains more than 97% of Earth’s water

Solar energy evaporates water, and it comes Solar energy evaporates water, and it comes back to Earth as precipitationback to Earth as precipitation

Chapter 28 31

The The Hydrologic Hydrologic

CycleCycleEvaporationEvaporationfrom land &from land &

transpirationtranspirationfrom plantsfrom plants

PrecipitationPrecipitationover landover land

Water vaporWater vaporin atmospherein atmosphere

Water inWater inoceanocean


EvaporationEvaporationfrom oceanfrom ocean

Water vaporWater vaporin atmospherein atmosphere



GroundwaterGroundwaterseepageseepage

SurfaceSurfacerunoffrunoff



PrecipitationPrecipitationover oceanover ocean



Chapter 28 32

The Hydrologic CycleThe Hydrologic Cycle

With human population growth, fresh water With human population growth, fresh water has become scarcehas become scarce

• Water scarcity limits crop growth Water scarcity limits crop growth • Pumping water from underground aquifers Pumping water from underground aquifers

is rapidly depleting many of them is rapidly depleting many of them • Contaminated drinking water is consumed Contaminated drinking water is consumed

by over 1 billion people in developing by over 1 billion people in developing countries each year, killing millions of countries each year, killing millions of childrenchildren

Chapter 28 33

What Causes Acid Rain?What Causes Acid Rain?

Beginning in the Industrial Revolution, we Beginning in the Industrial Revolution, we have relied heavily on fossil fuels for heat, have relied heavily on fossil fuels for heat, light, transportation, industry, and light, transportation, industry, and agricultureagriculture

Reliance on fossils fuels leads to two Reliance on fossils fuels leads to two environmental problemsenvironmental problems

• Acid rainAcid rain• Global warmingGlobal warming

Chapter 28 34

What Causes Acid Rain?What Causes Acid Rain?

Acid rain (Acid rain (acid depositionacid deposition) is due to excess ) is due to excess industrial production of sulfur dioxide and industrial production of sulfur dioxide and nitrogen oxides that our natural ecosystems nitrogen oxides that our natural ecosystems can’t absorb and recyclecan’t absorb and recycle

Sulfur dioxide Sulfur dioxide • Released primarily from coal and oil power Released primarily from coal and oil power

plantsplants• Forms sulfuric acid when it combines with Forms sulfuric acid when it combines with

water vaporwater vaporNitrogen oxides Nitrogen oxides

• Released from vehicles, power plants, and Released from vehicles, power plants, and industryindustry

• Combines with water vapor to form nitric acidCombines with water vapor to form nitric acid

Chapter 28 35

Acid RainAcid RainDays later, and often hundreds of miles from the Days later, and often hundreds of miles from the

source, the acids fallsource, the acids fall• Eat away at statues and buildingsEat away at statues and buildings• Damage trees and cropsDamage trees and crops• Alter lake communitiesAlter lake communities

Acid rain examplesAcid rain examples• Adirondack Mountains—dead lakesAdirondack Mountains—dead lakes• Mount Mitchell, N.C.—fog pH = 2.9Mount Mitchell, N.C.—fog pH = 2.9• Black Triangle in EuropeBlack Triangle in Europe

– Soil pH = 2.2Soil pH = 2.2– Thermal inversionsThermal inversions– Infant mortalityInfant mortality

Chapter 28 36

Interfering with the Carbon CycleInterfering with the Carbon Cycle

Between 345–280 million years ago, the Between 345–280 million years ago, the bodies of many plants and animals were bodies of many plants and animals were buried, escaping decompositionburied, escaping decomposition

Over time, these carbon sources were Over time, these carbon sources were converted to fossil fuels by heat and converted to fossil fuels by heat and pressure pressure

Fossil fuels remained untouched until the Fossil fuels remained untouched until the beginning of the Industrial Revolutionbeginning of the Industrial Revolution

• Burning the fuels released it as COBurning the fuels released it as CO22 into the into the airair

Chapter 28 37

Interfering with the Carbon CycleInterfering with the Carbon Cycle

Human activities release almost 7 billion Human activities release almost 7 billion tons of carbon (in the form of CO2,) into tons of carbon (in the form of CO2,) into the atmosphere each yearthe atmosphere each year

About half of this carbon is absorbed into About half of this carbon is absorbed into the oceans, plants and soilthe oceans, plants and soil

The other half remains in the atmosphere, The other half remains in the atmosphere, fueling fueling global warmingglobal warming

Chapter 28 38

Greenhouse EffectGreenhouse Effect

Gases which interfere with cooling of EarthGases which interfere with cooling of Earth• COCO22

– Use of fossil fuelsUse of fossil fuels– Global deforestation by slash & burnGlobal deforestation by slash & burn

• CFCs (A/C & refrigeration gases)CFCs (A/C & refrigeration gases)• MethaneMethane• NONO

Global warmingGlobal warming• What might be the consequences of global What might be the consequences of global

warming?warming?

Chapter 28 39

Greenhouse GasesGreenhouse GasesContribute to Global WarmingContribute to Global Warming

Chapter 28 40

Global Warming ParallelsGlobal Warming ParallelsCOCO2 2 IncreasesIncreases

Chapter 28 41

Severe ConsequencesSevere Consequences

A meltdown is occurringA meltdown is occurringGlaciers and ice sheets have been melting at Glaciers and ice sheets have been melting at

unprecedented ratesunprecedented rates• Rising sea levels will flood many coastal cities Rising sea levels will flood many coastal cities

and wetlands and may increase hurricane and wetlands and may increase hurricane intensityintensity

More extreme weather patterns are predictedMore extreme weather patterns are predictedWarming will alter air and water currents, Warming will alter air and water currents,

changing precipitation patternschanging precipitation patterns• More severe droughts and greater extremes in More severe droughts and greater extremes in

rainfall may lead to more frequent crop failures rainfall may lead to more frequent crop failures and flooding and flooding

Chapter 28 42

Chapter 28 43

Our Decisions Make a Difference Our Decisions Make a Difference

The U.S. has only 5% of the world’s The U.S. has only 5% of the world’s population but produces 25% of the population but produces 25% of the world’s greenhouse emissions world’s greenhouse emissions

Chapter 28 44

Kyoto TreatyKyoto Treaty

Negotiated in 1997 and implemented in 2005Negotiated in 1997 and implemented in 200535 industrialized countries have pledged to 35 industrialized countries have pledged to

reduce their collective emissions of reduce their collective emissions of greenhouse gases to levels 5.2 % below 1990 greenhouse gases to levels 5.2 % below 1990 levelslevels

As of Nov’07, 174 countries have ratified the As of Nov’07, 174 countries have ratified the treaty, the U.S. has not. treaty, the U.S. has not.

THE US IS THE THE US IS THE ONLYONLY INDUSTRIAL NATION INDUSTRIAL NATION NOT TO RATIFY THE TREATY!NOT TO RATIFY THE TREATY!

Chapter 28 45

Kyoto TreatyKyoto Treaty

Ten U.S. states and many city mayors have Ten U.S. states and many city mayors have pledged to adopt Kyoto-type standards pledged to adopt Kyoto-type standards independentlyindependently

Although worldwide efforts are essential, Although worldwide efforts are essential, our individual choices, collectively, can our individual choices, collectively, can also have a big impactalso have a big impact

Chapter 28Chapter 28

The EndThe End

how ecosystems work apbio

Technology

energy entry

energy conversion

energy orange

total energy

solar energy

suns energy

trophic levels energy

net energy transfer