Chapter 54: EcosystemsChapter 54: EcosystemsEcosystemEcosystemAll organisms living in an area along with All organisms living in an area along with the abiotic factors with which they interact. the abiotic factors with which they interact. Most inclusive level of biological Most inclusive level of biological organizationorganizationDynamics of an ecosystem:Dynamics of an ecosystem:

Energy flowEnergy flowChemical cycling Chemical cycling

Trophic levelsTrophic levels Primary producerPrimary producer

Autotrophs; usually photosynthetic; includes plants, Autotrophs; usually photosynthetic; includes plants, algae, & many species of bacteriaalgae, & many species of bacteria

Streams=Debris falling from terrestrial plants are major Streams=Debris falling from terrestrial plants are major source of organic materialssource of organic materials

Limnetic zone of lakes & open oceans= PhytoplanktonLimnetic zone of lakes & open oceans= Phytoplankton Shallow freshwater & marine ecosystems= Multi-cellular Shallow freshwater & marine ecosystems= Multi-cellular

algae & plants algae & plants Aphotic zones receive energy & nutrients from overlying Aphotic zones receive energy & nutrients from overlying

photic zonesphotic zones Deep ocean vents= chemoautotrophs oxidize HDeep ocean vents= chemoautotrophs oxidize H22S for energy S for energy

needsneeds Primary consumersPrimary consumers

HerbivoresHerbivores Secondary consumersSecondary consumers

Carnivore that eats herbivoresCarnivore that eats herbivores Tertiary consumersTertiary consumers

Carnivores that eat other carnivoresCarnivores that eat other carnivores

**many primary & higher order consumers are **many primary & higher order consumers are opportunistic feeders (supplement diet of autotrophs opportunistic feeders (supplement diet of autotrophs with heterotrophs if available)with heterotrophs if available)

Detrivores (decomposers)Detrivores (decomposers) Consumers that derive energy from detritus (organic waste) & Consumers that derive energy from detritus (organic waste) &

dead organisms from all trophic levelsdead organisms from all trophic levels Link between all organisms in an ecosystemLink between all organisms in an ecosystem

*Trophic relationships determine an ecosystem’s routes of *Trophic relationships determine an ecosystem’s routes of energy & chemical cyclingenergy & chemical cycling

Food chainFood chain Pathway along which energy flows from one trophic level to the Pathway along which energy flows from one trophic level to the

nextnext Food webFood web

Feeding relationships in an ecosystemFeeding relationships in an ecosystem ProductionProduction

Incorporation of energy & materials into bodies of organismsIncorporation of energy & materials into bodies of organisms ConsumptionConsumption

Metabolic use of assimilated molecules for growth & reproductionMetabolic use of assimilated molecules for growth & reproduction DecompositionDecomposition

Breakdown of organic molecules into inorganic moleculesBreakdown of organic molecules into inorganic molecules

Energy flow in ecosystemsEnergy flow in ecosystems Global energy budgetGlobal energy budget

Earth receives 10Earth receives 102222 joules of solar radiation/day (1J= joules of solar radiation/day (1J= 0.239 cal)0.239 cal)

Most intense radiation at equatorMost intense radiation at equator ~1% of total solar energy is converted by photosynthesis ~1% of total solar energy is converted by photosynthesis

into organic molecules (170 billion tons of biomass/year)into organic molecules (170 billion tons of biomass/year) Primary productivityPrimary productivity

Amount of light energy converted by ecosystem’s Amount of light energy converted by ecosystem’s autotrophs into organic compounds in a given time autotrophs into organic compounds in a given time periodperiod

Gross primary productivity (GPP): total primary Gross primary productivity (GPP): total primary productivityproductivity

Net primary productivity (NPP)Net primary productivity (NPP) NPP=GPP-RNPP=GPP-R R=energy for respiration of the producerR=energy for respiration of the producer Key measurement to ecologists Key measurement to ecologists Represents the stored chemical energy available to consumers Represents the stored chemical energy available to consumers

in the ecosystemin the ecosystem *varies with the ecosystem*varies with the ecosystem

Lack of nutrients (usually N or P) limits Lack of nutrients (usually N or P) limits primary productivity in aquatic ecosystems & primary productivity in aquatic ecosystems & terrestrial ecosystemsterrestrial ecosystems

Temperature & moisture limit primary Temperature & moisture limit primary productivity in terrestrial & wetland productivity in terrestrial & wetland ecosystemsecosystems

Measured through evapotranspirationMeasured through evapotranspiration

Secondary productivitySecondary productivity Rate at which consumers convert chemical Rate at which consumers convert chemical

energy in food into biomassenergy in food into biomass Energy is lost in fecesEnergy is lost in feces Respiration & body heat results in energy lostRespiration & body heat results in energy lost Some energy is used to generate growth & Some energy is used to generate growth &

reproduction (adds to biomass)reproduction (adds to biomass)

Ecological efficiency & ecological Ecological efficiency & ecological pyramidspyramids Trophic efficiencyTrophic efficiency

% of production transferred from one trophic level % of production transferred from one trophic level to the nextto the next

~5-20% of energy at each trophic level is ~5-20% of energy at each trophic level is passed on to the next level (average 10%)passed on to the next level (average 10%)

Loss of energy can be represented Loss of energy can be represented diagrammatically through:diagrammatically through:

Pyramid of productivityPyramid of productivity Pyramid of biomassPyramid of biomass

Can be inverted if turnover time for producers is shortCan be inverted if turnover time for producers is short Pyramid of numbersPyramid of numbers

Cycling of Chemical elements in ecosytemsCycling of Chemical elements in ecosytems Inexhaustible influx of solar energy but Inexhaustible influx of solar energy but

continuation of life depends on recycling of continuation of life depends on recycling of essential chemical compoundsessential chemical compounds

Biogeochemical cyclesBiogeochemical cycles Move nutrients among organic & inorganic, biotic & Move nutrients among organic & inorganic, biotic &

abioticabiotic Water cycleWater cycle Carbon cycleCarbon cycle Phosphorus cyclePhosphorus cycle Nitrogen cycleNitrogen cycle

NitrificationNitrification Aerobic soil bacteria oxidize NHAerobic soil bacteria oxidize NH44

++NONO22--NONO33

--

DenitrificationDenitrification Anaerobic bacteria obtain oxygen by converting NOAnaerobic bacteria obtain oxygen by converting NO33

-- NN22

Nitrogen fixation bacteriaNitrogen fixation bacteria Legumes… NLegumes… N22 NHNH33

++

Decomposition rates largely determine the Decomposition rates largely determine the rates of nutrient cyclingrates of nutrient cycling Availability of water, oxygen, & temperature Availability of water, oxygen, & temperature

influence the rate of decomposition & recyclinginfluence the rate of decomposition & recycling Tropical rain forest recycle rapidly resulting in soil Tropical rain forest recycle rapidly resulting in soil

with very little nutrientswith very little nutrients Soils in temperate deciduous forest may contain Soils in temperate deciduous forest may contain

50% of all of the organic materials in the ecosystem50% of all of the organic materials in the ecosystem Decomposition in tundra can take up to 50 yearsDecomposition in tundra can take up to 50 years

Field experiments reveal how vegetation Field experiments reveal how vegetation regulates chemical cycling regulates chemical cycling Hubbard Brook experiment (NH) Hubbard Brook experiment (NH)

Long term ecological research since 1963Long term ecological research since 1963 Plants control amount of nutrients leaving the Plants control amount of nutrients leaving the

ecosystemecosystem

Human impacts on ecosystemsHuman impacts on ecosystems Human population is disrupting chemical cycles Human population is disrupting chemical cycles

throughout the biospherethroughout the biosphere Agricultural effects on nutrient cyclingAgricultural effects on nutrient cycling

Nutrients in food crops removed from geographical areaNutrients in food crops removed from geographical area Soil nutrient depletion leads to use of fertilizersSoil nutrient depletion leads to use of fertilizers Introduction of toxic materialsIntroduction of toxic materials runoff &/or ground water runoff &/or ground water

contaminationcontamination Accelerated eutrophication of lakesAccelerated eutrophication of lakes algal blooms algal blooms

Result of fertilizer runoff, sewage, & factory wasteResult of fertilizer runoff, sewage, & factory waste Decrease in aerobic respiration as debris levels increaseDecrease in aerobic respiration as debris levels increase

Acid precipitationAcid precipitation Burning of fossil fuels adds sulfur & nitrogen oxides Burning of fossil fuels adds sulfur & nitrogen oxides

that react with water in the atmospherethat react with water in the atmosphere Falls as acid rainFalls as acid rain pH<5.6 pH<5.6

Affects soil chemistryAffects soil chemistry Leaching nutrients from soil & plantsLeaching nutrients from soil & plants Kills keystone species in aquatic ecosystemKills keystone species in aquatic ecosystem

Toxins can become concentrated in successive trophic Toxins can become concentrated in successive trophic levels of food webs= biological magnificationlevels of food webs= biological magnification Examples: DDT used to kill insect pests but found in high levels Examples: DDT used to kill insect pests but found in high levels

in osprey, eagles, & other birdsin osprey, eagles, & other birds Human activities are causing fundamental changes in Human activities are causing fundamental changes in

the composition of the atmospherethe composition of the atmosphere COCO22 emissions & greenhouse effect emissions & greenhouse effect

17% increase since 195817% increase since 1958 Depletion of atmospheric ozoneDepletion of atmospheric ozone

best documented in Antarcticabest documented in Antarctica Caused by CFC’s & refrigerantsCaused by CFC’s & refrigerants

Exploding human population is altering habitats & Exploding human population is altering habitats & reducing biodiversity worldwidereducing biodiversity worldwide Increasing population & related activities continue to disrupt Increasing population & related activities continue to disrupt

trophic structures, energy flow, & chemical cyclingtrophic structures, energy flow, & chemical cycling Human encroachment has resulted in:Human encroachment has resulted in:

Only 15% of original primary USA forest & 1% of original tall grass Only 15% of original primary USA forest & 1% of original tall grass prairie remainingprairie remaining

Tropical rainforest being cut at a rate of 500,000kmTropical rainforest being cut at a rate of 500,000km22/year /year Eliminated by 2020 at current rateEliminated by 2020 at current rate

Logging, war, oil spills continue to breakup & destroy habitatsLogging, war, oil spills continue to breakup & destroy habitats