EcosystemsEcosystems

Chapter 48Chapter 48

Ecosystem Ecosystem

An association of organisms and their An association of organisms and their

physical environment, interconnected by physical environment, interconnected by

ongoing flow of energy and a cycling of ongoing flow of energy and a cycling of

materialsmaterials

Modes of NutritionModes of Nutrition

AutotrophsAutotrophs Capture sunlight or chemical energyCapture sunlight or chemical energy

ProducersProducers

HeterotrophsHeterotrophs Extract energy from other organisms or Extract energy from other organisms or

organic wastesorganic wastes

Consumers, decomposers, detritivoresConsumers, decomposers, detritivores

Simple Simple EcosysteEcosystem Modelm Model

energy input from sun

nutrientcycling

PHOTOAUTOTROPHS(plants, other producers)

HETEROTROPHS(consumers, decomposers)

energy output (mainly heat)

Consumers Consumers

Herbivores Herbivores

Carnivores Carnivores

ParasitesParasites

Omnivores Omnivores

DecomposersDecomposers

Detritivores Detritivores

SPRING

rodents, rabbits

fruits

insects

birds

SUMMER

rodents, rabbits

fruits

insects

birds

Seasonal variation in the diet of an omnivore (red fox)

Trophic LevelsTrophic Levels

All the organisms at a trophic level are All the organisms at a trophic level are

the same number of steps away from the the same number of steps away from the

energy input into the systemenergy input into the system

Producers are closest to the energy input Producers are closest to the energy input

and are the first trophic leveland are the first trophic level

Trophic Levels in Trophic Levels in PrairiePrairie

5th

4th

3rd

2nd

1st

Fourth-level consumers (heterotrophs):

Top carnivores, parasites, detritivores, decomposers

Third-level consumers (heterotrophs):

Carnivores, parasites, detritivores, decomposers

Second-level consumers (heterotrophs):

Carnivores, parasites, detritivores, decomposers

First-level consumers (heterotrophs):

Herbivores, parasites, detritivores, decomposers

Primary producers (autotrophs):

Photoautotrophs, chemoautotrophs

Food ChainFood Chain

A straight-line A straight-line

sequence of who eats sequence of who eats

whom whom

Simple food chains Simple food chains

are rare in natureare rare in nature

marsh hawk

upland sandpiper

garter snake

cutworm

plants

Tall-Grass Prairie Food Tall-Grass Prairie Food WebWeb

earthworms, insects

sparrow

vole pocketgopher

groundsquirrel

coyotebadgerweasel

spider

frog

snake

sandpiper crow

marsh hawk

grasses, composites

Energy Losses Energy Losses

Energy transfers are never 100 percent Energy transfers are never 100 percent

efficientefficient

Some energy is lost at each stepSome energy is lost at each step

Limits the number of trophic levels in an Limits the number of trophic levels in an

ecosystem ecosystem

Two Types of Food WebsTwo Types of Food WebsProducers

(photosynthesizers)

Energy Input: Energy Input:

herbivores

carnivores

decomposers

decomposers

detritivores

energy in organic wastes, remains

Energy Output

Energy Output

energy lossesas metabolic heat & as net export from ecosystem

Producers (photosynthesizers)

decomposers

detritivores

Transfers: Transfers:

Grazing Food Web

Detrital Food Web

energy in organic wastes, remains

energy lossesas metabolic heat & as net export from ecosystem

Figure 48.7Page 871 

Biological MagnificationBiological Magnification

A nondegradable or slowly degradable A nondegradable or slowly degradable

substance becomes more and more substance becomes more and more

concentrated in the tissues of concentrated in the tissues of

organisms at higher trophic levels of a organisms at higher trophic levels of a

food webfood web

DDT in Food WebsDDT in Food Webs

Synthetic pesticide banned in United Synthetic pesticide banned in United States since the 1970sStates since the 1970s

Birds that are carnivores accumulate DDT Birds that are carnivores accumulate DDT in their tissues, produce brittle egg shellsin their tissues, produce brittle egg shells

DDT in an Estuary DDT in an Estuary (1967)(1967)

DDT Residues (ppm wet weight of whole live organism)

Ring-billed gull fledgling (Larus delawarensis)Herring gull (Larus argentatus)Osprey (Pandion haliaetus)Green heron (Butorides virescens)Atlantic needlefish (Strongylira marina)Summer flounder (Paralychthys dentatus)Sheepshead minnow (Cyprinodon variegatus)Hard clam (Mercenaria mercenaria)Marsh grass shoots (Spartina patens)Flying insects (mostly flies)Mud snail (Nassarius obsoletus)Shrimps (composite of several samples)Green alga (Cladophora gracilis)Plankton (mostly zooplankton)Water

75.5 18.5 13.8 3.57 2.07 1.28 0.940.420.33 0.30 0.26 0.16 0.083 0.040 0.00005

Primary ProductivityPrimary Productivity

GrossGross primary productivity is primary productivity is

ecosystem’s total rate of photosynthesisecosystem’s total rate of photosynthesis

NetNet primary productivity is rate at which primary productivity is rate at which

producers store energy in tissues in producers store energy in tissues in

excess of their aerobic respirationexcess of their aerobic respiration

Primary Productivity Primary Productivity VariesVaries

Seasonal variationSeasonal variation

Variation by habitatVariation by habitat

The harsher the environment, the The harsher the environment, the

slower plant growth, the lower the slower plant growth, the lower the

primary productivity primary productivity

Silver Springs StudySilver Springs Study

Aquatic ecosystem in FloridaAquatic ecosystem in Florida Site of a long-term study of a grazing food webSite of a long-term study of a grazing food web

5

decomposers, detritivores(bacteria, crayfish)

1.5

1.1

37

third-level carnivores(gar, large-mouth bass)

second-level consumers(fishes, invertebrates)

first-level consumers(herbivorous fishes,turtles, invertebrates)

primary producers (algae,eelgrass, rooted plants)

809

Pyramid of Energy FlowPyramid of Energy Flow

Primary producers trapped about 1.2 Primary producers trapped about 1.2 percent of the solar energy that entered the percent of the solar energy that entered the ecosystemecosystem

6-16% passed on to next level6-16% passed on to next level

21

383

3,368

20,810 kilocalories/square meter/year

top carnivores

carnivores

herbivores

producers

decomposers + detritivores = 5,080

Figure 48.11Page 874

Energy Flow In Energy Flow In Silver SpringsSilver Springs

20,810 1,679,190

Incoming solar energy not harnessed: 1,679,190 (98.8%)

ENERGY INPUT:

1,700,000 kilocalories

20,810 (1.2%)

Producers

To next trophic level:

Energy in organic wastes and remains:

Energy losses as metabolic heat & as net export from ecosystem:

Herbivores

Carnivores

Top carnivores

Decomposers, detritivores

4,245

720

5

90

3,368

383

21

13,197

2,265

272

16

5,060ENERGY OUTPUT:

Total annual energy flow: 1,700,000 (100%)Figure 48.12

Page 874

All Heat in the EndAll Heat in the End

At each trophic level, the bulk of the At each trophic level, the bulk of the energy received from the previous level energy received from the previous level is used in metabolismis used in metabolism

This energy is released as heat energy This energy is released as heat energy and lost to the ecosystemand lost to the ecosystem

Eventually all energy is released as heatEventually all energy is released as heat

Biogeochemical CycleBiogeochemical Cycle

The flow of a nutrient from the The flow of a nutrient from the

environment to living organisms and environment to living organisms and

back to the environmentback to the environment

Main reservoir for the nutrient is in the Main reservoir for the nutrient is in the

environmentenvironment

Three CategoriesThree Categories

Hydrologic cycleHydrologic cycle

WaterWater

Atmospheric cycles Atmospheric cycles

Nitrogen and carbonNitrogen and carbon

Sedimentary cycles Sedimentary cycles

Phosphorus and sulfurPhosphorus and sulfur

Hydrologic CycleHydrologic CycleAtmosphere

Ocean Land

evaporation from ocean

425,000

precipitation into ocean 385,000

evaporation from land plants (evapotranspiration)

71,000

precipitation onto land 111,000

wind-driven water vapor40,000

surface and groundwater flow 40,000

Figure 48.14Page 876

Hubbard Brook Hubbard Brook ExperimentExperiment

A watershed was experimentally stripped A watershed was experimentally stripped

of vegetationof vegetation

All surface water draining from watershed All surface water draining from watershed

was measuredwas measured

Removal of vegetation caused a six-fold Removal of vegetation caused a six-fold

increase in the calcium content of the increase in the calcium content of the

runoff waterrunoff water

Hubbard Brook Hubbard Brook ExperimentExperiment

losses fromdisturbed watershed

time ofdeforestation

losses fromundisturbed watershed

Figure 48.15Page 877

Carbon CycleCarbon Cycle

Carbon moves through the atmosphere Carbon moves through the atmosphere

and food webs on its way to and from and food webs on its way to and from

the ocean, sediments, and rocksthe ocean, sediments, and rocks

Sediments and rocks are the main Sediments and rocks are the main

reservoirreservoir

Figure 48.16 Page 878

diffusion between atmosphere and ocean

bicarbonate and carbonate in ocean water

marine food webs

marine sediments

combustion of fossil fuels

incorporation into sediments

death, sedimentation uplifting

sedimentation

photosynthesis aerobic respiration

Carbon Cycle - MarineCarbon Cycle - Marine

Carbon Cycle - LandCarbon Cycle - Land

photosynthesis aerobic respirationterrestrial

rocks

soil water

land food webs

atmosphere

peat, fossil fuels

combustion of wood

sedimentation

volcanic action

death, burial, compaction over geologic time

leaching, runoff

weathering

combustion of fossil fuels

Figure 48.16 Page 878

Carbon in the OceansCarbon in the Oceans

Most carbon in the ocean is dissolved Most carbon in the ocean is dissolved carbonate and bicarbonatecarbonate and bicarbonate

Ocean currents carry dissolved carbon Ocean currents carry dissolved carbon

Carbon in AtmosphereCarbon in Atmosphere

Atmospheric carbon is mainly carbon Atmospheric carbon is mainly carbon dioxidedioxide

Carbon dioxide is added to atmosphereCarbon dioxide is added to atmosphere Aerobic respiration, volcanic action, Aerobic respiration, volcanic action,

burning fossil fuels burning fossil fuels

Removed by photosynthesisRemoved by photosynthesis

Greenhouse EffectGreenhouse Effect

Greenhouse gases impede the escape Greenhouse gases impede the escape

of heat from Earth’s surfaceof heat from Earth’s surface

Figure 48.18, Page 880

Global WarmingGlobal Warming

Long-term increase in the temperature Long-term increase in the temperature

of Earth’s lower atmosphereof Earth’s lower atmosphere

Figure 48.19, Page 881

Carbon Dioxide IncreaseCarbon Dioxide Increase

Carbon dioxide levels fluctuate Carbon dioxide levels fluctuate

seasonally seasonally

The average level is steadily increasingThe average level is steadily increasing

Burning of fossil fuels and deforestation Burning of fossil fuels and deforestation

are contributing to the increaseare contributing to the increase

Other Greenhouse GasesOther Greenhouse Gases

CFCs - synthetic gases used in plastics CFCs - synthetic gases used in plastics

and in refrigerationand in refrigeration

Methane - produced by termites and Methane - produced by termites and

bacteriabacteria

Nitrous oxide - released by bacteria, Nitrous oxide - released by bacteria,

fertilizers, and animal wastesfertilizers, and animal wastes

Nitrogen CycleNitrogen Cycle

Nitrogen is used in amino acids and Nitrogen is used in amino acids and

nucleic acidsnucleic acids

Main reservoir is nitrogen gas in the Main reservoir is nitrogen gas in the

atmosphereatmosphere

Nitrogen CycleNitrogen Cyclegaseous nitrogen (N2)

in atmosphere

NO3-

in soil

nitrogen fixationby industry

fertilizers

NH3-,NH4

+

in soil

1. Nitrification leaching

uptake by autotrophs

excretion, death, decomposition

uptake by autotrophs

nitrogen fixation

leaching

ammonification 2. Nitrification

dentrification nitrogenous

wastes, remains

NO2-

in soil

food webs on land

Figure 48.21Page 882

Nitrogen FixationNitrogen Fixation

Plants cannot use nitrogen gasPlants cannot use nitrogen gas

Nitrogen-fixing bacteria convert Nitrogen-fixing bacteria convert

nitrogen gas into ammonia (NHnitrogen gas into ammonia (NH33))

Ammonia and ammonium can be Ammonia and ammonium can be

taken up by plantstaken up by plants

Ammonification & Ammonification & NitrificationNitrification

Bacteria and fungi carry out Bacteria and fungi carry out

ammonificationammonification

conversion of nitrogenous wastes to ammoniaconversion of nitrogenous wastes to ammonia

Nitrifying bacteria convert ammonium to Nitrifying bacteria convert ammonium to

nitrites and nitratesnitrites and nitrates

Nitrogen LossNitrogen Loss

Nitrogen is often a limiting factor in Nitrogen is often a limiting factor in

ecosystemsecosystems

Nitrogen is lost from soils via leaching Nitrogen is lost from soils via leaching

and runoff and runoff

Denitrifying bacteria convert nitrates and Denitrifying bacteria convert nitrates and

nitrites to nitrogen gasnitrites to nitrogen gas

Human EffectsHuman Effects

Humans increase rate of nitrogen loss by Humans increase rate of nitrogen loss by clearing forests and grasslandsclearing forests and grasslands

Humans increase nitrogen in water and Humans increase nitrogen in water and air by using fertilizers and by burning air by using fertilizers and by burning fossil fuelsfossil fuels

Too much or too little nitrogen can Too much or too little nitrogen can compromise plant healthcompromise plant health

Phosphorus CyclePhosphorus Cycle

Phosphorus is part of phospholipids and Phosphorus is part of phospholipids and

all nucleotidesall nucleotides

It is the most prevalent limiting factor in It is the most prevalent limiting factor in

ecosystems ecosystems

Main reservoir is Earth’s crust; no Main reservoir is Earth’s crust; no

gaseous phasegaseous phase

Phosphorus CyclePhosphorus Cycle

GUANO

FERTILIZER

TERRESTRIAL ROCKS

LAND FOOD WEBS

DISSOLVED IN OCEAN

WATER

MARINE FOOD WEBS

MARINE SEDIMENTS

excretion

weathering

mining

agricultureuptake

by autotrophs

death, decomposition

sedimentationsettling

out leaching, runoff

weathering

uplifting

over geologic time

DISSOLVED IN SOILWATER,

LAKES, RIVERS

uptake by

autotrophs

death, decomposition

Figure 48.23, Page 884

Human EffectsHuman Effects

In tropical countries, clearing lands for In tropical countries, clearing lands for

agriculture may deplete phosphorus-agriculture may deplete phosphorus-

poor soilspoor soils

In developed countries, phosphorus In developed countries, phosphorus

runoff is causing eutrophication of runoff is causing eutrophication of

waterwayswaterways