Chapter 54

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 54Chapter 54

Ecosystems


• Ecosystems

• Microcosm: aquarium

• Lakes, forests

Figure 54.1


Dynamics

• Energy flows

• Matter cycles


• Ecosystem ecologists

• Monitor energy & matter


• Energy flows

• Light - heat

Figure 54.2

Microorganismsand other

detritivores

Detritus

Primary producers

Primary consumers

Secondaryconsumers

Tertiary consumers

Heat

Sun

Key

Chemical cycling

Energy flow


Decomposition – connects levels

• Detritivores, (bacteria, fungi) recycle chemical elements

Figure 54.3


Primary production

– Amount of light energy converted to chemical energy by autotrophs during a given time period


Ecosystem Energy Budgets

• The extent of photosynthetic production

– Sets the spending limit for the energy budget of the entire ecosystem


The Global Energy Budget

• Only a small fraction of solar energy

– Actually strikes photosynthetic organisms


Gross and Net Primary Production

• GPP – total production

• Not all stored as organic material in growing plants


• NPP

– GPP minus energy used by 1o producers for respiration

• Only NPP is available to consumers


NPP varies in ecosystems– And in their contribution to the total NPP on Earth

Lake and stream

Open ocean

Continental shelf

Estuary

Algal beds and reefs

Upwelling zones

Extreme desert, rock, sand, ice

Desert and semidesert scrub

Tropical rain forest

Savanna

Cultivated land

Boreal forest (taiga)

Temperate grassland

Tundra

Tropical seasonal forestTemperate deciduous forest

Temperate evergreen forest

Swamp and marsh

Woodland and shrubland

0 10 20 30 40 50 60 0 500 1,000 1,500 2,000 2,500 0 5 10 15 20 25

Percentage of Earth’s netprimary production

Key

Marine

Freshwater (on continents)

Terrestrial

5.2

0.3

0.1

0.1

4.7

3.53.3

2.9

2.7

2.41.8

1.7

1.6

1.5

1.3

1.0

0.4

0.4

125

360

1,500

2,500

500

3.0

90

2,200

900

600

800

600

700

140

1,600

1,2001,300

2,000

250

5.6

1.2

0.9

0.1

0.040.9

22

7.99.1

9.6

5.4

3.50.6

7.1

4.9

3.8

2.3

0.3

65.0 24.4

Figure 54.4a–c

Percentage of Earth’ssurface area

(a) Average net primaryproduction (g/m2/yr)(b) (c)


Gobal NPP

• Terrestrial 2/3

• Marine 1/3

Figure 54.5

180 120W 60W 0 60E 120E 180

North Pole

60N

30N

Equator

30S

60S

South Pole


Primary Production in Marine and Freshwater Ecosystems


Light Limitation

• light penetration

– Affects primary production throughout the photic zone of an ocean or lake


Nutrient limitation

• Limiting nutrient: element that must be added

– for production to increase in a particular area

• Nitrogen and phosphorous

– most often limit marine production


Nutrient enrichment


• Iron may limit PP

Table 54.1


• The addition of large amounts of nutrients to lakes

– Has a wide range of ecological impacts


Eutrophication

• Sewage runoff may cause eutrophication

Figure 54.7


Primary Production in Terrestrial and Wetland Ecosystems

• Climate factors such as temperature and moisture affect primary production on a large geographic scale


Evapotranspiration measurements

• Actual evapotranspiration

– amount of water annually transpired by plants and evaporated from a landscape

– related to net primary production

Figure 54.8Actual evapotranspiration (mm H2O/yr)

Tropical forest

Temperate forest

Mountain coniferous forest

Temperate grassland

Arctic tundra

Desertshrubland

Net

prim

ary

prod

uctio

n (g

/m2 /

yr)

1,000

2,000

3,000

0500 1,000 1,5000


Nutrients

• local scale

– soil nutrient often limiting

Figure 54.9

EXPERIMENT Over the summer of 1980, researchers added phosphorus to some experimental plots in the salt marsh, nitrogento other plots, and both phosphorus and nitrogen to others. Some plots were left unfertilized as controls.

RESULTS

Experimental plots receiving just phosphorus (P) do not outproduce the unfertilized control plots.

CONCLUSION

Live

, ab

ove-

grou

nd b

iom

ass

(g d

ry w

t/m

2)

Adding nitrogen (N) boosts net primaryproduction.

300

250

200

150

100

50

0June July August 1980

N P

N only

Control

P only

These nutrient enrichment experiments confirmed that nitrogen was the nutrient limiting plant growth in this salt marsh.


Energy transfer

• Between trophic levels < 20% efficient

• 2o production

– amount of chemical energy in consumers’ food converted to own new biomass during a given period of time


Production Efficiency

• When a caterpillar feeds on a plant leaf

– Only about one-sixth of the energy in the leaf is used for secondary production

Figure 54.10

Plant materialeaten by caterpillar

Cellularrespiration

Growth (new biomass)

Feces100 J

33 J

200 J

67 J


Production efficiency of organism

– Fraction of energy stored in food that is not used for respiration


Trophic Efficiency and Ecological Pyramids

• Trophic efficiency

– percentage of production transferred from one trophic level to the next

– ranges from 5% to 20%


Pyramids of Production

Figure 54.11

Tertiaryconsumers

Secondaryconsumers

Primaryconsumers

Primaryproducers

1,000,000 J of sunlight

10 J

100 J

1,000 J

10,000 J

• Shows energy loss


Biomass pyramids

– Show a sharp decrease at successively higher trophic levels

Figure 54.12a

(a) Most biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data froma bog at Silver Springs, Florida.

Trophic level Dry weight(g/m2)

Primary producers

Tertiary consumers

Secondary consumers

Primary consumers

1.5

11

37809


• Certain aquatic ecosystems

– Have inverted biomass pyramids

Figire 54.12b

Trophic level

Primary producers (phytoplankton)

Primary consumers (zooplankton)

(b) In some aquatic ecosystems, such as the English Channel, a small standing crop of primary producers (phytoplankton)supports a larger standing crop of primary consumers (zooplankton).

Dry weight(g/m2)

21

4


Pyramids of Numbers

Figure 54.13

Trophic level Number of individual organisms

Primary producers

Tertiary consumers

Secondary consumers

Primary consumers

3

354,904

708,624

5,842,424


Energy flow dynamics

– important for human population

• Eating meat

– Is a relatively inefficient way of tapping photosynthetic production


• Worldwide agriculture could successfully feed many more people

– If humans all fed more efficiently, eating only plant material

Figure 54.14

Trophic level

Secondaryconsumers

Primaryconsumers

Primaryproducers


The Green World Hypothesis

• Terrestrial herbivores consume relatively little plant biomass because they are held in check by a variety of factors


• Most terrestrial ecosystems

– Have large standing crops despite large numbers of herbivores

Figure 54.15


• Several factors keep herbivores in check

– Plant defenses

– Nutrients

– Abiotic factors

– Intraspecific competition

– Interspecific interactions


Biogeochemical cycles

• Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem

• Life on Earth

– Depends on recycling of essential chemical elements


A General Model of Chemical Cycling

• Gaseous forms of carbon, oxygen, sulfur, and nitrogen

– Occur in the atmosphere and cycle globally

• Less mobile elements, including phosphorous, potassium, and calcium

– Cycle on a more local level


Model of nutrient cycling

– Includes main reservoirs of elements and processes that transfer elements between reservoirs

Figure 54.16

Organicmaterialsavailable

as nutrients

Livingorganisms,detritus

Organicmaterials

unavailableas nutrients

Coal, oil,peat

Inorganicmaterialsavailable

as nutrients

Inorganicmaterials

unavailableas nutrients

Atmosphere,soil, water

Mineralsin rocksFormation of

sedimentary rock

Weathering,erosion

Respiration,decomposition,excretion

Burningof fossil fuels

Fossilization

Reservoir a Reservoir b

Reservoir c Reservoir d

Assimilation, photosynthesis


• All elements

– Cycle between organic and inorganic reservoirs


Biogeochemical Cycles

• The water cycle and the carbon cycle

Figure 54.17

Transportover land

Solar energy

Net movement ofwater vapor by wind

Precipitationover ocean

Evaporationfrom ocean

Evapotranspirationfrom land

Precipitationover land

Percolationthroughsoil

Runoff andgroundwater

CO2 in atmosphere

Photosynthesis

Cellularrespiration

Burning offossil fuelsand wood

Higher-levelconsumersPrimary

consumers

DetritusCarbon compounds in water

Decomposition

THE WATER CYCLE THE CARBON CYCLE


• Water moves in a global cycle

– Driven by solar energy

• The carbon cycle

– Reflects the reciprocal processes of photosynthesis and cellular respiration


• The nitrogen cycle and the phosphorous cycle

Figure 54.17

N2 in atmosphere

Denitrifyingbacteria

Nitrifyingbacteria

Nitrifyingbacteria

Nitrification

Nitrogen-fixingsoil bacteria

Nitrogen-fixingbacteria in rootnodules of legumes

Decomposers

Ammonification

Assimilation

NH3 NH4+

NO3

NO2

Rain

Plants

Consumption

Decomposition

Geologicuplift

Weatheringof rocks

Runoff

SedimentationPlant uptakeof PO4

3

Soil

Leaching

THE NITROGEN CYCLE THE PHOSPHORUS CYCLE


Decomposition and Nutrient Cycling Rates

• Decomposers (detritivores) play a key role

Figure 54.18

Consumers

Producers

Nutrientsavailable

to producers

Abioticreservoir

Geologicprocesses

Decomposers


Nutrient cycling rates

– Are extremely variable, mostly as a result of differences in rates of decomposition


Vegetation and Nutrient Cycling: The Hubbard Brook Experimental Forest

• Nutrient cycling

– Is strongly regulated by vegetation


Hubbard Brook

• The research team constructed a dam on the site

– To monitor water and mineral loss

Figure 54.19a

(a) Concrete dams and weirs built across streams at the bottom of watersheds enabled researchers to monitor the outflow of water and nutrients from the ecosystem.


• Trees in one valley were cut down

• Sprayed with herbicides

Figure 54.19b(b) One watershed was clear cut to study the effects of the loss

of vegetation on drainage and nutrient cycling.


• Net losses of water and minerals

– Were found to be greater in disturbed area

Figure 54.19c(c) The concentration of nitrate in runoff from the deforested watershed was 60 times

greater than in a control (unlogged) watershed.

Nitr

ate

co

nce

ntr

atio

n in

ru

no

ff(m

g/L

)

Deforested

Control

Completion oftree cutting

1965 1966 1967 1968

80.0

60.0

40.0

20.0

4.0

3.02.0

1.0

0


• We are disrupting chemical cycles throughout the biosphere

• With human population increase

– Our activities disrupted trophic structure, energy flow, and chemical cycling of ecosystems in most parts of the world


Nutrient Enrichment

• Transporting nutrients

• Adding new materials (some toxic)


Agriculture and Nitrogen Cycling

• Agriculture constantly removes nutrients from ecosystems

– That would ordinarily be cycled back into the soil

Figure 54.20


• Agriculture has a great impact on nitrogen cycle

• Fertilizer used to replace nitrogen

– But the effects on an ecosystem can be harmful


Contamination of Aquatic Ecosystems

• The critical load for a nutrient

– Is the amount of that nutrient that can be absorbed by plants in an ecosystem without damaging it


• When critical load exceeded

– Remaining nutrients can contaminate groundwater and freshwater and marine ecosystems


• Sewage runoff contaminates freshwater ecosystems

• Eutrophication

• Change in species composition or species loss


Acid Precipitation

• Combustion of fossil fuels

– Is the main cause of acid precipitation


• North American and European ecosystems downwind from industrial regions

– Have been damaged by rain and snow containing nitric and sulfuric acid

Figure 54.21

4.6

4.64.3

4.14.3

4.6

4.64.3

Europe

North America




• Environmental regulations and new industrial technologies

– Have allowed many developed countries to reduce sulfur dioxide emissions in the past 30 years


Toxins in the Environment

• Humans release an immense variety of toxic chemicals

– Including thousands of synthetics previously unknown to nature

• One of the reasons such toxins are so harmful

– Is that they become more concentrated in successive trophic levels of a food web


• In biological magnification

– Toxins concentrate at higher trophic levels because at these levels biomass tends to be lower

Figure 54.23

Con

cent

ratio

n of

PC

Bs

Herringgull eggs124 ppm

Zooplankton 0.123 ppm

Phytoplankton 0.025 ppm

Lake trout 4.83 ppm

Smelt 1.04 ppm


• In some cases, harmful substances

– Persist for long periods of time in an ecosystem and continue to cause harm


Atmospheric Carbon Dioxide

• One pressing problem caused by human activities

– Is the rising level of atmospheric carbon dioxide


Rising Atmospheric CO2

• Due to the increased burning of fossil fuels and other human activities

– The concentration of atmospheric CO2 has been steadily increasing

Figure 54.24

CO

2 c

onc

en

trat

ion

(pp

m)

390

380

370

360

350

340

330

320

310

3001960 1965 1970 1975 1980 1985 1990 1995 2000 2005

1.05

0.90

0.75

0.60

0.45

0.30

0.15

0

0.15

0.30

0.45

Te

mp

era

ture

va

ria

tion

(C

)

Temperature

CO2

Year


How Elevated CO2 Affects Forest Ecology: The FACTS-I Experiment

• The FACTS-I experiment is testing how elevated CO2

– Influences tree growth, carbon concentration in soils, and other factors over a ten-year period

Figure 54.25


The Greenhouse Effect and Global Warming

• The greenhouse effect is caused by atmospheric CO2

– But is necessary to keep the surface of the Earth at a habitable temperature


• Increased levels of atmospheric CO2 are magnifying the greenhouse effect

– Which could cause global warming and significant climatic change


Depletion of Atmospheric Ozone

• Life on Earth is protected from the damaging effects of UV radiation

– By a protective layer or ozone molecules present in the atmosphere


• Satellite studies of the atmosphere

– Suggest that the ozone layer has been gradually thinning since 1975

Figure 54.26

Ozo

ne la

yer

thic

knes

s (D

obso

n un

its)

Year (Average for the month of October)

350

300

250

200

150

100

50

01955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005


• The destruction of atmospheric ozone

– Probably results from chlorine-releasing pollutants produced by human activity

Figure 54.27

1

2

3

Chlorine from CFCs interacts with ozone (O3),forming chlorine monoxide (ClO) and oxygen (O2).

Two ClO molecules react, forming chlorine peroxide (Cl2O2).

Sunlight causes Cl2O2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again.

Sunlight

Chlorine O3

O2

ClO

ClO

Cl2O2

O2

Chlorine atoms


• Scientists first described an “ozone hole”

– Over Antarctica in 1985; it has increased in size as ozone depletion has increased

Figure 54.28a, b

(a) October 1979 (b) October 2000

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Chapter 54