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Chapter 54. Ecosystems. Overview: Ecosystems, Energy, and Matter An ecosystem consists of all the organisms living in a community As well as all the abiotic factors with which they interact. Regardless of an ecosystem’s size

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Chapter 54

Chapter 54

Ecosystems




Ecosystems and physical laws
Ecosystems and Physical Laws

  • The laws of physics and chemistry apply to ecosystems

    • Particularly in regard to the flow of energy

  • Energy is conserved

    • But degraded to heat during ecosystem processes


Trophic relationships
Trophic Relationships

  • Energy and nutrients pass from primary producers (autotrophs)

    • To primary consumers (herbivores) and then to secondary consumers (carnivores)


Tertiary consumers

Microorganisms

and other

detritivores

Secondary

consumers

Primary consumers

Detritus

Primary producers

Heat

Key

Chemical cycling

Sun

Energy flow

Figure 54.2

  • Energy flows through an ecosystem

    • Entering as light and exiting as heat


Decomposition
Decomposition

  • Decomposition

    • Connects all trophic levels


Figure 54.3

  • Detritivores, mainly bacteria and fungi, recycle essential chemical elements

    • By decomposing organic material and returning elements to inorganic reservoirs



Ecosystem energy budgets
Ecosystem Energy Budgets production in ecosystems

  • The extent of photosynthetic production

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


Gross and net primary production
Gross and Net Primary Production production in ecosystems

  • Total primary production in an ecosystem

    • Is known as that ecosystem’s gross primary production (GPP)

  • Not all of this production

    • Is stored as organic material in the growing plants


  • Net primary production (NPP) production in ecosystems

    • Is equal to GPP minus the energy used by the primary producers for respiration

  • Only NPP

    • Is available to consumers


Nutrient limitation
Nutrient Limitation production in ecosystems

  • More than light, nutrients limit primary production

    • Both in different geographic regions of the ocean and in lakes



Figure 54.7 production in ecosystems

  • In some areas, sewage runoff

    • Has caused eutrophication of lakes, which can lead to the eventual loss of most fish species from the lakes


Primary production in terrestrial and wetland ecosystems
Primary Production in Terrestrial and Wetland Ecosystems production in ecosystems

  • In terrestrial and wetland ecosystems climatic factors

    • Such as temperature and moisture, affect primary production on a large geographic scale



Trophic efficiency and ecological pyramids
Trophic Efficiency and Ecological Pyramids usually less than 20% efficient

  • Trophic efficiency

    • Is the percentage of production transferred from one trophic level to the next

    • Usually ranges from 5% to 20%


Pyramids of production

Tertiary usually less than 20% efficient

consumers

10 J

Secondary

consumers

100 J

Primary

consumers

1,000 J

Primary

producers

10,000 J

Figure 54.11

1,000,000 J of sunlight

Pyramids of Production

  • This loss of energy with each transfer in a food chain

    • Can be represented by a pyramid of net production



Trophic level usually less than 20% efficient

Secondary

consumers

Primary

consumers

Primary

producers

  • Worldwide agriculture could successfully feed many more people

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

Figure 54.14


  • The green world hypothesis proposes several factors that keep herbivores in check

    • Plants have defenses against herbivores

    • Nutrients, not energy supply, usually limit herbivores

    • Abiotic factors limit herbivores

    • Intraspecific competition can limit herbivore numbers

    • Interspecific interactions check herbivore densities


  • Concept 54.4: Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem

  • Life on Earth

    • Depends on the recycling of essential chemical elements

  • Nutrient circuits that cycle matter through an ecosystem

    • Involve both biotic and abiotic components and are often called biogeochemical cycles


A general model of chemical cycling
A General Model of Chemical Cycling nutrients between organic and inorganic parts of the ecosystem

  • 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


  • Water moves in a global cycle nutrients between organic and inorganic parts of the ecosystem

    • Driven by solar energy

  • The carbon cycle

    • Reflects the reciprocal processes of photosynthesis and cellular respiration



Decomposition and nutrient cycling rates

Consumers nutrients between organic and inorganic parts of the ecosystem

Producers

Decomposers

Nutrients

available

to producers

Abiotic

reservoir

Geologic

processes

Figure 54.18

Decomposition and Nutrient Cycling Rates

  • Decomposers (detritivores) play a key role

    • In the general pattern of chemical cycling



Nutrient enrichment
Nutrient Enrichment cycles throughout the biosphere

  • In addition to transporting nutrients from one location to another

    • Humans have added entirely new materials, some of them toxins, to ecosystems



Contamination of aquatic ecosystems
Contamination of Aquatic Ecosystems cycles throughout the biosphere

  • The critical load for a nutrient

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




Acid precipitation
Acid Precipitation critical load is exceeded

  • Combustion of fossil fuels

    • Is the main cause of acid precipitation


4.6 critical load is exceeded

4.3

4.6

4.3

4.6

4.1

4.3

4.6

Europe

Figure 54.21

North America

  • North American and European ecosystems downwind from industrial regions

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


Field pH critical load is exceeded

5.3

5.2–5.3

5.1–5.2

5.0–5.1

4.9–5.0

4.8–4.9

4.7–4.8

4.6–4.7

4.5–4.6

4.4–4.5

4.3–4.4

Figure 54.22

4.3

  • By the year 2000

    • The entire contiguous United States was affected by acid precipitation


Toxins in the environment
Toxins in the Environment critical load is exceeded

  • 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


Herring critical load is exceeded

gull eggs

124 ppm

Lake trout 4.83 ppm

Concentration of PCBs

Smelt

1.04 ppm

Zooplankton

0.123 ppm

Phytoplankton

0.025 ppm

Figure 54.23

  • In biological magnification

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


Atmospheric carbon dioxide
Atmospheric Carbon Dioxide critical load is exceeded

  • One pressing problem caused by human activities

    • Is the rising level of atmospheric carbon dioxide


Rising atmospheric co 2

1.05 critical load is exceeded

390

0.90

380

0.75

370

Temperature

0.60

360

0.45

350

CO2 concentration (ppm)

Temperature variation (C)

0.30

340

CO2

0.15

330

0

320

0.15

310

 0.30

 0.45

300

1975

1980

1985

1990

1995

2000

2005

1960

1965

1970

Year

Figure 54.24

Rising Atmospheric CO2

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

    • The concentration of atmospheric CO2 has been steadily increasing


The greenhouse effect and global warming
The Greenhouse Effect and Global Warming critical load is exceeded

  • The greenhouse effect is caused by atmospheric CO2

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



Depletion of atmospheric ozone
Depletion of Atmospheric Ozone critical load is exceeded

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

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


350 critical load is exceeded

300

250

Ozone layer thickness (Dobson units)

200

150

100

50

0

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Year (Average for the month of October)

Figure 54.26

  • Satellite studies of the atmosphere

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


Chlorine from CFCs interacts with ozone (O critical load is exceeded3),forming chlorine monoxide (ClO) and

oxygen (O2).

1

Chlorine atoms

O2

Chlorine

O3

ClO

O2

Sunlight causes Cl2O2 to break down into O2and free chlorine atoms. The chlorine atoms can begin the cycle again.

3

ClO

Cl2O2

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

2

Sunlight

Figure 54.27

  • The destruction of atmospheric ozone

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


(b) October 2000 critical load is exceeded

(a) October 1979

  • Scientists first described an “ozone hole”

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

Figure 54.28a, b


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