Chapter 54
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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

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Chapter 54

Chapter 54

Ecosystems


Chapter 54

  • 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


Chapter 54

  • Regardless of an ecosystem’s size

    • Its dynamics involve two main processes: energy flow and chemical cycling

  • Energy flows through ecosystems

    • While matter cycles within them


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)


Chapter 54

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


Chapter 54

Figure 54.3

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

    • By decomposing organic material and returning elements to inorganic reservoirs


Chapter 54

  • Concept 54.2: Physical and chemical factors limit primary production in ecosystems

  • Primary production in an ecosystem

    • Is the amount of light energy converted to chemical energy by autotrophs during a given time period


Ecosystem energy budgets

Ecosystem Energy Budgets

  • 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

  • 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


Chapter 54

  • Net primary production (NPP)

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

  • Only NPP

    • Is available to consumers


Nutrient limitation

Nutrient Limitation

  • More than light, nutrients limit primary production

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


Chapter 54

  • A limiting nutrient is the element that must be added

    • In order for production to increase in a particular area

  • Nitrogen and phosphorous

    • Are typically the nutrients that most often limit marine production


Chapter 54

Figure 54.7

  • 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

  • In terrestrial and wetland ecosystems climatic factors

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


Chapter 54

  • Concept 54.3: Energy transfer between trophic levels is usually less than 20% efficient

  • The secondary production of an ecosystem

    • Is the amount of chemical energy in consumers’ food that is converted to their own new biomass during a given period of time


Trophic efficiency and ecological pyramids

Trophic Efficiency and Ecological Pyramids

  • 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

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


Chapter 54

  • The dynamics of energy flow through ecosystems

    • Have important implications for the human population

  • Eating meat

    • Is a relatively inefficient way of tapping photosynthetic production


Chapter 54

Trophic level

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


Chapter 54

  • 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


Chapter 54

  • 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

  • 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


Chapter 54

  • Water moves in a global cycle

    • Driven by solar energy

  • The carbon cycle

    • Reflects the reciprocal processes of photosynthesis and cellular respiration


Chapter 54

  • Most of the nitrogen cycling in natural ecosystems

    • Involves local cycles between organisms and soil or water

  • The phosphorus cycle

    • Is relatively localized


Decomposition and nutrient cycling rates

Consumers

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


Chapter 54

  • Concept 54.5: The human population is disrupting chemical cycles throughout the biosphere

  • As the human population has grown in size

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


Nutrient enrichment

Nutrient Enrichment

  • In addition to transporting nutrients from one location to another

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


Chapter 54

  • Nitrogen is the main nutrient lost through agriculture

    • Thus, agriculture has a great impact on the nitrogen cycle

  • Industrially produced fertilizer is typically used to replace lost nitrogen

    • But the effects on an ecosystem can be harmful


Contamination of aquatic ecosystems

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


Chapter 54

  • When excess nutrients are added to an ecosystem, the critical load is exceeded

    • And the remaining nutrients can contaminate groundwater and freshwater and marine ecosystems


Chapter 54

  • Sewage runoff contaminates freshwater ecosystems

    • Causing cultural eutrophication, excessive algal growth, which can cause significant harm to these ecosystems


Acid precipitation

Acid Precipitation

  • Combustion of fossil fuels

    • Is the main cause of acid precipitation


Chapter 54

4.6

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


Chapter 54

Field pH

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

  • 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


Chapter 54

Herring

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

  • One pressing problem caused by human activities

    • Is the rising level of atmospheric carbon dioxide


Rising atmospheric co 2

1.05

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

  • The greenhouse effect is caused by atmospheric CO2

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


Chapter 54

  • Increased levels of atmospheric CO2 are magnifying the greenhouse effect

    • Which could cause global warming and significant climatic change


Depletion of atmospheric ozone

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


Chapter 54

350

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


Chapter 54

Chlorine from CFCs interacts with ozone (O3),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


Chapter 54

(b) October 2000

(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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