f human impact. copyright © 2008 pearson education, inc., publishing as pearson benjamin cummings...

Human Impact

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Ch. 53.5 Population Change and Population Density

• In density-independent populations, birth rate and death rate do not change with population density

• In density-dependent populations, birth rates fall and death rates rise with population density


Density-Dependent Population Regulation

• Density-dependent birth and death rates are an example of negative feedback that regulates population growth

• They are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors


Competition for Resources

• In crowded populations, increasing population density intensifies competition for resources and results in a lower birth rate


Fig. 53-22

8000B.C.E.

3000B.C.E.

1000B.C.E.

0 2000C.E.

0

1

2

3

4

5

6

The Plague

Hu

man

po

pu

lati

on

(b

illio

ns)

7

Concept 53.6: The human population is no longer growing exponentially but is still increasing rapidly

• No population can grow indefinitely, and humans are no exception

– The human population increased relatively slowly until about 1650 and then began to grow exponentially

Fig. 53-23

2005

Projecteddata

An

nu

al p

erc

ent

incr

ease

Year1950 1975 2000 2025 2050

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

Though the global population is still growing, the rate of growth began to slow during the 1960s


Regional Patterns of Population Change

• To maintain population stability, a regional human population can exist in one of two configurations:

– Zero population growth = High birth rate – High death rate

– Zero population growth =Low birth rate – Low death rate

• The demographic transition is the move from the first state toward the second state

Fig. 53-24

1750 1800 1900 1950 2000 2050

Year

1850

Sweden MexicoBirth rate Birth rate

Death rateDeath rate0

10

20

30

40

50B

irth

or

dea

th r

ate

per

1,0

00 p

eop

le


• The demographic transition is associated with an increase in the quality of health care and improved access to education, especially for women

• Most of the current global population growth is concentrated in developing countries


Age Structure

• One important demographic factor in present and future growth trends is a country’s age structure

• Age structure is the relative number of individuals at each age

Fig. 53-25

Rapid growthAfghanistan

Male Female Age AgeMale Female

Slow growthUnited States

Male Female

No growthItaly

85+80–8475–7970–74

60–6465–69

55–5950–5445–4940–4435–3930–3425–2920–2415–19

0–45–9

10–14

85+80–8475–7970–74

60–6465–69

55–5950–5445–4940–4435–3930–3425–2920–2415–19

0–45–9

10–14

10 10 8 866 4 422 0Percent of population Percent of population Percent of population

66 4 422 08 8 66 4 422 08 8


• Age structure diagrams can predict a population’s growth trends

• They can illuminate social conditions and help us plan for the future


Global Carrying Capacity

• How many humans can the biosphere support?

– The carrying capacity of Earth for humans is uncertain

– The average estimate is 10–15 billion


Ch. 55.5: Human Impact on chemical cycles

• Humans release many toxic chemicals, including synthetics previously unknown to nature

• In some cases, harmful substances persist for long periods in an ecosystem

• One reason toxins are harmful is that they become more concentrated in successive trophic levels

• Biological magnification concentrates toxins at higher trophic levels, where biomass is lower


• Many pesticides such as DDT are subject to biological magnification in ecosystems

• In the 1960s Rachel Carson brought attention to the biomagnification of DDT in birds in her book Silent Spring


Fig. 55-20

Lake trout4.83 ppm

Con

cen

trat

ion

of

PC

Bs

Herringgull eggs124 ppm

Smelt1.04 ppm

Phytoplankton0.025 ppm

Zooplankton0.123 ppm


Greenhouse Gases and Global Warming

• One pressing problem caused by human activities is the rising level of atmospheric carbon dioxide

• Due to the burning of fossil fuels and other human activities, the concentration of atmospheric CO2 has been steadily increasing


Fig. 55-21

CO2

CO

2 con

cen

trat

ion

(p

pm

)

Temperature

1960300

Ave

rage

glo

bal

tem

per

atu

re (

ºC)

1965 1970 1975 1980Year

1985 1990 1995 2000 200513.6

13.7

13.8

13.9

14.0

14.1

14.2

14.3

14.4

14.5

14.6

14.7

14.8

14.9

310

320

330

340

350

360

370

380

390


The Greenhouse Effect and Climate

• CO2, water vapor, and other greenhouse gases reflect infrared radiation back toward Earth; this is the greenhouse effect

• This effect is important for keeping Earth’s surface at a habitable temperature

• Increased levels of atmospheric CO2 are magnifying the greenhouse effect, which could cause global warming and climatic change


• Increasing concentration of atmospheric CO2 is linked to increasing global temperature

• Northern coniferous forests and tundra show the strongest effects of global warming

• A warming trend would also affect the geographic distribution of precipitation


• Global warming can be slowed by reducing energy needs and converting to renewable sources of energy

• Stabilizing CO2 emissions will require an international effort


Depletion of Atmospheric Ozone

• Life on Earth is protected from damaging effects of UV radiation by a protective layer of ozone molecules in the atmosphere

• Satellite studies suggest that the ozone layer has been gradually thinning since 1975


Ozo

ne

laye

r th

ick

nes

s (D

obso

ns)

Fig. 55-23

Year’052000’95’90’85’80’75’70’65’601955

0

100

250

200

300

350


• Destruction of atmospheric ozone probably results from chlorine-releasing pollutants such as CFCs produced by human activity

Fig. 55-24

O2

Sunlight

Cl2O2

Chlorine

Chlorine atom

O3

O2

ClO

ClO


(a) September 1979 (b) September 2006

• Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased


• Ozone depletion causes DNA damage in plants and poorer phytoplankton growth

• An international agreement signed in 1987 has resulted in a decrease in ozone depletion

Ch. 56 Biodiversity crisis

Extinction ~ natural phenomenon, however, rate is of concern…..

50% loss of species when 90% of habitat is lost

Major Threats to Biodiversity Habitat destruction ~ single

greatest threat; species designation as extinct, endangered, vulnerable, rare; 93% of coral reefs

Competition by exotic (non-native) species ~ cause of species designation as extinct, endangered, vulnerable, rare; travel

Overexploitation ~ commercial harvest or sport fishing; illegal trade

Biodiversity: Human welfare

25% of all medical prescriptions

Genetic variability Aesthetic and ethical

reasons Species survival

Conservation biology focus Preservationism: setting

aside select areas as natural and underdeveloped

Evolutionary / ecological view: natural systems result from millions of years of evolution and ecosystem processes are necessary to maintain the biosphere

Geographic distribution of biodiversity

Energy availability ~ solar radiation

Habitat heterogeneity ~ environmental patchiness

Niche specialization ~ narrow resource range specialization

Population interactions ~ complex population interactions

Population & species level conservation

Biodiversity hot spot: small area with an exceptional concentration of species

Endemic species: species found nowhere else

Endangered species: organism “in danger of extinction”

Threatened species: likely to become endangered in the foreseeable future

Human Impact Biological magnification:

trophic process in which retained substances become more concentrated at higher levels

Ozone depletion: effect of chlorofluorocarbons (CFC’s) released into the atmosphere

Rainforest destruction Cause: Overpopulation?

Air Pollution Major contributions:

– CO2, CFCs, etc. Smog

– Thermal inversion traps pollution

Acid Rain Ozone Thinning

– CFCs convert O3 into O2 by reconfiguration of bonds

– Leads to increased incidence of ultraviolet radiation

Waste Management Density-

dependent factor that limits space available for other purposes

Green revolution- can we improve already existing agricultural lands rather than create more?

Deforestation Effects of

deforestation:– Reduced

productivity– Increased erosion

due to lessening of root structures

– Sediment build up

– Increase in CO2

Most water on earth is unusable (salt content)

Desalination- conversion of salt water into freshwater (energetically costly)

Agriculture accounts for massive water use worldwide

Water pollution Legislative measures may

influence water use

Water considerations

Sixty-six percent of a human being is water. Seventy-five percent of the human brain is water. Seventy-five percent of a living tree is water. You could survive about a month without food, but only 5 to 7 days

without water. On the average, each American uses about 160 gallons of water a day

at a cost of 27 cents. Bottled water may cost up to 1000 times more than municipal may not

be as safe. Two-thirds of the water used in an average home is used in the

bathroom. Typically 4 to 6 gallons of water are used for every toilet flush. On the average, a person uses 2 gallons of water to brush his or her

teeth each day. A 10-minute shower uses about 55 gallons of water. A leaking faucet can waste up to 100 gallons of water a day.

Water Facts

Energy Consumption Disappearance of non-

renewable fuel sources could be our biggest coming ecological issue

Non-renewable Sources– Fossil fuels (coal, petroleum,

nat. gas)– Nuclear Energy

Alternative Sources1. Solar-Hydrogen2. Wind3. Fusion

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