Ecology & Environmental
Problems
Dr. Ron Chesser
Lecture #3
27 January 2004
Assigned Reading: Chapter 5: The Human
Population as an Environmental Problem
Ecology & Environmental
Problems
• Lecture #1
• Dr. Ron Chesser
• Assigned Reading: Chapter 5: The
Human Population as an Environmental
Problem
THOMAS MALTHUS
Worries about human population growth are not new. Over 200 years
ago (1798) Thomas Malthus published An Essay on the Principle of
Population. In this book he pointed out that the human population
tends to grow geometrically, while the resources available to support it
tend to grow arithmetically. Under these conditions the population
must inevitably outgrow the supply of food that is available to fulfill its
needs. He postulated that population growth was already outpacing the
production of food supplies in 18th-century England. He predicted that
population growth would lead to degradation of the land, and
eventually massive famine, disease and war. Malthus presented his
theory in response to optimists of his day who thought that mankind's
ability to master the environment was limitless. Improvements in
agriculture and the industrial revolution postponed the disaster that
Malthus thought was imminent. But his ideas are even more applicable
today.
How Dense Can We Get?
• Human Population
Human Population
• More are born than can survive……
Human Population Growth
The current global population of a bit over 6 billion, at the historical
high r of about 2%:
N = 6 Bill * 0.02 = 120 million persons added per year
Whereas for the current global population of a bit over 6 billion and the
current r:
N = 6 Bill * .013 = 78 million persons added per year
(Note: since current population is 6.137 billion, this is actually nearly 80
million persons [79.8 million....)
This "small" difference in r translates into a difference of 42 million
people gained per year!
Human Population Growth
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The Earth's population was 6 billion in September, 1999.
It was only 2 billion in 1930!
Every second, three people are added to the world;
Every day a quarter of a million (about the size of
Lubbock) are added.
Every year, about 87 million people (about the population
of Mexico, or 3x the population of California) are added.
During the next 2.5 years, the equivalent of the U.S.
population will be added to the planet.
In the coming decade the increase is equal to adding an
extra China to the world's population.
Population is growing at a rate that will lead to doubling
by 2050.
China
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China's population in 2002 was estimated at 1.28 billion people, which is five
times higher than that of the U.S. and over 20% of the world’s total.
In China, a "one-child-per-couple" policy has been in effect since 1979, with
the (unmet) goal of limiting the nation's population to 1.2 billion by the year
2000.
The policy includes rewards for having only one child including monetary
grants, additional maternity leave, and increased land allocations for farmers.
The children of these couples are also given preferential treatment in
education, housing, and employment.
After her first child is born, a woman is required to wear an intrauterine
device, and removal of this device is considered a crime. Otherwise, one of
the parents must be sterilized. The penalties include fines, loss of land grants,
food, loans, farming supplies, benefits, jobs and discharge from the
Communist Party. In some provinces the fines can be up to 50% of a couple's
annual salary.
In many provinces sterilization is required after the couple has had two
children.
India
• In India, where family-planning efforts
have been less aggressive, the
population is growing much faster.
With 947 million inhabitants today,
India may overtake China as the world's
most populous nation, surpassing the 2
billion mark in 2025.
United States
• According to the U.S. Bureau of the Census, the resident population of
the United States, projected to 9/3/2003 at 6:22:06 PM EDT is
• 291,971,473
• COMPONENT SETTINGS
• One birth every.................................. 7 seconds
• One death every.................................. 13 seconds
• One international migrant (net) every............ 22 seconds
• Net gain of one person every..................... 9 seconds
Growth Rates
Region
Inhabitants/
% annual
sq.km. agricultural land growth rate
Asia
423
1.8
Europe
Africa
213
80
0.2
3.0
Former Soviet Union
Latin America
North America
69
58
55
0.7
1.9
0.7
Oceania
15
1.4
Human Population Growth
•96% of the projected addition of 3.6 billion people
during the period between now and 2030 will occur in
the developing nations.
•the overall growth rate is 2.1% per year.
•The fastest growing continent is Africa, which is
predicted to double in 23 years; it contains the fastest
growing nation, Kenya, with a doubling time of 20
years.
•The population of Latin America will double in 30
years, and Asia 36 years.
r = intrinsic rate of
increase
r  Births  Deaths
Numberalive
Growth = there are more born than die.
World Vital Events Per Time Unit: 2004
Natural
Time unit
Births
Deaths
increase
------------------------------------------------Year
Month
128,970,393
56,202,306
72,768,087
10,747,533
4,683,526
6,064,007
Day
352,378
153,558
198,820
Hour
14,682
6,398
8,284
Minute
245
107
138
Second
4.1
1.8
2.3
-------------------------------------------------
Especially since 1960, several developments have
dramatically reduced infant and child mortality
throughout the world
• the use of DDT to eliminate mosquito-borne
malaria
• childhood immunization programs against cholera,
diphtheria and other often-fatal diseases
• antibiotics.
• During the same period, the "Green Revolution"
greatly boosted food output through the cultivation
of new disease-resistant rice and other food crops,
and the use of fertilizers and more effective
farming methods.
World Population Growth
Models of population growth
Exponential growth: Nt = Nt-1 + rNt-1
= N0er t
0
t=generation
r=intrinsic increase rate
N
Nt = population size at time t.
Nt-1=population size in prior generation
N0=initial population size
e=exponential
r0=ln(1+r)
t
Carrying Capacity
The theoretical number of individuals that can be
supported by the resources within an ecosystem.
Earth’s Resources
• we have already transformed or degraded 39-50% of the Earth's land
surface (agriculture, urban).
• we use 8% of the primary productivity of the oceans.
• we have increased atmospheric CO2 concentration by 30%
• we use more than half of the accessible surface fresh water
• over 50% of terrestrial nitrogen fixation is caused by human activity
(use of nitrogen fertilizer, planting of nitrogen-fixing crops, release of
reactive nitrogen from fossil fuels into the atmosphere)
• on many islands, more than half of plant species have been
introduced by man; on continental areas the fraction is 20% or more
• about 20% of bird species have become extinct in the past 200 years,
almost all of them because of human activity
• 22% of marine fisheries are overexploited or depleted, 44% more are
at the limit of exploitation
POPULATION AND AVAILABILITY OF
RENEWABLE RESOURCES
1990
Population (millions)
2010
Total
Change (%)
Per Capita
Change (%)
5,290
7,030
33
85
102
20
-10
237
277
17
-12
Cropland (million hectares)
1,444
1,516
5
-21
Rangeland and Pasture
(million hectares)
3,402
3,540
4
-22
Forests (million hectares)
3,413
3,165
-7
-30
Fish Catch (million tons)
Irrigated Land
(million hectares)
Models of population growth
Logistic Population growth:
Nt = K/(1+[[K-N0]/N0]e-rt)
t=generation
r=intrinsic increase rate
Nt = population size at time t.
K=carrying capacity
N0=initial population size
e=exponential
N
K
t
Carrying Capacity = 15 Bil
14 000 000 000
Population Size
13 000 000 000
12 000 000 000
11 000 000 000
10 000 000 000
9 000 000 000
8 000 000 000
7 000 000 000
6 000 000 000
0
20
40
60
80
100
Years
120
140
160
180
200
Human Population Growth
Was Thomas Malthus correct?
I.Practice problems
A. At the beginning of 2000, the human population had reached a size of
6,000,000,000. Assuming that r=0.001 (the intrinsic rate of growth of
Lithuania) and an exponential growth model, what will the size of the human
population be in 2025?
Press
B. Now, assuming the same information in A, but with r=0.018 (the intrinsic
rate of growth of Rwanda), use the exponential growth model to estimate the
size of the human population in 2025?
Press
C. Using the information in Problem A, plus a hypothetical carrying capacity,
K=10,000,000,000 for the earth, estimate the size of the human population in
2025, using the logistic growth model?
Press
D. Repeat C, except assume that r=0.018.
Press
r = 0.001 (as in Latvia)
Human Population Growth
6,350,000,000.00
Population Size
6,300,000,000.00
6,250,000,000.00
6,200,000,000.00
6,150,000,000.00
6,100,000,000.00
6,050,000,000.00
6,000,000,000.00
5,950,000,000.00
0
10
20
30
Years
40
50
r=0.001 and r=0.013
Human Population Growth
12,000,000,000
Population Size
11,000,000,000
10,000,000,000
9,000,000,000
8,000,000,000
7,000,000,000
6,000,000,000
0
10
20
30
Years
40
50
60
Rising Death Rates
• In 1999 the Worldwatch Inst. reported that rising death rates are
slowing world population growth for the first time since famine killed 30
million people in China in 1959-61. Partly because of these rising death
rates, the U.N. revised its estimate for world population in 2025 from 9.4
to 8.9 billion. Three factors are pushing the death rates up, especially in
sub-Saharan Africa and the Indian sub-continent:
• the HIV epidemic - between a fifth and a quarter of adults are already
infected in Zimbabwe, Botswana, Namibia, Zambia and Swaziland. In
India, four million adults are now HIV positive, more than in any other
country.
• the depletion of aquifers - another serious problem in India, where water
tables are falling annually by 1- 3 meters over much of the country.
• shrinking cropland area per person. More than half of the children in
India are already malnourished and underweight. Dwindling cropland
also threatens food security in Nigeria, Ethiopia and Pakistan.