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Population Dynamics
Unit 2
APES
Why study Human Population?
• The World may or may be soon overpopulated.
• Environmental Problems of Overpopulation:
▫ Resource Depletion
▫ Environmental Degradation
Essential Questions
• What is the history of human population growth,
and how many people are likely to be here by
2050?
• How is population size affected by birth, death,
fertility, and migration rates?
• How is population size affected by percentages
of males and females at each level?
• How can we slow population growth?
• What success have India & China had in slowing
population growth?
• What are major impacts of human activities on
the world’s natural ecosystems?
Is the World Overpopulated?
• World pop is projected to increase from 6.6 billion
to 8.9 billion between 2006 & 2050.
• The debate over interactions between population
growth, economic growth, politics, and moral beliefs
is one of the most important and controversial
issues in environmental science.
• Much of the world’s population growth is occurring
in developing countries like China & India.
Is the World Overpopulated?
• Some people argue that the planet has too many
people.
• Some feel that the world can support billions of
more people due to technological advances.
• There is a constant debate over the need to
reduce population growth.
▫ However, moral, religious, and personal freedoms
must be considered.
Brief History of
Human Population Growth
• Grew slowly at first but has grown rapidly
recently because of the expansion of agriculture
and industrial production (Industrial
Revolution) AND lower death rates from
improvements in hygiene and medicine.
• In 2006, the population of developed countries
grew exponentially at 0.1% per year, while,
developing countries grew at 1.5% per year (15x
faster)
Where is the World Population
Headed?
• We do not know how long we can continue to
increase the Earth’s capacity for human before
the environment breaks down.
▫ There are likely to be between 7.2-10.6 billion
people of Earth by 2050.
▫ 97% of the population growth will come from
people in developing countries living in acute
poverty (< $2 USD/day ~12 Yuan/day)
UN Projections for Pop Growth
Projections based on high,
medium, or low world
average fertility rates (# of
children/woman).
•High 2.5
•Medium 2.0
•Low 1.5
Opposite Views Of Population Growth
& Issues
• Thomas Malthus
Human Pops grow
exponentially until
disease or famine, or
social conditions
reduced fertility
rates.
Opposite Views Of Population Growth
& Issues
Pop Growth results from
• Karl Marx
poverty and social ills. Pop
Growth would slow if all
people were treated justly.
Population Dynamics ~ The Basics
• Biotic Potential: reproductive rate of an organism if
resources were unlimited & conditions were ideal.
• For example the common housefly can lay 120 eggs
in each generation (56 days). If nothing hurt the
eggs or the flies, in 7 generations (1 year) there
would be 5.6 trillion flies from 1 proud parent!
• However, there are of course limiting factors.
▫ Scarcity of resources, competition, predation, disease,
accidents, etc.
“J Curve”
Environmental Resistance
• Exponential growth can only with unlimited
resources, but factors usually limit growth
(environmental resistance).
• Carrying Capacity (K): Number of organisms
that an area can support without depleting
Rapid
resources
Growth
Pop Rise
Below
K
Overshoot
K
Pop Crash
Adapting to Environmental Resistance
• Over time species may increase their carrying
capacity by developing adaptations.
• Some species maintain their carrying capacity by
migrating to other areas.
• So far, technological, social, and other cultural
changes have extended the earth’s carrying
capacity for humans.
Growth Patterns:
• EXPONENTIAL GROWTH:
pop growth increases at a
constant rate per unit of time.
• 2-4-8-16-32-64-….
• LOGISITIC GROWTH: pop
growth is slowed as it
approached carry capacity due
to scarcity of resources, etc.
Logistic
Growth
“S Curve”
Rapid
Growth
Pop Rise
Below
K
Overshoot
K
Pop Crash
Population Density
• Number of organisms in a defined space
• Density Dependent: growth rate depends on the
population density.
▫ Disease, stress, predation, etc.
▫ Logistic Growth is density dependent
• Density Independent: population control factors
not dependent on population density.
▫ Drought, fire, habitat destruction, weather
Reproductive Strategies
r-selected & K-selected species
Responding to Limits:
Survivorship Curves
Late loss
Early loss
Age
Factors that Affect Population Growth
• r = (B+I) – (D+E)
•
•
•
•
•
rate of growth
B = births
I = immigration
D = deaths
E = emigration
Demographics
• Vital statics about people such as
▫
▫
▫
▫
▫
▫
▫
Births,
Deaths,
Immigration
Emigration
Where they live
Population size,
Etc.
The Young, Poor, & Growing Countries
• Asia, Africa, & Latin America
• 80% of the world population, 90% of projected
growth
• Highest growth “hot spots”
▫ Sub-Saharan Africa, Middle East
▫ Economics, politics, religion, civil unrest,
▫ High birth rates, low contraceptive use)
• Highest growth rates
▫ United Arab Emirates @ 6.8%
The Older, Rich, Relatively Stable
Countries
• N. America, W. Europe, Japan, Australia, & New
Zealand
• Italy, Germany, Hungary & Japan have declining
growth rates.
▫ Average age = 40, Life expectancy = 90, women
are choosing to not have children
▫ Japan is currently around 127 million and
expected to decrease to 100 million in 2050
1) Fertility/Birth Rates
• Crude Birth Rate (B): number of births in a year per
1000 people
• Total Fertility Rate (TFR): number of children born
to an average woman in her reproductive life.
• Replacement Level Fertility (RLF): number of
children needed to replace the parents.
▫ About 2.1 children in developed countries
▫ Higher in other countries with a high infant mortality
rate
1) Fertility/Birth Rates Cont.
• Rates have declined in every region except for
Africa
▫ Thailand reduced their TFR from 7.0 in 1979 to
1.64 in 2009
▫ China went from a TFR 6.0 in 1970 to 1.8 in 1990
to 1.6 in 2009 due to the one-child policy
▫ Macao has lowest TFR in the world with 0.9
• World Average TFR = 2.6
Factors Affecting Fertility & Birth
Rates
•
•
•
•
•
•
•
•
•
Cost of raising & educating the children
Availability of pensions
Urbanization
Education & employment opportunities
Infant deaths
Marriage age
Availability of contraception & abortion
Women’s Rights within a culture
Cultural beliefs, traditions, & cultural norms
2) Mortality (Death) Rates
• Crude Death Rate: number of deaths per 1000
people in year
▫ Less Developed countries, such as Africa, see
death rates of 20+/1000.
▫ Wealthier countries see about 10/1000
• Infant Mortality Rate: Number of child/infant
deaths.
• Natural Increase = crude birth rate – crude death rate
Factors Affecting Mortality Rates
• Increased food supplies and distribution.
• Better nutrition
• Medical & public health technology
(immunizations/antibiotics)
• Improved sanitation & personal hygiene
• Safety of water supplies
2006
3) Immigration & Emigration
• Immigration (I): people migrating into a population
• Emigration (E): people migrating out of a population
• Net Migration (I-E): Total number of people moving in
and out of a population
r = (B+I) – (D+E)
• Total Growth rate (r): calculate using crude
rates (per 1000) and divide by 10 = percentage
• Zero Population Growth (ZPG): when B+I =
D+E
• Doubling time: amount of time it takes for a
population to double
▫ Rule of 70s: Divide 70 by annual natural increase
equal the approximate doubling time
r = (B+I) – (D+E)
If a population of 10,000
experiences 100 births, 40 deaths,
10 immigrants and 30 emigrants in
a year, what is the net annual
percentage growth rate?
Doubling Time
• If a population of a country grows at a
rate of 5% a year, the number of years
required for the pop to double is
what?
• The world’s 10 most
populous countries
in 2006 with
projections in 2025.
U.S. Trends
• Nearly 2.9 million people added to the US in
2006.
▫ 59% occurred because of births outnumbering
deaths.
▫ 41% came from illegal and legal immigration.
• Sharp Rise in US birth rates during 1946-1964
called the Baby boom.
▫ Economic success & Men returning home from
war.
US Trends
• The baby bust that followed the baby boom was
largely due to delayed marriage, contraception, and
abortion.
Case Study: Fertility and Birth Rates
in the United States
• In 2006, the total fertility rate in the United
States was slightly > 2.0
U.S. Trends
Since 1820, the U.S.
has admitted almost
twice as many
immigrants and
refugees as all other
countries combined.
U.S. Trends
• U.S. infant mortality is higher than it could be
(ranked 46th world-wide) due to:
▫ Inadequate pre- and post-natal care for poor.
▫ Drug addiction.
▫ High teenage birth rate.
4) Life Expectancy (LE)
• Age that a newborn infant can be expected to live
to (average age of death)
• Most population growth is due to a decline in
death rates b/c of longer life expectancy.
• General Trends:
▫ More developed countries have higher LE
▫ Women tend to have higher LE than men
▫ More money, longer life
Implications of Longer Lives on
Populations
• Increased dependency ratio:
▫ Number of non-working compared to working
individuals in a population.
▫ Countries, such as US & Japan, are seeing the
number in the working force decline as the
number of retiring individuals increases.
Age Structure
• Percentage of people in young, middle, and older
age groups determines how fast populations grow or
decline.
• Generation time: time it takes for one generation to
pass
• The number of people younger than age 15 is the
major factor determining a country’s population
growth.
• Changes in the distribution of a country’s age groups
have long-lasting economic and social impacts.
Histograms
• Graphs that shows the different age classes of a
population
▫ Pre-reproductive age (14 and under)
 Not mature enough to reproduce
▫ Reproductive age (15-45)
 Able to reproduce
▫ Post-reproductive age (46 and older)
 To old to reproduce
• Broken down by age. You can see the birth rate,
maturity rate and death rate of an entire
population. Usually broken down by country
Histograms
• Populations with a large proportion of its
people in the reproductive ages 1-14 have a
large potential for rapid population growth.
• 32% of the people in
developing
countries were
under 15 years old
in 2006 versus only
17% in developed
countries.
• Today, baby boomers make up nearly half of
all adult Americans and dominate the
populations demand for goods and services.
Expansive/rapid growth
• Birth rate exceeds the death rate.
Population is getting larger.
Pyramid shaped histogram.
• Ex’s. Kenya, Nigeria and Saudi
Arabia.
Stable/Slow Growth (Zero Growth)
• Birth rate almost equals death rate. The
population is not getting any larger or is growing
very slowly. Histogram shape is straighter and
more box-like until about age 45-85.
• Ex. US, Australia & Canada has slow
• Denmark, Austria and Italy has stable
Declining (negative growth)
• When the birth rate is smaller
than the death rate. The pyramid
bulges near the top or is inverted.
• Ex. Germany, Bulgaria &
Hungary.
Declining (negative growth)
• When the birth rate is smaller
than the death rate. The pyramid
bulges near the top or is inverted.
•
• Ex. Germany, Bulgaria &
Hungary
5) Social & Economic Impacts
• More Children
▫
▫
▫
▫
Needed to help with income & chores
High infant mortality rates
Societal status/pride
Unmet need for contraceptives
• Less Children
▫ Higher education
▫ Career women
▫ Cost of raising child
Demographic Transitions
• Increased economic development accompanies
as decrease in death rates and birth rates.
•
•
•
•
Stage 1:
Stage 2:
Stage 3:
Stage 4:
Pre-Industrial
Transitional
Industrial
Post Industrial
Demographic Transitions
• Generalized model of demographic transition.
▫ Some developing countries may have difficulty making the
demographic transition.
Figure 9-14
Pre-Industrial
•
•
•
•
•
Kenya, Yemen, Libya, Jordan
Food shortage
Malnutrition
Lack of sanitation
Lack of medicine
• High Death rate ~35/1000
• High birth rate
• Little population growth
Demographic Transitions
• Generalized model of demographic transition.
▫ Some developing countries may have difficulty making the
demographic transition.
Figure 9-14
Transitional
•
•
•
•
Better sanitation
Economic development
Better jobs
Increase in medicine
• Death rate rapidly declining
• Birth rate increases (at first)
• Rapid Increase in population
Demographic Transitions
• Generalized model of demographic transition.
▫ Some developing countries may have difficulty making the
demographic transition.
Figure 9-14
Industrial
• Low birth rate
▫ better access to birth control
▫ decline in the infant mortality rate increased job
opportunities for women
▫ Spend more resources on fewer children
• Population grows due to population momentum
▫ More people in at the reproductive age
Conditions Needed for Demo Transition
• Improved standard of living
• Confidence that children will survive to maturity
• Improved social status of women
• Increase availability of birth control
Demographic Transitions
• Generalized model of demographic transition.
▫ Some developing countries may have difficulty making the
demographic transition.
Figure 9-14
Postindustrial
•
•
•
•
Low birth rate
Low death rate
Reaches ZPG - Stable but with more people
Then birth rates fall below death rates and negative
population growth occurs.
• 37 countries have reached this stage. (mainly in W.
Europe)
• To most population experts, the challenge is to help
the remaining 88% of the world to get to this stage.
Demographic Transitions
• Generalized model of demographic transition.
▫ Some developing countries may have difficulty making the
demographic transition.
Figure 9-14
Developing Countries• China is the largest but has taken drastic
population control methods.
• By 2050, India is predicted to pass it. Pakistan is
projected to become 3rd with Iran and Ethiopia
following.
• However, Russia is losing 600,000 people a year,
after being the 4th largest country in 1950. This is
because of environmental pollution, hyperinflation,
crime, corruption, disease and despair.
Controlling Population Growth
• Family Planning – allows couples to determine the
number & spacing of their children
▫ Women tend to have fewer children if they are
educated, holding a paying job, do not have their
rights suppressed.
• Birth control: method used to reduce birth
• China Vs India’s Family Planning Programs
▫ India has tried to slow their population growth with
only little success
▫ Since 1970, China has had the 1 child policy to cut its
birth rate in half and sharply reduce its fertility rate.
Percentage
of world
population
Population
20%
1.1 billion
1.3 billion
1.4 billion
1.6 billion
Population (2050)
(estimated)
Illiteracy (% of adults)
Total fertility rate
Infant mortality rate
47%
17%
36%
Population under age 15 (%)
Population growth rate (%)
20%
1.6%
0.6%
2.9 children per women (down from 5.3 in 1970)
1.6 children per women (down from 5.7 in 1972)
58
27
62 years
70 years
Life expectancy
Percentage living
below $2 per day
GDP PPP per capita
India
China
17%
80
47
$3,120
$5,890
Fig. 9-15, p. 186
China’s Family Planning Program
• 1 child policy
• TFR ~ 1.6 children/woman
• Moved 300 million people out of poverty
• Problems:
▫ Male preference = gender imbalance
▫ Average population age is increasing
▫ Not enough resources to support aging population
China’s Family Planning Program
• Couples who pledge to have only 1 child can receive:
▫
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Extra food
Larger pensions
Better housing
Free medical care
Salary bonuses
Free school tuition for their 1 child
Preferential treatment in employment for their child
▫
▫
▫
▫
Increase fees/ taxes
Eliminating tax deductions
Loss of health care benefits
Loss of job options
• More than 1 child?
• Boys vs. Girls
▫ Girls are aborted at a higher rate than boys
▫ Some infant girls are killed
▫ Male children are sometimes fed better than female children
India’s Family Planning Program
•
•
•
•
•
•
•
Failing
Poor Planning
Bureaucratic inefficiency
Low status of women
Extreme poverty
Lack of administrative financial support
Disagreement over the best ways to slow
population growth
Environmental Impact
• Paul Ehrlich Formula
• Environmental Impact = population X affluence X technology
• I=PAT
Environmental Impact: Developed
Countries
• High rate of resource use
• Results in high levels of pollution & environmental
degradation per person
• Estimated that US citizens consume 35X as much as
the average citizen of Indian and 100X as much a
person in the poorest countries.
▫ Poor parents in a developing country would need to
have 70-200 kids to have the same environmental
impact as 2 US kids.
Environmental Impact: Urbanization
• Urbanization leads to slums, fecal snow, disease
• Must import its food, water, energy, minerals, &
other resources
• Produce large amount of waste that pollutes air,
land, and water.
• 44% of world pop lives in urban areas that only
occupy 5% of the worlds land & consume 75% of the
world’s resources
Natural Capital Degradation
Altering Nature to Meet Our Needs
Reduction of biodiversity
Increasing use of the earth's net
primary productivity
Increasing genetic resistance of pest
species and disease-causing bacteria
Elimination of many natural predators
Deliberate or accidental introduction
of potentially harmful species into
communities
Environmental
Impact: Natural
Degradation
Using some renewable resources
faster than they can be replenished
Interfering with the earth's chemical
cycling and energy flow processes
Relying mostly on polluting fossil
fuels
Fig. 9-17, p. 188
Environmental Impact: World Hunger
•
•
•
•
Unequal distribution of available food
Loss of arable land
Increasing pop growth
Increasing poverty in developing countries
Strategies for ensuring adequate
nutrition for a growing population:
• Increase the number of new food crops from a
diversity of plant species
• Distribute food more equitably
• Increase land are that is dedicated to grain
production rather than meat production
• Assist developing countries in efficient crop
irrigation systems.
SOLUTIONS: INFLUENCING
POPULATION SIZE
• The best way to slow population growth is a
combination of:
▫ Investing in family planning.
▫ Reducing poverty.
▫ Elevating the status of women.
1994 Global Summit on Population
Development
• Cairo, Egypt
• Encouraged action to stabilized the world’s
population at 7.8 billion by 2050, instead of the
projected 11-12.5 billion
The major goals are to:
• Provide universal access to family-planning
services.
• Improve the health care of infants, children &
pregnant women
• Encourage development of national population
policies
• Improving the status of women by expanding
education & job opportunities
Major goals continued:
• Increase access to education for girls
• Increase men’s involvement in childrearing responsibility & family planning
• Take steps to eradicate poverty
• Reduce & eliminate unsustainable
patterns of production & consumption.