Human Population Growth
Big Question
Why Is Human Population Growth the Underlying Environmental Problem?
China’s One Child Policy
In the 1970’s China began a one child policy to
control population growth in their country.
Chinese culture values males as more
important than female. This policy has lead to
some killing of girl babies and high number of
abortions in China. Incentives are given to
have one child and if a family has more than
one, the incentives are taken away.
What do you think about the policy of only
allowing 1 child per family?
Basic Concepts of Population
Dynamics
– A population is a group of individuals of the same
species living in the same area or interbreeding.
– A species is all individuals that are capable of
interbreeding and is made up of populations.
– Abundance is the size of a population.
– The birth rate is the number of individuals born
during a specified time interval.
– The death rate is the number of individuals who die
during that same time interval.
– The growth rate is the difference between birth rate
and death rate; the net change in the size of the
population.
Factors Governing Changes
in Population Size
• Four variables
– births, deaths, immigration and emigration
• Population Change = (births + immigration) – (deaths +
emigration)
• Crude Birth Rate = CBR = (births/population)*1000
• Crude Death Rate = CDR = (deaths/population) *1000
• Immigration and emigration are calculated the same way
• Crude Growth Rate = CBR = CDR
• Population Growth Rate = CGR * 100
Calculating Population Growth
•
•
•
•
•
N0 is the starting population
N is the population
after a certain time, t ,
has elapsed,
r is the rate of natural increase expressed as a
percentage (birth rate - death rate) and
• e is the constant 2.71828... (the base of natural
logarithms)
Doubling Time
• The time it takes for a population to double at a specific growth rate
• Rule of 70
– to find the doubling time of a quantity growing at a given annual
percentage rate, divide the percentage number into 70 to obtain
the approximate number of years required to double.
• For example, at a 10% annual growth rate, doubling time is 70 / 10 =
7 years.
Factors that Drive Human
Population Growth
• Demography- the study of human
populations and population trends.
• Changes in Population Size
• Fertility
• Life Expectancy
• Age Structure
• Migration
Fertility
• Total fertility rate- an estimate of the average
number of children that each woman in a
population will bear.
• Replacement level fertility- the total fertility
rate required to offset the average number of
deaths in a population and for the current
population size to remain stable.
Fertility
• Varies drastically among developed and
developing nations
– Developed countries- countries with relatively high
levels of industrialization and income.
– Developing countries- countries with relatively low
levels of industrialization and income of less that $3
per person per day.
Life Expectancy
• Life expectancy- the average number of years
that an infant born in a particular year in a
particular country can be expected to live, given
the current average life span and death rate of
that country.
Life Expectancy
• Infant mortality rate- the number of deaths of
children under 1 year of age per 1,000 live births.
• Child mortality rate- the number of deaths of
children under age 5 per 1,000 live births.
Age Structure
• Age structure diagrams (population pyramids)visual representations of age structure within a
country for males and females.
• Arranged in cohorts – age groups
Four general types:
–
–
–
–
Pyramid
Column
Inverted pyramid
Column with bulge
Population Change, cont.
– Kenya has pyramid shape with many young people – rapid growth
– United States has column shape – slow growth
– Italy is slightly top-heavy – slow/negative growth
Major Periods of Human History
– The early period of hunters and gatherers - less than a few million
people
– The rise of agriculture - first major increase in the human
population
– The Industrial Revolution - improvements in the food supply and
health care led to a rapid population growth
– Today -growth has slowed in industrialized nations but is
increasing rapidly in many less developed nations
Is the Logistic Growth Curve Realistic?
– Requires accurate knowledge of the inflection
point where growth rate declines.
– Unrealistic assumptions for human populations.
– Death rates do not increase if there are ongoing
improvements in health care and food supplies.
– See the estimated US population at Population
Clocks:
http://www.census.gov/main/www/popclock.h
tml
The Demographic Transition
• The theory of the demographic transition is the theory
that as a country moves from a subsistence economy to
industrialization and increased affluence, it undergoes a
predictable shift in population growth.
The Stages of the Demographic Transition
• Phase 1: Slow population growth because there are high
birth rates and high death rates which offset each other.
• Phase 2: Rapid population growth because birth rates
remain high but death rates decline due to better sanitation,
clean drinking water, increased access to food and goods,
and access to health care.
• Phase 3: Stable population growth as the economy and
educational system improves and people have fewer
children.
• Phase 4: Declining population growth because the relatively
high level of affluence and economic develop encourage
women to delay having children.
The Demographic Transition
Longevity and Its Effect on Population Growth
– The maximum lifetime
(longevity) is the genetically
determined maximum
possible age to which an
individual can live.
– Life expectancy is the average
number of years an individual
can expect to actually live.
– The human population has
grown despite little or no
change in longevity.
The Demographic Transition, cont.
– Some nations are slow to move from stage II to stage III
– Medical advances can affect the demographic transition
by decreasing death rates
Limiting Factors to Population Growth
– Short-term factors: drought, disruption to
energy supply, disease
– Intermediate-term factors: desertification,
pollutants, disruption to supply of nonrenewable resources
– Long-term factors: Soil erosion, groundwater,
climate change
Quality of Life and the Human Carrying
Capacity of the Earth
– What is the human carrying capacity of Earth?
– Logistic curve predictions
– Packing space
– Deep Ecology – moral imperative to preserve
the biosphere by limiting human population
– The higher the quality of life, the lower the
Earth’s carrying capacity
How Can We Achieve Zero Population
Growth?
– Raise the age of first childbearing
– Social pressures to delay marriage
– Birth control
• Breast feeding
• Family planning
National Programs to Reduce Birth
Rates
– The first country to adopt an official population policy
was India in 1952.
– Many countries now have a family-planning program.
– China has one of the oldest and most effective familyplanning programs:
• encourages couples to have only one child.
• relies on education, family planning control, and a system of
rewards and penalties.
– Should governments force people to limit family size?
Family Planning
• Family planning- the regulation of the number
or spacing of offspring through the use of birth
control.
Ecological Footprints
• Affluence - having a lot of wealth such as
money, goods, or property.
How Many People Can Earth Support?
Estimates range from 2.5 billion to 40 billion.
Critical factors are
– Food supply
– Land and soil resources
– Water resources
– Population density
– Technology