3. Outline
Population Characteristics
A Population Growth Curve
Factors That Limit Population Size
Categories of Limiting Factors
Carrying Capacity
Reproductive Strategies and Population
Fluctuations
Human Population Growth
4. Outline
Human Population Characteristics and
Implications
Factors That Influence Human Population
Growth
Population Growth Rates and Standard of Living
Hunger, Food Production, and Environmental
Degradation
The Demographic Transition Concept
The U.S. Population Picture
What Does the Future Hold?
5. Population Characteristics
A population is a group of individuals of the same
species inhabiting the same area.
• Natality: The number of individuals added to a
population through reproduction over a particular time
period.
– Birth Rate = Humans born per 1,000 individuals per year.
• Mortality: The number of deaths in a population over a
particular time period.
– Death Rate = Humans died per 1,000 individuals per year.
7. Population Characteristics
A survivorship curve shows the proportion of
individuals likely to survive to each age.
Three types of survivorship curves can be
recognized:
• Species with high mortality in young.
• Species with mortality equitable among age classes.
• Species with mortality high only in old age.
8. Population Growth Curve
Population growth rate is the birthrate minus
the death rate.
In human population studies it is often
expressed as a percentage of the total
population.
9. Sex Ratio and Age Distribution
Sex ratio refers to the relative number of males
and females in a population.
• The number of females is important because females
determine the number of offspring produced in sexually
reproducing populations.
Age distribution is the number of individuals of
each age in the population.
• Age distribution greatly influences the population growth
rate.
11. Population Density and
Spatial Distribution
Population density is the number of individuals
per unit area.
• High population density injures all individuals within the
population because they compete severely for
necessary resources.
– Dispersal: Movement of individuals from densely
populated locations to new areas.
– Emigration: Movement from an area.
– Immigration: Movement into an area.
12. A Population Growth Curve
Biotic potential is the inherent reproductive
capacity of a species (biological ability to
produce offspring).
Generally, biotic potential is much above
replacement level.
• There is a natural tendency for increase.
13. A Population Growth Curve
Population growth follows a pattern consisting of a
lag phase, an exponential growth phase, a
deceleration phase, and a stable equilibrium
phase.
• Lag Phase: This is the first portion of the curve; slow
population growth.
14. A Population Growth Curve
• Exponential Growth Phase (Log Phase): More
organisms are reproducing, causing accelerated
growth; this continues as long as birth rate exceeds
death rate.
• Deceleration Phase: The population growth rate
slows as the death rate and birthrate come to equal
one another.
• Stable Equilibrium Phase: The death rate and birth
rate become equal and the population stops growing.
16. Factors That Limit Population Size
Factors that prevent unlimited population growth
are known as limiting factors.
All of the different limiting factors that act on a
population are collectively known as
environmental resistance.
Extrinsic limiting factors are those that come
from outside the population.
• Predators
• Loss of food source
• Lack of sunlight
• Accidents of nature
17. Factors That Limit Population Size
Intrinsic limiting factors are those factors that
originate within the population and exercise
control over it.
• Behavioral changes amongst the population cause
lower birthrates and higher death rates.
Density-dependent limiting factors are those
that become more effective as the density of the
population increases.
Density-independent limiting factors are
population-controlling influences that are not
related to the density of the population.
18. Categories of Limiting Factors
For most populations, limiting factors recognized
as components of environmental resistance can
be placed into four main categories:
• Raw material availability
• Energy availability
• Accumulation of waste products
• Interactions among organisms
19. Carrying Capacity
Carrying capacity is the maximum sustainable
population for an area.
It is not an inflexible number; it can be influenced
by environmental differences such as:
• Successional changes
• Climate variations
• Disease epidemics
• Forest fires, floods, or natural disasters
• Nutrient levels in aquatic ecosystems
21. Reproductive Strategies
and Population Fluctuations
Species can be divided into two broad categories
based on their reproductive strategies:
• K-strategists: Organisms that typically reach a stable
population as the population reaches the carrying
capacity.
• r-strategists: Typically, these are small organisms that
have a short life, produce many offspring, exploit
unstable environments, and do not reach a carrying
capacity.
22. Reproductive Strategies
and Population Fluctuations
K-strategist characteristics include:
• Usually occupy relatively stable environments.
• Large organisms
• Long-lived
• Produce few offspring
• Provide substantial parental care
• Reproductive strategy is to invest a great deal of energy
in producing a few offspring that have a good chance of
living to reproduce.
K-strategists are controlled by density-dependent
limiting factors.
23. Reproductive Strategies
and Population Fluctuations
r-strategist characteristics include:
• Small, short-lived organisms
• Produce many offspring
• Little if any parental care
• Exploit unstable environments.
• Usually do not reach carrying capacity (boom-bust
cycles).
• Reproductive strategy is to produce large numbers of
offspring to overcome high mortality.
r-strategists are controlled by density-independent
limiting factors.
24. Human Population Growth
The human population growth curve has a long
lag phase followed by a sharply rising
exponential growth phase that is still rapidly
increasing.
A major reason for the increasing human
population growth rate is an increase in medical
care, and a consequential decrease in death
rates.
28. Human Population
Characteristics and Implications
The world can be divided into two segments
based on economic development.
• More-developed countries typically have per capita
income exceeding $10,000.
– Europe, Canada, the U.S., Japan, Australia, New
Zealand.
– Combined population of 1.2 billion.
– Relatively stable populations.
– Expected to grow 3% by 2050.
29. Human Population
Characteristics and Implications
• Less-developed countries typically have a per
capita income less than $5,000.
– All other remaining countries of the world.
– Combined population of 5.3 billion.
– Nearly 3 billion live on less than $2 per day.
– High population growth rates.
– Expected to grow 52% by 2050 (8 billion people, or
86% of the world’s population).
30. Human Population
Characteristics and Implications
Population growth and economic development
31. Human Population
Characteristics and Implications
Human population growth is tied to economic
development and is a contributing factor to nearly
all environmental problems.
Population density relates the size of the
population to available resources.
• Countries with abundant resources can sustain higher
population densities than resource-poor countries.
The degree of technological development and
affluence is also significant; people in highly
developed countries consume huge amounts of
resources.
32. Human Population
Characteristics and Implications
The ecological footprint is a measure of the
land area required to provide the resources and
absorb the wastes of a population.
Most of the more-developed countries of the
world have a much larger ecological footprint
than is represented by their land area.
• Japan is highly developed but has few resources; its
ecological footprint is 5 times larger than its locally
available resources.
• The ecological footprint of the U.S. is 1.5 times locally
available resources.
33. Factors That Influence
Human Population Growth
Humans, unlike other kinds of organisms, are
influenced by social, political, economic, and
ethical factors.
We can make conscious decisions based on the
likely course of events and adjust our lives
accordingly.
34. Factors That Influence
Human Population Growth
Biological Factors
• Demography is the study of populations and their
characteristics, how those characteristics affect growth,
and the consequences of that growth.
• The most important determinant of the rate at which
human populations grow is related to how many women
in the population are having children and the number of
children each woman will have.
• The total fertility rate of a population is the number of
children a woman has during her lifetime.
35. Factors That Influence
Human Population Growth
Biological Factors
• A total fertility rate of 2.1 is known as replacement
fertility; parents produce 2 children who will replace
the parents when they die.
• Zero population growth is when the birth rate equals
death rate.
• The age distribution is the number of people of each
age in the population.
36. Factors That Influence
Human Population Growth
Social Factors
• Reducing fertility rates would be advantageous,
especially in LDCs, but not everyone agrees.
• Several factors (religious, traditional, social, and
economic) influence the number of children a couple
would like to have.
• The major social factors determining family size are
the status and desires of women in the culture.
• In male-dominated cultures, traditional role of women
is to marry and raise children.
37. Factors That Influence
Human Population Growth
Social Factors
• Early marriages foster high fertility rates.
– In Africa, 17% of births are to women in the 15-19 year-
old range.
– Total Fertility Rate of 5.1%
• Childrearing practices also influence population growth
rates.
– In countries where breast feeding is practiced, several
benefits accrue.
– Breast milk is an excellent source of nutrients and
antibodies.
– During the months a woman is breast feeding, she is less
likely to become pregnant again.
38. Factors That Influence
Human Population Growth
Social Factors
• Lack of education opportunities for women reduces
their options.
• When level of education increases, fertility rates fall.
– Financial independence leads to marriage later in life.
– Better-educated women are more likely to have access
to and use birth control.
39. Factors That Influence
Human Population Growth
Social Factors:
• In some cultures women desire large families:
– In countries where infant mortality is high, it is traditional to
have large families since several of a woman’s children may
not live to adulthood.
– Parents are more secure when there are many children to
look after their own needs in old age.
40. Factors That Influence
Human Population Growth
Economic Factors:
• In less developed countries, the economic benefits of
children are extremely important.
– Even young children can be given jobs that contribute
to the family economy, such as protecting livestock,
gathering firewood, or carrying water.
• In the developed world, large numbers of children are
an economic drain.
– They are prevented from working.
– They must be sent to school at great expense.
– They consume large amounts of the family income.
41. Factors That Influence
Human Population Growth
Political Factors
• Governments can either reward or punish high fertility
rates.
• Several European countries are concerned about low
birth rates and have instituted policies to encourage
couples to have more children.
– Paid maternity leave and guaranteed job availability
upon the mother’s return to work.
– Childcare facilities make it possible for both parents to
work.
– Child tax deductions provide an indirect payment to
families.
42. Factors That Influence
Human Population Growth
Political Factors
• Most developing countries are concerned that
population growth is too rapid and have instituted
programs to limit growth:
– They provide information on family planning and
maternal and child health.
– Sometimes governments provide free or low-cost
contraceptives.
– One-child policy in China
43. Factors That Influence
Human Population Growth
Immigration Policies
• Birthrates are so low in some countries that
immigration is encouraged to offset a potential decline
in the number of working-age citizens.
• Developed countries are under intense pressure to
accept immigrants.
– The higher standard of living is a magnet for refugees or
people who seek a better life than is possible where they
currently live.
44. Population Growth Rates
and Standard of Living
There appears to be an inverse relationship
between a country’s growth rate and its average
standard of living.
Standard of living is a difficult concept to
quantify since various cultures have different
desires.
Factors usually included in an analysis of
standard of living:
• Economic well-being
• Health conditions
• Social status and mobility
45. Population Growth Rates
and Standard of Living
An important economic measure of standard of
living is the average purchasing power per
person.
Gross national income (GNI) is an index of
purchasing power measuring total goods and
services generated by citizens of a country.
• Gross national income purchasing power parity
(GNIPPP) is used to account for varying prices of
goods and services between countries.
46. Population Growth Rates
and Standard of Living
Standard of living and population growth in three countries.
47. Hunger, Food Production, and
Environmental Degradation
As human population grows, so does the demand
for food.
• Most people in developed countries must purchase
their own food.
• Most people in less-developed countries must grow
their own food.
Human populations can only increase in size if
other plant and animal populations decrease in
size.
48. Hunger, Food Production and
Environmental Degradation
People in less-developed countries generally feed
at lower trophic levels than those in the developed
world.
• People in less-developed countries must eat plants
themselves instead of feeding the plants to animals and
eating the animals.
• A lack of protein in the diet can lead to malnutrition.
Many people in more-developed countries suffer
from overnutrition.
• 50% of North Americans are overweight, and 25% are
obese.
50. Hunger, Food Production and
Environmental Degradation
In countries where food is in short supply,
agricultural land is already being exploited to its
limit and there is still a need for more food.
Many more-developed countries are net food
exporters.
Improved plant varieties and agricultural
techniques have dramatically increased food
production in some parts of the world.
Political activities such as war, repayment of
foreign debt, corruption, and poor management
often determine food availability.
51. Hunger, Food Production and
Environmental Degradation
Solving the problem of food distribution is not an
easy question.
• Humanitarian food aid provides an excellent service,
but:
– It provides a temporary relief of symptoms.
– It works against self-reliance.
– The emphasis must be on self-sufficiency.
52. The Demographic Transition Concept
Demographic transition is a model of
population growth based on historical, social,
and economic development of Europe and N.
America.
• Initially, countries have a stable population (high birth
and death rates).
• The death rate falls and the population grows.
• Industrialization occurs and the birth rate falls.
• Death rates and birth rates find equilibrium (low birth
rates and low death rates).
54. The Demographic Transition Concept
This is a comfortable model, because it
suggests industrialization will naturally lead to
population stabilization.
Can a model developed in Europe and N.
America be applied to less-developed countries?
• Resources are no longer abundant.
• Human population is growing much faster than
before.
55. The U. S. Population Picture
United States population had a post-war baby
boom period, significantly affecting population
trends.
• 1947 – 1961: birthrates were much higher than today.
– This created a population bulge.
– As members of this group have raised families, they
have had a significant influence on U.S. population
growth and trends.
Legal and illegal immigration significantly
influence future population growth trends.
56. The U. S. Population Picture
Changing age distribution of U.S. population
57. What Does the Future Hold?
We must remember that interactions with other
species and with other humans will help
determine our carrying capacity.
Four basic factors are involved in this
consideration:
1. Available raw materials
2. Available energy
3. Waste disposal
4. Interactions with other organisms
58. What Does the Future Hold?
1. Available raw materials
– This issue is not limited to the amount of food
available.
– We are also dependent on technology.
– Our lifestyles are tied to use of other resources such as
irrigation water, genetic research, and antibiotics.
2. Available energy
– This issue is similar to that of raw materials.
– Increases in energy efficiency and the development of
renewable fuels can reduce dependence on fossil
fuels.
59. What Does the Future Hold?
3. Waste disposal
– Pollution is the waste product of human activity.
– Lack of adequate sewage treatment and safe drinking
water causes large numbers of deaths.
3. Interactions with other organisms
– We are not the only species of importance.
– Converting land to meet our needs displaces other
species from their habitats.
– What today seems like an unimportant organism may
one day be seen as an important link to our own
survival.
60. What Does the Future Hold?
Social Factors Influence Human Population
• Current technology and medical knowledge are
available to control human population growth and
improve the health of the people of the world.
• But humans are social animals who have freedom of
choice and frequently do not do what is considered
“best” from an unemotional, uninvolved, biological
point of view.
• People make decision based on history, social
situations, ethical and religious considerations, and
personal desires.
61. What Does the Future Hold?
If the world continues to grow at its current rate,
population will surpass 12 billion by 2060.
• The human population is subject to same biological
constraints as other species.
• The human population will ultimately reach a carrying
capacity and stabilize.
– Disagreement about exact size and primary limiting
factors.
62. Summary
The birthrate (natality) is the number of individuals
entering the population by reproduction during a
certain period.
The death rate is the number of deaths in a
population in a certain period.
A typical population growth curve shows a lag
phase followed by an exponential growth phase, a
deceleration phase, and a stable equilibrium
phase at the carrying capacity.
The world’s population is growing rapidly. The
causes of population growth are biological, social,
political, philosophical, and theological.
63. Summary
Most of the growth is occurring in less-
developed countries of the world.
Demography is the study of human populations
and the things that affect them.
Population growth rates are determined by
biological factors, but also by social and
economic factors.
The demographic transition model suggests that
as a country becomes industrialized, its
population becomes stabilized.
