Here are the key features of this population pyramid:
- It has a very wide base, indicating high birth and fertility rates
- The population decreases rapidly as the age groups increase, showing high mortality rates, especially among males
- The pyramid narrows significantly at older age groups, demonstrating low life expectancy
- The shape is characteristic of a developing country with high birth/death rates and a youthful population
2. • 3.1.-Population Dynamics
• 3.1.1-Describe the nature and explain the
implications of exponential growth in human
populations.
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3. What is the carrying capacity of Earth
for humans?
This question is difficult to answer.
• Estimates are usually based on
food, but human agriculture limits
assumptions on available
amounts.
• Human population growth rate
has been growing more than
exponentially.
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4. HUMAN POPULATION GROWTH
1999
1975
domestication of plants,
animals 9000 B.C. (about
11,000 years ago)
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agriculturally based
urban societies
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beginning of industrial,
scientific revolutions
4
5. What is HUMAN POPULATION?
• The total number of persons inhabiting a co
untry, city, or any district or area.
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6. What is Exponential growth?
• Exponential population growth is when
the birth rate is constant over a period of
time and isn't limited by food or disease
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8. Measures of population changes are
1. Crude Birth Rate
2. Crude Death Rate
3. Rate of Natural Increase
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9. What is CRUDE BIRTH RATE?
• Crude birth rate is the childbirths per
1,000 people per year. This is a common
measure of fertility for a given
population.
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10. • Therefore, the formula for crude birth rate is
The crude birth rate = number of births per year
Total population
x 1000
Example.
In 2007, there were 3,250 births in a city with
population of 223,000. Therefore:
CBR = 3,250 x1000
223,000
CBR =14.57
So, there were 14.57 births for every 1,000 people in
the city.
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11. • The crude birth rate could be of concern for
particular countries who may be experiencing
population decline, or for national
governments who are worried about
population growth rates that are higher than
their country can sustain
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16. • The birth rate is usually the dominant
factor in determining the rate of
population growth. It depends on both the
level of fertility and the age structure of
the population.
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17. CRUDE DEATH RATE
• The death rate, while only a rough indicator of the
mortality situation in a country, accurately
indicates the current mortality impact on
population growth.
• This indicator is significantly affected by age
distribution, and most countries will eventually
show a rise in the overall death rate, in spite of
continued decline in mortality at all ages, as
declining fertility results in an aging population.
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18. How to calculate Crude Death Rate?
The crude death rate = number of death per year
Total population
x 1000
Example.
In 2007, there were 4,000 death in a city with population of
2,000,000. Therefore:
CBR =
4,000 x1000
2,000,000
CDR =2
So, there were 2 death for every 1,000 people in the city.
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23. Rates of Global Pop. Change
• CBR (crude birth rate) = number of births per 1000
population
– 1990: 24
Today: 21.3
• CDR (crude death rate) = number of deaths per 1000
population
– 1990: 9
Today: 8.93
• Growth rate = birth rate - death rate (often in %)
– 1990: 1.5%
Today: 1.3%
– growth rates have come down
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24. Special Kinds of Fertility and
Mortality Rates
• TFR (total fertility rate) =
– number of children born to a woman during her
reproductive years (or life time)
– 1990: 3.1
2000: 2.8
• IMR (infant mortality rate) =
– infant deaths per 1000 live births (infant < 1 yr)
– 1990: 62
2000: 56 (1900: 200)
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25. RECAP
What is Human population?
What is Crude Birth Rate? Formula
What is Crude Death Rate? Formula
What is Exponential growth?
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26. Population, population change, growth
rates
• Population: number of persons
• Population change: increase in the number of
persons (per year)
• Growth rates: rate of change (per year)
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30. Doubling Time
Doubling time = the number of years it
would take a population to double its size
at its current growth rate.
Doubling time (T) =
70
.
annual percentage rate
Doubling time (T) = 70 . = 50 years
1.4
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31. Doubling Time
• Number of years in which a population reaches
twice its size
• Doubling time can be approximated using growth
rates
• doubling time = 70 : growth rate
–
–
–
–
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rate: 1.4 doubling time: 49
rate: 2.0 doubling time: 34.5
rate: 0.5 doubling time: 138
rate: -0.5
doubling time: ????
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32. How to calculate Rate of Natural Increase?
• The rate of natural increase shows the
rate at which people are added to a given
population by births and deaths (ignoring
migration). It is usually represented as
follows:
• Rate of Natural Increase
Crude Birth Rate - Crude Death Rate
10
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33. For example,
Madagascar's crude birth rate 37.89
The crude death rate 7.97
37.89 -7.97
10
29.92
=2.992%
10
divide that by 10 and the result is 2.992%,
Madagascar's rate of natural increase
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34. Why has the world’s population
grown at such different rates
throughout history?
• Births
• Deaths
• Migration
Natural increase = births – deaths
Net migration = immigrants – emigrants
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35. What is mortality?
• Mortality rate is a measure of the number of
deaths (in general, or due to a specific cause)
in a population, scaled to the size of that
population, per unit of time
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36. What is fertility rate ?
• The total fertility rate (TFR), sometimes also
called the fertility rate, period total fertility
rate (PTFR) or total period fertility rate (TPFR)
of a population is the average number of children
that would be born to a woman over her lifetime
• The number, which ranges from more than 7
children per woman in developing countries in
Africa to around 1 child per woman in Eastern
European and highly-developed Asian countries.
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37. Fertility Rates
Births per woman
<2
4-4.9
2-2.9
5+
3-3.9
No
Data
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38. What affects fertility rates?
•
•
•
•
•
•
•
•
•
Importance of children to labor force
Urbanization
Cost of raising and educating children
Education and employment options for women
Average age of marriage
Availability of pension plans
Availability of legal abortions
Availability of birth control
Religious beliefs, traditions and culture
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39. What affects death rates?
•
•
•
•
•
Higher food supplies
Better nutrition
Improved medical and health technology
Improved sanitation
Safer water supplies
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40. Indicators of overall health
• Life expectancy
• Infant mortality
Growth = natural increase – net migration
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41. Infant deaths
per 1,000 live births
<10
<10-35
<36-70
<71-100
<100+
Data not
available
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46. Age Structure
• Age structure—the proportion of the
population in each age class.
• Age structure influences whether a population
will increase or decrease in size.
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47. Age Structure
• Countries that have high rates of growth
usually have more young people than older
people.
• In contrast, countries that have slow growth or
no growth usually have an even distribution of
ages in the population.
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48. Age Structure
• Age structure can be graphed in a
population pyramid, a type of double
sided bar graph.
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51. Population Pyramids
• Graphic device: bar graph
• Shows the age and gender composition of a
region
• Horizontal axis: gender
– male: left-hand
female: right-hand
– absolute number of people or %
• Vertical axis: age
– 5-year or 10-year age groups
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52. What is Population Pyramid?
• A population pyramid, also called an age
structure diagram, is a graphical illustration
that shows the distribution of various age
groups in a population which forms the shape
of a pyramid when the population is growing.
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53. • It show how many individuals are alive in
different age groups in a country for a given year.
• They also show how many are male and female.
• Population numbers are always on the x-axis and
age groups on the y-axis.
• The overall stage can depict the stage of
development of the country at a particular time.
• LEDC’s tend to have expanding populations so
they are wide at the bottom, whereas MEDC’s
tend to have stationary or contracting pyramids as
birth rates fall and individuals live longer.
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54. Stage 1: High birth rate; rapid fall in each upward age group due high death rates; short life
expectancy.
Stage 2: High birth rate; fall in death rate as more living to middle age; slightly longer life
expectancy.
Stage 3: Declining birth rate; low death rate; more people living to old age.
Stage 4: Low birth rate; low death rate; higher dependency ratio; longer life expectancy.
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55. • It typically consists of two back-to-back bar
graphs, with the population plotted on the Xaxis and age on the Y-axis, one showing the
number of males and one showing females in a
particular population in five-year age groups
• Males are conventionally shown on the left
and females on the right, and they may be
measured by raw number or as a percentage of
the total population.
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57. Describe and explain the main features of the population pyramid below
This population pyramid has a very wide base showing that there are a lot of babies born
every year.
This shows that there is a good medical service within the country. The different sectors from
5 - 9 up to 25 - 29 decreases very quickly and decreases even more quickly on the male side.
This is good for the country, as there are fewer people to feed and educate. As the ages
increase up through the pyramid, it gets narrower and narrower.
This might be because as people get older they leave the country in search of a job or a better
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standard of living
58. 3.1.3• Analyse age/sex pyramids and diagrams
showing demographic transition model
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59. How can economic development help
reduce birth rates?
• Demographers have developed a hypothesis
known as the DEMOGRAPHIC
TRANSITION.
• It states that as countries become
industrialized, first death rates go down and
then their birth rates decline.
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63. What is Demographic Transition?
• The "Demographic Transition" is a model that
describes population change over time.
• The demographic transition model (DTM) is
the transition from high birth and death rates to
low birth and death rates as a country develops
from a pre-industrial to an
industrialized economic system.
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64. FIVE STAGES IN DTM
Stage 1 - High Fluctuating
Stage 2 - Early Expanding
Stage 3 - Late Expanding
Stage 4 - Low Fluctuating
Stage 5- Only Possible in some countries
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66. Stage One-DTM
Both high birth rates and death rates fluctuate in the first stage of the
population model giving a small population growth. There are many
reasons for this:
Birth Rate is high as a result
of:
1. Lack of family planning
2. Need for workers in
agriculture
3. Religious beliefs
Death Rate is high
because of:
1. High levels of disease
2. Famine
3. Lack of health care
4. War
5. Lack of education
Typical of Britain in the 18th century and the Least
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67. STAGE TWO-DTM
• Birth Rate remains high. Death Rate is falling.
Population begins to rise steadily.
• Reasons
Death Rate is falling as a result of:
1.
2.
3.
4.
Improved health care (e.g. Smallpox Vaccine)
Improved Hygiene (Water for drinking boiled)
Improved sanitation
Improved food production and storage
• Typical of Britain in 19th century; Bangladesh;
Nigeria
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72. STAGE THREE-DTM
Birth Rate starts to fall. Death Rate continues to
fall slowly. Population rising.
Reasons:
1. Family planning available
2. Lower Infant Mortality Rate
3. Increased standard of living
4. Changing status of women
• Typical of Britain in late 19th and early 20th
century; China; Brazil
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76. STAGE FOUR-DTM
• Both birth rates and death rates remain
low, fluctuating with 'baby booms' and
epidemics of illnesses and disease. This
results in a steady population.
Typical of USA; Sweden; Japan; Britain
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79. STAGE FIVE-DTM
• A stage 5 was not originally thought of as part
of the DTM, but some northern countries are
now reaching the stage where total population
is declining where birth rates have dropped
below death rates.
• One such country is Germany, which has
taken in foreign workers to fill jobs.
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80. Area
Birth Rate
Reason
No contraception
Death Rate
Couples have many babies to
compensate for the high death
rate caused by poor health
care
LEDCs
High
Large families need to work
on the land to contribute to
family income
Reason
Poor medical facilities
Disease
High
Poor nutrition
High Infant mortality
Children look after old
Religious reasons
NICs
People are used to having
many children. Takes time for
culture to change
Decreasing
High/
Decreasing
As an economy develops
money becomes available for
better health care
Housing improves
Changing status of women
Better childcare
Children are expensive
MEDCs
People know their children
are going to survive so they
can keep their families small
Low
Better health care
Low
Widely available
contraceptives
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Changing status of women
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Better standard of living
80
82. What are the main factors that affect
the growth of a population?
The main factors that make populations
grow are births and immigration.(The
action of coming to live permanently)
The main factors that make populations
decrease are deaths and
emigration.(moving from one place)
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83. • Two types of population curve
• S Population Curve
• J Population Curve
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84. TYPES OF POPULATION CURVE
• Two modes of population growth.
• J-Shape curve is also known as- Exponential
curve occurs when there is no limit to
population size.
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86. • S-Shape curve is also known as - Logistic
curve shows the effect of a limiting factor
• S-Sigmoid
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87. What is S-Shaped Curve?
• In S - shaped or sigmoid growth the population
show an initial gradual increase in population
size in an ecosystem, followed by an
exponential increase and then a gradual decline
to near constant level.
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88. • In population of an ecosystem which
factors determining the S shape curve?
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89. The curve obtained by plotting growth and
time is called a growth curve. It is a typical
sigmoid or S- shaped curve.
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90. What is J shaped?
• A curve on a graph that records the situation in which, in a new
environment, the population density of an organism increases rapidly but
then stops abruptly as environmental resistance
• It may be summarized mathematically as:
I.
dN/dt = rN (with a definite limit on N)
II.
where N is the number of individuals in the population, t is time, and
III. r is a constant representing the rate of increase for the organism concerned.
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91. • The growth of population is measured as increase in
its size over a period of time and populations show
characteristic patterns of growth with time.
• These patterns are known as population growth
forms.
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93. What is Carrying Capacity ?
• Carrying Capacity is the maximum number of
a species or load that can be sustainably
supported by a given environment i.e without
destroying the stock
• Population remain stable when the death rate
and the birth rate are equal and so there is no
net gain or reduction in population size
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95. Semester Syllabus
•
•
•
•
•
Systems & Models
The Ecosystem
Conservation & Biodiversity
Global Warming
Human Population
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