3.1.2 Human Population Size & Composition (Cambridge International AS Environmental Management)

Human Population Size & Composition

Spec point — 3.1.2

• Population dynamics involve the study of how populations change in size and structure over time
• Various changing factors, including birth rates, death rates, migration, and child mortality, contribute to the complexity of population dynamics
• Understanding these components is essential for analysing the *demographic characteristics of a population

Factors Influencing Population Size & Composition

• Birth rate:

  • The number of live births per 1 000 people in a population during a given year
  • High birth rates contribute to population growth, while low birth rates may lead to population decline

• Death rate:

  • The number of deaths per 1 000 in a population during a given year
  • High death rates can decrease population size, while low death rates contribute to population growth

• Child mortality rate:

  • The number of deaths of children under 5 years old per 1 000 live births
  • High child mortality rates may result in a younger population due to a higher proportion of births needed to compensate for child deaths

• Natural increase:

  • The difference between birth rates and death rates, excluding migration
  • Positive natural increase indicates population growth, while negative natural increase signifies a decline

• Net migration (migration rate):

  • The difference between the number of immigrants and emigrants
  • Positive net migration contributes to population growth, while negative net migration can lead to decline

Dependency Ratio

• Population structures and pyramids can be divided into three age-group categories, depending on level of economic activity

  • Young dependents - from 0-14 years, they rely on their economically active parents to support them
  • Economically active - from 15-64 years, they are the working population who earn income, pay taxes and contribute to the support of the young and elderly
  • Elderly dependents- from 65 years onwards, they are no longer economically active and so rely on support from the state and younger family members

• The dependency ratio shows the relationship between a country’s working population (people who are economically active or independent) and non-working population (people who are economically inactive or dependent)

  • In other words, the dependency ratio is a way to measure the amount that the young and elderly people in a population depend on the economically active people in that population

Dependency ratio = ((young dependents + old dependents) ÷ economically active) × 100

Worked Example A country has a total population of 200 000 people. There are:

• 50 000 children under the age of 15
• 110 000 people between the ages of 15 and 64
• 40 000 people aged 65 or older

What is the dependency ratio for this country?

Step 1: use the formula

Dependency ratio = ((young dependents + old dependents) ÷ economically active) × 100

Step 2: substitute in the known values

Dependency ratio = ((50 000 + 40 000) ÷ 110 000) × 100

= 0.82 x 100

= 82%

Population Pyramids

Spec point — 3.1.2

• A population pyramid (also known as an age-gender pyramid, or sometimes referred to as an age structure diagram) is a graphical representation of a population's age and gender structure

  • It displays the percentage or number of individuals in each age group and gender within a given population, typically a country or region

• The population pyramid is usually represented as a horizontal bar graph, with the age groups displayed along the vertical axis, and the percentage or number of individuals in each age group displayed along the horizontal axis

  • The left side of the graph displays the male population, while the right side shows the female population

• The shape of the population pyramid can provide insights into the demographic characteristics of a population

  • For instance, a pyramid with a broad base and a narrow top indicates a young population with high fertility rates and low life expectancy
  • Whereas a pyramid with a narrow base and a broad top indicates an ageing population with low fertility rates and high life expectancy

An example of a population pyramid

• Population pyramids are widely used by demographers, economists, and policymakers to understand population trends, forecast future population growth, and plan for social and economic policies

• They are also used in fields such as public health, education, and social welfare to plan for the needs of specific age groups within a population

  • This means that governments can estimate and plan for spending

• As countries develop and pass through the stages of demographic transition, the shape of the population pyramid changes

• A population pyramid can be used to identify the following groups:

  • Young dependents
  • Old dependents
  • Economically active (working population)
  • Dependency ratio

Population Structures of LICs and HICs

Population pyramid for Niger

• Low-income countries (LICs) like Niger typically have a concave pyramid shape

• This indicates:

  • High birth rate
  • Low life expectancy
  • High death rate
  • High infant mortality rate
  • Young dependent population dominates

Population pyramid for Nepal

• More developed LICs like Nepal typically have a pyramid shape with a taller base, like the one shown above

• This indicates:

  • Decreasing birth rate
  • Increasing life expectancy
  • Decreasing death rate
  • Decreasing infant mortality
  • Decreasing young dependents and increasing economically active population

Population pyramid for USA

• High-income countries (HICs) such as the USA typically have a column shape

• This indicates:

  • Low birth rate
  • High life expectancy
  • Low death rate
  • Low infant mortality
  • Large working age population