Human Population Size & Composition (Cambridge (CIE) AS Environmental Management)

Human Population Size & Composition

• 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

Population Pyramids

• 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

• 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

• 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

• 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

• 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