Age Structure Diagrams (College Board AP® Environmental Science) : Study Guide

Interpreting age structure diagrams

• The composition and growth rate of human populations can be modelled and compared using age structure diagrams

  • These are sometimes referred to as age-sex pyramids, population pyramids or age-gender pyramids

• An age structure diagram is a graphical representation of a population's age and sex structure

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

  • They typically show data for a particular country or region

• Age groups in a population are typically divided into three main categories:

  1. Pre-reproductive: Individuals not yet old enough to reproduce

  2. Reproductive: Individuals currently of reproductive age

  3. Post-reproductive: Individuals beyond reproductive age

• The age structure diagram is usually represented as a horizontal bar graph

  • The age groups are displayed along the vertical axis

  • The percentage or number of individuals in each age group is displayed along the horizontal axis

  • The left side of the graph displays the male population

  • The right side shows the female population

• The shape of the age structure diagram can provide insights into the population growth rate:

  • A pyramid shape indicates a rapidly growing population with a high proportion of young individuals

  • A bell shape indicates a stable population with balanced age groups

  • An inverted shape indicates a declining population with fewer young individuals compared to older ones

• Age structure diagrams are used by policymakers and economists to:

  • Understand population trends

  • Forecast future population growth

  • 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

• An age–sex pyramid can be used to identify the following groups:

  • Young dependents

  • Old dependents

  • Economically active (working population)

Rapidly growing populations

• A rapidly growing population has a broad base in its age structure diagram

  • This reflects a high proportion of younger individuals in the pre-reproductive and reproductive stages

  • Example: Many developing countries, such as Niger, exhibit this structure due to high birth rates

• Characteristics of rapidly growing populations:

  • High fertility rates and short generation times

  • Potential for increased demand on resources like food, water, and education

  • Challenges include strain on healthcare and infrastructure systems

• 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

  • High population growth rate