Environmental Engineering Reference
In-Depth Information
Industrial stage: Birth rates stabilize because more people are working outside the home as opposed to
farming, and there are increased work opportunities for women. Birth control becomes more commonly
used. Death rates remain stable at their low levels from the transitional stage. Population growth slows.
Post-industrial stage: Both birth and death rates are low and stable, leading to a stabilization or small
decline in population.
Age structure diagrams, also called age pyramids, are used to show the distribution of ages throughout a pop-
ulation and can help to forecast what might happen to a population over time. There are three general struc-
tures with some variation depending on the changes within a population:
• A balanced age structure generally has the same number of individuals throughout each age group and
represents a stable population and no growth. Examples include Denmark, Austria, and Spain.
• A pyramid-shaped diagram reflects a population with a large number of young people. This is a growing
population, and in the long term this population will increase assuming no major changes to any particu-
lar group. A pyramid can represent either rapid growth or slow growth. Examples of rapid growth (a
steep-sided pyramid) include Afghanistan, Angola, Kenya, Nigeria, and Guatemala. Examples of slow
growth (a gently sloping pyramid) include the United States and Canada.
• An inverted pyramid structure, or diamond-shaped structure, shows an aging population with fewer
young. This population will decline over time, but it may put pressure on the young to take care of the
elderly. Also, there could be a decline in the economy and in the strength of that nation's military, with
fewer young entering the workforce. Examples include China and Germany.
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