- Bell-shaped age pyramids develop when the proportions of pre- and reproductive individuals are about equal, while the post-reproductive population is substantially smaller. A constant population of this kind is anticipated.
- Age pyramids take on a triangular shape when there are a large number of people in the pre-and reproductive age groups and a small number of people in the post-reproductive age group. It is expected that this population will increase or spread.
- Age pyramids in the shape of an urn show low proportions of pre-reproductive people, the greatest number of people in the reproductive age group, and the smallest number of people in the post-reproductive age group. One claims that this population is dwindling.
Demographers use age pyramids to analyse human populations and forecast how a population will grow in the future. Because extinct organisms no longer exist, age pyramids cannot be built for them, and instead, there is no reason to build age pyramids for extinct organisms.
A bell-shaped age pyramid represents -(a) expanding population(b) stable population(c) extinct population(d) declining population
Age pyramids in the form of bells indicate stable populations. Population stability occurs when pre- and post-reproductive individuals are relatively few and equal in percentage to reproductive individuals.
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