Class 12th Biology 2017 Set1 Delhi Board Paper Solution
Name three representative kinds of age pyramids for human population and list the characteristics for each one of them.
For human population age pyramids generally show age distribution of males and females. The shape of pyramids reflects the growth status of the population.
i. whether it is growing
ii. stable
iii declining
Population having large number of young members grow rapidly, while, the population bearing more number of post-reproductive members tends to be declining. There are basically three types of age pyramids found to be present in human population. These are as follows:
(i) Expanding or Triangular Age Pyramid : In this, number of pre-reproductive individuals is very lar ge, number of age reproductive individuals is moderate, while post-repr oductive individuals are fewer. This type of age pyramid shows that population is growing. The rate of growth depends upon the size of pre-reproductive population. This type of population growth is observed in developing cou ntries like India, Brazil.
(ii) Stable or Bell-shaped Age Pyramid : In this, the number of pre-reproductive and reproductive in dividuals is almost equal. Post-reproductive individuals are comparat ively fewer. The population size remains stable, neither growing nor diminishing. This type of population growth is o bserved in countries like USA, Denmark.
(iii) Declining or Urn-shaped Pyramid : The proportion of reproductive age group is higher than the i ndividuals in pre-reproductive age group. The number of post-reproducti ve individuals in also sizeable. It is declining or diminishing population with negative growth. This type of p opulation growth is observed in countries like Japan.
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