Age Distribution - Population Parameters and Regulation
It is obvious that individuals in a population will be of different age groups. Relative numbers of young and old individuals in a population will significantly influence the behaviour of a population such as natality and mortality. The age structure of any population can be classified into three categories, i.e. pre-reproductive, reproductive and post-reproductive ages. Mortality usually varies with age as chances of death are more in early pre- reproductive and late post-reproductive periods. Likewise, natality is restricted to the reproductive age of individuals in a population.
The relative duration of these ages in proportion to life span is different in different organisms. For example, in modern man the three 'ages' are relatively equal in length, about one third of the life span. In comparison, the primitive man had much shorter post reproductive period. Many animals and plants have quite long pre-reproductive period. For example, a locust in its seventeen years of life has an extremely long development history with adult life lasting only less than a year.