Population Age Distribution

A population's age distribution is the proportion of its members falling into each of three broad age classes — pre-reproductive, reproductive, and post-reproductive — at a given point in time. Because this distribution reflects how many individuals are currently capable of breeding versus how many are yet to reach, or have already passed, reproductive age, it directly determines the population's present reproductive status and serves as a useful indicator of where its total size is headed next. As a general pattern, a rapidly growing population carries a disproportionately large share of young, pre-reproductive individuals; a stable population shows a roughly even spread across all three age classes; and a declining population carries a disproportionately large share of older, post-reproductive individuals. Plotting these three age classes as stacked horizontal bands produces the population's characteristi …