In a growing population younger population (or pre-reproductive individuals) size is larger than that of reproductive individuals . Such population is represented by a triangular-shaped age pyramid .
Whereas , the equal number of reproductive and pre-reproductive individuals represents a stable population and the age pyramid is bell-shaped
Less number of pre-reproductive individuals than reproductive individuals represents declining population and age pyramid appears urn-shaped . The similar case is seen when reprodutive individuals are less than the post - reproductive individuals .
