Final answer:
The age structure in rapidly growing countries is characterized by a pyramidal shape with a preponderance of younger individuals. Slowly growing countries have fewer young and reproductive-aged individuals and a larger proportion of older individuals. Countries with zero population growth have an age structure that is more conical, with a higher percentage of middle-aged and older individuals.
Step-by-step explanation:
The age structure of a population is an important factor in population dynamics. Age structure is the proportion of a population in different age classes. Countries with rapid growth have a pyramidal shape in their age structure diagrams, showing a preponderance of younger individuals, many of whom are of reproductive age. This pattern is most often observed in underdeveloped countries where individuals do not live to old age because of less-than-optimal living conditions, and there is a high birth rate. Age structures of areas with slow growth, including developed countries such as the United States, still have a pyramidal structure, but with many fewer young and reproductive-aged individuals and a greater proportion of older individuals. Other developed countries, such as Italy, have zero population growth. The age structure of these populations is more conical, with an even greater percentage of middle-aged and older individuals.