Final answer:
Stage 4 represents a stage in population age structure diagrams where the population has low birth and death rates and is stabilized, which is typical for developed countries with advanced economies and healthcare systems.
Step-by-step explanation:
Populations can be divided into three ecologically important age classes: prereproductive, reproductive, and postreproductive.
Age structure diagrams for rapidly growing, slow growing, and stable populations are shown in stages 1 through 3. Stage 4 in such diagrams typically represents a population with low birth and death rates and a stabilized population size. This is characteristic of some developed countries where the population has reached a level of stability due to low fertility rates and low mortality rates, often as a result of improved healthcare, better education, and advanced economic development.
Stage 3 reflects a transition where children are seen less as economic assets, leading to a dramatic fall in birth rate and slowing population growth. Thus, stage 4 is a continuation and culmination of this trend, associated with a stabilized population in an urban-industrial society with comprehensive social security systems.