A sharply narrowing base in an age pyramid indicates:
“Declining birth rate” for a sharply narrowing base in an age pyramid indicates. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Life-history traits reflect allocation among growth, maintenance, survival, and reproduction. Energy invested in many offspring cannot simultaneously be invested in large offspring, prolonged care, or future breeding, creating measurable trade-offs. The remaining alternatives—“High natality”, “High mortality in old age”, “Overpopulation”—refer to different states, proces
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 10