What type of ecosystem supports a spindle-shaped pyramid of numbers?
Tree-dominated forests often produce spindle-shaped pyramids of numbers. A small number of large trees forms the producer base, many herbivorous insects and other primary consumers occupy the broad middle, and fewer predatory birds or arthropods occur above them. Parasites can complicate the upper tiers further. The spindle results from individual size and host–consumer relationships, not from increased energy at higher levels; producer biomass and energy flux can remain strongly upright despite the numerical pattern. Turnover explains many apparent paradoxes: a small, fast-renewing stock can
Ref: Fundamentals of Ecology, Odum & Barrett, 5th Ed., Ch. 3
