Question

Which ecological pyramid is always upright?

Hint:

Energy is never recycled back up the food chain — this forces the pyramid upright.

Answer 1

Step 1: Comparing the three pyramids:
The pyramid of numbers and the pyramid of biomass can sometimes be inverted (e.g. many insects feeding on one large tree; small phytoplankton biomass supporting larger fish biomass in a pond).

Step 2: Why energy is different:
The pyramid of energy shows the rate of energy flow at successive trophic levels. Since energy is progressively lost as heat at each transfer (2nd law of thermodynamics) and is never recycled, the energy available at a higher trophic level can never exceed that at the level below it.

Final Answer:
The pyramid of energy is always upright.