Question

Describe the different types of ecological pyramids with a diagram.

Hint:

Numbers/biomass: can invert. Energy: always upright (2nd law of thermodynamics).

Answer 1

Step 1: Pyramid of Numbers:
This shows the number of individual organisms at each trophic level. It is usually upright in a grassland ecosystem (many producers, progressively fewer consumers), but it can be inverted in a case such as a single large tree (one producer) supporting a large number of insects feeding on it (a parasitic food chain).

Step 2: Pyramid of Biomass:
This shows the total dry-weight biomass present at each trophic level. It is usually upright on land (e.g. a forest, where producer biomass exceeds consumer biomass), but it is characteristically inverted in a pond/aquatic ecosystem, where a small standing biomass of rapidly reproducing phytoplankton (producers) supports a larger standing biomass of zooplankton and fish at any given time.

Step 3: Pyramid of Energy:
This shows the rate of energy flow (and/or standing crop of energy) at successive trophic levels, measured over a fixed time period. Because energy is progressively lost as heat at every transfer (roughly only about 10% passes to the next level, per Lindeman's ten percent law), and lost energy is never recycled back, the pyramid of energy is always upright, without exception, in every ecosystem.

Final Answer:
Ecosystems can be represented by three ecological pyramids — numbers, biomass, and energy — of which only the pyramid of energy is always upright in every case; the other two can sometimes be inverted.