How does an energy pyramid differ from a pyramid of numbers?

Look at the label on each pyramid: it tells you what the width of each level represents.

1. Pyramid of energy: the energy flowing through each trophic level over a period of time. It can be expressed as energy per area per year.
2. Pyramid of numbers: the count of organisms at each trophic level.

A trophic level is a feeding position, such as producers at the base or consumers above them. These pyramids can describe the same food system using different measurements, so their shapes need not match. An energy pyramid is always upright; a pyramid of numbers can be upright or inverted. [S1]

Here is a simplified, hypothetical forest example. The bars are sketches, not measured data.

• Energy: width represents energy flowing through a level over time. Its shape is upright, with a broad producer base and narrower levels above.
• Numbers: width represents the number of organisms at a level. Its shape may be upright or inverted.

ENERGY (upright)       NUMBERS (possible inversion)
      /\\                         /----\\  many insects
     /  \\                         |    |
    /----\\                        \\----/
   /      \\                          ||   few trees
  /--------\\                         ||
 producers                    producers

For the numbers sketch, imagine a few large producer trees supporting many insect consumers. The count can increase from the producer level to the consumer level, even though the energy pyramid remains upright. This illustrates why a count is not a measure of energy. [S1]

The diagrams differ because energy and organism count are different measures. As energy passes between trophic levels, some is lost, so less energy is available at higher levels; that is why an energy pyramid is upright. [S1]

Organism counts do not have to shrink at every step. One producer can be large and support many smaller consumers, giving a pyramid of numbers a narrow base and a wider level above it. [S1] That does not mean the consumers contain more energy than the producers: the number pyramid counts individuals, rather than tracking energy flow.

A biomass pyramid is another distinct measure: it represents biomass at a point in time, and it too can be inverted. [S1] Check the title and units before interpreting a diagram. These examples describe general distinctions, not measurements for a particular ecosystem.

Use this short template, then fill in the bracketed details from your diagram:

“This is a pyramid of [energy / numbers / biomass]. Its levels represent [energy flowing over time / organism counts / biomass at a point in time]. The [widest or narrowest] level is [trophic level]. Its shape is [upright / inverted]. I know this because the diagram shows [explain what the measured quantity indicates]. It should not be read as a pyramid of [a different measure].”

For a hypothetical example: “This is a pyramid of numbers. It counts organisms at each level. It is inverted because the diagram shows a few producer trees and many insect consumers. It does not show that the insects have more energy than the trees.”

Before handing in your explanation, check that you have named the measure, described the shape, and connected your reason to that measure. If a diagram gives units, include them; if it gives no units or key, avoid guessing what its widths mean.