Unit A

Module 1 ~ Lesson 2

  Ecological Pyramids


Ecological pyramids are an effective way to represent the energy, mass, or number relationships between organisms at different trophic levels for a given ecosystem.

Click each coloured row for more information about each pyramid.

Represents the available energy at each trophic level

All pyramids of energy reflect the flow of energy through an ecosystem with loss of energy (about 90%) at each trophic level. All pyramids of energy are upright as the most energy is always available to the first trophic level, decreasing as it moves up the trophic levels.

Represents the number of organisms at each trophic level

Though most pyramids of numbers have an upright shape, the shape can vary for some ecosystems. For example, if the size of one organism is very large, it can feed a number of consumers. Also, organisms that reproduce very quickly can feed a larger number of consumers as they are always replenishing their numbers.

Represents the mass of organisms at each trophic level

Biomass is the dry mass of living organisms per area, usually measured in g/m2. Like a pyramid of numbers, the shape of a pyramid of biomass is sometimes inverted, for example, in the case of quickly reproducing organisms.

CC 3.0. Thompsma.

Digging Deeper

Stable ecosystems have a greater biodiversity than unstable ecosystems.

Ecosystems with a greater diversity of organisms are better able to withstand change. For example, a primary consumer in a tropical rainforest will have more types of food available to them than a primary consumer in a temperate grassland ecosystem. In a drought year where the growing season is short, all consumers in a temperate grassland will feel the impacts of decreased grasses. In a tropical rainforest, the variety of producers will allow some organisms to use alternate food sources, making them less likely to perish.


Read "Modelling Feeding Relationships through Ecological Pyramids" on pages 18 to 24 of your textbook.