Ecological Pyramids: Numbers, Biomass & Energy in a Snap! Unlock the full A-level Biology course at [ Ссылка ] created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University.

SnapRevise is the UK’s leading A-level and GCSE revision & exam preparation resource offering comprehensive video courses created by A* Oxbridge tutors. Our courses are designed around the OCR, AQA, SNAB, Edexcel B, WJEC, CIE and IAL exam boards, concisely covering all the important concepts required by each specification. In addition to all the content videos, our courses include hundreds of exam question videos, where we show you how to tackle questions and walk you through step by step how to score full marks.

Sign up today and together, let’s make A-level Biology a walk in the park!

The key points covered in this video include:

1. Pyramids of Numbers
2. Pyramids of Biomass
3. Pyramids of Energy

Pyramids of Numbers

As we have seen, food chains are one way of illustrating which organism consumes what other organisms in an ecosystem. Another way of illustrating how components in an ecosystem interacts is by using pyramid of numbers. A pyramid of numbers is an illustration of how many organisms there are at each trophic level in a food chain. In most food chains, the number of organisms at each trophic level decreases, giving a pyramid of numbers a pyramid shape. However, pyramids of numbers do not accurately reflect what is happening in an ecosystem. E.g. one tree may support thousands of aphids and although a tree is far larger than all the aphids, this is not shown on this pyramid.

Pyramids of Biomass

Pyramids of biomass are another way of illustrating which organism consumes what other organisms in an ecosystem. A pyramid of biomass shows the amount of dry biomass at each trophic level in a food chain. Dry biomass is more accurate to use than wet biomass, as wet biomass is affected by water uptake and loss whereas dry mass is constant. Using biomass at each trophic level shows how “much” of each organism there is collectively, as opposed to how many. However, even pyramids of biomass have their disadvantages: 1. Calculating dry biomass is time consuming as you have to take samples and get rid of the entire water content in the sample. 2. Biomass pyramids only show data at one point in time in one sample e.g. sample of pondwater with phytoplankton and zooplankton.

Pyramids of Energy

Another way of showing which organism consumes what other organisms in an ecosystem is a pyramid of energy. A pyramid of energy represents the total energy store of the organisms at each trophic level in a food chain. Each organism at each trophic level has a store of energy in their bodies e.g. as fat stores in animals. At each trophic level, energy is lost from the organism in one way or another, which the other pyramids do not account for. Therefore, this illustration most accurately shows how energy in an ecosystem moves.

Summary

Pyramids of numbers show the number of organisms at every trophic level
Pyramids of biomass show the amount of dry biomass at every trophic level
Pyramids of energy show the energy store in all organisms collectively at every trophic level
Pyramids of energy are the best way of showing how energy and resources move in an ecosystem
However, as it is difficult to get the information needed to construct a pyramid of energy, we usually use pyramids of biomass instead.

свернуть