Explain the three types of ecological pyramids. Mention their limitations.
1. Pyramid of numbers - the number of organisms at each trophic level is represented. The first bar (producers) represents the number of green plants or algae in the first trophic level. These will be eaten by a smaller number of primary consumers (herbivores) represented in the second trophic level on the chart. The last bar represents the tertiary consumers since there are only four levels in this food chain.
However, it is not always of the pyramid shape, because organisms at the last levels in food chain could be rather small, for example, if they are parasites. Thus, the last bar can be wider than expected. Alternatively, the producer could be much larger than organisms, which feed on it. For example, beetles feeding on oak tree are likely to have a much larger population than oak.
2. Pyramid of biomass - the total biomass of organisms at each trophic level is represented. Biomass is the dry mass of the organisms. Again, there may be a shape different from the pyramidal one. Some organisms may accumulate fat, while others accumulate carbohydrates, and thus, organisms with the same mass could have different energy content.
3. Pyramid of energy – the most accurate method. Pyramids of energy are always large at the base and show approximately 10% energy passed on at each level. However, it cannot work with live organisms, because they should be burnt for the identification of energy content. Thus, it is destructive and time consuming.