Energy and biomass in ecosystems
Trophic levels
Communities of organisms are organised in the ecosystem according to their feeding habits.
The Food chain
Food chains show the organisms that consume other organisms and the transfer of energy and materials from organism to organism.
Energy from the sun enters most food chains when green plants absorb sunlight to photosynthesise. Biomass for the Earth is produced by photosynthetic and chemosynthetic organisms. This energy and biomass is passed along the food chain from one organism to the next by feeding.
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Pyramids of Biomass
Pyramids of Biomass deal with the dry mass of living materials in the chain. The width of each trophic level can be calculated by multiplying the number of organisms by their dry mass.
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Flow of energy and biomass along the food chain
All food chains start with the producer (plant matter).
The primary consumer then feeds on the plant matter (e.g. rabbit a herbivore).
The secondary consumer then feeds on the primary consumer (e.g. stoat a carnivore).
A tertiary consumer is the top carnivore in the food chain (e.g. fox).
Each consumer or producer occupies a trophic level (feeding level).
Level 1 are producers.
Level 2 are primary consumers.
Level 3 are secondary consumers.
Level 4 are tertiary consumers.
Excretory products and uneaten parts of organisms can be the starting point for other food chains, especially those involving decomposers e.g. fungi.
Efficiency of energy transfer
If you know the amount of energy stored in the living organisms at each level of the food chain you can calculate the efficiency of energy transfer.
Efficiency of energy transfer formula
Energy efficiency (%) = energy used usefully / total energy taken in x 100
Example a rabbit eats 50KJ of energy in the form of grass by only 4.5KJ becomes new body tissue; the rest is lost as faeces, urine or heat.
Energy efficiency = 4.5/50 x 100
= 9%
Similar calculations can also be performed for biomass.
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