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Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.

Loss of biomass and energy between trophic levels

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This information could be used in the consideration of the (ecological) efficiency of production of different food items, or of meat production compared with arable farming.
If humans eat meat, they are acting as secondary consumers (the animal eats plants like grass or feed like grain derived from plants), whereas if the humans eat plant material (not necessarily grass!) they are primary consumers. The same area of ground could be used to feed many more people this way. By shortening the food chain there is less energy and biomass lost in the conversion from one trophic level to the next.

Some themes that have been suggested include:

meat versus wheat,

rabbits vs carrots,
beef vs beans,
chicken vs corn etc


Sheep vs grass could be considered as a different theme, since humans do not eat grass, and (some varieties of) sheep can survive and grow on very poor land - mostly upland areas - which is unsuitable for crop production. But some sheep are still fed on lowland grass and concentrated food from other vegetable sources.

The lifestyle of each trophic level in an ecosystem has specific features which affect the efficiency of transfer of energy and biomass to the next level.

Producers

Take in only some of the light energy shining on them - perhaps only 1%


Loss is due to:

Advantages Disadvantages
of this trophic level
> Light supply is fairly reliable > Relies on sun+water+soil etc
> Life style requires little energy > Consumers take some productivity

Primary Consumers [herbivores]

Cellulose (main polysaccharide carbohydrate - plant cell walls) is difficult to digest

Loss is due to:

Advantages Disadvantages
of this trophic level
> Large amount of plant food material usually available > Takes long time to digest food
> Takes long time (all day?) to collect food So :Vulnerable to predators
> Easy to find plant material for grazing/browsing > Cellulose wears away teeth
> Food plants availability may change with seasons

Secondary, (also tertiary, quaternary) Consumers [carnivores]

Animals' flesh (high in protein) is easy to digest



Only about 10% of the energy in producers is passed on to primary consumers, and only about 10% of the energy in primary consumers is passed on to secondary consumers, and so on.
In practice, this limits the length of actual food chains to a maximum of 4 links.

What percentage of the energy already absorbed by producers is passed on to secondary consumers?
> 1%

Loss is due to:

Advantages Disadvantages
of this trophic level
> Takes short time to digest protein > Time taken to hunt for prey may not be successful: prey animals may escape!
> Prey availability may change with seasons
> Well maintained teeth, claws etc essential




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