Energy transfer
Only part of the energy at one trophic level reaches the next. Much is lost as heat through respiration or stays in uneaten parts. A rough rule is about 10 percent passes on, so food chains rarely have more than four or five levels.
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Analogy
A leaky bucket passed from person to person.
Example
Producers: 10,000 kJ.Herbivores: 1,000 kJ.Carnivores: 100 kJ.Top carnivores: 10 kJ.
In practice
It takes many kilograms of plants to produce one kilogram of a top predator.
Practice
Flashcards
- Why do food chains have few levels?Only about 10 percent of energy passes to each next level, so little is left.
Interview questions
- Explain why energy transfer limits the length of food chains and the number of top predators.
- About 10 percent passes on
- Losses as heat and uneaten parts
- Little energy left at top
- Fewer, larger predators
Questions people ask
Why is eating lower on the food chain more energy efficient?
Each step in the chain loses about 90 percent of the energy. Growing crops for people to eat directly uses all the energy at the producer level. Feeding the crops to animals first and then eating the animals wastes much of that energy, so more land is needed per person.
What is biomagnification?
Biomagnification is the build-up of a toxic substance as it moves up a food chain. Chemicals that do not break down or leave the body, such as DDT or mercury, get stored in tissues. Predators eat many prey, so top predators end up with the highest levels.