How long can a food chain be?

Answer 1

A food chain can only be up to 5 trophic levels in length, including the producer.

Only a small proportion of the previous organism's energy is passed down through trophic levels to the next organism. This diminishes the energy available, so there is little or no energy to be gained after the 5th stage of a food chain.

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Answer 2

Food chains can vary quite a lot in length. The factors affecting food chain length are many and varied, however a normal, average food chain is going to be somewhere between 3 and 4 links long. This food chain normally looks as follows:

Primary Producer -> Herbivore (primary consumer) -> Primary Predator -> Secondary Predator.

An example of this kind of food chain might be:

Plant -> Mouse -> Snake -> Eagle

Energy transfer up the food chain is the limiting factor (of most food chains). In systems where there is a lot of nutrients at the lower levels, or where the efficiency of the nutrient transfer up the chain is high, a food chain might reach a length of 5 or 6 links. It is very rare to have food chains that exceed this length.