Publication Extract

The following extract is the background information page about food chains, from the BES Publication, "Food Chains and Food Webs"

Food Chains

Plants and animals in an ecosystem are linked together by their feeding relationships. The sequence of steps within these feeding relationships is a food chain. As green plants are usually the main source of energy input into an ecosystem, food chains generally begin with a green plant.

For example, in a woodland an oak leaf produces energy-rich sugars and starch through the process of photosynthesis. A caterpillar of a buff-tip moth, in its search for energy (in the form of food), eats the leaf. In turn, the caterpillar is eaten by a blue tit. Thus there is a transfer of energy from leaf to caterpillar to bird, in a food chain:

In food chains, we group organisms according to their feeding level or trophic level:

• green plants are at Feeding Level 1 or Trophic Level 1
• herbivores (e.g. caterpillars) are at Feeding Level 2 or Trophic Level 2
• carnivores (e.g. blue tits which eat herbivores) are at Feeding Level 3 or Trophic Level 3
• carnivores (e.g. sparrowhawks) which eat other carnivores are at Feeding Level 4 or Trophic Level 4.
• the leaf is the producer
• the buff-tip moth caterpillar is the primary consumer or herbivore
• the blue tit is the secondary consumer or carnivore
• if a sparrowhawk successfully hunted the blue tit, it would represent a tertiary consumer or top carnivore.

In a food chain diagram, arrows indicate the direction of energy transfer. A common mistake children make when representing food chains is to point the arrows the wrong way, so it is important to emphasise the direction of transfer.

Many producers and consumers die without being eaten, so decomposers such as woodlice and earthworms, which themselves may become prey items, form an important additional link, decomposing the dead bodies and wastes of plants and animals at all trophic levels in the chain. This way, the materials of life are recycled and can be used again and again (i.e. in nutrient cycles).

Parasite food chains, characterised by one or more parasites such as tapeworms or parasitic wasps, are touched on in Investigation 3 (The holly Ieafminer) and Investigation 5 (Oak leaf galls).

Food chains show simple relationships between herbivores and carnivores and the predator-prey relationship, but to get a better and more detailed knowledge of ecosystems we need to look at food webs and pyramids.

© British Ecological Society