Food Chains and Food Webs

Food chains detail the flow of energy and nutrients in an ecosystem. It starts from a producer (usually a plant) and ends with a top predator.
Each stage in a food chain is known as a trophic level.
Each arrow in a food chain represents the transfer of energy and nutrients, pointing in the direction of energy flow – from the food to the eater.
Producers (usually green plants) make up the first trophic level. They can make their own food through photosynthesis, using energy from sunlight.
Herbivores, which eat plants, compose the second trophic level. They are called primary consumers.
Carnivores that eat herbivores are called secondary consumers, forming the next trophic level.
Tertiary consumers are carnivores that eat other carnivores.

A food web is a network of interlinked food chains in an ecosystem. It provides a more realistic illustration of feeding relationships compared to a single food chain.
Food webs show the several different food chains that exist within a habitat. They help illustrate biodiversity and can demonstrate the impact of changes on an ecosystem.
The complex nature of food webs demonstrate that animals often have varied diets and do not just rely on a single food source.

As energy moves through a food chain, approximately 90% of it is lost at each trophic level, mainly as waste heat.
Only about 10% of the energy is passed on to the next trophic level. This is why food chains rarely include more than four trophic levels.
The energy losses limit the length of food chains and the size of populations in each trophic level.
These losses explain why there are fewer top predators – such as lions or eagles – than primary consumers in any ecosystem.

Decomposers, including bacteria and fungi, break down dead organisms or waste material. The nutrients are returned to the soil, where they can be used by plants in photosynthesis.
The role of decomposers closes the cycle in food chains and webs, ensuring no nutrients are wasted in an ecosystem.