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Biology > Food Chains
A food chain is essentially an order of who eats who within a specific habitat.
Every living organism needs energy to survive. Some animals eat plant matter, some eat other animals.
Food chains start with a producer, usually a plant of some kind which gets its energy from the sun or hydrothermal vent. Primary consumers feed on this producer, for example a fieldmouse may eat wheat. A secondary consumer such as a fox may then feed on fieldmice and so on. Each food chain ends up with a top predator, an animal with no natural enemies.
The arrows that run through a food chain show the flow of energy from the sun (or hydrothermal vent) all the way through to the top predator.
In any food web, energy is lost each time one organism eats another. Because of this, there have to be many more plants than there are plant-eaters and therefore more primary consumers than top predators.
As the number of carnivores in a specific habitat increases, they eat more of the herbivores, decreasing the herbivore population. It then becomes more difficult for the carnivores to find herbivores to eat, and the population of carnivores then decreases. In this way, a relatively stable equilibrium occurs in any one habitat.
The table below shows simple food chains for three different habitats.