Producers and Consumers

Organisms in an ecosystem can be grouped by how they obtain their energy and nutrients.Producers make their own organic compounds, usually by photosynthesis, using light energy to convert carbon dioxide and water into sugars. Green plants, algae and some bacteria are producers. They are also called autotrophs. Almost all the energy in an ecosystem enters through producers.Consumers cannot make their own food, so they obtain energy by eating other organisms. They are heterotrophs.
• Primary consumers eat producers. They are herbivores, such as rabbits, caterpillars and zooplankton.
• Secondary consumers eat primary consumers, for example a blackbird eating caterpillars.
• Tertiary consumers eat secondary consumers, for example a hawk eating blackbirds.Decomposers, mainly bacteria and fungi, feed on dead organisms and waste, breaking them down and releasing nutrients back into the environment.These feeding relationships are shown in a food chain, where arrows point in the direction energy flows (from the organism eaten to the organism that eats it):grass → rabbit → foxMost animals eat more than one type of food and are eaten by more than one predator, so the chains link into a food web. In a food web the same animal can be a primary consumer in one chain and a secondary consumer in another, for example a badger that eats both berries and earthworms.