Food chain
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A food chain is a linear network of links in a food web, often beginning with an autotroph, also called a producer, and typically ending at an apex predator, detritivore, or decomposer. A food web is
This food web of waterbirds from Chesapeake Bay is a network of food chains
The sea otter is a prime example of a keystone species
Trophic level
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The trophic level of an organism is the position it occupies in a food web. Within a food web, a food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves.
Food chain
…A food web is distinct from a food chain. A food chain illustrates the associations between organisms according to the energy sources they consume in trophic levels, and the most common way to quantify them is in length: the number of links between a trophic consumer and the base of the chain. Studies of food chains…
First trophic level. The plants in this image, and the algae and phytoplankton in the lake, are primary producers. They take nutrients from the soil or the water, and manufacture their own food by photosynthesis, using energy from the sun.
Second trophic level Rabbits eat plants at the first trophic level, so they are primary consumers.
Third trophic level Foxes eat rabbits at the second trophic level, so they are secondary consumers.
Fourth trophic level Golden eagles eat foxes at the third trophic level, so they are tertiary consumers.