A food chain is the sequence of who eats whom in a biological community (an ecosystem) to obtain nutrition. A network of many food chains is called a food web. The food chain starts with plants or other autotrophs (organisms that make their own food from light and/or chemical energy) - these organisms are called primary producers. The primary producers are eaten by herbivores (plant-eaters) called primary consumers. The herbivores are eaten by carnivores (meat-eaters) and omnivores (animals that eat both animals and plants) - these organisms are called secondary consumers. Secondary consumers may be eaten by other carnivores called tertiary consumers. When any organism dies, it is eaten by tiny microbes (detrivores) and the exchange of energy continues.

Numbers of Organisms:
As in any food web, there are more plant-eaters in the rain forest than there are meat-eaters. There are also many more plants than there are plant-eaters. There are also more small animals than large animals. Insects are the most numerous animals in rainforests.

Although there is intense competition between animals, there is also an interdependence. When one species goes extinct, it can affect an entire chain of other species and have unpredictable consequences.

Equilibrium
As the number of carnivores in a community increases, they eat more and more of the herbivores, decreasing the herbivore population. It then becomes harder and harder for the carnivores to find herbivores to eat, and the population of carnivores decreases. In this way, the carnivores and herbivores stay in a relatively stable equilibrium, each limiting the other's population. A similar equilibrium exists between plants and plant-eaters.

Related Terms:

AUTOTROPH An autotroph (or producer) is an organism that makes its own food from light energy or chemical energy without eating. Most green plants, many protists (one-celled organisms like slime molds) and most bacteria are autotrophs. Autotrophs are the base of the food chain.	CARNIVORE Carnivores are animals that eat meat. They usually have sharp teeth and powerful jaws.	CONSUMER A consumer is a living thing that eats other living things to survive. It cannot make its own food (unlike most plants, which are producers). Primary consumers eat producers, secondary consumers eat primary consumers, and so on. There are always many more primary consumers than secondary consumers, etc.	FOOD WEB A food chain is the sequence of who eats whom in a biological community (an ecosystem) to obtain nutrition. A network of many food chains is called a food web. The chain starts with plants or other autotrophs (organisms that make their own food from light and/or chemical energy) that are eaten by herbivores (plant-eaters). The herbivores are eaten by carnivores (meat-eaters). These are eaten by other carnivores. When any organism dies, it is eaten by tiny microbes (detrivores) and the exchange of energy continues.
HERBIVORE Herbivores are animals that eat plants. Most animals are herbivores.	HETEROTROPH A heterotroph (or consumer) is a living thing that eats other living things to survive. It cannot make its own food (unlike plants, which are autotrophs). Animals are heterotrophs.	OMNIVORE Omnivores are animals that eat both animals and plants. Some monivores include people, many monkeys and marmosets, lion tamarins, chimpanzees, and most bears.	PREDATOR A predator is an animal that hunts and kills other animals for food.
PRODUCER A producer (or autotroph) is an organism that makes its own food from light energy (using photosynthesis), or chemical energy (using chemosynthesis). Most green plants, many protists (one-celled organisms like slime molds) and most bacteria are producers. Producers are the base of the food chain.	TOP PREDATOR A top predator is an animal at the top of the food chain, like the jaguar or bald eagle. Top predators have little or no natural enemies.	TROPHIC LEVEL A trophic level of an organism is the position it holds in a food chain. Trophic level 1 is plants and other autotrophs (also called primary producers) - organisms at this level are also called primary producers. Trophic level 2 is herbivores (organisms that eat autotrophs) - organisms at this level are also called primary consumers. Trophic level 3 is predators that eat herbivores - organisms at this level are also called secondary consumers. Trophic level 4 is predators that eat secondary consumers - organisms at this level are also called tertiary consumers. Trophic level 5 is predators that eat tertiary consumers - organisms at this level are also called quaternary consumers. Decomposers (such as bacteria) start the cycle again.