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Beginning the Food Chain
A food chain starts with the primary energy source, usually the sun. -
Autotrophs or Primary Producers
http://youtu.be/WHMLq3bqGwkThe next link in the chain is an organism that make its own food from the primary energy source - an example is photosynthetic plants that make their own food from sunlight (using a process called photosynthesis) -
Herbivores or Primary Consumers
Next come organisms that eat the autotrophs; these organisms are called herbivores or primary consumers. -
Secondary Consumers
The next link in the chain is animals that eat herbivores - these are called secondary consumers - an example is a snake that eats rabbits. Consumers that are not herbivores are either carnivores (meat eaters) or omnivores (eat both plants and meats) -
Tertiary Consumers
In turn, these animals are eaten by larger predators - an example is an owl that eats snakes. -
Quaternary Consumers
http://youtu.be/ezXimG1bwtgThe tertiary consumers are eaten by quaternary consumers, an example is a hawk that eats owls. Each food chain ends with a top predator, and animal with no natural enemies (like an alligator, hawk, or polar bear). -
Energy Loss
The arrows in a food chain show the flow of energy, from the sun or hydrothermal vent to a top predator. As the energy flows from organism to organism, energy is lost at each step. A network of many food chains is called a food web. -
Exchange of Energy Continues
When any organism dies, it is eventually eaten by detrivores (like vultures, worms and crabs) and broken down by decomposers (mostly bacteria and fungi), and the exchange of energy continues. -
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. -
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Numbers of Organisms
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. There are more autotrophs than heterotrophs, and more plant-eaters than meat-eaters. 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.
