Organisms rely on and interact with each other in a number of different ways. Some species serve as food for carnivores. Some organisms are parasites that derive their resources at the expense of other species, while others engage in mutualistic relationships, in which both organisms benefit. Other species depend on similar resources so they are in competition with each other.
Animals that eat other animals are called predators. Examples of predators include spiders, snakes and sharks. The animals these predators consume are called prey species. For example, some prey species of spiders include flies, roaches and beetles. Many animals are both predators and prey, such as a snake that eats a rodent but is in turn eaten by a hawk.
Examples of parasites include intestinal worms, protozoans and ticks. These animals derive nutrition from other animals, called hosts. For example, a tick attaches itself to an animal and then begins to drink blood from the host. Often, the host only experiences a minor inconvenience from the parasite’s activities, but in some cases, the parasites can cause the host to become weak or even die.
In some cases, organisms have a mutually beneficial relationship. As an example, the activities of leaf-cutter ants encourage the growth of fungus that serves as food for the ants. In this case, the fungus benefits from the ants, while ants benefit from the fungus.