SYMBIOSIS

Symbiotic relationships are those in which two kinds of organisms live together consistently. All symbiotic relationships provide the potential for coevolution between the organisms involved, and in many instances the results of this coevolution are fascinating. The major kinds of symbiotic relationships include commensalism, in which one species benefits whereas the other neither benefits nor is harmed; mu' tualism, in which both participating species benefit; and parasitism, in which one species benefits but the other is harmed. Parasitism, as mentioned , can also be viewed as a form of predation, in which the organism that is parasitized does not necessarily die.
Examples of symbiosis include lichens, which are associations of certain fungi with green algae or cyanobacteria. Another important example is the association between fungi and the roots of most kindi of plants, called mycorrhizae, in which the fungi expedite the absorption of certain nutrients by the plants, which in turn provide them with carbohydrates. Similarly, root nodules occur in legumes and certain other kinds of plants, in which bacterii occur that fix atmospheric nitrogen and make it available for [heir host plants and thus for the ecosystems in which they occur. Turning to marine systems, a coral reef is a highly complex symbiotic system, involving not only the coral animals bur ib coralline algae and other autotrophic organisms that are intermingled with the coral animals and contribute greatly to the overall productivity of the reef. More broadly,
coral reef provides the basis for the existence of an entire associated biological corn munity, one in which symbiotic relationships are especially prominent.
Some of the most spectacular examples of symbioses are those between flowerini plants and their animal visitors, including insects, birds, and bats. The characteristics of flowers have been formed in large part, during th course of their evolution,. in relation to the characteristics of the mouthparts and li;-habits of the animals that visit them for food and, in doing so, may spread their pollen from individual to individual. At the same time, the characteristics of the animal have changed in relation to increasing specialization for obtaining food or other sub stances from flowers. Such symbiotic relationships, which also provide excellent ex amples of coevolution, can be observed all around us.
Symbiotic relationships are those in which two or more kinds of organisms live together in often elaborate, more or less permanent relationships.