Many special scientific words are used in biology and you need to know them. In ecology, the place where an organism lives is called its habitat.The habitat of a fish might be a pond. There will probably be many fish in the pond, forming apopulation of fish. A population is a group of organisms of the same species. But fish will not be the only organisms living in the pond. There will be many other kinds of animals and plants which together make up the pond community. A community is all the organisms, all of the different species, living in the same habitat. The living organisms in the pond, the water in it, the stones and the mud at the bottom, make up an ecosystem. An ecosystem consists of a community and its environment.
Within the ecosystem each living organism has a role to play. The way in which an organism lives its life is called its niche. Fish, for example, eat algae or small animals in the pond, disturb peddles, excrete ammonium salts into the water, and breathe out carbon dioxide and breathe in oxygen. All these activities, and many others, help to describe the niche of fish in the ecosystem.
Symbiosis
Symbiosis means living together. When two different species live together intimately their relationship is called symbiosis. There are three types of symbiosis.
1. Parasitism – The tapeworm which affects humans and cattle is a parasite. The tapeworm gains nourishment and shelter from its host and gives nothing in return. Humans with tapeworms have to eat more than usual or they will lose weight and could die. Plasmodium, a unicellular animal, is a parasite which causes malaria in humans. Many plant diseases are caused by parasite fungi. Sugarcane smut is the result of plant becoming parasitised by fungus.
2. Commensalism – One of the best known examples of commensalism involves two species of fish, Remora and shark. The remora is a small fish which has a suction cap on the top of its head. It uses this to attach itself to the body of the shark. It is carried around the by the shark and eats leftover scraps when the shark feeds. Although the remora may remove parasite crustaceans from the shark’s skin, the shark can live in the absence of its passenger. The remora benefits greatly from this association.
3. Mutualism – When both partners of a symbiotic relationship are unable to live without each other, the relationship is said to be an obligate one. That is, the two species are obliged to live together. Many mutualisms are obliged. Termites feed on wood but like most organisms cannot digest wood’s main constituent, cellulose. Small unicellular animals are found in the intestines of termites. These animals are able to break down the cellulose into sugars. The termite is able to digest many of these sugars and thus is able to live on a diet of wood. A similar relationship is found between rabbits and bacteria.