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Friday, January 29, 2010

Social interaction in environment

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The social dimensions include interactions also that go on among organisms continuously in different ecosystems. The social interactions have been grouped into Positive and Negative interactions. Positive interactions include mutualism, commensalisms, amensalism and protocooperation. Negative social interactions include exploitation, predation, antibiosis and competitions.

1. Positive Interactions

(i) Mutualism: The social relationship between two species in which both the species derive benefits from each other, is called as mutualism. Pollination by animals; dispersal of fruits and seeds by birds, insects and even by human beings; symbiotic associations in Lichens etc. are some examples of mutualism.

 Lichen is an association of an alga and a fungus. The alga synthesizes food as it is blessed with chlorophyll but fungus can only live on the food prepared by the alga. In return it offers protection, moisture and nutrients to the alga. Such an association is called as symbiosis
There are symbiotic nitrogen fixers also. The bacterium Rhizobium lives in the root nodules of leguminous plants. It receives food from the leguminous plant and in turn it fixes atmospheric nitrogen for the host plant.  Non- leguminous plants of about 400 species have been reported to have symbiotic associations through their leaves.

(ii) Commensalism: The social relationship between two species of organisms in which one species is benefited but no one is harmed, is called as commensalisms. Sheltering of birds and animals on trees; presence of the bacterial species E. coli in human intestine; Lianas; and epiphytes like Orchids, banyan plants, peepal plants and Loranthus etc. are called as commensalism. Epiphytes are green plants that grow on other plants but do not harm to their hosts. The Lianas are vascular plants rooted in soil but stand erect by the support of other plants. These are very common plants in the dense forests of moist tropical climates.

(iii) Protocooperation (non-obligatory mutualism): An association of members of two populations, in which both are benefited, is called as Protocooperation. An important example of this association is the association of the Sea- anemone and the Hermit crab. The crab carries the sea-anemone to the fresh feeding sites where as it gets protection by the sea – anemone, though this is not always necessary.

2. Negative Interactions

            (i) Exploitation: In nature, it has been observed that organisms of one species harm the organism of other species by taking support, shelter and by exploiting food from the other species. Under these conditions relations between species are differently called as Parasitism and Predation. We have already discussed this relationship in earlier paragraphs. In predation an animal kills its prey for food, but a parasite derives its food from the host and does not kill it. The host may die due to some disease caused due to the parasite.  

Root Nodules


(ii)Amensalism: The association between organisms of two different species in which one is inhibited or destroyed and the other is unaffected, is called as amensalism. There are two modes of amensalism (a) competition and (b) antibiosis

(a) Competition: The relation which involves struggle among organisms for water, nutrients, space, sunlight or organic food is called as competition. Competition may either be Interspecific or intraspecific. The Interspecific Competition occurs between members of the same species due to overcrowding or overpopulation. Intraspecific Competition occurs between members of different species. It is also called as contest or interference competition. This type of competition has been reported in cases of insects, paramecia etc.

(b) Antibiosis: Secretion of substances by the organisms of one species to kill or repel another organism of a different species is called as antibiosis. Species of Actinomycetes (bacteria) and some Lichens have been reported by researchers to produce substances inhibiting certain fungi and bacteria. The classic example of antibiosis is the destructive effects of the mould Penicillium upon certain bacteria.. The secretion, known as Penicillin has remained a potent medicine in combating bacterial infections in early days of antibiotic discoveries.

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