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| Positive Interactions |
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| Positive Interactions amongst different species in a community |
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| Positive interactions amongst different species in a community are broadly classified into four types. They are: |
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| 1) Proto cooperation |
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| 2) Mutalism |
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| 3) Commensalism |
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| 4) Scavenging . |
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| 1) Proto cooperation |
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| It is a positive inter specific interaction in which both the partners are mutually benefitted and increase the chance of their survival. However, the interaction is not obligatory for their survival as both can live without this interaction. |
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| For e.g., |
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| a) Crocodile bird (Pluvianus aegyptius) enters the mouth of the crocodile and feed on parasitic leeches. By this the bird gets food and the crocodile gets rid of blood sucking parasites. |
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| b) Red billed ox-pecker (Buphagus erythrorhynchus) and yellow billed ox-pecker (Buphagus africanus) feeds on the ectoparasites, lice, ticks and mites etc which will be on the skin of rhinoceros (Diceros dicornes). So the bird gets food and the richnoceros is relieved of its sanguivorous ectoparasites. |
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| c) Hermit crab (Eupagurus prideauxi) lives inside an empty gastropod shell and fixes a sea- anemone (Adamsia pallicata) on the shell. The sea- anemone provide camouflage (protective colouration) and defence to the crab, while crab helps in dispersal of the sea anemone and provide new feeding grounds. |
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| Protocooperation between sea anemone and hermit crab |
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| d) Beautifully coloured antennae of the shrimp on the coral reefs attract the fishes. When the fishes approach the shrimp it feeds on the parasites on the fishes body. Fishes get a cleaning service done and shrimp obtains its food. |
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| 2) Mutualism |
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| It is a positive interspecific interaction in which members of two different species favour the growth and survival each other and their association is obligatory. Both the partners are benefitted by this interaction and it is a short or life long association as a means of obtaining food by one or both the partners. |
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| Mutualism is also referred as ' symbiosis' (sym-together; bios-life) or 'symbiotic interaction' and the partners are referred as 'symbionts'. |
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| For e.g., |
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| a) Mutualism between animal and animal species |
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| Termites (white ants) are not capable of digesting wood, which they ingest as food. A multi flagellate protozoan Trichonympha campanula, which lives in the intestine of white ant secretes 'cellulase' enzyme to digest the cellulose of wood. In return, the ant provides food and shelter to the protozoan. |
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| b) Mutualism between bacteria and plant species |
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| Symbiotic nitrogen fixation by Rhizobium leguminosarum (bacteria) occurs in the nodules on the secondary roots of leguminous plants like pea, gram etc. |
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| The bacteria obtain carbohydrates and shelter from leguminous plants while in return they fix nitrogen as nitrites and nitrates for the plant which is required for their growth. |
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| Symbiotic, Nodulated root system of a legume having nitrogen fixing, |
| Rhizobium bacteria in the nodules |
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| c) Mutualism between plant and animal species: |
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 Green alga Zoo chlorella is a symbiont in the parenchyma of flatworm. |
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 Brown alga Zoo xanthella lives as a symbiont with the mollusc -Tridacna. |
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 Pollination of flowers by insects is a mutual interaction. |
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| d) Mutualism between animal and bacteria |
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| Ruminococcus, a symbiotic bacteria, lives in the rumen part of compound stomach in cud chewing mammals like cattle, sheep, goat etc. which secrete cellulase enzyme and digest the cellulose of plant food. In turn, the bacteria obtain food and shelter by the ruminants. |
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| 3) Commensalism |
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| It is a positive interspecific interaction in which a smaller member called 'commensal', is benefitted, while the larger member called 'host', is neither benefitted nor harmed. |
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| Commensalism represents a beneficial relation. |
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| For e.g., |
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| a) Epiphytes are small green plants found growing on other plants for space only. They absorb water and minerals from the atmosphere by their hygroscopic roots and prepare their own food. The plants are not harmed in any way. |
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| Examples: Orchids, lianas and Vanda hanging mosses are common epiphytes found on the tree of tropical rain forests. |
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| b) Epizoans are animals, which grow on other plants or animals exhibiting Commensalism. |
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| Examples: |
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| 1) Several species of Barnacles (molluscs) grow on the hard shell of Limulus polyphemus (horse shoe crab). |
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| 2) Sucker fish (echeneis) gets attached to the under surface of sharks by its sucker. This provides easy transport for new feeding grounds and also food pieces falling from the sharks prey, to Echeneis. |
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| 3) Entamoeba coli ( protozoan) lives as a commensal in the intestine of man. |
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| 4) Scavenging |
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| Is a direct food related interspecific interaction in which one partner called scavenger or saprobiont eats the dead bodies of other animals, which have died either naturally or killed by some other animals. |
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| Scavengers clean the environment and the available food is ultimately disposed off by which a major part of nutrients again enter for recycling. |
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| Animals such as foxes, hyenas, vultures etc. are the animals, which are natural scavengers. Dogs, crows, ants are occasionally seen to do the work of scavengers. |
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