- Competition
- It is a rivalry between two or more organisms for obtaining the same resources.
- It can be intraspecific (among individual of same species) or interspecific (among members of different species).
Table: Differences between intraspecific and interspecific competition
Intraspecific competition Interspecific competition
(i) It is competition among individuals of the same species. It is competition amongst the members of different species.
(ii) The competition is for all the requirements. The competition is for one or a few requirements.
(iii) The competing individuals have similar type of adaptations. The competing individuals have different types of adaptations.
(iv) It is more severe due to similar needs and adaptations. It is less severe as the similar needs are few and the adaptations
are different.
Gause’s hypothesis (Principle of competitive exclusion)
“Competitive Exclusion Principle” states that two closely related species competing for same resources cannot co-exist indefinitely
and competitively inferior one will be eliminated eventually.
- Predation
- It is an interaction between members of two species in which members of one species capture, kill and eat up members of
other species. The former are called predators while the latter are spoken as preys.
- Examples of simple predation include tigers and deer, frogs and insects, owls and rats, sea snake and eggs.
- For plant, herbivores are the predators. Nearly 25% of all insects are known to be phytophagous (feeding on plant sap
and other parts of plants).
- Plants, have evolved an astonishing variety, of morphological and chemical defences against herbivores. Thorns and spines
($FDFLD, cactus) are the most common, morphological means of defence.
- Many plants produce and store chemicals that make the herbivore sick when eaten, inhibit feeding or digestion, disrupt its
reproduction or even kill it. For example,&DORWURSLV a type of weed growing in abandoned fields produces highly poisonous
cardiac glycosides which acts as defences against grazers and browser (any cattle or goat).
- Amensalism
- In amensalism one organism inhibits the effect of the other and the organisms inhibiting does not gain much benefit. This
inhibition is done by secreting allochemics.
- The process of preventing growth of other organisms through secretion of toxic chemicals is called allelopathy.
- Examples : &RQYROYXOXVDUYHQVLV inhibits germination of wheat seeds. 7ULFKRGHUPD checks growth of fungus $VSHUJLOOXV
&KORUHOOD in case of diatom 1LW]VFKLDIUXVWXOXP, 7DJHWHVkills soil nematodes by secreting toxic chemicals while black walnut
(-XJODQVQLJUD) produces allochemic juglone for preventing growth of apple, tomato, alfalfa, etc.
- Commensalism
- When two or more animals live together and if there is no physiological dependence between them, they are referred to as
commensals and the relationship between such organisms is called commensalism. In commensalism one animal might
get the benefit from the association while the other is neither benefitted nor harmed.
- Many epiphytes, HJ orchids, bromeliads and some ferns are found growing on the branches and in the forks of trees. These
epiphytes use the trees only for attachment and manufacture their own food by photosynthesis.
- (JSucker fish (5HPRUD, (FKHQHLV) attaches itself to the under-surface of shark with the help of its dorsal fin which is modified
into holdfast.
- Mutualism
- It is the mutual beneficial relationship between individuals of two different species where none are capable of living separately.
(Mutualism and symbiosis are synonym). The association is obligatory, LH, necessary for existence of both.
- The classical example of this type of associations is seen in lichens. The lichens are composed of a matrix formed by a fungus
within which cells of alga are embedded. The alga depends upon the fungus for water, minerals and protection and fungus
receives carbohydrates prepared by the alga.
