Class 12 Biology Organisms and Populations Predation


It is an interspecific interaction where organisms of higher trophic levels feed on organisms of lower trophic level.

Herbivores are predators as they feed on grass.

Exotic species have no predators hence they grow very rapidly. Example- The prickly pear cactus introduced into Australiaand the invasive cactus was brought under control only after a cactus-feeding moth was introduced in the country.

Fig. cactus  

Importance of predation in an ecosystem are –

  • Predator keeps prey populations under control.
  • Predator acts as a passage for transfer of energy across trophic levels.
  • Predators help in maintaining species diversity in a community by reducing the intensity of competition among competing prey species.

Some species of insects and frogs are cryptically-colored (camouflaged) to avoid being detected easily by the predator.

Fig. colored frogs  

Some are poisonous and therefore avoided by the predators. 

The Monarch butterfly is highly distasteful to its predator (bird) because of a special chemical present in its body which is acquired by feeding a poisonous weed during caterpillar stage.

All insects are known to be phytophagous as these feed on plant sap and other parts of plants.

Thorns in Acacia, cactus are morphological means of defense against insects.

Many plants produce and store some chemical which make the herbivores sick if eaten and even kill the predators.

Calotropisproduce poisonous cardiac glycosides against herbivores.

Fig. calotropis  

Nicotine, caffeine, quinine, opium are produced by plant as defenses against the grazers and browsers.

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