Population Interactions – Mutualism


An association between two organisms in which both are mutually benefitted. It is a close physical & an obligatory relationship. Organisms provide resources to each other.

  • Lichens – an association between fungus and algae.
  • Mycorrhizae – an association between fungi and roots of higher plants.
  • Plant-animal relationships – animals help in pollination and seed dispersal.
  • Rhizobium grows in the root nodules of leguminous plants.
  • Coralloid roots in Cycas.
  • Ruminant mammals have microorganisms in their intestine that help in cellulose digestion.

Mutualistic relationship occurs between plants & animals. Animals help in pollination & dispersal of fruits and seeds.They obtain nectar from the flower.

Coevolution can be seen in mutualism. Evolution of the flower and it’s pollinator takes place.

  • Yucca & pronuba moth. Pronuba moth stays in the flower laying eggs in the ovary. They carry out pollination.
  • Fig and pollinator species of wasp. Female wasp lays the egg in the ovary and feeds its larvae on developing seeds. Wasp pollinates the fig in search of a suitable site for laying eggs.
  • Mediterranean orchid Ophrys and bumblebees. One petal of its flower resembles the female bee in size, color, and markings. The male bee pseudocopulates with the flower and in the same process brings out pollination.


It is an interaction between two organisms, benefits both. It is non-obligatory interaction.

  • Bird Ox pecker feeding on ticks and other parasites sticking to the skin of rhinoceros.
  • Plover bird feeding on the leeches attached to the buccal cavity of the crocodile.
  • Association between Sea anemone and Hermit crab. Sea anemone moves from one place to another by attaching itself to the snail’s shell. Hermit crab is protected from enemies by the sea anemone having nematocysts.


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