More Mutualistic Relationships

Plants of the pea family, leguminous plants, have hundreds of little round structures called nodules on their roots. The roots secrete a chemical substance which stimulates certain bacteria to grow and divide. These bacteria which live inside the root nodules can take nitrogen from the air and make nitrates. These nitrates are needed by the plant for growth. In return the bacteria are protected in the root nodules and gain certain nutrients from the plant which are necessary for their own growth.

Not all mutualistic relationships involve one organism living inside another organism. Dairy ants and aphids have a mutualistic relationship. The ants protect the aphids from possible predators. In return, the aphids provide the ants with honeydew.

The Egyptian plover takes insects from the backs of buffaloes, giraffes and rhinos. The plover has also been observed taking leeches from the open mouths of crocodiles! In this association the plover receives a supply of food and the other animal rids itself of unwelcome pests.

Some flowers have a mutualistic association with a specific insect. One species of orchid found in Madagascar, keeps its nectar at the bottom of a tube which is between 20cm to 35cm long. It is totally dependent on a species of hawkmoth for pollination. This hawkmoth has a proboscis which is 22,5cm long.

With some associations it is not so easy to decide whether the other partner is gaining something or being harmed in the relationship. Sometimes the partner may be totally unaffected by the relationship.

One example is to be found between the sea anemone and the clown fish. The clown fish is able to live amongst the tentacles of the sea anemone, even though the anemone's stinging cells are fatal to other kinds of fish. It is easy to see that the clown fish benefits from protection and, perhaps, from scraps of food which the sea anemone does not take into its body. It is not so clear, however, what the sea anemone gains from the relationship.

Another example is a small crab (Lissocarcinus) which lives on the surface of the sea cucumber. The crab is well camouflaged in this position since it is the same colour as the sea cucumber. Also, it benefits from some of the plankton which escapes the filtering mouthparts of the host. It would appear that the sea cucumber remains unaffected by the presence of the crab on its body.

Mutualistic Relationships Homepage

• Introduction
• Parasitic Relationships
• Chapter Summary (useful for revison)
• Questions relating to this chapter
• Top of Page