Topic – Species Interactions

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Read about species interactions, or click on the play button below to listen aloud.

Species Interactions

All organisms in a community have specific roles to play. Each species interacts with one or more other species. Most interactions involve competition for resources. Resources are things an organism needs to survive. These include food, water, air, sunlight, and shelter.

In a healthy community, there is a balance of organisms so each one gets what it needs. An example is the food pyramid. There are more species and individuals at the bottom of the pyramid. There are fewer and fewer as you move up the pyramid. When a community works the way it should, there is a balance in the number of species at all levels.


Some organisms have a special relationship with other organisms. Symbiosis is a close relationship between two or more organisms. At least one organism receives a benefit from this relationship. There are three categories of symbiosis.

  MutualismBoth organisms benefit from the relationship. One example is between a zebra and a bird called an oxpecker. The oxpecker eats ticks and other parasites that live on the zebra’s skin. The oxpecker gets food, and the zebra benefits from having the pests removed.

Some birds eat the meat between an alligators teeth, this is mutualism

  CommensalismOne organism benefits from the relationship and the other is not affected. One example is the remora. This fish has an adhesive disk on its head. The remora uses this to stick to a larger animal such as a shark. When the shark is eating, scraps of food float away from the shark’s mouth. The remora eats the scraps of food. The shark is not affected by the presence of the fish.

  ParasitismOne organism benefits from the relationship and the other is harmed in the process. One example is the flea. Fleas live on a host, such as a dog or cat. They bite their host’s skin and suck their blood. The fleas get food and a warm home. But the host gets bitten repeatedly and is very itchy and uncomfortable.

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