Mutualistic Relationships: Examples & Types

Mutualistic Relationships: Examples & Types
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  • 0:01 Mutualistic Relationships
  • 0:24 Types of Mutualism
  • 0:35 Obligate Mutualism
  • 1:19 Facultative Mutualism
  • 3:06 Lesson Summary
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Lesson Transcript
Instructor: Laura Enzor

Laura has a Master's degree in Biology and is working on her PhD in Biology. She specializes in teaching Human Physiology at USC.

In this lesson, you will explore a type of symbiotic relationship, mutualism. This describes the interaction between two organisms where both benefit from the relationship. You will also learn several examples of different types of mutualistic relationships.

Mutualistic Relationships

Mutualism is a type of symbiosis; this is a term that describes any relationship between two organisms. Specifically, mutualism describes a relationship between two organisms (a host and a symbiont) where both benefit in some way. We find these relationships in animals, plants, and even in ourselves!

There are two main types of mutualistic relationships: obligate mutualism and facultative mutualism. We'll explore both by looking at examples of each type.

Obligate Mutualism

In obligate mutualism, one organism cannot survive without the other. This term is easy to remember because both organisms are obligated, or forced to, rely on one another.

An example of obligate mutualism is the relationship between ants and the Acacia plant. The plant provides food for the ant, as well as shelter. In return, the ants defend the plant from other herbivores, or organisms that eat plants, as well as remove other plants from the vicinity of their plant so it can grow better.

Another example is the mycorrhizal (pronounced 'my-core-rye-zal') fungi that live on plant roots. The plant roots take advantage of the increased water uptake from the fungi, and the fungi get nutrients from the plant.

Facultative Mutualism

In facultative mutualism, each organism can survive independently, but it benefits both to remain together.

Facultative mutualism can be described in one of three ways:

1. Resource-resource mutualism: This describes a relationship where one resource is traded for another. A great example of resource-resource mutualism is between corals and the symbiotic algae zooxanthellae (pronounced 'zo-zan-thel-ae'). The algae get inorganic nutrients from the corals, and the corals get sugars that are byproducts of photosynthesis from the algae. When a coral 'bleaches,' it is actually kicking out the zooxanthellae that live in it, so all you see is the coral's skeleton, which is white.

2. Service-resource mutualism: This relationship occurs between two organisms where one gets a resource, and the other gets a service. An example of service-resource mutualism is honeybees and flowers. The honeybee gets pollen from the flower (the resource), and the flower gets its pollen spread to other areas (the service).

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