Symbiotic Relationships

Symbiotic Relationships

Middle School

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Learning Objectives

• Define symbiosis as a close, long-term interaction between different species.

• Differentiate between mutualism, commensalism, and parasitism.

• Analyze examples to classify types of symbiotic relationships.

• Understand the effects of each relationship using (+/+), (+/0), and (+/-).

Key Vocabulary

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Symbiosis

A close, long-term interaction between two different species where at least one species benefits.

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Mutualism

A symbiotic relationship where two different species both benefit from interacting with each other.

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Commensalism

A symbiotic relationship where one species benefits and the other is not affected by it.

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Parasitism

A relationship where one species benefits at the expense of the other species, called the host.

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Host

An organism that harbors another organism, like a parasite, providing it with food and shelter.

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Coevolution

A process where two or more species reciprocally affect each other's evolution over a long time.

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What is Symbiosis?

• Symbiosis means ‘living together’ and is a close relationship between different species.

• In any symbiotic relationship, at least one of the species will benefit.

• The second species can be helped, harmed, or completely unaffected by the interaction.

• The three main types of symbiosis are mutualism, commensalism, and parasitism.

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Multiple Choice

What is the minimum requirement for a relationship to be considered a symbiosis?

• At least one species must benefit.

• Both species must be unaffected.

• One species must be harmed.

• Both species must benefit.

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What is Mutualism?

• Mutualism is a relationship where both species benefit from their interaction.

• ​This beneficial interaction is known as a win-win or (+/+) relationship.

• This can lead to coevolution, where the two species evolve together.

• Goby fish warn shrimp of any danger in return for a home.

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Multiple Choice

Based on the description, why is the relationship between the Goby fish and shrimp considered mutualism?

• The shrimp benefits, and the Goby fish is unaffected.

• The Goby fish benefits, and the shrimp is harmed.

• The Goby fish benefits, and the shrimp is unaffected.

• The fish gets a safe home, and the shrimp gets a warning of danger.

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What Is Commensalism?

• Commensalism is when one species benefits, but the other is not affected.

• ​One organism may use another for transportation, housing, or access to more resources.

• For example, barnacles attach themselves to whales for a safe place to live.

• The whale is not harmed, while the barnacles get a home and food.

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Multiple Choice

What correctly describes a commensal relationship?

• Both species benefit (+/+).

• One species benefits, and the other is harmed (+/-).

• One species benefits, and the other is unaffected (+/0).

• Neither species is affected (0/0).

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Parasitism: One Benefits, One is Harmed

• In parasitism, the parasite benefits while the host is harmed.

• This is known as a (+/-) relationship because one organism benefits.

• A tick on a dog is an example; it feeds on the dog's blood.

• Parasites do not usually kill their hosts because they need them for survival.

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Multiple Choice

How is parasitism different from predation?

• Parasites often do not kill their hosts, while predators do.

• In parasitism, both species are harmed.

• Parasitism only occurs in plants.

• Parasites are always larger than their hosts.

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Common Misconceptions

Misconception	Correction
All symbiosis is a "win-win" for both organisms.	Only mutualism is a "win-win." Others can be "win-neutral" or "win-lose."
Parasites always kill their host.	A parasite usually doesn't kill its host because it needs it to survive.
Anemones get nothing from clownfish living in them.	The clownfish can protect the anemone from predators and also help keep it clean.
All interactions between different species are symbiotic.	Symbiosis refers to close, long-term relationships, not all interactions like predator-prey.

Multiple Choice

How does the outcome for the species involved differ between a commensal and a parasitic relationship?

• In commensalism one is harmed and one benefits; in parasitism both benefit.

• In commensalism one is unaffected and one is harmed; in parasitism one benefits and one is unaffected.

• In commensalism both benefit; in parasitism both are harmed.

• In commensalism one benefits and one is unaffected; in parasitism one benefits and one is harmed.

Multiple Choice

Cattle egrets are birds that feed on insects stirred up by grazing cattle. The cattle are not affected by the birds. Why is this relationship an example of commensalism and not mutualism?

• Because both the birds and the cattle benefit.

• Because the birds benefit, but the cattle do not receive any benefit or harm.

• Because the birds are harmed by the cattle.

• Because the cattle are harmed by the birds.

Multiple Choice

A scientist discovers a new fungus growing on a tree. What evidence would suggest the relationship is parasitism rather than commensalism?

• The fungus provides the tree with extra water.

• The fungus is getting more sunlight by being on the tree.

• The tree's health is declining because the fungus is absorbing its nutrients.

• The tree's growth and health are completely unchanged by the fungus.

Multiple Choice

Analyze the relationship between a mosquito and a mammal. What is a likely consequence for the mosquito population if they evolve to become so harmful that they immediately kill their mammal hosts?

• The mammals would evolve to become immune to the mosquitos.

• The mosquitoes would find it easier to reproduce.

• The mosquito population would likely decline due to the loss of their food source.

• The mosquito population would likely thrive and increase.

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Summary

• Symbiosis describes close interactions between different species over a long time.

• Both species benefit in mutualism, a "win-win" relationship.

• One species benefits while the other is unaffected in commensalism.

• Parasitism is a "win-lose" interaction where one organism benefits by harming another.

Poll

On a scale of 1-4, how confident are you about identifying the three types of symbiosis?

• 1

• 2

• 3

• 4