Who gains what?

When two animals come together, look at what each gets or loses. Sometimes both benefit. Sometimes only one gains and the other may even lose something.

Start with the same question for every encounter: what changes for each animal?

Three outcomes to compare

1

Mutualism

Both partners benefit.
2

Commensalism

One benefits and the other is largely unaffected.
3

Parasitism

One benefits by taking resources from a host that bears a cost.

A fish that comes to clean

The client can interrupt the visit. The option to leave helps explain why taking mucus can cost the cleaner a meal.

The little fish is a cleaner wrasse. It eats parasites, tiny animals that live on the grouper. Sometimes it takes a bite of mucus, the slippery layer that protects the grouper’s skin. The big fish may swim away.

A shelter for two

A snapping shrimp digs a hiding place in the sand. A fish called a goby keeps watch. The shrimp rests one antenna against the goby and can feel it move if danger comes close. Both can dart into the burrow.

A goby watches a burrow entrance as a shrimp moves sand.
The shrimp digs a burrow and the goby watches the surroundings. © dive.explo360.fr — All rights reserved. Reproduction requires permission.

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