All organisms depend on others to survive, but some take their relationships with other species to extremes.
When different species live in very close association with each other it's called symbiosis.
When this relationship is beneficial to both organisms, it's known as mutualism.
Mutualism can be seen in most ecosystems and between all sorts of organisms - plants and fungi, animals and plants, or between different animals.
In this coral reef ecosystem, clownfish live closely with sea anemones - animals that use their stinging tentacles to catch prey.
The anemone releases chemicals into the water to attract the clownfish, which is protected from the lethal sting of the anemone by a protective mucus coating.
This allows the clownfish to live in the safety of the anemone's tentacles, protected from predators.
In exchange, the clownfish drives off intruders, like the butterfly fish, stopping them from eating the anemone.
Clownfish and sea anemone mutualism:
Sea anemone protects clownfish
Clownfish drives off invaders
In the same ecosystem, another mutualistic relationship exists between the goby fish and pistol shrimp.
The shrimp digs and cleans a burrow in the sand in which the goby lives and lays its eggs.
The pistol shrimp has poor vision. Whilst the shrimp is digging, the goby keeps watch.
It touches the shrimp with its tail to warn it of approaching predators, and both retreat into their burrow.
Goby fish and pistol shrimp mutualism:
Shrimp digs burrow for goby
Goby watches for predators
Mutualism can produce surprising relationships, and strong interdependence between species, each helping the other so that both can survive.