The Ecology Book

59

Service-service mutualisms, in

which both organisms offer each

other protection, are far less

common. One unusual relationship

takes place in the western Pacific

Ocean, between around 30 species

of clownfish and 10 species of

venomous sea anemones. The sea

anemones’ stinging, toxin-filled

nematocysts, or capsules, on their

tentacles kill most small fish that

come close, but not the clownfish.

Its thick layer of protective mucus

provides immunity against the

anemone’s sting, allowing the fish

to live within the tentacles. In

return for the protection offered

by the sea anemones’ venomous

tentacles, the clownfish deters

predatory butterfly fish, removes

parasites from its host, and also

provides nutrients from its faeces.

Cooperative evolution

Relationships between service and

resource providers have developed

over millions of years in a process

called “coevolution”—the evolution

of two or more species that affect

each other reciprocally.

The term coevolution was

coined by American biologists Paul

Ehrlich and Peter Raven in 1964,

but a century before the word

existed, the naturalists Charles

Darwin and Alfred Russel Wallace

were already aware of the concept,

not least through their observation

ECOLOGICAL PROCESSES

of orchids. Like many other

flowering plants, orchids rely on

insects to pollinate them. Some

have extraordinary structures in

which to hold nectar and pollen.

To lure the insect pollinators, the

plants offer them a drink of energy-

giving nectar. This fascinated

Darwin, who was given a specimen

of the Madagascar orchid in 1862.

The flower stores its nectar in a

hollow spur nearly 30 cm (12 in)

long. Darwin and Wallace

speculated that only a large moth

could have a proboscis long enough

to reach the nectar—a theory

eventually proven in 1997. If the

orchid’s spur were shorter, a moth

could drink without picking up

pollen and so would not pollinate

the flower. If the spur were longer,

a moth would not visit. ■

The clownfish and sea anemone

could both survive without the other’s

protection, but their coevolved mutual

relationship gives them a much higher

chance of survival.

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