The Ecology Book

193

Rockpools in a wave-cut platform

form a metacommunity on Eysturoy

in the Faroe Islands. The rockpools are

separate between tides, but become

joined as one when the tide comes in.

has been theoretical and abstract

rather than rooted in fieldwork.

Some metacommunities are easy

to identify, such as islands in an

island group, or rockpools that are

separate between tides but joined

when the tide comes in. In their

2004 paper, Leibold and his

colleagues acknowledged that local

communities, or patches, do not

always have clear boundaries that

make them recognizably separate,

and that different species may

respond to things happening at a

different scale. They identified three

kinds of metacommunity: markedly

separate patches; short-lived but

distinct patches that appear in a

habitat from time to time at varying

size; and permanent patches with

vague or “blurred” boundaries.

Distinct patches

The most obvious markedly separate

patches are islands in the ocean.

These are a convenient subject to

study and there is a vast literature

on island biogeography, reaching

back to Charles Darwin’s famous

study of variations between finches

in the Galapagos Islands in the

Pacific Ocean. Neatly separate

patches make good subjects for

study, which is why they have been

popular with community ecologists.

But, of course, birds and many

other organisms blown across by

the wind or washed in by the sea

ensure that even island communities

are never completely isolated. This

is why some metacommunity

studies focus on the space between

the communities even where the

patches are distinct, as they are

with ponds and lakes, and analyse

how species move between them.

Short-lived but distinct patches

may be much harder to identify,

simply because of their ephemeral

nature. Nonetheless, ecologists

have made metacommunity studies

of holes in trees that fill with water

ORGANISMS IN A CHANGING ENVIRONMENT

for a period of time following a

storm, patches of fungal fruiting

bodies that live just a few days

or weeks, and even pitcher plants

that, after dew or rain, provide a

short-lived aquatic home for both

bacteria and insects.

Blurred communities

Leibold’s 2004 paper acknowledged

that the metacommunities with

blurred boundaries are perhaps the

hardest to define. Coral reefs, for

example, may look neatly separate,

but many of the species that live

among them swim freely and

respond to a host of changing

outside influences, such as

shifts in ocean currents.

Since most of the world’s life

exists within such vaguely defined

patches, theorists have attempted

further clarification. Leibold and

his colleagues have suggested

two different ways of identifying

metacommunities for study:

distinct communities embedded

within a “matrix” habitat, such

as clearings in a forest rich in

resources; and arbitrary sampling

patches in a continuous habitat,

such as a random circle of trees

within a forest.

The work is still at an early

stage. The world is entering a

biodiversity crisis, and countless

species and communities appear

to be under threat from the effects

of human activity. Metacommunity

theory may, in time, help to provide

a better understanding of how

natural communities will respond,

and how local changes to habitats

may ripple through a region, either

adversely or positively. ■

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