The Ecology Book

192

The answer may be that both are

right, and the difference simply

depends on scale. The benefit of

metacommunity theory is that it

allows ecologists to reconcile these

differences. It enables them to look

for explanations on both a local and

regional scale.

A metacommunity might be a

set of half a dozen deciduous trees

within a park, with each tree an

individual community. However,

it could equally be all the deciduous

forests in temperate zones all around

the world. What metacommunity

theory does is allow ecologists to

work at any scale, at least in theory.

Umbrella framework

According to Mathew Leibold, the

study of metacommunities brings

together many seemingly disparate

branches of ecology and apparently

conflicting theories. It may make

it easier, for example, to resolve

the century-old debate between the

“deterministic,” niche-based theory

of community ecology, in which

species diversity is determined

by each species’ ecological

niche, and “stochastic” (random)

theory, which emphasizes the

importance of chance colonization

and ecological drift (random

fluctuations in population sizes).

Metacommunity theory provides

an umbrella framework for seeing

how deterministic and stochastic

processes can interact to form

natural communities. It allows

ecologists to state that patterns

of biodiversity are determined both

by local biological features, such

as the balance of sun and shade in

rock pools or variations in water

quality in streams, and by regional

METACOMMUNITIES

stochastic processes, such as the

spread of a species by freak storms

or a die-off due to an epidemic.

It also acknowledges that regional

changes can be caused by the

combined effect of local ones.

Finding metacommunities

One of the problems with Leibold’s

concept is that in practice it is

not so straightforward to identify

the separate components of a

metacommunity. For the fish and

other water creatures in different

lakes within a lake district, for

instance, each lake may clearly be

a distinct community. However, for

those birds able to fly between the

lakes in minutes, the different lakes

are all part of the same single

community. This may explain why

much of the continuing work and

research on metacommunities

Metacommunity

lake 4

lake 2

lake 5

rushes

rushes

frog

frog

mosquito

dragonfly

pond weed

lake 3

algae

algae

lake 1

duck

perch

perch

In this example of a metacommunity, arrows show

how species move between lakes to feed or breed. Seeds

and the spores of algae are dispersed by the wind.

heron

heron

carp cormorant

cormorant

dragonfly

mosquito

mayfly

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