The Ecology Book

191

theory the different patches consist

of entire communities that include

a number of interacting species.

What is a metacommunity?

Metacommunities are essentially

groups or sets of communities.

The communities making up a

metacommunity are separated in

space, but they are not completely

isolated and independent. They

interact as various species move

between them. For example, a

metacommunity might consist of a

set of separate forest communities,

spread across a region. The various

species within each patch of forest

habitat interact as an independent

community. However, certain

species, including deer or rabbits,

may migrate or disperse to another

community in the metacommunity,

moving to a different patch of forest

in search of better opportunities to

feed, shelter, or breed. Differing

types of habitat will influence this

balance between interlinked and

independent development. The

theory of metacommunities provides

a framework for studying how and

why variations develop and their

impact on biodiversity and

population fluctuations.

Local versus regional

A major advantage of looking at

communities in this spatial way

is that it may help resolve a number

ORGANISMS IN A CHANGING ENVIRONMENT

Wildlife crossings Many different species cross

naturally between separate

habitat patches. This movement

can be seasonal, as in annual

migrations, or prompted by

natural disasters, such as fire or

flood, or may take place over long

timespans. It creates connections

that are often essential for the

health and survival of species and

communities, providing renewal

or new resources at pivotal

moments. Increasingly, however,

manmade barriers, such as

clearances for agriculture, road,

railroads, and urban sprawl, are

breaking up this natural interflow

from one habitat to another. The

idea of providing wildlife with

ways through is not new. For

example, fishways for fish to

bypass dams go back centuries.

Wildlife crossings—from bridges

for bears in Canada to tunnels

for California’s desert tortoises—

are becoming an increasingly

common feature of construction

work. Thousands of crossings,

among them bridges, viaducts,

and underpasses—often planted

with vegetation—have been

built to conserve habitats and

to avoid fatal collisions between

animals and vehicles.

of seemingly contradictory

observations. One ecologist’s study,

for instance, might look at the way

species live and interact together

in a small local community. This

narrowly focused study finds that

competition between species for

resources is a crucial factor in the

workings of the community.

Another study might look at the

picture across a larger community.

This macro-study discovers that

competition plays virtually no

part. So which result is correct? ❯❯

Mountain goats in Colorado live

in a metacommunity of species in

a mountain range—the Rocky

Mountains—but within a population

of goats on one single peak.

See also: Competitive exclusion principle 52–53 ■ The ecosystem 134–137 ■ The neutral theory of biodiversity 152

■ Metapopulations 186–187

US_190-193_Metacommunities.indd 191 12/11/18 6:25 PM