173
The Sonora Desert is often seen as
an example of a climax community. It
has both winter and summer rains, so
its unique plants, which include the
tall saguaro cactus, are unusually lush.See also: The ecosystem 134–137 ■ The distribution of species over space and time 162–163 ■ Ecological succession
170–171 ■ Open community theory 174–175 ■ The ecological guild 176–177 ■ Biomes 206–209ORGANISMS IN A CHANGING ENVIRONMENT
German botanists to produce
a theory of the development of
natural communities.
Clements suggested that the
way to understand patterns of
vegetation across the world is
to think in terms of “formations.”
A formation is a large, natural
community of plants dominated
by a range of life forms that reflects
the regional climate. In each region,
plants go through stages or
successions until they reach the
most complex, highly developed
form of vegetation possible. Once
it finally reaches this climax, the
community stabilizes, in what
was later termed a “steady state,”
and stops changing.
Clements then proposed that
climax communities are bound
together. Although an ecological
community is made up of a
multitude of plants at differentstages of growth, he argued that
it can be considered as a single
complex organism. A community
grows toward a climax in the
same way that an individual
develops through life stages.
Clements expanded the idea to
embrace all organisms in a “biome”
that comprised “all the species of
plants and animals at home in a
particular habitat.” From this,
the idea of the ecosystem as a
“superorganism” later developed.A fluctuating process
Clements’s ideas were challenged
from the start, although the idea of
a “steady state” proved influential
and dominated thinking about
ecosystems up until the 1960s.
However, scientists realized that
communities change constantly in
response to conditions, and it is
almost impossible to observe a true
climax community. A $10,000 prizefor identifying such a community,
offered by American botanist Frank
Egler in the 1950s, was never
claimed. Despite the difficulties,
ecologists continued to use the
theory of a climax community to
decide how to respond to invasive
species that threatened to disturb
an established native community,
and in recent decades Clements’s
ideas have regained support.
Succession remains a core
principle of ecology. In general,
early succession phases consist of
fast-growing and well-dispersed
species that are replaced by more
competitive species. Initially,
ecologists thought that ecological
succession ended in what they
described as the climax phase,
when the ecosystem reached a
stable equilibrium. However, it
is now accepted that ecological
succession is a dynamic process
that is constantly in flux. ■For Clements, climates are
like genomes, and vegetation
is like an organism whose
characteristics its
genome determines.
Christopher Elliott
Philosopher of scienceUS_172-173_Climax_Community.indd 173 17/12/2018 14:33