CHAPTER
5
Evolution and Community
Ecology
5-4
Community Stability
A 2010 report on invasive species
suggests that they cost the U.S.
$120 billion a year in
environmental losses and
Invasive kudzu
Lesson 5.4 Community Stability
Ecological Disturbances
• A community in
equilibrium is generally
stable and balanced,
with most populations
at or around carrying
capacity.
• Disturbances or
changes in the
environment can throw
a community into
disequilibrium.
• Severe disturbances
can cause permanent
changes to a
Forest fire
Lesson 5.4 Community Stability
Primary Succession
• Occurs when there are no traces of the original
community remaining, including vegetation and soil
• Pioneer species, such as lichens, are the first to
colonize.
• The environment changes as new species move in,
adding nutrients and generating habitat.
QuickTime™ and a
decompressor
are needed to see this picture.
Lesson 5.4 Community Stability
Secondary Succession
• Occurs when a disturbance dramatically
alters a community but does not completely
destroy it
• Common after disturbances such as fire,
logging, or farming
• Occurs significantly faster than primary
succession
QuickTime™ and a
decompressor
are needed to see this picture.
Lesson 5.4 Community Stability
Succession in Water
• Primary aquatic succession occurs when an
area fills with water for the first time.
• Disturbances such as floods or excess
nutrient runoff can lead to secondary aquatic
succession.
QuickTime™ and a
decompressor
are needed to see this picture.
Lesson 5.4 Community Stability
Climax Communities
• Ecologists once thought
succession leads to
stable “climax”
communities.
• Today, ecologists see
communities as
temporary, everchanging associations
of species.
• Communities are
influenced by many
factors and constant
Beech-maple forest, a classic “climax community”
Lesson 5.4 Community Stability
Invasive Species
• Nonnative organisms that
spread widely in a community
• A lack of limiting factors such
as predators, parasites, or
competitors enables their
population to grow unchecked.
• Not all invasive species are
Did You
Know? Although the European
harmful.
honeybee is invasive to North America, it
is beneficial because it pollinates our
agricultural crops.