Download Lesson 5.4 Community Stability

Lesson 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
damages.
Catalyst: Vocabulary
and Reading Strategy
Section in Study Guide
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 community and initiate
a predictable series of
changes called
succession.
Forest fire
Lesson 5.4 Community Stability
Primary Succession
• Occurs when there are no traces of the original community
remaining, including vegetation and soil
• Primary succession begins with bare rock
• Pioneer species, such as lichens, are the first to colonize.
• The environment changes as new species move in, adding
nutrients and generating habitat.
Lesson 5.4 Community Stability
Primary Succession
• Over the course of ecological succession, species diversity
increases over time.
• Lichens are great pioneer species because they can grow
on bare rock.
• They are made up of algae that provide food and energy through
photosynthesis and fungi that attach to rock and capture moisture.
Lesson 5.4 Community Stability
Secondary Succession
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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
Lesson 5.4 Community Stability
Primary vs. Secondary
Succession
Talk about it: What’s the difference between primary
and secondary succession?
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Both establish new ecological communities
Primary succession begins with no vegetation or soil
left behind after the disturbance (ex: volcanic eruption)
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Pioneer species must begin to grow on bare rock
Secondary succession begins with vegetation that
existed prior to the disturbance
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.
Lesson 5.4 Community Stability
Secondary Succession in Water
• Occurs when a lake fills in, creating a grassy meadow.
1. Algae and other organisms grow, reproduce, and die,
creating nutrients to support more plant life.
2. This gradually fills the pond with organic matter. The lake
becomes shallow and marshy as decaying matter piles
up.
3. Eventually, the pond may completely fill up and a
terrestrial ecosystem can establish itself.
Lesson 5.4 Community Stability
Climax Communities
• Ecologists once thought
succession leads to stable
“climax” communities.
• Today, ecologists see
communities as temporary,
ever-changing associations
of species.
• Communities are influenced
by many factors and
constant disturbances.
Beech-maple forest, a classic “climax community”
Lesson 5.4 Community Stability
Invasive Species
• Nonnative organisms that spread widely in a
community
• A species becomes invasive when a lack of
limiting factors such as predators, parasites,
or competitors enables their population to
grow unchecked.
• Not all invasive species are harmful.
Did You Know? Although the European honeybee is
invasive to North America, it is beneficial because it
pollinates our agricultural crops.
Cane Toads: An Unnatural History