Transcript Succession

Chapter 3: How ecosystems
work
Section 3.3: How ecosystems
change
What is succession?
 Succession is a regular pattern of
changes over time in the types of
species in a community.
 The process of succession may take
hundreds or thousands of years.
The community that eventually
forms if the land is left
undisturbed is called the
climax community.
How does succession begin?
 Pioneer species are the first organisms
to colonize any newly available area
and start the process of succession.
 Some pioneer species include grasses,
weeds and lichen.
There are two types of
succession:
 Secondary succession
 Primary succession
Secondary succession is a
pattern of change that occurs
on a surface where an
ecosystem has previously
existed.
Ex. Mt. St. Helens and old
field succession.
In succession, each new
community that arises makes
it more difficult for the
previous one to survive.
Old Field Succession
Natural fires caused by
lightning are a necessary part
of secondary succession in
some communities.
 Some species of trees depend on fire
for survival.
 Some species of animals depend on fire
because they feed on new plant life that
sprouts after land is cleared.
Primary succession is
succession that occurs on
surfaces where no
ecosystems previously
existed.
Ex. new land after volcanic
eruptions and glaciers.
Primary succession is slower
than secondary succession
because it occurs where there
is no soil.
How is soil formed?
 Algae and fungus (lichen) break down
rocks.
 Water may also break down rocks.
 Soil accumulates as dust particles in the
air are trapped in cracks in rocks and
lichen remains accumulate.
 Fertile soil is formed from the broken
rocks, decayed organisms, water and
air.