Interactions in the Environment:
Organisms Depend on a Healthy
Environment
 Learning
Goals:
• Distinguish between primary and secondary
succession.
 Success
Critera:
• I can explain primary succession.
• I can explain secondary succession.
• I can explain some effects of human interference
on succession.
 Have
you ever noticed grass or other
plants growing in a an old parking lot?
 Definition
of succession: A series of
gradual changes that result in a the
replacement of one community of plants
and animals by another
 So, what
may be dominant plants and
animals at one time are gradually
replaced by new species over time.
Plants play a key role in this.
 Definition:
succession that develops a
community of plants and animals in an area
where no living things existed before.
 Imagine
a volcano, landslide or earthquake
has created a large area of newly exposed
bare rock. Lichen are the first organisms to
start growing on the rock and they begin the
process of building soil.
Lichen use
photosynthesis to
make food and to
grow and they
produce acids that
help them to absorb
nutrients from the
rock and air. These
acids break down
rock into soil. Soon
moss begins to
grow.
The decay of lichen
and moss builds
more new soil and
soon small plants
begin to grow. Plant
roots continue to
break up the rock
and keep the
existing soil in place.
Soon, grasses and
weeds start to grow.
As each generation
of plant grows and
dies, more soil is
created which allow
bigger plants to
grow. The bigger
plants compete for
sunlight and
shorter plants die
out.
The process will continue until eventually a
forest is developed.
An example of primary succession
after a volcano has created a new
island.
 Definition:
succession that develops a
community in an area after it has been
disturbed
 Examples:
forest fires, strong winds,
human-made disturbances (eg. Clear
cutting forests)
 In
secondary succession, soil already
exists and needs to be revitalized.
 Seeds from grasses and wildflowers may
blow in from neighbouring communities.
They grow and enrich the soil which in
turn promote growth of bigger plants.
 The process begins again.
An example of secondary succession
after a forest fire.
 The
following video illustrates both
primary and secondary succession:
 http://www.youtube.com/watch?v=V49Io
vRSJDs
 As
each new plant species begins to
grow, consumers that feed on that
species move into the community.
 Early communities are simple with few
species interacting.
 As succession progresses, communities
become more complex and contain many
interactions.
 Humans
often replace complex ecosystems
with simple ones designed for their own
needs which are not sustainable.
 Example: reforestation companies may
plant trees after clear-cutting, but only one
species of tree is planted resulting in less
complex food web. Few organisms can be
supported and problems like disease or
insect invasion are likely to occur.
 It is best when succession can occur
naturally.
In our next lesson, you will be
studying Human Impacts on
Ecosystems.
In the meantime the following
video may help you remember
today’s lesson! 
http://www.youtube.com/watch
?v=rzE6BNNLew0