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and reinforce your understanding.
Secondary succession
is the orderly and predictable change that takes place after a
community of organisms has been removed but the soil has remained intact. Pioneer
species – mainly plants – that establish in the disturbed area are the first species to start
secondary succession. Over time, there is a natural tendency for the species that belong
to the mature community to return.
During secondary succession, as in primary succession, the community of organisms
changes over a period of time.
Figure 3
on the previous page shows how species compo-
sition changes after a forest fire. Secondary succession usually occurs faster than
primary succession because soil already exists and some species will still be present
(although there might be fewer of them). Also, undisturbed areas nearby can be sources
of seeds and animals.
Succession’s end point
Ecological succession is a complex process that involves many factors. The end point of
succession after a disturbance cannot be predicted. Natural communities are continu-
ously changing at different rates, and the process of succession is very slow.
Summary
• A biological community is a
group of interacting popula-
tions that occupy the same
area at the same time.
• Ecological succession occurs
when one community replaces
another as a result of changing
abiotic and biotic factors.
• Primary succession occurs on
areas of exposed rock or bare
sand (no soil).
• Communities progress until
there is little change in the
composition of species.
• Secondary succession occurs
as a result of a disturbance in a
mature community.
Check Your Progress
Demonstrate Understanding
1.
Predict
how unfavorable abiotic and biotic factors
affect a species.
2.
Classify
the stage of succession of a field that is
becoming overgrown with shrubs after a few years of
disuse.
3.
Contrast
primary and secondary succession.
Explain Your Thinking
4.
Describe
how the stages of succession can change a
rocky field into a mature forest.
5.
Connection
WRITING
List
at least five organisms
that are present in your biological community. Then
write a paragraph that provides evidence of how an
abiotic factor supports each organism.
6.
Predict
what might happen to your backyard if it was
left unattended for several years. Use information from
this lesson to explain your prediction.
Get It?
Describe
how the community where you live may have changed over time
because of succession.
Lesson 1 • Community Ecology
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