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Lecture
Objectives
Ecological
Succession
Primary
Succession
Secondary
Succession
Disclimax
Succession
Summary
Community
Change
Lecture
Syllabus
IB 100/101 Home
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Text readings in Life
Chapter 44 (Communities and Ecosystems), Pages 869-872
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Select the text chapter you want and
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Web Crossing
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questions in Web Crossing in the "Talk to Sarah and Ed" discussion.
Ecosystems in Time
The content of today's lecture will help you answer
question #2 on
this assignment:
Objectives:
Note that exam questions and written assignments will be
based on
the learner objectives included in this lecture outline. Not all the
questions provided at the chapter ends in the text or on the text web
pages may be appropriate study aids. Use those that reflect the lecture
objectives.
After studying this material you should be able to:
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Describe the effects of disturbance, or lack there of, in
(natural
and managed) ecosystems and explain its relationship to the process of
biological succession.
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Define the term 'invasive species', give an example of an
invasive
plant or animal and describe its impact on an ecosystem.
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Distinguish between the terms "primary succession"and
"secondary
succession" and describe some examples of each.
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Distinguish between the terms "soil" and "mineral
substrate".
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Describe how pioneer species in primary and secondary
succession
change nonliving components of an ecosystem (temperature, light,
moisture, humidity, mineral substrate, etc.) during the early stages of
succession.
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give an example of disclimax and explain how some
ecosystems are
maintained in a state of disclimax by natural means or by the
intervention of people.
Key Terms:
| succession |
climax community |
pioneer species |
| disturbance |
primary succession |
secondary succession |
| disclimax |
environmental
change |
soil formation |
| prescribed burning |
organic matter |
mineral substrate |
Ecological Succession - Overview
From the Latin, succedere, to follow after
"Change in the species composition of a community over time."
(Lewis, Life glossary)
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Primary Succession follows the formation of new
land
surfaces
consisting of rock, lava, volcanic ash, sand, clay, or some other
exclusively mineral substrate.
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This means that there is NO SOIL present.
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Soil is a mixture of mineral material, decaying organic
material,
and living organisms.
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Secondary Succession follows the destruction or
partial
destruction of the vegetation area by some sort of disturbance, like a
fire, windstorm, or flood that leaves the soil intact.
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Pioneer species initiate recovery following
disturbance in
both primary AND secondary successions
Pioneers "pave the way" for later colonists by altering the
biotic
and abiotic environment:
Species composition tends towards a
Climax Community
through succession.
The climax community describes an end product of succession
that
persists until disturbed by environmental change.
Succession occurs at large scales involving higher plants and
animals, but may involve microbial communities on a smaller scale.
Primary Succession
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Illustration of Primary Succession from Department of
Geosciences, University of Arizona
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The processes involved in changing an area from one
lacking
any
community (no plants, no animals, no insects, no seeds, AND NO SOIL) to
one consisting of individuals, populations, communities, and
ecosystems. CAUTION!! The text definition of
primary
succession is misleading.
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Starts WITHOUT SOIL.
This is the confusing part - there may have been a previous
community, but if a disturbance removes or in some way covers the soil
so only mineral substrate is left to support pioneer plants we would
classify it as Primary succession.
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No organic matter, only mineral material (e.g. sand, bare
rock,
gravel from glacial outwash, volcanic ash and lava.
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PIONEER PLANTS of primary succession (e.g. lichens
and mosses).
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Examples:
Secondary succession
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Illustration of Secondary Succession from Department of
Geosciences, University of Arizona
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Follows disturbance of an existing community that removes
or damages
the vegetation, but does not remove, destroy, or cover the soil.
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Starts WITH SOIL.
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PIONEER PLANTS of secondary succession (the first
plants to
become established after the disturbance) start from roots or seeds
remaining in the soil or from seeds carried in by wind or animals from
surrounding communities.
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Faster than primary succession.
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Examples:
Disclimax
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Disclimax or "disturbance climax" describes
a
community that
is held at an earlier successional stage by repeated but unpredictable
disturbances that prevent succession from reaching the climax community
that might be expected for the climate of the area.
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The original prairies of Illinois are examples of
disclimax
communities. The early successional grass and perennial plants are fire
tolerant because of their underground roots and stems. Repeated fires
destroy shrubs, young trees, and other plants that would change the
environment and result in further successional changes that would
eventually result in the establishment of a deciduous forest.
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Agricultural practices are essentially an artificial form
of
maintaining disclimax. Crops like corn and soybeans as well as the
common weeds found in agricultural fields have the characteristics of
pioneer species and require repeated soil disturbance.
A summary of changes that occur during
succession:
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Pioneer species colonize first.
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Pioneer species alter the environmental conditions
remaining after
the disturbance.
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Eventually new species of plants become established in the
conditions altered by the pioneer species and displace the pioneer
plants.
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Animals come in with or after the plants they need to
survive.
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Further environmental change by the new plants and animals
result in
the establishment of different species.
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With infrequent disturbance, a stable climax community
consisting of
plants and animals that can reproduce themselves in the existing
conditions will become established.
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Disturbance of the ecosystem will start the process of
succession
anew.
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In a given area there are usually small patches of land in
different
stages of succession, depending on the time and severity of the last
disturbance. This adds diversity in the types of vegetation and animals
living in the greater region.
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Various stages of succession in one area
Community Change
Community change is initiated by disturbances of all scales:
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