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Ecological Succession
Ponder this….
Do communities change?
Ponder this….
Do communities change?
yes, of course
What makes them change?
Ponder this….
Do communities change?
yes, of course
What makes them change?
something about the environment changes, may be huge
or small, natural or man-made, sudden (a disturbance) or
gradual (abiotic factors change as the community
changes)
How do they change?
Ponder this….
Do communities change?
yes, of course
What makes them change?
something about the environment changes, may be huge
or small, natural or man-made, sudden (a disturbance) or
gradual (abiotic factors change as the community
changes)
How do they change?
gradual change over time as species are replaced by other
species
Ponder this….
Do communities change?
yes, of course
What makes them change?
something about the environment changes, may be huge
or small, natural or man-made, sudden (a disturbance) or
gradual (abiotic factors change as the community
changes)
How do they change?
gradual change over time as species are replaced by other
species
For a given area, is change predictable?
Ponder this….
Do communities change?
yes, of course
What makes them change?
something about the environment changes, may be huge
or small, natural or man-made, sudden (a disturbance) or
gradual (abiotic factors change as the community
changes)
How do they change?
gradual change over time as species are replaced by other
species
For a given area, is change predictable?
sort of…. If you could stand in a cleared field in Georgia for
500 years, what would you expect to see?
disturbance
This change in a
community over
time is called
ecological succession
Ecological Succession
• Definition: a gradual process of change and
replacement of the types of species in a community
• The sequence of changes is somewhat predictable
• May take place over hundreds or thousands of years
Two types of ecological succession
Primary succession: occurs on a surface where
no ecosystem existed before (no soil)
Secondary succession: occurs on a surface where
an ecosystem has previously existed but has been
disturbed (soil is present)
Primary Succession
• On new islands
created by volcanic
eruptions
• On sand dunes
Primary Succession
• Where glaciers have retreated
Primary Succession
• Paved areas that are abandoned
Primary Succession
Begins with pioneer species (defined as the first
species to colonize a disturbed area), like lichens,
that can grow directly on rock; begin the
breakdown of the rock to form soil
Primary Succession
Once rocks begin to weather and crack, soil
forms and small plants can take root
Primary Succession
Larger plants continue to move in until the bare
ground is covered with life
Secondary Succession
Definition: type of ecological succession that occurs on a site
where an ecosystem previously existed (soil is present)
Due to a disturbance to the ecosystem – something upsets the
natural balance
May be natural or man-made (anthropogenic) disturbances
Think of examples of each….
Examples of natural disturbances
tornadoes, floods, trees falling, fire, hurricanes,
disease
Examples of man-made (anthropogenic) disturbances
deforestation, pollution, urbanization, harvesting
‘General Ecology’, D.T. Krohne
Secondary Succession
After a disturbance, pioneer species move in,
followed by other species in a somewhat predictable
sequence
Typical stages of secondary succession
in woodlands
• Early: plants typically small with short lifecycles
(annuals, grasses), rapid seed dispersal,
environmental stabilizers (pioneer species)
• Middle: plants typically longer lived, slower seed
dispersal, and usually larger
• Late: plants and animal species are those
associated with older, more mature ecosystem:
larger, slower dispersal, better competitors, slower
growth
• Climax community: final stage of succession that
will last as long as there is no disturbance
• Each stage of succession brings about changes in the
ecosystem that enable or prevent certain species from
moving in – better soil, less light, more competition as
ecosystem matures
• Some changes may help other species – called facilitation
(example: dogwood trees grow well under the shade of
larger trees)
• Some changes may hinder other species – called inhibition
(example: black walnut produces a chemical that keeps
other plants from growing near it)
Even though the stages can be generally
predicted, stages of succession can vary,
depending on local conditions
Amount of rain,
temperature, terrain,
latitude, altitude, soil
type, human impact
Succession in two forests: What causes the
difference in these climax communities?
For example,
eastern U.S. climax species are
oak, hickory, maple
Succession in the boreal forest (for example in Canada) – climax
species are fir, spruce, hemlock
Even in one location, the climax community
depends on many factors
Current way of thinking: instead of
one stable, final climax community,
there are patches that are constantly
changing within an ecosystem (called
patch dynamics)
Identify the “patches” around this school in
the southeastern U.S. Although in the
“deciduous forest”, it is not that simple….
We can see changes in the animal
communities over time, too
Ecological Succession can occur in
aquatic ecosystems
Fig 10.7 Diagram of bog
succession.
© 2003 John Wiley and Sons Publishers
Changes in Biota
Fig 10.8 Graphs
showing changes in
biomass and diversity
with succession.
© 2003 John Wiley and Sons Publishers
Changes in Abiotic Factors
Fig 10.9 Changes in soil
nitrogen and
phosphorus.
© 2003 John Wiley and Sons Publishers