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Communities and Succession
Communities and Succession
A community consists of all the plants and
animals that occupy a particular area.
The individual populations within a community
interact with each other.
The community is a constantly changing and
dynamic unit, which passes through a number of
stages from its origin to its climax.
The transition from one stage to the next is
called succession.
nothing
Climax
community
Have you ever seen something
like this?
How does it happen?
This is bare
rock.
Nothing lives
here.
Why?
•Exposed.
•No soil.
•Absorbs and reflects heat.
•Dry.
•No nutrients.
How does succession work?
A bare patch of ground will not stay bare. It will rapidly be
colonized by a variety of plants.
A recently cleared patch of ground
The same ground 2 years later,
How Does Succession Work?
There are 2 types of succession:
PRIMARY- Plants grow where NO PLANTS HAVE GROWN
BEFORE.
SECONDARY- Plants grow where there has been a previous
population. These will have been destroyed, eg: by fire
The 1st species to colonise are called PIONEER SPECIES.
The “ultimate” species to colonise are called the CLIMAX
COMMUNITY.
Sand dune succession.
The pioneer species is
marram grass.
Pioneer species
Pioneer species are often 'opportunist' species which are able to
rapidly exploit a sudden new opening in ground plant cover.
They must be able to grow quickly. They are usually short-lived.
EXAMPLE: Mosses
They are low growing, carpeting the
ground and with little height.
They then provide a microhabitat
equivalent to a miniature forest for a
variety of invertebrates such as mites
and spiders.
The moss also acts like a sponge when
wet, in some cases providing a semiaquatic microhabitat.
Task
• In pairs, come up with a list of features that
pioneer species may have, which would help
them to colonise inhospitable environments
Features of Pioneer Species
• Production of a lot of wind-dispersed seeds to
easily reach isolated areas
• Rapid germination of seeds
• The ability to photosynthesise
• The ability to fix nitrogen from the
atmosphere
• Tolerance to extreme conditions
Looking again at our example….
Bare Ground
No plant competition for light,
space, nutrients or water.
Soil mobile and liable to erosion
and loss.
A more extreme surface
microclimate because the bare soil
both absorbs and reflects heat
more than soil covered in
vegetation.
A drier environment because there
is no plant cover to hold moisture
above ground and little humus to
hold it in the soil.
Lower nutrient levels in the soil.
Two Years Later
Intense plant competition for
space and other resources.
Soil bound by roots and plant
cover.
The plant cover provides a certain
amount of ground insulation from
extremes of temperature. There
are now also a variety of
microclimates within the vegetation.
Plant cover and increasing humus
levels help to retain water.
The nutrient levels in the soil will
have increased.
Bare Ground
No plant competition for light,
space, nutrients or water.
Soil mobile and liable to erosion
and loss.
A more extreme surface
microclimate because the bare soil
both absorbs and reflects heat
more than soil covered in
vegetation.
A drier environment because there
is no plant cover to hold moisture
above ground and little humus to
hold it in the soil.
Lower nutrient levels in the soil.
Two Years Later
Intense plant competition for
space and other resources.
Soil bound by roots and plant
cover.
The plant cover provides a certain
amount of ground insulation from
extremes of temperature. There
are now also a variety of
microclimates within the vegetation.
Plant cover and increasing humus
levels help to retain water.
The nutrient levels in the soil will
have increased.
Stages of Plant Succession
Each stage of succession changes the abiotic
environment and makes it less hostile
For example:
• Colonisers (lichens): when they die, they
release nutrients. This changes the abiotic
environment by creating soil.
• Mosses, then Ferns: rock is continually
eroded, as these die organic matter increases,
building up soil
• Small flowering plants, shrubs then trees
establish
Over time…
• Undisturbed, an area will pass through a number
of further different successional stages, each
with its own characteristic mix of species.
• Each new community will be better adapted to
the changed environment which has been provided
by the previous community.
•Eventually, a climax or 'final' community is
reached. At this point, the succession will not go
any further. However, this does not imply that
there will be no further change.
Climax Community
• The organisms that make up the final stage of
ecological succession
• A balanced equilibrium
• In the UK, this is deciduous woodland
Animal Succession
• Animal species present depend on the plant
species found in the area
• For example, mosses and grasses provide food
and habitats for insects and worms. These can
then support secondary consumers.
Infographic on succession to
include:
Definition of succession
•
• Stages of succession (illustrated
with an example)
• Comparison of the 2 different
types of succession
• Features of pioneer species
• Description of the way each stage
of succession affects the
environment to suit the plants of
the following stage.
Questions.
1. What kind of problems would a pioneer species
encounter?
2. Describe the kind of adaptations you might expect to
see in a pioneer species in order to overcome these
challenges.
3. Explain the difference between primary and secondary
succession.
4. Early stages of ecological succession contain short-lived
plants which devote enormous amounts of energy
producing seeds. More mature communities do not need
to do this. Why?