Transcript Succession presentation

Index of Diversity
Index of
Diversity
Nature of
Environment
Explanation
Low value
Unfavourable
(eg desert, Arctic
tundra, upper
seashore)
•Few species present, often
small populations
•Generally abiotic factors
determine species present
•Usually unstable ecosystems
High value
Favourable
(eg tropical
forest, temperate
woodland, lower
seashore)
•Many species present, usually
large populations
•Generally biotic factors
determine species present
•Usually stable ecosystems
Ecological Succession
Media Film
• Watch the following film and
TAKE NOTES
• tut_vid_3.mov
Ecological Succession
Ecological succession is the directional change
in the composition of species that occupy a
given area through time
It involves initial colonisation and establishment
of pioneer plant species, followed by their
replacement with other species until a
relatively stable community is formed
Occurs because, through the processes of living,
growing and reproducing, organisms interact with
and affect the environment within an area,
gradually making it more suitable for other species
Ecological Succession
• Succession is directional
• Different stages in a particular habitat
succession can usually be accurately
predicted
• These stages, characterised by the
presence of different communities, are
known as 'seres'
• Each sere is a less hostile environment
than the previous
• The seres are not totally distinct from
each other
Primary Succession
A type of ecological succession that
occurs in an area where there were no
organisms initially
Secondary Succession
A type of ecological succession that occurs in
an area where an existing community has
been severely cleared by disturbance
An Example of SuccessionSand Dune Ecosystem
Mobile dunes
Fixed dunes
(lots of visible sand)
(very little sand visible)
Dune building
•
High winds move sand along beach
•
Sand is dropped and builds up on debris left at high
tide forming small wind breaks
•
Sand piles up further in these areas as wind speed
drops locally
•
This provides a bigger wind break and more sand
piles beginning the process of dune building
Pioneer Stage (Sere 1)
•Little organic matter
•Sand does not retain water and dries out rapidly
•High concentration of sodium and calcium (from sea
spray)
•Soil nutrients in short supply
Pioneer Stage Plants
•Intolerant of being
buried by sand
•Tolerant of salt
•Able to colonise bare
sand
•Unable to stabilize the
dunes
•Species include sea
spurge and sea holly
Portland Spurge
Euphorbia portlandica
Yellow Dune Stage (Sere 2)
•Organic matter staring to build up
•Less spray from the sea water
•Some areas shielded from the wind
•Sand will continue to deposit
•Environmental conditions slowly improving
Yellow Dune Plants
• Leaves grow vertically so can withstand more sand deposits
• Leaves have waxy coating to retain water
• Leaves often rolled to reduce exposed surface area,
reducing transpiration and water loss
• Deep vertical root system and extensive horizontal root
network helps to stabilize the sand
Marram Grass
(Ammophila
breviligulata)
stabilizes the sand
Grey Dune Stage – Sere 3
• Humus layers are building up, retaining some moisture
but water is scarce in summer months
• Sand is no longer being deposited
• Developing soil will be lime rich (from crushed sea
shells) or acidic
• Wind speed is considerably lower
Grey Dune Plants
•Grey-green lichens (Peltigera, Cladonia) will colonize the
dune extensively, combining with accumulating humus to
give the dune sand a characteristic dirty grey colour.
•Other larger plants are able to take advantage of the
improving conditions
Heather (Calluna vulgaris)
Pyramidal Orchid
(Anacamptis pyramidalis)
Dune Scrub Stage- Sere 4
• Build-up of humus from previous stages has produced a sandy
soil, capable of supporting pasture grasses and bushes
• Soil now retains moisture and contains more nutrients (ie
nitrates) although rain may leach Na and K ions from the soil
• Almost no bare sand is now visible
• Environment is less harsh and abiotic factors (ie competition)
begin are shaping species composition
Dune Scrub Plants
• Bushes will develop on the tops and in the hollows of
the dunes. These will include:
Hawthorn, Crataegus monogyna, Elder, Sambucus,
Brambles, Rubus and Sea Buckthorn.
• Sea Buckthorn (Hippophae
rhamnoides) has often
been introduced onto
dunes to help stabilize
them. It has nitrogen
fixing root nodules and
thrive even on nutrientpoor young dunes.
Climax Community- Sere 5
• Climax communities are those that tend to remain stable
for relatively long periods of time
• Even in the absence of tree planting, the dunes will
eventually develop into woodland, the final stage
• This does not however, imply that there will be no
further change. When large organisms such as trees, die
and fall down, then new openings are created in which
secondary succession will occur.
There has been an increase in species diversity from
the sparsely populated, unstable dunes at the
beginning of succession to the fixed, more stable dune
community populated by shrubs and flowering plants
Sub-climax community
Sometimes succession does not proceed all the way
to a climax community, often prevented by mans
activities or other factors:
Rabbits
•May heavily crop the
vegetation and expose bare
soil
•Droppings may add nutrients
to the sand
•Other plants, typical of waste
ground, may colonize these
bare patches
Succession occurs on many different timescales
It may take hundreds of
years for a climax woodland
to develop, while the
succession of invertebrates
and fungi within a single cow
pat may be over within as
little as 3 months.
By this time, the dung has been transformed into humus and
nutrients and has been recycled back into the soil. The holes
clearly visible in the cow pat have been made by the animals
which have colonized it.
Stages of succession- bare rock example
Pioneer
species
Climax
Community
Low
Diversity
High
Diversity
Harsh
Environment
Bare
Rock
Sere
1
Lichens
Less Harsh
Environment
Sere
2
Mosses
Sere
3
Sere
4
Sere
5
Ferns
Shrubs
Trees
How do we study succession?
• We are unable to study succession in situ
as the process takes place of many years
• However, many ecosystems exhibit all the
stages of succession
• Therefore we can walk through different
areas of a particular ecosystem and observe
the different stages as we progress, using
distance as a surrogate for time
Transects
• Starting from the strand line a line is established at
right angles to the shore.
• A tape is set down along the line of the transect.
• The vegetation can be sampled at intervals along the
line by using a quadrat