Download Ecological Succession

Ecological Succession
What is ecological succession?
• Ecological succession is the gradual and
predictable process by which ecosystems
change and develop over time.
• Nothing remains the same and habitats
are constantly changing.
Primary Succession
• Occurs after the creation of a new habitat
• e.g. lava flow, glacier retreat, sand dune
formation, artificial ponds, artificial reefs
• Areas which have never had organisms
growing on them
• Conditions are unfavorable for life at first
Primary Ecological Succession
Occurs on surfaces
where no soil exists.
After a Lava flow or
retreating glacier
Primary
species
Primary Succession
Secondary Succession
• Community development in areas that were previously
occupied by a community
• Occurs after a disturbance
• e.g. loss of trees by disease, wind or fire; logs clearing
areas in intertidal zone; overturning of boulders in
intertidal zone
• Conditions are therefore favorable since seeds, spores
and even resistant animals or plants may remain and
there is often a well developed soil
• More rapid than primary succession
Secondary Ecological Succession
Occurs when
a climax
community
is disturbed.
Soil already
exists.
Ex. Land after a
forest fire, land
cleared for
farming is
abandoned
Secondary Succession
How does Succession Occur?
•
Through a series of stages:
– Pioneer species arrive
– Early colonizers with good dispersal
mechanisms (r-selected species); fast
growth rate; high photosynthetic rate;
minimal environmental demands
– Opportunistic organisms settle
– e.g. diatoms, sea lettuce, scotch broom
How does succession occur?
Seral stages
• waves of temporary organisms displace
pioneer species through competition
Climax community
• End point of succession
• Climax community – VA is a deciduous
oak-hickory (hardwood) forest.
Climax Community
• Most permanent of all the stages
• Stage at which system has reached
steady-state equilibrium
• May take 100’s or 1000’s of years to reach
this stage.
• During succession species modify the physical
environment making it more suitable for new
species and less suitable for those already there
• Pioneer species are often poor competitors and
are replaced by stronger competitors that have
greater environmental demands
• Later communities are often more complex than
earlier communities