Transcript Ch. 14 Succession

Ecological Succession
– Syllabus Topics 2.3.5 to 2.3.7
– 2.3.5. Describe the concept and processes of
succession in a named habitat.
– 2.3.6 Explain the changes in energy flow, gross and
net productivity, diversity and mineral cycling in
different stages of succession.
– 2.3.7 Describe factors affecting the nature of climax
communities.
Ecological Succession
– orderly process of change over time in a
community” (IB definition)
• What is a “community”?
• Sequence of appearance and
disappearance of species
• Pattern of colonization and extinction
• Directional, non-seasonal, continuous
• Two types: primary and secondary
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
Lichens
Exposed
and mosses
rocks
Fig. 7-11, p. 156
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 favourable since seeds, spores
and even resistant animals or plants may remain and
there is often a well developed soil
• More rapid than primary succession
Fig. 7-12, p. 157
IN YOUR NOTEBOOK…
• Describe the steps you would take to
measure PRIMARY succession in the
wake of a melting glacier in glacier
national park.
• In another paragraph describe what you
would do to measure SECONDARY
succession in the forest in the abandoned
farms of Long Valley.
Why does succession occur?
– Ecosystem changes result from:
– Changes in physical environment disturbance or creation of new habitat
– Competition between organisms
– Shift in energy flow from production to
respiration
How does succession occur?
•
Through a series of stages:
–
Pioneer species arrive
–
Early colonizers with good dispersal mechanisms (rselected species); fast growth rate; high
photosynthetic rate; minimal environmental
demands
–
Opportunistic organisms settle
–
e.g. diatoms, sea lettuce, scotch broom
Stages of Succession
• Sere - “set of communities that succeed one another over the
course of succession at a given location” (IB definition)
• process of succession from beginning to end
– Seral stages
• waves of temporary organisms displace pioneer species through
competition
– Climax community
– End point of succession
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
• Difficult to identify
• Determined by climatic or edaphic (soil) factors unless
humans maintain an equilibrium at subclimax (e.g. poor
soil quality, grazing, preventing forest fires, selective
logging)
• 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
Changes in Community with
Succession
• Biomass
• Size of individuals
• Biodiversity increases then may stabilize or slightly
decline as size of individuals increases
• Shift from linear food chains to complex food webs
• Gross productivity (GPP is low initially, rising in the
middle stages of succession, then GPP declines again in
the climax phase)
More Changes…
– Net productivity from goes from high in the early
stages to zero as succession approaches climax
– Initially low amount of energy lost through respiration
therefore high NPP
• Respiration with shift in community to more
consumers so net productivity approaches zero
as Photosynthesis:Respiration ratio (P:R)
approaches 1
– internal cycling of materials
– mineral cycles become more closed