Ecological Succession

1
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.
• Reading
• Environmental Science pp. 96 - 100
• Biology (Campbell) p. 1124

2
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

3
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 unfavourable for life at
  first
• Animations

4
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

5
IN YOUR NOTEBOOK

• Describe the steps you would take to measure
  PRIMARY succession on the Pearson College Docks
• In another paragraph describe what you would do
  to measure SECONDARY succession in the forest at
  Pearson College or in the intertidal zone at Race
  Rocks

6
Why does succession occur?

• Ecosystem development results from
• Changes in physical environment - disturbance or
  creation of new habitat
• Competition between organisms
• Shift in energy flow from production to
  respiration

7
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

8
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

9
Climax community

• Most permanent of all the stages
• Stage at which system has reached steady-state
  equilibrium
• May take 100s or 1000s 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)

10

• 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

11
Changes in community with succession

• ? number of individuals
• ? biomass
• ? size of individuals
• ? biodiversity which may stabilize or ? as size
  of individuals ?s
• Shift from linear food chains to complex food
  webs
• ? Gross productivity (initially low GPP due to
  conditions and low autotroph density)

12
More changes

• ? Net productivity from high to zero
• 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
  PR approaches 1
• ? internal cycling of materials
• mineral cycles become more closed

13
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.