Mechanisms and Models of Succession

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Mechanisms and Models of Succession
Succession mechanisms/models

• Early ideas Clements and Gleason
• The mechanisms Connell and Slatyer
• The models Egler, Grime, Tilman, Huston/Smith

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Early Ideas
Succession mechanisms/models

• Influenced greatly by community concepts,
  sampling methodologies, and type of flora being
  studied

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Clements
Succession mechanisms/models

• Relay floristics fig 12.13

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Clements
Succession mechanisms/models

• Relay floristics
• Each seral stage is discrete
• Endpoint is predictable
• Biotic interactions central

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Gleason
Succession mechanisms/models

• Coincidence, dynamic processes important
• Seral stages, like communities, intergrade
• Endpoint is spatially variable
• Abiotic conditions and chance migration important

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The mechanisms Connell and Slatyer 1977
Succession mechanisms/models

• Facilitation
• Early successional species modify environment,
  making it more suitable for later species
• Only pioneer species can establish on open
  space
• Early species eventually eliminated by
  competition
• Example primary succession

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The mechanisms Connell and Slatyer 1977
Succession mechanisms/models

• Inhibition
• Early successional species modify environment,
  making it less suitable for later species
• Any species can invade
• Early species can exclude later species for
  extended periods, unless external stresses
  intervene
• Example canopy trees inhibit understory (or
  sometimes, vice versa)

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The mechanisms Connell and Slatyer 1977
Succession mechanisms/models

• Tolerance
• Modification of environment, if it occurs, has no
  effect on subsequent recruitment
• Any species can invade
• Winners may be longer lived or larger, or
  better able to withstand adverse environment
• Example differences in ability to exploit
  resources, e.g. shade tolerance

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Problem 2

• The figure to left is from Chapin et al., 1994
  (Ecological Monographs 64149-175), and shows the
  biomass of roots, stems, and leaves of naturally
  occurring spruce seedlings in four stages of
  primary succession at Glacier Bay, Alaska. Using
  the terminology of Connell and Slatyer, explain
  the ecological processes that might underlie
  these results.

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Models Egler (1954)
Succession mechanisms/models

• Initial floristic composition model
• Progression of seres unpredictable
• Any species can invade, but differences in growth
  rate and life history lead to different
  communities
• Emphasizes chance migration, differential
  longevity

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Models Egler (1954)
Succession mechanisms/models
Fig. 12.13
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Models Grime (1977, 1979)
Succession mechanisms/models

• Triangular life history model
• C competitive
• S stress tolerant
• R ruderal weedy

C
R
S
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Models Grime (1977, 1979)
Succession mechanisms/models

• Triangular life history model
• C competitive
• S stress tolerant
• R ruderal weedy

C
CS
CR
CSR
SR
R
S
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Models Grime (1977, 1979)
Succession mechanisms/models

• Early species are ruderal take over empty space
• Less empty space favors competitive species in
  mid seral stages
• When resources are depleted (later seral stages),
  expect stress tolerators

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Models Grime (1977, 1979)
Succession mechanisms/models
C
Trees and shrubs Perennials Biennials Annuals Lich
ens Bryophytes
S
R
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Models Grime (1977, 1979)
Succession mechanisms/models

• Made predictions about which life histories, and
  speed of succession, would occur in habitats with
  different amounts of resources
• Expect few competitive species when environment
  is not productive
• More productive environments can support more
  species, and more kinds of species
• Rate of change in species identities positively
  related to productivity

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Models Grime (1977, 1979)
Succession mechanisms/models
Competitive
P1 high productivity P2 moderate P3 low
Ruderal
Stress tolerant
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Models Tilman (1985, 1988)
Succession mechanisms/models

• Resource-ratio hypothesis
• Different species do best at different
  combinations of resources (usually Nitrogen and
  light)
• Not unlike relay floristics, but allows for less
  predictability and abiotic influences

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Models Tilman (1985, 1988)
Succession mechanisms/models
A
B
E
F
G
D
C
Abundance
Nutrients or Light
Time ?
A-G are species, dashed is nutrients, solid is
light
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Models Tilman (1985, 1988)
Succession mechanisms/models

• Made predictions about speed of succession when
  resource availability varied for Tilman,
  resources Nitrogen
• Low resource environments have longer seres,
  starting with species A in figure
• High resource environments have shorter seres,
  e.g. start with species E or F
• Rate of change in species identities negatively
  related to productivity

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Tilman vs. Grime
Succession mechanisms/models

• We will revisit these guys when we do competition
• Different predictions about the pace of
  succession due to different definitions of
  competition
• A good reference Grace, 1991. Functional
  Ecology 5 583-587.

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Models Huston and Smith (1987)
Succession mechanisms/models

• Dynamic equilibrium model
• Includes competition, life history, and
  physiology
• Facilitation and inhibition change in
  environment changes competitive outcomes
• Physiological/life history constraints preclude a
  single superplant

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Models Franklin et al. (2002)
Succession mechanisms/models

• Emphasize abiotic factors, landscape patterns,
  and structural complexity rather than competition
  or life history
• A re-acknowledgement of the importance of chance
  and historic processes in succession

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Processes in community dynamics
Succession mechanisms/models
Fig 12.1