endpoint? : revisited climax community “relatively steady-state condition with no directional...
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Endpoint? : Revisited
Climax community
“Relatively steady-state condition with no directional changes in species composition”
Traditional view
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Equilibrium View
time
Su
cce
ssio
nal
sta
te “Climax”
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time
Su
cce
ssio
nal
sta
te
Equilibrium View?
“Climax”
Disturbance
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Disturbance
Definition: “The interruption of tranquility, peace, rest, or a settled condition; interference with the due course of any action or process.
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time
Su
cce
ssio
nal
sta
te
Equilibrium View?
“Climax”
Disturbance
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time
Su
cce
ssio
nal
sta
te
Non-equilibrium View
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Disturbance
Definition: “The interruption of tranquility, peace, rest, or a settled condition; interference with the due course of any action or process.
Disturbance is viewed as something disrupting natural events tending to equilibrium.
Equlibrium view
Disturbance is viewed as a natural component of a community, producing change over time. Small disturbances are always occurring, but do not necessarily lead to successional processes.
Non-equlibrium view
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Many Small Disturbancesa study by Jane LubchenkoCoastal tidal pools
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Elements in studyDisturbance agent
Litorina littorea
Plant species
(periwinkle snail)
– density varies among pools
– herbivore
Chondrus crispus (Irish moss)
– red alga
– only eaten as last resort
Eneteromorpha
– green alga
– relatively small
– Tender and highly edible
Numerous ephemeral algae species
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Disturbance rate
Disturbance Effects
(herbivory)
Disturbance rate
Sp
ecie
s ri
chn
ess
Sp
ecie
s d
iver
sity
Low snail density
Enteromorpha smothers Chondra
Intermediate snail density
Competitive exclusion reduced due to con- sumption of Entero- morpha by snails
High snail density
All but Chondrus eaten
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Conclusion
Disturbance is a constant influence
that defines community structure
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Intermediate Disturbance Hypothesis
Michael Huston 1977
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Two Species Succession
High growth rate;poor competitor
Low growth rate;good competitor
Competitive exclusion
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Impact of disturbanceDisturbance removes 25% biomass
Competitive exclusionhalted or delayed
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Potential Reversal of Fortunes
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Multiple species extensionEventual winner
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Multiple species extension
• Competitive exclusion is delayed
• Species diversity maintained at a higher level
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Multiple species extension
At high disturbance rates diversity declines again
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Intermediate Disturbance Hypothesis
Frequency of disturbance
Div
ersi
ty
Highest diversity will be found at intermediate disturbance levels
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A Field Test of the Intermediate
Disturbance Hypothesis
Wayne Sousa 1979
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Study Location
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Rocky Intertidal Plant Community
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Rocky Intertidal Plant Community
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Boulder Size and Disturbance
Small……….………………LargeNewtons of pull = weight
Low disturbance
Medium disturbance
High dist.
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Diversity and Disturbance
High Medium Low
Disturbance rates
Ma
xim
um
div
ers
ity
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Predicting Species Distributions
mid-successional species
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Mid-succession species and disturbance
Distribution aspredicted
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Assessing impact of disturbance
Early successionMid-successionLate succession
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Conclusion
Results of this experiment are consistent with the intermediate disturbance hypothesis
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Further studies examining
diversity-disturbance relationships
Mackey and Currie 2001
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Meta-analysis
pattern predicted by intermediate disturbance hypothesis
Disturbance response
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Conclusion
The intermediate disturbance hypothesis is only one of many possible relationships observed between diversity and disturbance
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Ecology at the Global Scale
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Global Climate Change:
Impacts on Vegetation
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Part #1:
The Driving Force behind
Climate Change
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The Greenhouse Effect
CO2 (Carbon dioxide)NH4 (Methane)N20 (Nitrous oxide)O3 (Ozone)CFCs
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Mauna Loa: CO2 Measurements
4,170 m
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Mauna Loa: [CO2]
Summer minimum
Winter maximum
Mean trend
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Does this represent
a long term trend?
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Fossil AtmospheresMauna Loa
Further Evidence
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Further Evidence: Methane
Atmospheric levels
Anthropogenic emissions
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Direct Evidence of Warming