Endpoint? : Revisited

Climax community

“Relatively steady-state condition with no directional changes in species composition”

Traditional view

Equilibrium View

time

Su

cce

ssio

nal

sta

te “Climax”

time

Su

cce

ssio

nal

sta

te

Equilibrium View?

“Climax”

Disturbance

Disturbance

Definition: “The interruption of tranquility, peace, rest, or a settled condition; interference with the due course of any action or process.

time

Su

cce

ssio

nal

sta

te

Equilibrium View?

“Climax”

Disturbance

time

Su

cce

ssio

nal

sta

te

Non-equilibrium View

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

Many Small Disturbancesa study by Jane LubchenkoCoastal tidal pools

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

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

Conclusion

Disturbance is a constant influence

that defines community structure

Intermediate Disturbance Hypothesis

Michael Huston 1977

Two Species Succession

High growth rate;poor competitor

Low growth rate;good competitor

Competitive exclusion

Impact of disturbanceDisturbance removes 25% biomass

Competitive exclusionhalted or delayed

Potential Reversal of Fortunes

Multiple species extensionEventual winner

Multiple species extension

• Competitive exclusion is delayed

• Species diversity maintained at a higher level

Multiple species extension

At high disturbance rates diversity declines again

Intermediate Disturbance Hypothesis

Frequency of disturbance

Div

ersi

ty

Highest diversity will be found at intermediate disturbance levels

A Field Test of the Intermediate

Disturbance Hypothesis

Wayne Sousa 1979

Study Location

Rocky Intertidal Plant Community

Rocky Intertidal Plant Community

Boulder Size and Disturbance

Small……….………………LargeNewtons of pull = weight

Low disturbance

Medium disturbance

High dist.

Diversity and Disturbance

High Medium Low

Disturbance rates

Ma

xim

um

div

ers

ity

Predicting Species Distributions

mid-successional species

Mid-succession species and disturbance

Distribution aspredicted

Assessing impact of disturbance

Early successionMid-successionLate succession

Conclusion

Results of this experiment are consistent with the intermediate disturbance hypothesis

Further studies examining

diversity-disturbance relationships

Mackey and Currie 2001

Meta-analysis

pattern predicted by intermediate disturbance hypothesis

Disturbance response

Conclusion

The intermediate disturbance hypothesis is only one of many possible relationships observed between diversity and disturbance

Ecology at the Global Scale

Global Climate Change:

Impacts on Vegetation

Part #1:

The Driving Force behind

Climate Change

The Greenhouse Effect

CO2 (Carbon dioxide)NH4 (Methane)N20 (Nitrous oxide)O3 (Ozone)CFCs

Mauna Loa: CO2 Measurements

4,170 m

Mauna Loa: [CO2]

Summer minimum

Winter maximum

Mean trend

Does this represent

a long term trend?

Fossil AtmospheresMauna Loa

Further Evidence

Further Evidence: Methane

Atmospheric levels

Anthropogenic emissions

Direct Evidence of Warming