DisturbanceDisturbance – – discrete punctuated killing, discrete punctuated killing, displacement, or damaging of one or more displacement, or damaging of one or more individuals (or colonies) that creates an individuals (or colonies) that creates an opportunity for new individuals (or colonies) opportunity for new individuals (or colonies) to become established.to become established.

Agents of disturbance:Agents of disturbance:– Physical – water motion (logs, tearing, Physical – water motion (logs, tearing,

roll boulders), desiccation, flood, roll boulders), desiccation, flood, freezingfreezing

– Biological – predation, grazing, Biological – predation, grazing, bulldozingbulldozing

Disturbance regime:Disturbance regime:

• Areal extentAreal extent

• FrequencyFrequency

• PredictabilityPredictability

• Turnover rateTurnover rate

Repopulation/Colonization of Repopulation/Colonization of Disturbed PatchesDisturbed Patches• Source of colonists and distance of that Source of colonists and distance of that

source source – Asexual (colonial) vs. sexual (individual)Asexual (colonial) vs. sexual (individual)– Lecithotrophic larvae vs. planktotrophic larvaeLecithotrophic larvae vs. planktotrophic larvae

• Time of patch creationTime of patch creation– Must be competent larvae availableMust be competent larvae available

• Size and shape of disturbed patchSize and shape of disturbed patch– Influence of surrounding organismsInfluence of surrounding organisms

• Nature of disturbanceNature of disturbance– Physical vs. biological (selective/nonselective Physical vs. biological (selective/nonselective

mortalitymortality

Intermediate Disturbance Intermediate Disturbance HypothesisHypothesis – Disturbance at – Disturbance at intermediate intensity or intermediate intensity or frequency will allow high frequency will allow high diversity by maintaining diversity by maintaining communities in a non-communities in a non-equilibrium state (Connell equilibrium state (Connell 19781978))

-- disturbance-mediated -- disturbance-mediated coexistencecoexistence

Time

Evidence for Intermediate Evidence for Intermediate Disturbance Hypothesis Disturbance Hypothesis from marine systems:from marine systems:

• Age of disturbed patches – link to Age of disturbed patches – link to diversitydiversity

• Boulders – intermediate-sized Boulders – intermediate-sized boulders are most diverse boulders are most diverse

DisturbanceDisturbance(opens space, releases resources)(opens space, releases resources)

Of those that arrive,Of those that arrive,only “early successional” only “early successional”

species survivespecies survive

Of those that arrive,Of those that arrive,any that establish themselves any that establish themselves

can survivecan survive

Growth of early speciesGrowth of early speciesmodifies the environmentmodifies the environment

to allow later speciesto allow later species

Environment Environment modified somodified so

less suitable forless suitable for any other colonistany other colonist

Environment Environment modified somodified so

some early arrivers some early arrivers can no longer can no longer

survivesurvive

Original colonists Original colonists persist until persist until damaged or damaged or

destroyeddestroyed

Less tolerantLess tolerantspecies diespecies dieand/or areand/or are

forced out byforced out bybetter competitorsbetter competitors

1 2, 3

1 = Facilitation1 = Facilitation

2 = Inhibition2 = Inhibition

3 = Tolerance3 = Tolerance

2 3

Patchiness on hard Patchiness on hard substrates:substrates:

• DisturbanceDisturbance

• Larval site selectionLarval site selection

• Fluctuations in availability of larvaeFluctuations in availability of larvae

• Heterogeneity in substrateHeterogeneity in substrate

• TerritorialityTerritoriality

Differences Subtidal vs. Differences Subtidal vs. IntertidalIntertidal

• Subtidal always covered by waterSubtidal always covered by water

• No refuge from predation in subtidalNo refuge from predation in subtidal

• Space appears 100% occupied in Space appears 100% occupied in subtidalsubtidal

• Dominant role of colonial species in Dominant role of colonial species in subtidalsubtidal

John SutherlandJohn Sutherland

• Subtidal hard substrate (pier Subtidal hard substrate (pier pilings in North Carolina)pilings in North Carolina)

• Followed what happened after a Followed what happened after a disturbance – wasn’t always the disturbance – wasn’t always the samesame

• Why?Why?

Styela

Ascidia

Tunicates (Sea Tunicates (Sea squirts)squirts)

Aplidium (Sea Pork)

Schizoporella

Encrusting bryzoanEncrusting bryzoan

Colonial tunicateColonial tunicate

Bugula

Bryzoans (fleshy)Bryzoans (fleshy)

Tubularia

HydroidsHydroids

Sutherland’s experimentSutherland’s experiment• Followed colonization of plates he Followed colonization of plates he

placed underwater at different times, placed underwater at different times, or cleared at different timeor cleared at different time

• Results:Results:– SchizoporellaSchizoporella dominated when fish dominated when fish

predators were common (fish eat predators were common (fish eat StyelaStyela recruits)recruits)

– StyelaStyela dominated when few fish were dominated when few fish were present, present, TubulariaTubularia and and BugulaBugula were were present (present (StyelaStyela recruits hide under these recruits hide under these speciesspecies

Sutherland’s conclusions:Sutherland’s conclusions:• Community on any given patch depends Community on any given patch depends

on:on:– Larval recruitmentLarval recruitment

– Fish predation intensityFish predation intensity

• Once established, the dominant maintains Once established, the dominant maintains self/excludes others by feeding on larvae, self/excludes others by feeding on larvae, overgrowth on marginsovergrowth on margins

• Overturn by:Overturn by:– StyelaStyela sloughing off sloughing off

– disturbancedisturbance

Multiple State Points/Alternate Multiple State Points/Alternate Stable StatesStable States

• Have a different community on the same Have a different community on the same physical site over long period of timephysical site over long period of time

• Each persists – remains stable – until the Each persists – remains stable – until the next major disturbancenext major disturbance

Is not one “mature” community, but Is not one “mature” community, but severalseveral

Inhibition model of successionInhibition model of succession

Other examples:Other examples:

• Horizontal faces – with urchins, Horizontal faces – with urchins, without urchins – coralline algae, or without urchins – coralline algae, or foliose algaefoliose algae

• Tidepools – with Tidepools – with Littorina Littorina or without or without Littorina Littorina