Disturbance – discrete punctuated killing, displacement, or damaging of one or more individuals (or colonies) that creates an opportunity for new individuals (or colonies) to become established. Agents of disturbance: –Physical – water motion (logs, tearing, roll boulders), desiccation, flood, freezing –Biological – predation, grazing, bulldozing

Disturbance regime: Areal extent Areal extent Frequency Frequency Predictability Predictability Turnover rate Turnover rate

Repopulation/Colonization of Disturbed Patches Source of colonists and distance of that source Source of colonists and distance of that source –Asexual (colonial) vs. sexual (individual) –Lecithotrophic larvae vs. planktotrophic larvae Time of patch creation Time of patch creation –Must be competent larvae available Size and shape of disturbed patch Size and shape of disturbed patch –Influence of surrounding organisms Nature of disturbance Nature of disturbance –Physical vs. biological (selective/nonselective mortality

Intermediate Disturbance Hypothesis – Disturbance at intermediate intensity or frequency will allow high diversity by maintaining communities in a non- equilibrium state (Connell 1978) -- disturbance-mediated coexistence

Time

Evidence for Intermediate Disturbance Hypothesis from marine systems: Age of disturbed patches – link to diversity Age of disturbed patches – link to diversity Boulders – intermediate-sized boulders are most diverse Boulders – intermediate-sized boulders are most diverse

Disturbance (opens space, releases resources) Of those that arrive, only “early successional” species survive Of those that arrive, any that establish themselves can survive Growth of early species modifies the environment to allow later species Environment modified so less suitable for any other colonist Environment modified so some early arrivers can no longer survive Original colonists persist until damaged or destroyed Less tolerant species die and/or are forced out by better competitors 12, 3 1 = Facilitation 2 = Inhibition 3 = Tolerance 23

Patchiness on hard substrates: Disturbance Disturbance Larval site selection Larval site selection Fluctuations in availability of larvae Fluctuations in availability of larvae Heterogeneity in substrate Heterogeneity in substrate Territoriality Territoriality

Differences Subtidal vs. Intertidal Subtidal always covered by water Subtidal always covered by water No refuge from predation in subtidal No refuge from predation in subtidal Space appears 100% occupied in subtidal Space appears 100% occupied in subtidal Dominant role of colonial species in subtidal Dominant role of colonial species in subtidal

John Sutherland Subtidal hard substrate (pier pilings in North Carolina) Subtidal hard substrate (pier pilings in North Carolina) Followed what happened after a disturbance – wasn’t always the same Followed what happened after a disturbance – wasn’t always the same Why? Why?

Styela Ascidia Tunicates (Sea squirts)

Aplidium (Sea Pork) Schizoporella Encrusting bryzoan Colonial tunicate

Bugula Bryzoans (fleshy)

Tubularia Hydroids

Sutherland’s experiment Followed colonization of plates he placed underwater at different times, or cleared at different time Followed colonization of plates he placed underwater at different times, or cleared at different time Results: Results: –Schizoporella dominated when fish predators were common (fish eat Styela recruits) –Styela dominated when few fish were present, Tubularia and Bugula were present (Styela recruits hide under these species

Sutherland’s conclusions: Community on any given patch depends on: Community on any given patch depends on: –Larval recruitment –Fish predation intensity Once established, the dominant maintains self/excludes others by feeding on larvae, overgrowth on margins Once established, the dominant maintains self/excludes others by feeding on larvae, overgrowth on margins Overturn by: Overturn by: –Styela sloughing off –disturbance

Multiple State Points/Alternate Stable States Have a different community on the same physical site over long period of time Have a different community on the same physical site over long period of time Each persists – remains stable – until the next major disturbance Each persists – remains stable – until the next major disturbance Is not one “mature” community, but several Inhibition model of succession

Other examples: Horizontal faces – with urchins, without urchins – coralline algae, or foliose algae Horizontal faces – with urchins, without urchins – coralline algae, or foliose algae Tidepools – with Littorina or without Littorina Tidepools – with Littorina or without Littorina