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Disturbance and Succession
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Disturbance Disturbance - any agent which causes complete or partial destruction of the community resulting in the creation of bare space Disturbance agents: both physical and biological processes may cause disturbances, though we usually focus on physical processes - Physical - fires, ice storms, floods, drought, high winds, landslides, large waves Biological - severe grazing, predation, disease, things that inadvertently kill organisms - digging and burrowing
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Wind Damage – July 4, 1999 Derecho
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Wildfire – Southern California
October 22, 2007
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Northern California Wildfires - 2017
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Intermediate Disturbance Hypothesis
Disturbance maintains communities in a "non-equilibrium state" (never reach equilibrium) and by renewing colonizable space, disturbance allows the persistence of species that might otherwise go extinct due to competitive exclusion. – from Joe Connell
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Rocky coast near Santa Barbara, CA
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Intertidal boulder field - California
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Waves, boulders and disturbance
Wayne Sousa
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Species diversity on intertidal boulders with
different degrees of disturbance – from Sousa
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Species diversity on intertidal boulders with different degrees of disturbance – from Sousa
Boulder size Small Medium Large turnover chance 49% / month 9 % /month 0.1%/ month bare space most medium little diversity low - mostly Ulva high - several species low - mostly Gigartina
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Tree fall in Gabon
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In an ecosystem, disturbance
1) clears space and interrupts competitive dominance 2) changes relative abundance of species 3) is a source of spatial and temporal variability 4) is an agent of natural selection in terms of life history characteristics
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Succession Succession is the non-seasonal, directional and continuous pattern of colonization and extinction on a site by populations of species - this definition incorporates a range of successional sequences that occur over widely different time scales and have very different mechanisms.
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Types of Succssion Primary - succession on a site that has not experienced life before - extremely severe disturbance may have killed all life so no seeds or roots or individuals survive - lava flow, volcanic explosion, glacial retreat, landslides, weathering of bare rock Secondary - succession on a site that may have remnants of previous life on it - some survivors of the disturbance - fire, floods, windstorms, wave battering, severe grazing Degradative - succession in which the substrate is decaying and being exploited by various organisms - succession of decomposers on carcass, rotting log, etc.
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Body Farm – University of Tennessee
FBI Forensics Class
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Facilitation Succession
Early species change community or ecosystem in a way that allows later species to move in and changes the system so that the early species can no longer survive there.
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Retreat of Muir Glacier
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Retreat of Muir Glacier – 1941 – 1950 - 2004
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Retreat of Pederson Glacier – Kenai Fjords NP - 1930-2005
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Succession at Glacier Bay
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Glacier Bay terminal moraine
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Terminal Moraine – Close Up
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Early succession – Moss on bare soil
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Fireweed at Glacier Bay
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Dryas - herbal rose at Glacier Bay
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Alder thicket – Glacier Bay
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Sitka spruce seedlings
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Mature Spruce–Hemlock Forest – Glacier Bay
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Tolerance Succession All species arrive at start of succession, but longer lived individuals eventually outlive short lived species and grow to dominate in the succession - long lived species can tolerate shade and competition early in life.
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Old Field Succession
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Old field succession – bare ground
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Old field succession – annual weeds
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Old field succession – perennials
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Old field succession – pine invasion
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Old field succession – hardwood forest
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Inhibition Succession
First species to arrive occupies space and prevents the settlement of later arriving species - the first species are replaced only after they die.
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Ulva – above and Gigartina overgrowing Ulva – right
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Typical Succession In most successional sequences, all three mechanisms operate at different times in the sequence.
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Henry C. Cowles (center) about 1920
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Lake Michigan sand dune ecosystem
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Marram grass establishment
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“Blow-out” in sand dune ecosystem
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Successional Species Types
Early successional, pioneer, opportunist Late successional seed dispersal distance long, good short, poor growth rate fast slow reach maturity early late number of offspring high low competitive ability
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The Kabetogama Peninsula
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Kabetogama Peninsula
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Beaver – Castor Canadensis
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Beaver Dam
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Pond and Bog Succession
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Climax Community
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Many Communities Experience Constant Disturbance or Change
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Fir Wave on Mt. Coe, Baxter State Park, Maine
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Fir Wave Up Close
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