Presentation on theme: "Disturbance and Succession. Intermediate Disturbance Hypothesis Disturbance maintains communities in a "non-equilibrium state" (never reach equilibrium)"— Presentation transcript:
Disturbance and Succession
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
Intertidal boulder field - California
Waves, boulders and disturbance Wayne Sousa
Species diversity on intertidal boulders with different degrees of disturbance – from Sousa
Species diversity on intertidal boulders with different degrees of disturbance – from Sousa Boulder sizeSmallMediumLarge turnover chance 49% / month9 % /month0.1%/ month bare spacemostmediumlittle diversitylow - mostly Ulva high - several species low - mostly Gigartina
Tree fall in Gabon
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
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.
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.
Body Farm – University of Tennessee FBI Forensics Class
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.
Retreat of Muir Glacier
Retreat of Muir Glacier – 1941 –
Retreat of Pederson Glacier – Kenai Fjords NP
Succession at Glacier Bay
Glacier Bay terminal moraine
Terminal Moraine – Close Up
Early succession – Moss on bare soil
Fireweed at Glacier Bay
Dryas - herbal rose at Glacier Bay
Alder thicket – Glacier Bay
Sitka spruce seedlings
Mature Spruce–Hemlock Forest – Glacier Bay
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.
Old Field Succession
Old field succession – bare ground
Old field succession – annual weeds
Old field succession – perennials
Old field succession – pine invasion
Old field succession – hardwood forest
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.
Ulva – above and Gigartina overgrowing Ulva – right
Typical Succession In most successional sequences, all three mechanisms operate at different times in the sequence.