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
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
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
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.