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Disturbance and Succession

Explore how disturbances create space for species, impacting ecosystems and enabling succession to thrive over time. Learn about types of succession, from primary to secondary, and understand the role of different species in shaping ecological communities. Discover the interplay between disturbance events and the evolution of ecosystems in a non-equilibrium state.

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Disturbance and Succession

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  1. Disturbance and Succession

  2. 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

  3. Wind Damage –July 4, 1999 Derecho

  4. Wildfire – Southern California October 22, 2007

  5. Northern California Wildfires - 2017

  6. 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

  7. Rocky coast near Santa Barbara, CA

  8. Intertidal boulder field - California

  9. Waves, boulders and disturbance Wayne Sousa

  10. Species diversity on intertidal boulders with different degrees of disturbance – from Sousa

  11. Species diversity on intertidal boulders with different degrees of disturbance – from Sousa

  12. Tree fall in Gabon

  13. 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

  14. 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.

  15. 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.

  16. Body Farm – University of Tennessee FBI Forensics Class

  17. 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.

  18. Retreat of Muir Glacier

  19. Retreat of Muir Glacier – 1941 – 1950 - 2004

  20. Retreat of Pederson Glacier – Kenai Fjords NP - 1930-2005

  21. Succession at Glacier Bay

  22. Glacier Bay terminal moraine

  23. Terminal Moraine – Close Up

  24. Early succession – Moss on bare soil

  25. Fireweed at Glacier Bay

  26. Dryas - herbal rose at Glacier Bay

  27. Alder thicket – Glacier Bay

  28. Sitka spruce seedlings

  29. Mature Spruce–Hemlock Forest – Glacier Bay

  30. 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.

  31. Old Field Succession

  32. Old field succession – bare ground

  33. Old field succession – annual weeds

  34. Old field succession – perennials

  35. Old field succession – pine invasion

  36. Old field succession – hardwood forest

  37. 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.

  38. Ulva – above and Gigartina overgrowing Ulva – right

  39. Typical Succession • In most successional sequences, all three mechanisms operate at different times in the sequence.

  40. Henry C. Cowles (center) about 1920

  41. Lake Michigan sand dune ecosystem

  42. Marram grass establishment

  43. “Blow-out” in sand dune ecosystem

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