Disturbance and Succession

1. Disturbance and Succession

2. 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

4. Rocky coast

5. Intertidal boulder field - California

6. Waves, boulders and disturbance Wayne Sousa

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

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

9. Tree fall in Gabon

10. 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

11. 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.

12. 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.

13. Body Farm – University of Tennessee FBI Forensics Class

15. 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.

19. Retreat of Muir Glacier

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

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

22. Succession at Glacier Bay

23. Glacier Bay terminal moraine

24. Terminal Moraine – Close Up

25. Early succession – Moss on bare soil

26. Fireweed at Glacier Bay

27. Dryas - herbal rose at Glacier Bay

28. Alder thicket – Glacier Bay

29. Sitka spruce seedlings

30. Mature Spruce–Hemlock Forest – Glacier Bay

31. 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.

32. Old Field Succession

33. Old field succession – bare ground

34. Old field succession – annual weeds

35. Old field succession – perennials

36. Old field succession – pine invasion

37. Old field succession – hardwood forest

38. 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.

39. Ulva – above and Gigartina overgrowing Ulva – right

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

42. Lake Michigan sand dune ecosystem

43. Marram grass establishment

44. “Blow-out” in sand dune ecosystem