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Disturbance and Succession. Intermediate Disturbance Hypothesis Disturbance maintains communities in a "non-equilibrium state" (never reach equilibrium)

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Presentation on theme: "Disturbance and Succession. Intermediate Disturbance Hypothesis Disturbance maintains communities in a "non-equilibrium state" (never reach equilibrium)"— Presentation transcript:

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

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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 Boulder sizeSmallMediumLarge turnover chance 49% / month9 % /month0.1%/ month bare spacemostmediumlittle diversitylow - mostly Ulva high - several species low - mostly Gigartina

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

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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.

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19 Retreat of Muir Glacier

20 Retreat of Muir Glacier – 1941 –

21 Retreat of Pederson Glacier – Kenai Fjords NP

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.

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42 Lake Michigan sand dune ecosystem

43 Marram grass establishment

44 “Blow-out” in sand dune ecosystem

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