Plant Ecology - Chapter 12

1. Plant Ecology - Chapter 12 Disturbance & Succession

2. Succession • Temporal patterns in communities • Replacement of species by others within particular habitat (colonization and extinction) • Non-seasonal, continuous, directional

3. Degradative succession • Decomposers breaking down organic matter • Leads to disappearance of everything, species included

4. Autotropic succession • Does not lead to degradation • Habitat continually occupied by living organisms

5. Two types of autotropic succession • Allogenic succession • Autogenic succession

6. Allogenic succession • Serial replacement of species driven by changing external geophysical processes • Examples: • 1) silt deposition changing aquatic habitat to terrestrial habitat • 2) increasing salinity of Great Salt Lake

7. Autogenic succession • Change of species driven by biological processes changing conditions and/or resources • Example: organisms living, then dying, on bare rock

8. In an area that previously did not support any community Primary succession Example: terrestrial habitat devoid of soil In an area that previously supported a community, but now does not Secondary succession Example: terrestrial habitat where vegetation was destroyed, but soil remained Autogenic succession can occur under 2 different conditions

9. Disturbances • Relatively discreet event in time that causes abrupt change in ecosystem, community, or population structure • Changes resource availability, substrate availability, or the physical environment

10. Disturbances • Intensity, size, frequency • Small disturbances of low intensity are much more frequent than large disturbances of high intensity

11. Disturbances • Gaps • Fire • Wind • Water • Animals • Earthquakes, volcanoes • Disease • Humans

12. Primary succession • Volcanic eruptions • Glaciers

13. Secondarysuccession • Floods • Fires

14. Rate of succession • Primary - slow - may take 1000s of years • Secondary - faster - fraction of the time to reach same stage

15. Autogenic succession begins… • First community comprised of r-selected species - pioneer species

16. r-selected species • Good colonizers • Tolerant of harsh conditions • Reproduce quickly in unpredictable environs • Example: lichens

17. r-selected species • Primary - colonized by seeds, spores, via wind, water • Secondary - wind-dispersed seeds, seed banks

18. Pioneer species • Carry out life processes and begin to modify habitat • Extract resources from bare rock • Break up/fragment rock with roots • Collect wind-blown dust, particles • Waste products accumulate • Die and decompose • Soil development begins

19. Continuing change • Colonizers joined by other species suited for modified habitat • Eventually replace colonizers • Better competitors in modified habitat • Less r-selected, more K-selected

20. More change • Communities may gradually become dominated by K-selected species • Good competitors, able to coexist with others for long periods of time

21. Stability • Communities may become stabilized on some scale • Reach equilibrium (dynamic) • Little or no change in species composition, abundance over long periods of time • Climax community • End stage of succession

22. Will climax stage be reached? • Rarely is climax stage reached quickly • Slow succession most common, climax stage almost never achieved • Community usually affected by some major disturbance (e.g., fire) before climax stage is reached • Resets succession, forces it to start again from some earlier stage

23. Terrestrial succession

24. Relay Floristics

25. Relay Floristics

26. Predictability of Succession Deterministic- process with a fixed outcome Community restoration via succession?