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Plant Ecology - Chapter 12

Chapter 12 of Plant Ecology presents a comprehensive overview of disturbance and succession in ecological communities. It discusses the temporal patterns of species replacement, emphasizing the roles of colonization and extinction within habitats. The chapter explores allogenic and autogenic succession, detailing how both abiotic and biotic processes impact community structure. It highlights primary and secondary succession, and the effects of various disturbances such as fire, floods, and human activities. The balance between r-selected and K-selected species is examined, along with the concept of climax communities and their stability.

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Plant Ecology - Chapter 12

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  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?

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