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Section 4 – Community Stability

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  1. Section 4 – Community Stability

  2. Ecological Succession • Equilibrium: stable and balanced • Disequilibrium: unstable and off balance • Limiting factors shift – carrying capacities altered • Population sizes change • Succession: a somewhat predictable series of changes over time in a community • Following a Disturbance • Ex. Fire, Flood, Natural Disasters

  3. Primary Succession • Primary Succession: the somewhat predictable series of changes in a community that follows a disturbance so severe that no vegetation or soil life remains • Starting from scratch – from rock, sand or sediment • Glaciers retreat, lakes dry up, volcanic lava or ash spreads across a landscape • Pioneer Species: one of the first species to colonize newly exposed land • Well adapted for colonization • Seeds can travel long distances to spread quickly

  4. Primary Succession • Lichens: formed by a mutualistic relationship between algae and fungi • Algae provides food and energy – photosynthesis • Fungi holds onto rocks and captures moisture • Lichen grows – releases acid the breaks down rock • Soil begins to form, small plants, insects and worms move in

  5. Secondary Succession • Secondary Succession: the somewhat predictable series of changes in a community that follows a disturbance (e.g., a fire, logging, or farming) that dramatically alters the community but does not destroy all vegetation or soil life • Occurs faster than primary succession

  6. Succession in Water • Primary Aquatic Succession: when an area fills with water for the first time • Glaciers retreat and leave depressions in the ground • Over time, aquatic communities are established • Secondary Aquatic Succession: follows disturbance to aquatic community • Pond fills with organic matter • Pond may fill in completely, and a terrestrial system begins

  7. Climax Communities • Climax Community: stable community that “completes” the succession process • Climate, Soil Conditions and other factors influence a community’s composition • These factors can also promote or inhibit a community’s progression between succession stages. • Communities – temporary, ever-changing associations among species

  8. Invasive Species • Invasive Species: a nonnative (exotic) species that spreads widely in a community • A community DISTURBANCE. • Do not have sufficient limiting factors, and end up taking over.

  9. What makes a species Invasive? • Some nonnative species are NOT invasive • Populations remain Small and Localized, eventually dying out. • Others exist without causing problems • Invasive when limiting factors are not present in their new environment. • Limiting Factors: predators, parasites, competitors • Population growth of exotic species is not held in check. • Community thrown out of balance.