6.2_ Ecological Disturbances and Succession (Pages 182-185)
SC.912.L.17.4 Describe changes in ecosystems resulting from seasonal variations, climate change and succession.
LEARNING OBJECTIVES:
1. Describe the potential changes to an ecosystem, resulting from seasonal variations, climate change, and/or succession. 2. Explain how ecosystems recover from a disturbance. 3. Compare primary and secondary succession. |
Tutorial: Changing with Time
Classwork: Succession Student Guide Homework: Use a copy paper to complete this assignment.
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What Is Disturbance?
A disturbance is an event that changes a community (both biotic and abiotic are affected)
Natural: They are common in ecosystems
- Removes organisms from a community
- Alters resource availability
Natural: They are common in ecosystems
- May be cyclical
- Examples: Seasonal Variations (summer, fall, winter, spring), Fire, Hurricanes, Floods, Volcanic Eruptions
- Usually reduces species diversity
- Humans also prevent some naturally occurring disturbances
- Examples: Deforestation and land cleared for farming or urbanization (Developments)
What is Ecological Succession?
Ecological succession is the progressive series of changes in the composition of an ecosystem after a disturbance. These changes can happens in both terrestrial and aquatic ecosystems where one community of organisms will replace another over time.
- In primary succession, newly exposed or newly formed rock is colonized by living things for the first time.
- In secondary succession, an area previously occupied by living things is disturbed—disrupted—then recolonized following the disturbance.
Primary Succession
Shown below is a representation of forest succession over time. There is a steady increase in biodiversity, biomass and thickness of soil layer as succession proceeds, and as time passes.
- Notice it begins with bare rocks, then it is slowly colonized by one group of organisms after another.
- pioneer species commence the colonization of the rock, breaking it down slowly. As these organisms die, they contribute organic matter, building soil over time.
- Pioneer species: Tough organisms capable of colonizing bare rock. Examples include lichen, mosses, fungi, and bacteria. It's important to remember that they are the first organisms to colonize an area where no life existed before. These species modify the surface they attach to as they grow. They are gradually replaced by more complex organisms as soil and shade are produced.
- Intermediate Species: Includes plants and other organisms that continue to alter the habitat and soil composition as they colonize an area. Examples of intermediate species include perennial herbaceous plants, shrubby plants and softwood trees such as pine trees.
Secondary Succession
In secondary succession, an area previously occupied by living things is disturbed—disrupted—then recolonized following the disturbance.
- Notice how both the biotic and abiotic factors may change
- Example: as the trees grow taller (biotic), they cast a shade (light= abiotic) over the smaller trees
Notice in this graph the pioneer species are small grasses, and perennial flowering plants.
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