Biology 4.1

Intro to topic 5

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  • Created by: Jeralee
  • Created on: 26-03-12 18:19

Key Words

Biosphere: Part of earth inhabited by living organisms

     Abiotic factors: Physical/ Chemical factors
     Biotic factors: Living
e.g. predation & competition

Population: Group of individuals of the same species found in an area

Community: Various populations sharing a habitat

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Abiotic Factors

Solar energy input: Affected by latitude, season, cloud cover.
Light essetial for photosynthesis, initiating germination & in many animals, light controls behaviour

Climate: Includes rainfall, wind exposure, and temperature

Topography: Includes altitutde, slope, aspect & drainage

Oxgen availability: Fast flowing streams are better oxygenated than stagnant pools

Edaphic factors: Soil, pH, soil texture

Pollution: Of air, water or land

Catastrophes: Infrequent events that disturb conditions

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Biotic factors

Competition: For resources like food, light, water, space

Grazing, predation & parasitism: Relaionships between 2 organisms, 1 benefits at other's expense


Mutualism: Relationship where both partners benefit

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Primary Succession

= Newly formed habitats, where there has never been a community before.

1. Pioneer species lichens & algae, first to colonise bare rock. Can cope with extreme conditions.

2. Pioneers breeak up rock surface= organic matter accumulate. Chanage conditions in habitat to make more suitable for other species.

3. Wind Blown moss spores start growing.

4. Mosses build up more organic matter= soil: can hold water.

5. Development of soil enables seeds of small, shallow rooted plants to establish.

6. Conditions in habitat improve, seeds from larger, taller plants appear.

7. Plants out compete existing community.

8. Eventually a stable climax community is reached, usually dominated by trees.

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Secondary & deflected succession

Secondary succession= on bare soil where an existing community has been cleared.

In absence of human interference, secondary succession would lead to re-establishment of a climax community.
Bare Soil does not stay bare for long. Seeds of many other species will already be lying dormant in the soil, others brought by wind/ animals.

Groundsel is an example of a pioneer species adapted to take advantage of bare soil with little competition.

  • Seeds widely dispersed by wind
  • Rapid Growth
  • Short life cycle
  • Abundant seed production

Deflected succession= community that remains stable because human activity prevents succession from running its course.
Grazing, mowing/ burning may be used to deflect succession.

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