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Biotic and Abiotic


  • Living components such as plants and animals


  • Non-living components such as climate, soil, relief, drainage and altitude
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Inputs, Outputs, Transfers and Stores of Energy

  • Ecosystem is an open system


  • Nutrients from weathered rock
  • Precipitation
  • Solar energy (insolation)
  • Gases from atmosphere


  • Animals
  • Plants
  • Soil


  • Involve energy and materials in the form of nutrients


  • Nutrients from leached soil
  • Gases (CO2)
  • Water
  • Energy as heat
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Energy Flows and Trophic Structure

  • Energy moves through a series of trophic levels and leaves via heat
  • Sun is primary source of energy
  • Light energy is used by autotrophs in photosynthesis which creates chemical food energy
  • This energy fixed by photosynthesis becomes available to subsequent trophic levels forming a food chain
  • First Trophic Level: plants that produce their own food directly- autotrophs or producers
  • All other levels consume plants and other organisms in previous level- consumers or heterotrophs
  • Second Trophic Level: herbivores consume plants from first level and in turn provide food for Third Trophic Level: smaller carnivores
  • Fourth Trophic Level: made up of larger carnivores and omnivores (this is usually the last level)
  • At each level detrivores are consumers that decompose dead organic matter
  • Transfer of energy is not very efficient as energy is lost via life processes in organisms eg respiration, excretion, heat and movement
  • This is why there is usually no more than four trophic levels
  • Trophic structure can be illustrated as a trophic pyramid- each box represents a level and size indicates amount of energy stored in that level
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Nutrient Cycling

  • Within an ecosystem, nutrients are found in one of three stores: biomass, litter and soil
  • Nutrients are transferred in a single cycle: soil to biomass to litter to soil and can be shown in a diagram known as the Gersmehl model
  • Circle size represents proportion of ecosystem nutrients found at any given time in that store
  • Arrow width shows nutrient flow as proportion of nutrients in store compartment
  • Nutrients leave biomass store and are transferred by fallout into litter store where dead organic matter is broken down by decomposers and transferred by decay into soil store
  • Nutrients come from precipitation and weathering from bed rock
  • Nutrient losses come from runoff from litter and leaching from soil

Nutrient transfer affected by:

Climate: hot, wet tropical rainforests, rate of decomposition is high as well as leaching

Soils: acidic soils have fewer soil organisms and thus decomposition is quite slow

Vegetation Type: Leaves from coniferous trees take longer to decompose than those from deciduous trees

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