Trophic Level, Energy Flow, Food Chain YouTube Lecture Handouts

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Watch Video Lecture on YouTube: Ecosystem: Energy Flow, Food Chain, Pyramids of Number, Energy & Biomass

Ecosystem: Energy Flow, Food Chain, Pyramids of Number, Energy & Biomass

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Trophic Level


Food Chain


  • Parasitic Food Chain

  • Detritus Food Chain

  • Grazing Food Chain

Food Web

Energy Flow

  • 1st law of thermodynamics - Energy can neither be created nor destroyed

  • 2nd law of thermodynamics – every activity involving energy transformation is accompanied by dissipation of energy

  • 50% energy from sun to Par (photosynthetically active radiation)


  • Decrease in content & flow of energy

  • 10% energy is passed (Lindeman’s law, 1942)

  • This means tiger requires an area of 240 km2 to support itself

Ecological Pyramids (By Charles Elton)

Also called Eltonian pyramid


  • Biomass – amount of living organic matter both dry and wet (maximum in producers and reduces with hierarchy – 10-20% is transferred to the next level)

    • Inverted – aquatic ecosystem

    • Upright – terrestrial ecosystem

  • Energy – energy trapped at different trophic levels –kcal/m2/yr (maximum in producers) – always upright

  • Number – number of individuals per unit area (top carnivores are few but grass is lot)

    • Upright – terrestrial or pond

    • Inverted – parasitic food chain

    • Spindle shaped – tree birds hawk

Ecological Efficiency

  • Ratio between energy assimilated over the energy available between two trophic levels – also called progressive efficiency

Ecological Succession

  • Natural development of series of biotic communities at same site one after another till climax community develops which does not change further because it is in perfect harmony with environment

  • Pioneer community – 1st community on bare land – little diversity – longest time to change

  • Climax community – stable, self-perpetuating & final biotic community that develops at end – maximum diversity and niche specialization

  • Seral or transitional community – biotic communities that develop during biotic succession

  • Sere – series from pioneer to climax community

    • Lithosere – on land (Lichens Moss Annual Grass Perennial Grass Shrub Climax)

    • Psammosere – on sand

    • Hydrosere – on water (Planktons Submerged Floating Reed Swamp Marsh Meadow Woodland Climax)

    • Psammosere – on sand

Changes in Biotic Succession

Increase in respiratory consumption and decrease in productivity until two become equal, P=R


  • Primary Succession – biotic succession that occurs on a previously sterile bare area (no soil, no humus) – newly exposed sea floor, igneous rocks & sand dunes

  • Secondary Succession – Occurs in area which became secondarily bared due to destruction of community previously there (fugitive species – species adapted to colonize newly disturbed habitats)

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