1. Energy Flow

• The Sun is the ultimate source of energy.
• Energy flow is Unidirectional (Sun -> Producer -> Consumer -> Heat). It cannot be reused.
• 10% Law (Lindeman, 1942): Only 10% of energy is transferred from one trophic level to the next. 90% is lost as heat/metabolism.
• Implication: Food chains usually have only 4-5 levels because energy runs out.

2. Food Chains & Webs

• Grazing Food Chain (GFC): Starts with green plants.
• Grass -> Grasshopper -> Frog -> Snake -> Hawk.
• Detritus Food Chain (DFC): Starts with dead organic matter.
• Dead Leaves -> Woodlouse -> Blackbird.
• Food Web: A network of interlinked food chains. It provides stability. If one prey is extinct, the predator can eat another.

3. Ecological Pyramids

Graphical representation of trophic structure.

• Pyramid of Number: Can be Upright (Grassland) or Inverted (Single Tree supporting many insects).
• Pyramid of Biomass: Total dry weight. Upright (Forest) or Inverted (Pond - Phytoplankton biomass is less than Zooplankton).
• Pyramid of Energy: ALWAYS Upright. Energy always decreases as we move up.

4. Ecological Succession

The process by which the structure of a biological community evolves over time.

• Primary Succession: Starts on bare rock/lava (No soil). Slower.
• Secondary Succession: Starts where soil exists but vegetation was destroyed (Forest fire). Faster.
• Stages: Pioneer Species (Lichens) -> Intermediate Stages (Shrubs) -> Climax Community (Forest).