8.1.3 Energy Flow in Ecosystems

10% rule

each trophic level biomass is 10% of the level below

primary productivity

• biomass of the primary producers

• energy limitation of the entire ecosystem

types of ecological pyramids

1. Energy pyramid

2. Biomass pyramid

3. Numbers pyramid

Energy pyramid

each level represents amount of energy available to that trophic level

10% rule

Biomass pyramid

each level represents the amount of biomass consumed by the level above it

Number pyramid

each level represents the number of individual organisms consumed by the level above it

Trophic cascade

Indirect interaction between trophic levels that control an ecosystem

1. Bottom-up cascade — lower trophic levels limit upper ones

2. Top-down cascade — upper trophic levels affect lower ones

   • often creates keystone species