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Ecosystem Energy Flow Cheat Sheet

The core ideas of Ecosystem Energy Flow distilled into a single, scannable reference — perfect for review or quick lookup.

PiqCue — piqcue.com/ecosystem-energy/cheatsheet

Quick Reference

Trophic Levels

The hierarchical positions organisms occupy in a food chain based on their feeding relationships. Each level represents a step in the transfer of energy, from producers at the base to apex predators at the top. The number of trophic levels in an ecosystem is limited by the energy available at each successive step.

Producers (Autotrophs)

Organisms that synthesize their own food from inorganic molecules using energy from sunlight or chemical reactions. Photoautotrophs such as plants and algae use photosynthesis, while chemoautotrophs such as deep-sea vent bacteria use chemical energy. Producers form the foundation of all ecosystem energy flow.

Primary Consumers

Herbivorous organisms that feed directly on producers, occupying the second trophic level. They convert plant biomass into animal biomass and serve as the critical link between autotrophic production and the rest of the consumer food web.

Secondary and Tertiary Consumers

Organisms that feed on other consumers. Secondary consumers eat primary consumers and occupy the third trophic level, while tertiary consumers eat secondary consumers at the fourth level. Because each transfer loses approximately 90 percent of energy, these higher-level consumers require large foraging ranges to meet their energy needs.

Decomposers

Organisms such as bacteria, fungi, and detritivores that break down dead organic matter and waste products, releasing nutrients back into the soil and atmosphere. While they recycle matter for reuse by producers, the energy they extract is ultimately lost as heat through respiration.

Ten Percent Rule

The ecological generalization that approximately 10 percent of the energy at one trophic level is converted into biomass at the next trophic level. The remaining 90 percent is lost primarily as metabolic heat during cellular respiration, with smaller amounts lost through incomplete digestion and excretion.

Energy Pyramid

A graphical model showing the relative amount of energy available at each trophic level of an ecosystem. The pyramid shape results from energy loss at each transfer, with the broadest bar at the producer base and progressively narrower bars for each consumer level. Unlike biomass or numbers pyramids, energy pyramids are never inverted.

Primary Productivity (GPP and NPP)

Gross primary productivity (GPP) is the total rate at which producers capture and store chemical energy through photosynthesis. Net primary productivity (NPP) is GPP minus the energy producers use for their own respiration. NPP represents the energy actually available to consumers and decomposers in the ecosystem.

Key Terms at a Glance

Trophic Level:The feeding position an organism occupies in a food chain or food web, from producers (level 1) through successive consumer levels.
Producer:An organism (autotroph) that synthesizes organic molecules from inorganic substances using energy from sunlight (photosynthesis) or chemical reactions (chemosynthesis).
Consumer:An organism (heterotroph) that obtains energy by eating other organisms. Primary consumers eat producers; secondary consumers eat primary consumers.
Decomposer:An organism, typically bacteria or fungi, that breaks down dead organic material and recycles nutrients back into the ecosystem.
Food Chain:A linear sequence showing the transfer of energy from one organism to the next, beginning with a producer and ending with a top predator or decomposer.
Food Web:A complex network of interconnected food chains in an ecosystem, illustrating the multiple feeding relationships among organisms.
Ten Percent Rule:The ecological generalization that roughly 10% of energy at one trophic level is converted to biomass at the next level, with 90% lost as metabolic heat.
Energy Pyramid:A diagram showing the relative amount of energy available at each trophic level, always tapering upward due to energy loss at each transfer.
Gross Primary Productivity (GPP):The total rate of energy capture by producers through photosynthesis in an ecosystem, measured in energy per unit area per unit time.
Net Primary Productivity (NPP):The rate of energy storage by producers after subtracting their own respiratory energy use; NPP = GPP minus plant respiration.
Biological Magnification:The increasing concentration of persistent, non-degradable substances (such as pesticides or heavy metals) in organisms at successively higher trophic levels.
Trophic Cascade:An ecological phenomenon where changes at one trophic level cause cascading effects through other levels, often triggered by the addition or removal of top predators.
Cellular Respiration:The metabolic process by which organisms convert chemical energy in organic molecules to ATP, releasing carbon dioxide and water. This is how energy is lost as heat at each trophic level.
Biomass:The total mass of living organisms in a given area or at a given trophic level, usually expressed as dry weight per unit area.

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Ecosystem Energy Flow Cheat Sheet - Quick Reference Guide | PiqCue