energyflow

Energy flow refers to the passage of energy through an ecosystem or other system, moving in one direction from producers through consumers and detritivores before dissipating as heat. It contrasts with biogeochemical cycles, where matter cycles among exchange pools.

In ecosystems, the ultimate source of energy is solar radiation captured by photosynthetic organisms (plants, algae, some bacteria). These producers convert light energy into chemical energy via photosynthesis, establishing gross primary production (GPP). Net primary production (NPP) is the portion stored as biomass after respiration.

Energy then moves through trophic levels as organisms feed on producers and other consumers. At each transfer, only a fraction of energy is stored in new biomass; typical transfer efficiencies range from 5% to 20%, with the remainder lost as heat and waste. This inefficiency creates energy pyramids, with usable energy and biomass decreasing from producers to apex predators. Detrital pathways also play a major role, as energy enters the detritus pathway and is consumed by decomposers.

Energy flow is modeled through food chains, food webs, and Sankey diagrams; practical estimates use measures such as GPP, NPP, respiration, and calorimetric data.

The concept emphasizes that energy supply, rather than nutrient availability, often limits ecosystem productivity.

Human activities affect energy flow by altering primary production (for example, through land-use change and climate change) and by changing detrital pools and decomposer communities, with cascading effects on ecosystem structure and function.