Ecosystem - Energy Flow and Food Chains

Energy flow in an ecosystem is unidirectional, moving from the sun to producers and then to consumers, following the laws of thermodynamics.

First Law of Thermodynamics: Energy is neither created nor destroyed, but transformed. In ecosystems, solar energy is transformed into chemical energy by producers.

Second Law of Thermodynamics: During every energy transfer, a portion of energy is lost as heat, increasing the entropy of the system.

Photosynthetically Active Radiation (PAR): Of the total incident solar radiation, less than $50\%$ is PAR. Plants and photosynthetic bacteria capture only $2-10\%$ of the PAR to sustain the entire living world.

Gross Primary Productivity ($GPP$): The total rate at which organic matter is produced during photosynthesis.

Net Primary Productivity ($NPP$): The available biomass for the consumption of heterotrophs, calculated as $GPP$ minus respiration losses ($R$).

Lindeman's $10\%$ Law: Only $10\%$ of the energy available at a particular trophic level is transferred to the next higher trophic level.

Grazing Food Chain (GFC): Starts with producers (e.g., Grass $\rightarrow$ Goat $\rightarrow$ Man). In aquatic ecosystems, GFC is the major conduit for energy flow.

Detritus Food Chain (DFC): Starts with dead organic matter and involves decomposers like fungi and bacteria. In terrestrial ecosystems, a much larger fraction of energy flows through the DFC.

Ecological Pyramids: Graphical representation of trophic structures. The pyramid of energy is always upright because energy is lost as heat at each step. Pyramids of biomass can be inverted (e.g., in oceans where phytoplankton biomass is less than fish biomass).