Concept of Ecosystem - Energy Flow in Ecosystem

Energy flow in an ecosystem is a fundamental concept in understanding how life sustains itself. All living organisms can be classified based on their mode of nutrition into producers, consumers, saprotrophs (also known as saprophytes), and decomposers. These categories form the backbone of the food chain and the trophic structure of ecosystems.

Producers, such as green plants, form the base of the food chain by converting sunlight into chemical energy through photosynthesis. Consumers, including herbivores, carnivores, and omnivores, depend on these producers or other organisms for energy. Meanwhile, saprotrophs and decomposers break down dead organic matter, recycling nutrients back into the ecosystem.

This classification and interaction between organisms facilitate the flow of energy from one trophic level to the next, ensuring the survival of all forms of life and maintaining ecological balance.

• PAR → Less than 50% of total incident solar radiation is Photosynthetically Active Radiation (PAR) — the only portion usable by plants.
• Energy Captured by Plants → Plants use only 2–10% of PAR to sustain the entire living world through photosynthesis.
• Energy Flow is Unidirectional → Energy flows from producers → consumers in one direction only; it is never recycled back.
• Trophic Levels → Organisms are arranged in a feeding hierarchy called trophic levels — Producers (1st) → Primary Consumer/Herbivore (2nd) → Secondary Consumer/Carnivore (3rd) → Tertiary Consumer/Top Carnivore (4th).
• Two Types of Food Chains → GFC (Grazing Food Chain) starts with producers (e.g., Grass → Goat → Man); DFC (Detritus Food Chain) starts with dead organic matter and involves decomposers (e.g., Dead leaves → Wood louse → Blackbird).
• Food Web → A network of interconnected food chains involving producers, consumers, and decomposers is called a Food Web.
• 10% Law → Only 10% of energy is transferred from one trophic level to the next. Given by Lindemann (1942). This limits food chains to usually 4–5 trophic levels. A species can occupy more than one trophic level (e.g., a sparrow eats seeds as a primary consumer and insects as a secondary consumer).