Ecosystem (Tansley, 1935): Living organism living in any area and non-living substances of that area interact upon each other form a system. Examples, a pond, a forest a desert area, etc.

Odum divided ecosystem from purely functional point in 2 components:

• Autotrophic component: organisms that depend on the environment for raw materials (simple inorganic substances) for the production of food. Fix light energy and use simple inorganic substances (C, N, CO2, H2O, etc) to produce complex substances e.g. Plants.
• Heterotrophic component (other nourishing): utilizes, rearranges and decomposes complex materials synthesized by autotrophs – very few plants and most of animal lives.

Constituents of Ecosystems

Four components

1. Abiotic substances (component): In organic and organic substances eg. Water, CO2, oxygen, calcium, nitrogen phosphorus salts, amino acids, humic acids, soil, temperature etc (Physical environment).

2. Biotic components:

• Producer (Self feeder): Autographs – Green plants e.g. Phytoplankton, algae, and large footed plants.
• Consumers: Consume other organism or particulate organic matter.
  • Herbivores (plant eaters) – primary consumers.
  • Carnivores (meat eaters) – secondary consumers. Feeding on other carnivores is called tertiary (higher-level) consumers).
  • Omnivores (Pigs, rats, foxes, bears, and humans) - feed on plants and animals.

3. Scavengers: Feeds on dead organisms e.g. Vultures, flies, hyenas, etc.

4. Decomposer: (Micro-consumers, bacteria and fungi, etc). Break down the complex compounds of dead tissues of producers and consumers. Absorb some of the decomposition products and release simple substances consumable by the autotrophic organisms (producers) to begin the cycle over again.

Trophic Level in an Ecosystem: Each successive level of nourishment.

Ecological pyramids (balanced ecosystem)