Concept of Ecosystem

Definition

"An ecosystem is a system formed by the interaction of all living organisms with each other and with the physical and chemical factors of their environment, linked by energy flow and nutrient cycling." — E.P. Odum

Key Components

1. Abiotic (Non-living) Components

• Climatic factors: sunlight, temperature, rainfall, humidity, wind
• Edaphic factors: soil type, pH, mineral content
• Inorganic substances: water, CO₂, O₂, nitrogen, phosphorus
• Organic compounds: proteins, carbohydrates, humus

2. Biotic (Living) Components

Structural Aspects

Food Chain & Food Web

• Food chain: linear sequence of energy transfer — Producer → Herbivore → Carnivore
• Food web: interconnected network of multiple food chains; more realistic representation of feeding relationships

Trophic Levels

1. 1st trophic level – Producers (plants)
2. 2nd trophic level – Primary consumers (herbivores)
3. 3rd trophic level – Secondary consumers
4. 4th trophic level – Tertiary consumers (top predators)

Ecological Pyramids

• Pyramid of numbers – number of organisms at each level
• Pyramid of biomass – total dry weight at each level
• Pyramid of energy – energy available at each level (always upright; follows 10% law)

Functional Aspects

Energy Flow

• Unidirectional – energy enters as sunlight, passes through trophic levels, and is lost as heat; it cannot be recycled
• Governed by the Laws of Thermodynamics
• Only ~10% of energy is transferred from one trophic level to the next (Lindeman's 10% rule)

Nutrient Cycling (Biogeochemical Cycles)

• Carbon cycle
• Nitrogen cycle
• Phosphorus cycle
• Water (hydrological) cycle

Productivity

• Gross Primary Productivity (GPP): total rate of photosynthesis including respiration losses
• Net Primary Productivity (NPP): GPP − Respiration = energy available to consumers
• Secondary Productivity: rate of formation of new organic matter by consumers

Types of Ecosystems

Ecosystem Stability & Succession

• Ecological succession: directional, predictable change in species composition over time
  • Primary succession: begins on bare, lifeless substrate (e.g., bare rock)
  • Secondary succession: begins where an existing community is disturbed (e.g., after fire)
• Climax community: stable, self-perpetuating community at the end of succession
• Resilience: ability of an ecosystem to recover from disturbance
• Resistance: ability to withstand disturbance without change

Ecosystem Services

1. Provisioning – food, water, timber, medicine
2. Regulating – climate regulation, flood control, pollination
3. Cultural – recreation, spiritual value, ecotourism
4. Supporting – soil formation, nutrient cycling, oxygen production

Recent Developments (2025)

• Terrestrial ecosystem transitions driven by climate change, as tracked via remote sensing
• Ecosystem restoration frameworks centered on human communities (5-pillar frameworks)
• Coral reef ecosystem dynamics — fish protection shown to regulate coral-eating starfish across the Great Barrier Reef
• Growing emphasis on urban ecosystems and their role in climate adaptation

Summary