Introduction to Ecosystem

An ecosystem is the fundamental functional unit of the biosphere, consisting of a community of living organisms (biotic) interacting with their non-living physical environment (abiotic). The term was coined by A.G. Tansley in 1935. It represents a self-sustaining system where energy flows through food webs and nutrients are recycled continuously.

Components of an Ecosystem

Ecosystems are comprised of two primary interacting components: Abiotic and Biotic factors.

Abiotic Components (Non-living)

These physical and chemical factors determine the type of organisms that can survive in a specific habitat.

• Inorganic substances: Carbon, Nitrogen, Hydrogen, Phosphorus, and Water (H₂O).
• Organic compounds: Proteins, carbohydrates, and lipids which link the abiotic and biotic parts.
• Climatic factors: Sunlight (the ultimate energy source), temperature, humidity, precipitation, and wind.
• Edaphic factors: Soil texture, pH, and mineral composition.

Biotic Components (Living)

Based on their nutritional role, biotic components are classified into three groups:

• Producers (Autotrophs): Green plants and chemosynthetic bacteria that fix solar energy to produce food through photosynthesis.
• Consumers (Heterotrophs): Organisms that depend on producers.
  • Primary Consumers (Herbivores): Feed directly on plants (e.g., Deer, Grasshopper).
  • Secondary Consumers (Carnivores): Feed on herbivores (e.g., Frog, Small fish).
  • Tertiary Consumers (Top Carnivores): Feed on other carnivores (e.g., Lion, Tiger, Eagle).
• Decomposers (Saprotrophs): Microorganisms like fungi and bacteria that break down dead organic matter into simpler inorganic nutrients, completing the nutrient cycle.

Classification of Ecosystems

Ecosystems vary in scale from a small pond to the entire global biosphere. They are generally categorized into Natural and Artificial types.

Functional Aspects of an Ecosystem

For an ecosystem to remain stable, four key processes must occur:

1. Productivity: The rate of biomass production. Primary productivity is the rate at which solar energy is captured by producers.
2. Decomposition: The breakdown of complex organic matter into inorganic raw materials (CO₂, water, nutrients).
3. Energy Flow: The unidirectional movement of energy from producers to top consumers. Only about 10% of energy is transferred to the next trophic level (Lindeman’s 10% Law).
4. Nutrient Cycling: Also known as Biogeochemical cycles (e.g., Nitrogen cycle, Carbon cycle), where nutrients move between biotic and abiotic components.

Key Ecological Concepts for Prelims

Ecotone

An ecotone is a zone of transition between two or more diverse ecosystems.

• Examples: Mangroves (between terrestrial and marine), Estuaries (between freshwater and saltwater), and Grasslands (between forest and desert).
• Edge Effect: The tendency for an ecotone to have greater species diversity and higher population density than either of the flanking communities.
• Edge Species: Organisms that occur primarily or most abundantly in this transition zone (e.g., specific bird species in forest-grassland edges).

Ecological Niche

The niche is the functional role and specific position a species occupies within an ecosystem.

• It includes the species’ habitat, its activities (what it eats), and its interactions with other species.
• Trivia: No two species can occupy exactly the same niche in the same habitat for long; one will eventually outcompete the other (Gause’s Competitive Exclusion Principle).

Ecocline

An ecocline is a gradual and continuous change in species composition or community structure along an environmental gradient (such as altitude, salinity, or temperature), lacking a sharp boundary.

Ecosystem Properties

• Homeostasis: The inherent capacity of an ecosystem to self-regulate and maintain a state of equilibrium despite disturbances.
• Anthropogenic Influence: Human-made ecosystems (like monoculture plantations) are often unstable and require constant external energy or chemical inputs (fertilizers, pesticides) to survive, unlike natural ecosystems which are self-regulating.