Ecosystem

1. Ecosystem – Structure and Function

Definition

An ecosystem is a complex network of living organisms (biotic components) and their physical environment (abiotic components) interacting as a system. It includes all the organisms in a given area, along with the non-living components of the environment, such as air, water, and soil.

Structure of Ecosystems

• Biotic Components: These include all living organisms, such as plants, animals, fungi, and microorganisms.
• Abiotic Components: These include non-living elements like sunlight, temperature, water, soil, and nutrients.

Stratification

• Definition: Stratification refers to the layering that occurs in an ecosystem, particularly in aquatic and forest ecosystems.
• Examples:
  • In forests, strat ification can be seen in the different layers: the forest floor, understory, canopy, and emergent layer.
  • In aquatic ecosystems, stratification occurs in the form of different zones: the photic zone (light penetration), aphotic zone (no light), and benthic zone (bottom).

2. Productivity

Definition

Productivity in an ecosystem refers to the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances. It is typically measured in terms of biomass produced per unit area over a specific time period.

Types of Productivity

• Primary Productivity: The rate at which producers (like plants) create organic material through photosynthesis. It can be further divided into:

  • Gross Primary Productivity (GPP): Total amount of organic matter produced.
  • Net Primary Productivity (NPP): GPP minus the energy used by producers for respiration (NPP = GPP - Respiration).

• Secondary Productivity: The generation of biomass by heterotrophic organisms (consumers) through the consumption of primary producers.

3. Decomposition

Definition

Decomposition is the process by which complex organic matter is broken down into simpler inorganic substances. This process is crucial for nutrient cycling in ecosystems.

Importance of Decomposers

• Decomposers, such as bacteria, fungi, and detritivores (e.g., earthworms), play a vital role in breaking down dead organic matter and recycling nutrients back into the ecosystem.

Process of Decomposition

1. Detritus: Dead plant remains (leaves, bark, flowers) and animal remains (including fecal matter) constitute detritus, which serves as the raw material for decomposition.
2. Steps in Decomposition:
   • Fragmentation: Detritivores break down detritus into smaller particles.
   • Leaching: Water-soluble inorganic nutrients are washed down into the soil and may precipitate as unavailable salts.
   • Catabolism: Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.
   • Humification: The process of forming humus, a stable organic matter that enriches the soil.
   • Mineralisation: The conversion of organic matter into inorganic nutrients that can be taken up by plants.

Simultaneous Processes

All the above steps in decomposition operate simultaneously on the detritus, contributing to nutrient cycling in the ecosystem.

4. Energy Flow

Definition

Energy flow refers to the transfer of energy through the food chain in an ecosystem, from producers to consumers and decomposers.

Standing Crop

• Definition: The standing crop is the total biomass of living organisms in a given area at a specific time. It reflects the productivity of the ecosystem and can vary with seasons and environmental conditions.

5. Ecological Pyramid and Exceptions

Ecological Pyramid

• Definition: An ecological pyramid is a graphical representation of the distribution of biomass, energy, or numbers of organisms across different trophic levels in an ecosystem.
• Types:
  • Pyramid of Numbers: Represents the number of individual organisms at each trophic level.
  • Pyramid of Biomass: Represents the total biomass at each trophic level.
  • Pyramid of Energy: Represents the flow of energy at each trophic level, showing that energy decreases as it moves up the food chain.

Exceptions to Ecological Pyramids

• In some ecosystems, the typical pyramid structure may be inverted. For example:
  • In a forest ecosystem, a few large trees (producers) may support a large number of herbivores (primary consumers), leading to an inverted pyramid of numbers.
  • In aquatic ecosystems, the biomass of phytoplankton (producers) may be less than that of zooplankton (primary consumers) at certain times, creating an inverted pyramid of biomass.