Structure and Function of an Ecosystem

An ecosystem is a self-sustained unit where living organisms interact with their physical environment. It consists of biotic (living) and abiotic (non-living) components, both of which interact to maintain the ecological balance.

1. Components of an Ecosystem

A) Biotic Components (Living Organisms)

The biotic components of an ecosystem include all living organisms that play different roles in maintaining ecological stability. They can be divided into three main groups:

i) Producers (Autotrophs)

• • These are organisms that produce their own food through photosynthesis (plants, algae, and some bacteria) or chemosynthesis.
  • Examples: Green plants, cyanobacteria, phytoplankton.

ii) Consumers (Heterotrophs)

• • They depend on producers or other organisms for food. They are further categorized as:
    • Primary Consumers (Herbivores) – Eat producers (e.g., deer, grasshoppers).
    • Secondary Consumers (Carnivores) – Eat herbivores (e.g., frogs, foxes).
    • Tertiary Consumers (Top Carnivores) – Eat secondary consumers (e.g., tigers, eagles).
    • Omnivores – Eat both plants and animals (e.g., humans, bears).

iii) Decomposers (Saprotrophs)

• • These organisms break down dead organic matter and recycle nutrients back into the ecosystem.
  • Examples: Fungi (mushrooms), bacteria, actinomycetes.

B) Abiotic Components (Non-Living Factors)

The abiotic components provide the necessary environmental conditions for life to exist and sustain ecological processes. They include:

i) Physical Factors

• • Solar radiation – Primary energy source for ecosystems.
  • Temperature – Influences biological activities.
  • Moisture (Water availability) – Essential for all living organisms.
  • Soil – Provides minerals and anchorage for plants.

ii) Chemical Factors

• • Inorganic Substances – Carbon dioxide (CO₂), water (H₂O), nitrogen (N), calcium (Ca), and phosphorus (P) are involved in biogeochemical cycles.
  • Organic Substances – Proteins, carbohydrates, lipids, and amino acids are produced by living organisms and returned to the ecosystem as waste or dead matter.

2. Functions of an Ecosystem

An ecosystem function refers to the ability of natural systems to provide goods and services for human and environmental sustainability. These functions arise from the interaction of biotic and abiotic components.

a) Types of Ecosystem Functions

Ecosystem functions are classified into four primary groups:

i) Regulatory Functions

• • Maintain essential ecological processes and life-supporting systems.
  • Include biogeochemical cycles (carbon, nitrogen, water cycle) and biological control mechanisms.
  • Example: Purification of air and water, climate regulation, decomposition of organic matter.

ii) Habitat Functions

• • Provide shelter and breeding spaces for organisms.
  • Contribute to biodiversity conservation and evolution.
  • Example: Coral reefs as fish breeding grounds, forests as bird habitats.

iii) Production Functions

• • Convert solar energy into chemical energy through photosynthesis.
  • Provide food, raw materials, and energy resources.
  • Example: Crop production, timber from forests, fisheries.

iv) Information Functions

• • Support human well-being by providing recreation, cultural value, and knowledge.
  • Example: National parks for tourism, ecosystems influencing artistic inspiration.

3. Ecosystem Productivity

Productivity in an ecosystem refers to the rate at which energy is converted into organic substances by autotrophs and then transferred through the food chain.

i) Primary Productivity

• • Rate at which producers store energy from sunlight via photosynthesis.
  • Measured in weight (g/m²/year) or energy (kcal/m²).
  • Divided into:
    • Gross Primary Productivity (GPP): Total amount of energy captured by plants.
    • Net Primary Productivity (NPP): Energy remaining after plant respiration, available to consumers.

ii) Secondary Productivity

• • Rate at which consumers store energy from their food.
  • It depends on the efficiency of herbivores and carnivores in utilizing energy from producers.

4. Interactions Among Living Organisms

The interactions among organisms in an ecosystem can be classified into positive and negative interactions.

a) Positive Interactions (Beneficial Relationships)

Commensalism

• • One species benefits while the other remains unaffected.
  • Example:
    • Fungi breaking down cellulose to release organic acids that bacteria can use.
    • Certain microorganisms excreting nutrients that help others grow.

Proto-cooperation (Non-Obligatory Mutualism)

• • Both species benefit, but their survival is not dependent on this relationship.
  • Example:
    • Azotobacter (nitrogen-fixing bacteria) benefits from cellulose decomposers, which break down cellulose into simple sugars.

b) Mutualism (Obligatory Beneficial Relationship)

• • Both species benefit and require the association for survival.
  • Examples:
    • Pollination: Bees and butterflies obtain nectar while aiding in plant pollination.
    • Legume-Rhizobium symbiosis: Bacteria fix atmospheric nitrogen for plants while receiving nutrients in return.

c) Negative Interactions (Harmful Relationships)

i) Competition

• • Two organisms compete for limited resources (food, space, water).
  • Example: Fusarium oxysporum competes with Agrobacterium radiobacter for nutrients.

ii) Predation

• • One organism (predator) hunts and kills another (prey) for food.
  • Examples:
    • Lions hunting deer.
    • Carnivorous plants (e.g., Nepenthes) trapping insects.
    • Protozoans consuming bacteria.

iii) Parasitism

• • One organism (parasite) lives on or inside another (host) and derives nutrients at the host’s expense.
  • Examples:
    • Cuscuta (Dodder plant) – A total stem parasite that depends entirely on host plants for food.
    • Hyperparasitism: A parasite living on another parasite (e.g., Cicinnobolus cesatii growing on powdery mildew fungi).

iv) Antibiosis

• • One organism produces a substance that inhibits the growth of another.
  • Examples:
    • Streptomycin produced by Streptomyces griseus.
    • Penicillin from Penicillium notatum.
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Producers, Consumers, and Decomposers in an Ecosystem

Our environment, consisting of both living and non-living systems, influences each other in form, function, and property, which is necessary to maintain life. The composition of these systems forms the building blocks of an ecosystem.

Producers

Producers are organisms that use photosynthesis to capture energy from sunlight, water, and carbon dioxide to create carbohydrates. They then use this energy to form more complex molecules such as proteins, lipids, and starches, which are essential for life processes. Producers, primarily green plants, are also known as autotrophs.

Producers serve as the foundation of the food chain by supplying energy to the ecosystem. The carbohydrates and other organic compounds they generate are utilized by heterotrophs, or consumers. First, herbivores consume the plants—these are known as primary consumers. Then, carnivores feed on herbivores, forming the secondary and tertiary consumers. However, at each level of consumption, a significant amount of energy is lost. Less than 10 percent of the energy stored in plants is transferred to herbivores, and a similar loss occurs as energy moves from herbivores to predators. Therefore, ecosystems require a continuous input of energy, primarily from the sun.

Producers: Organisms that produce their own food using energy from the sun.

Consumers

Consumers are organisms that rely on other organisms for their energy and food supply. They obtain their energy by feeding on producers or other consumers, forming different levels in the food chain.

For example, when an organism consumes a plant, it is classified as a primary consumer. If another organism then eats this primary consumer, it becomes a secondary consumer. The chain continues with tertiary consumers feeding on secondary consumers.

Scientifically, all consumers can be categorized into four main types based on their feeding habits:

• Herbivores – Consume only plants (e.g., deer, rabbits, cows).
• Carnivores – Consume only other animals (e.g., lions, eagles, snakes).
• Omnivores – Consume both plants and animals (e.g., humans, bears, raccoons).
• Detritivores – Consume dead organic matter (e.g., earthworms, vultures, crabs).

These trophic levels illustrate the flow of energy within an ecosystem.

Consumers: Organisms that do not produce their own food but obtain it by consuming plants or other animals.

Decomposers

Decomposers play a crucial role in breaking down organic matter into simpler substances, recycling nutrients back into the environment. They convert all organic material into carbon dioxide (which they respire) and essential nutrients such as nitrogen, phosphorus, and magnesium. These nutrients become available to plants and algae, which incorporate them into their growth processes.

Although decomposers are often placed at the bottom of ecosystem diagrams such as food chains, food webs, and energy pyramids, they are essential for maintaining ecological balance. By feeding on dead and decaying organisms, they replenish the ecosystem with vital nutrients, enriching the soil and promoting plant growth.

Decomposers: Organisms that digest or break down formerly living material, aiding in nutrient cycling.