Environment Biology | Calicut University Second Semester BSc. Zoology Notes PDF | Module 1 Unit 2 |

Ecosystem: Concept, Structure, and Functions

In Module 1 Unit 1, we introduced the basic idea of an ecosystem. In this unit, we move deeper. In this study material for Module 1, Unit 2 of Environmental Biology, I have covered the key concepts of ecosystems, including their structure, components, and functions. This module is essential for understanding how energy flows through ecosystems and how different organisms interact within their environment.

What You Will Learn in Module 1 Unit 2: 

🌍 Concept of Ecosystem

An ecosystem is a complex, self-supporting system formed by the interaction between living (biotic) and non-living (abiotic) components of the environment. These components interact in such a way that energy flows through the system while nutrients are recycled within it. The total collection of organisms in an ecosystem is known as the biota.

🌱 Structure of an Ecosystem

Abiotic Components

These are the non-living physical and chemical factors that shape ecosystems by controlling species distribution, productivity, and ecological balance. These include climatic factors like temperature, light, wind, and precipitation; edaphic factors such as soil texture, structure, pH, and nutrients; and topographic factors like altitude, slope, and aspect. Together, these factors create environmental conditions and microclimates that regulate life in an ecosystem.

Biotic Components

These include all living organisms and their interactions. These are classified into autotrophs, heterotrophs, decomposers, and transformers. Autotrophs (producers) synthesize organic matter from inorganic substances; phototrophs use sunlight while chemotrophs use chemical energy, forming the base of food chains. They drive primary production, release oxygen, absorb carbon dioxide, and provide habitat structure. Heterotrophs (consumers) depend on producers for food, transfer energy across trophic levels, regulate populations, and support processes like pollination and seed dispersal. Decomposers break down dead organic matter into simpler substances, and transformers convert these into inorganic nutrients that plants can reuse.

🔥 Energy Flow in Ecosystems

The Sun is the ultimate source of energy in an ecosystem and energy flow is one of the fundamental functions of an ecosystem. Primary producers capture solar energy and convert it into chemical energy through photosynthesis. When herbivores consume plants, a portion of this energy is transferred to them. Carnivores then obtain energy by feeding on herbivores. Eventually, energy reaches decomposers. This step-wise transfer of energy across trophic levels is known as energy flow.

Energy flow is always unidirectional. It moves from producers to consumers and finally to decomposers. At each trophic level, a significant portion of energy is lost as heat due to metabolic activities.

The 10 percent law, proposed by Raymond Lindeman, states that only about 10% of energy is transferred from one trophic level to the next. The remaining energy is lost, which limits the number of trophic levels in an ecosystem.

🌾 Primary and Secondary Productivity

Primary productivity refers to the rate at which autotrophs produce organic matter per unit area per unit time. It represents the conversion of solar energy into chemical energy. 

Gross Primary Productivity (GPP) is the total organic matter produced through photosynthesis. Net Primary Productivity (NPP) is the portion remaining after subtracting respiration losses. Net Community Productivity (NCP) represents the energy stored in the ecosystem after accounting for energy transfer to consumers.

Secondary productivity refers to the rate at which consumers accumulate biomass by utilizing energy from primary producers.

📊 Ecological Efficiency

Ecological efficiency is the percentage of energy transferred from one trophic level to another. It includes consumption efficiency, assimilation efficiency, production efficiency, and trophic efficiency. On average, trophic efficiency is around 10%, though it may range between 5–20%.

Energy transfer is inefficient because energy is continuously lost through respiration, excretion, and heat production.

🔺 Trophic Structure and Ecological Pyramids

Trophic structure describes the feeding relationships within an ecosystem. Organisms are arranged into trophic levels: producers, primary consumers, secondary consumers, and tertiary consumers.

Ecological pyramids graphically represent the distribution of energy, biomass, or numbers across trophic levels. In most ecosystems, energy pyramids are always upright due to energy loss at each level. However, biomass pyramids in aquatic ecosystems may sometimes appear inverted.

🌐 Food Chain and Food Web

A food chain is a linear sequence showing the transfer of energy from producers to consumers and finally to decomposers. However, in reality, organisms interact in complex ways, forming interconnected networks called food webs.

Food webs provide stability because organisms have multiple feeding relationships. Disturbance in one trophic level can affect the entire web.

📝 Important Exam Questions

• Define ecosystem and explain its components.
• What are abiotic factors? Classify them with examples.
• Differentiate between GPP and NPP.
• State Lindeman’s 10 percent law.
• What is ecological efficiency?
• Define standing crop and production rate.
• What is an ecotone?

This study material is designed to help you focus on exam-relevant topics efficiently. Feel free to utilise the PDF below and start preparing!

📌 [Embed PDF Here]

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