Ecosystem: Complete Overview (NCERT)

An ecosystem is a functional unit of nature where living organisms interact among themselves and with their physical environment.

Overview of an Ecosystem

Types of Ecosystems

Ecosystems vary in size and can be broadly classified into:

1. Natural Ecosystems
   • Terrestrial Ecosystems (Land-based)
     • Forest
     • Grassland
     • Desert
   • Aquatic Ecosystems (Water-based)
     • Freshwater Ecosystems: Pond, Lake, River, Wetland
     • Marine Ecosystems: Estuary, Ocean
2. Man-Made Ecosystems
   • Crop Fields
   • Aquarium

Structure of an Ecosystem

To understand ecosystem functioning, we analyze its structure, which includes:

1. Input (Productivity) – The process of energy capture through photosynthesis.
2. Energy Transfer
   • Food Chains & Food Webs – The movement of energy among organisms.
   • Nutrient Cycling – The recycling of essential nutrients like carbon, nitrogen, and phosphorus.
3. Output
   • Degradation – Breakdown of organic matter.
   • Energy Loss – Dissipation of energy as heat.

Interrelationships in an Ecosystem

Ecosystems maintain balance through:

• Food Chains & Webs – Interlinked feeding relationships.
• Biogeochemical Cycles – Continuous movement of elements like carbon, nitrogen, and oxygen.

Ecosystem: Structure & Function – The Interplay of Life & Environment

An ecosystem is a self-sustaining unit where biotic (living) and abiotic (non-living) components interact, ensuring the continuous flow of energy and matter. Understanding how these elements function together helps us grasp the balance of nature!

Structure of an Ecosystem

✅ Biotic Components (Living)

• Producers (Autotrophs): Plants, algae, and phytoplankton that produce energy through photosynthesis.
• Consumers (Heterotrophs): Herbivores, carnivores, omnivores, and decomposers.
• Decomposers: Fungi, bacteria, and microorganisms that recycle nutrients.

✅ Abiotic Components (Non-Living)

• Physical Factors: Sunlight, temperature, water, soil, air, and minerals.
• Chemical Factors: Oxygen, carbon dioxide, nitrogen, and other nutrients.

✅ Species Composition & Stratification

• Different species occupy specific vertical layers within an ecosystem.
• Example (Forest Ecosystem):
  🌳 Trees – Top layer
  🌿 Shrubs – Middle layer
  🌱 Herbs & Grasses – Bottom layer

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Functions of an Ecosystem

An ecosystem operates as a functional unit through four main processes:

1️⃣ Productivity 🌞

• Plants (producers) convert solar energy into food through photosynthesis.
• Measured as Gross Primary Productivity (GPP) & Net Primary Productivity (NPP).

2️⃣ Decomposition 🔄

• Breakdown of dead organisms by fungi & bacteria.
• Releases nutrients back into the soil for plants to reuse.

3️⃣ Energy Flow ⚡

• Unidirectional movement of energy from the sun → plants → herbivores → carnivores.
• Energy dissipates as heat at each trophic level.

4️⃣ Nutrient Cycling ♻️

• The continuous recycling of nutrients like carbon, nitrogen, and phosphorus.
• Maintains ecosystem stability and productivity.

Case Study: Pond Ecosystem

A pond is a self-sustaining aquatic ecosystem that showcases all these interactions:

✅ Abiotic Factors: Water, soil, dissolved nutrients, sunlight.
✅ Producers: Phytoplankton, algae, submerged & floating plants.
✅ Consumers: Zooplankton, fish, insects, amphibians.
✅ Decomposers: Bacteria, fungi, and flagellates breaking down organic matter.

💡 Key Insight:

• Energy moves one way (Sun → Plants → Animals → Decomposers).
• Nutrients are recycled by decomposers for reuse by producers.
• These processes keep the ecosystem balanced and functional.

Fun Fact

🌍 Every ecosystem on Earth follows this same structure and function, from tiny ponds to vast forests!

Productivity in Ecosystems: The Flow of Energy & Biomass

A constant input of solar energy is the foundation of life on Earth. Productivity in an ecosystem refers to the rate at which biomass (organic matter) is produced, driving the entire food chain.

What is Productivity?

• Productivity = Rate of Biomass Production
• Expressed in:
  ✅ gm⁻² yr⁻¹ (grams per square meter per year)
  ✅ kcal m⁻² yr⁻¹ (kilocalories per square meter per year)

Types of Productivity

1️⃣ Gross Primary Productivity (GPP) 🌱

• Total organic matter produced by plants during photosynthesis.
• Some of this is used by plants for respiration.

2️⃣ Net Primary Productivity (NPP) 🍃

• NPP = GPP – R (Respiration Losses)
• Usable biomass available to herbivores & decomposers.

3️⃣ Secondary Productivity 🐄

• Rate of new organic matter formation by consumers (herbivores, carnivores).
• Energy is transferred through the food chain.

Factors Affecting Productivity

✅ Plant species present
✅ Environmental conditions (sunlight, temperature, rainfall)
✅ Availability of nutrients
✅ Photosynthetic capacity of plants

Global Productivity Insights

📊 Total Annual NPP of the Biosphere: ~170 billion tons (dry weight)
🌊 Oceans (70% of Earth’s surface): Only 55 billion tons
🌿 Land ecosystems: Higher productivity than oceans

💡 Why are oceans less productive?

• Lack of nutrients in open waters
• Deep waters limit sunlight penetration

🌳 Tropical rainforests have the highest NPP, while deserts have the lowest!

Decomposition: Nature’s Recycling System

Decomposition is the breakdown of complex organic matter into simpler inorganic substances. It plays a crucial role in nutrient cycling, ensuring the ecosystem remains balanced and productive!

What is Decomposition?

• The process of breaking down dead organisms into simpler substances.
• Converts organic material into nutrients, carbon dioxide, and water.
• Essential for soil fertility and ecosystem sustainability.

✅ Raw Material for Decomposition:

• Detritus (Dead plant & animal remains, fecal matter).
• Example: Leaves, bark, flowers, animal carcasses.

Steps of Decomposition

1️⃣ Fragmentation 🪱

• Detritivores (e.g., earthworms) break detritus into smaller pieces.

2️⃣ Leaching 💧

• Water dissolves and carries away inorganic nutrients deep into the soil.

3️⃣ Catabolism 🦠

• Bacteria & fungi break down detritus into simpler compounds using enzymes.

4️⃣ Humification 🏞️

• Formation of humus, a dark-colored, nutrient-rich substance.
• Humus resists microbial decay and stores nutrients.

5️⃣ Mineralization ⚡

• Microbes further degrade humus, releasing inorganic nutrients back into the soil.

Factors Affecting Decomposition

✅ Detritus Composition

• Rich in lignin & chitin → Slower decomposition
• Rich in nitrogen & sugars → Faster decomposition

✅ Climatic Factors

• Warm & Moist Environment → Faster decomposition
• Cold & Anaerobic Conditions → Slower decomposition

✅ Microbial Activity

• Oxygen is essential for decomposition!
• Lack of oxygen slows down the process (e.g., peat bogs).

Why is Decomposition Important?

🌿 Recycles nutrients back into the soil.
🌱 Supports plant growth by enriching soil fertility.
🔄 Maintains ecosystem balance by breaking down waste naturally.

Examples of Decomposers

🌱 Fungi: Mushrooms, Molds, Yeasts
🦠 Bacteria: Actinomycetes, Nitrobacter, Pseudomonas
🐛 Detritivores: Earthworms, Millipedes, Termites

Fun Fact

🪱 Earthworms are called “Farmers’ Friends” because they speed up decomposition and improve soil quality!

🌍 Fungi are among the largest decomposers—Armillaria ostoyae (Honey Fungus) in Oregon, USA, spans over 3.8 km², making it the largest living organism on Earth!

Energy Flow in Ecosystem: The Power Transfer Chain

Energy flows through an ecosystem in a unidirectional manner, from the Sun to producers and then to consumers. This process supports all life forms by transferring energy through different trophic levels.

What is Energy Flow?

• The transfer of energy from one organism to another through the food chain.
• Sun → Producers → Consumers → Decomposers

Trophic Levels in Energy Flow

1️⃣ Producers (Autotrophs) – Plants, algae, and cyanobacteria capture solar energy via photosynthesis.

2️⃣ Primary Consumers (Herbivores) – Eat plants (e.g., Deer, Cows, Grasshoppers).

3️⃣ Secondary Consumers (Carnivores/Omnivores) – Eat herbivores (e.g., Frogs, Small Birds).

4️⃣ Tertiary Consumers (Top Predators) – Eat secondary consumers (e.g., Tigers, Eagles).

5️⃣ Decomposers – Break down dead organisms, returning nutrients to the soil (e.g., Fungi, Bacteria).

The 10% Energy Rule

⚡ Only 10% of energy is transferred from one trophic level to the next; 90% is lost as heat.

• Example: If plants capture 1000 kcal of energy,
  • Herbivores get 100 kcal
  • Carnivores get 10 kcal
  • Top predators get 1 kcal

Types of Energy Flow

🔄 Grazing Food Chain (GFC) – Energy moves from plants to herbivores to carnivores.

🪸 Detritus Food Chain (DFC) – Energy moves from dead organic matter to decomposers and detritivores.

Importance of Energy Flow

✅ Maintains ecological balance.
✅ Supports biodiversity and food web stability.
✅ Helps in energy conservation at different trophic levels.

Fun Fact

🌱 Plants only capture about 1% of the Sun’s energy! Yet, this tiny fraction supports all life on Earth.

Ecological Pyramids: The Structure of Energy & Biomass in Ecosystems

Ecological pyramids visually represent the relationships between different trophic levels in an ecosystem. These pyramids show how energy, biomass, and numbers of organisms decrease as we move up the food chain.

What are Ecological Pyramids?

• Graphical representations of trophic levels in an ecosystem.
• Show how energy, biomass, or number of organisms change from producers to top consumers.
• Always base-wide and taper towards the top, except in special cases.

Types of Ecological Pyramids

1️⃣ Pyramid of Energy (Always Upright)

• Shows the flow of energy at different trophic levels.
• Follows the 10% Energy Rule (90% energy is lost as heat).
• Example: Sun → Grass (1000 kcal) → Grasshopper (100 kcal) → Frog (10 kcal) → Snake (1 kcal).

2️⃣ Pyramid of Biomass (Usually Upright)

• Shows the total dry weight of organisms at each level.
• Example: A forest ecosystem (plants have the most biomass, followed by herbivores and carnivores).
• Exception: In aquatic ecosystems, this pyramid is inverted because phytoplankton (producers) have less biomass than zooplankton (consumers).

3️⃣ Pyramid of Numbers (Can be Upright or Inverted)

• Represents the number of organisms at each level.
• Example: A grassland ecosystem has many plants at the base, fewer herbivores, and even fewer carnivores (upright pyramid).
• Exception: In a parasitic food chain, one tree supports many birds, which in turn host even more parasites (inverted pyramid).

Key Observations

✅ Pyramid of Energy is Always Upright (energy decreases at higher levels).
✅ Pyramid of Biomass is Inverted in Aquatic Ecosystems (phytoplankton reproduce fast despite their small biomass).
✅ Pyramid of Numbers Varies (depends on the nature of the ecosystem).

Fun Fact

🌍 An oak tree can support thousands of insects, making the pyramid of numbers inverted in a forest ecosystem!

Ecological Succession: Nature’s Way of Rebuilding Ecosystems

Ecological succession is the natural process of change in the structure and composition of an ecosystem over time. It helps restore balance and biodiversity after disturbances like volcanic eruptions, forest fires, or climate changes.

What is Ecological Succession?

• Gradual replacement of one community by another in an ecosystem.
• Leads to a stable and mature community called the climax community.

Types of Ecological Succession

1️⃣ Primary Succession (Starts from Scratch)

• Occurs on bare land where no life existed before (e.g., lava flows, glacial retreats).
• Pioneer Species like lichens and mosses break down rocks to form soil.
• Takes hundreds to thousands of years to establish a stable ecosystem.
• Example: Volcanic eruption forming new land → Colonization by lichens → Growth of grasses → Development of a forest.

2️⃣ Secondary Succession (Rebuilding After Disturbance)

• Occurs in previously inhabited areas where an ecosystem existed but was disturbed (e.g., forest fires, floods, human activities).
• Soil is already present, so succession is faster than primary succession.
• Example: Abandoned farmland → Growth of grasses → Shrubs → Return of forests.

Stages of Ecological Succession

1️⃣ Pioneer Stage 🌱 – Hardy species like lichens, mosses, and bacteria start colonizing.
2️⃣ Intermediate Stage 🌿 – Small plants, shrubs, and insects move in as soil develops.
3️⃣ Climax Community 🌳 – A stable and mature ecosystem with large trees, animals, and biodiversity.

Importance of Ecological Succession

✅ Restores damaged ecosystems.
✅ Increases biodiversity and species richness.
✅ Helps maintain ecological balance.
✅ Enhances soil fertility and water retention.

Fun Fact

🔥 After the eruption of Mount St. Helens (USA) in 1980, ecological succession helped forests and wildlife recover within decades!

Nutrient Cycling: Nature’s Recycling System

Nutrient cycling ensures the continuous movement of essential elements (like carbon, nitrogen, and phosphorus) between living organisms and the environment. Without it, ecosystems would run out of nutrients needed for life!

What is Nutrient Cycling?

• The circular movement of nutrients between the biotic (living) and abiotic (non-living) components of an ecosystem.
• Essential for maintaining ecosystem productivity and balance.

Types of Nutrient Cycles

1️⃣ Gaseous Cycles 🌍

• Nutrients move between the atmosphere and living organisms.
• Examples: Carbon Cycle, Nitrogen Cycle, Oxygen Cycle.

2️⃣ Sedimentary Cycles 🌱

• Nutrients move through soil, rocks, and water.
• Examples: Phosphorus Cycle, Sulfur Cycle.

Major Biogeochemical Cycles

1. Carbon Cycle (CO₂ Cycle)

🔄 Plants absorb CO₂ → Herbivores eat plants → Animals release CO₂ through respiration → Decomposers return carbon to soil & atmosphere.
🔥 Human Impact: Burning fossil fuels increases CO₂, causing climate change.

2. Nitrogen Cycle

☁️ 78% of air is nitrogen, but plants can’t use it directly!
🔹 Nitrogen Fixation (Bacteria convert N₂ into usable forms).
🔹 Nitrification (Ammonia → Nitrites → Nitrates for plants).
🔹 Denitrification (Bacteria return nitrogen to the air).
🚜 Human Impact: Fertilizers disturb the balance, leading to pollution.

3. Phosphorus Cycle

🪨 Phosphorus comes from rocks (not the atmosphere).
🌱 Plants absorb phosphorus → Animals eat plants → Decomposers return phosphorus to soil.
🏭 Human Impact: Excess phosphorus from fertilizers causes water pollution (eutrophication).

Importance of Nutrient Cycling

✅ Maintains ecosystem balance.
✅ Supports growth of plants & animals.
✅ Prevents nutrient depletion in the environment.
✅ Helps in energy flow & food chain stability.

Fun Fact

🌍 The same carbon atoms you breathe out today could have been in a dinosaur’s breath millions of years ago!

Ecosystem Services: Nature’s Free Benefits to Humanity

Healthy ecosystems are the foundation of life and provide essential economic, environmental, and aesthetic goods and services. From clean air to fertile soil, nature sustains us in ways we often take for granted.

What are Ecosystem Services?

• The products of ecosystem processes that benefit humans directly or indirectly.
• Example: Forests purify air and water, regulate climate, and support biodiversity.

Types of Ecosystem Services

1️⃣ Provisioning Services (Nature’s Resources) 🌾

• Provide tangible goods like food, water, and raw materials.
• Examples: Crops, fish, timber, fresh water, medicinal plants.

2️⃣ Regulating Services (Nature’s Protection) 🌱

• Control environmental conditions and maintain balance.
• Examples:
  • Air and water purification.
  • Pollination by bees.
  • Flood control by wetlands.
  • Climate regulation (forests absorb CO₂).

3️⃣ Cultural Services (Nature’s Inspiration) 🎨

• Non-material benefits that enrich human life and culture.
• Examples:
  • Tourism and recreation (forests, wildlife sanctuaries).
  • Spiritual and religious values (sacred groves, pilgrimage sites).
  • Aesthetic and educational benefits.

4️⃣ Supporting Services (Nature’s Foundation) 🔄

• Enable all other services to function.
• Examples:
  • Soil formation.
  • Nutrient cycling.
  • Photosynthesis.
  • Biodiversity maintenance.

Economic Valuation of Ecosystem Services

📊 Robert Constanza et al. (1997) estimated the global value of ecosystem services at
💰 US $33 trillion per year – nearly twice the global GNP (US $18 trillion)!

💡 Breakdown of Ecosystem Service Value:
✅ Soil formation – 50% of total value.
✅ Climate regulation & wildlife habitat – 6% each.
✅ Recreation & nutrient cycling – Less than 10% each.

Importance of Ecosystem Services

✅ Ensure food security and freshwater supply.
✅ Regulate climate, air, and water quality.
✅ Support biodiversity and ecosystem stability.
✅ Provide economic benefits (tourism, agriculture, medicine).

Fun Fact

🐝 Pollinators like bees contribute over $500 billion annually to global agriculture by increasing crop production!

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