Concept of an Ecosystem

The term ecosystem was first coined by A.G. Tansley (1935).
An ecosystem is a functional ecological unit in which living organisms (biotic components) interact with the physical environment (abiotic components) through energy flow and nutrient cycling.

It includes:

• All living organisms (plants, animals, microbes)
• The physical environment (soil, water, air, sunlight, minerals)
• Interactions like predation, competition, symbiosis, decomposition

Ecosystems may be:

• Natural: Forests, grasslands, lakes, oceans, deserts
• Artificial: Croplands, aquariums, gardens, reservoirs

An ecosystem maintains ecological balance and supports life through self-regulating processes.

Structure of an Ecosystem: Ecosystem structure refers to the physical organization of different components. It has two major parts:

a) Abiotic Components

These are non-living chemical and physical factors that influence life forms.

• Solar Radiation: Provides energy for photosynthesis.
• Water: Essential for metabolic processes and organism survival.
• Temperature: Determines species distribution.
• Air and Gases: CO₂ for plants, O₂ for respiration.
• Minerals: Nitrogen, phosphorus, potassium, etc.
• Soil: Provides nutrients and anchorage to plants.
• pH and Climatic Factors: Affect chemical reactions and living conditions.

Abiotic components set the environmental conditions that determine the type of biotic life present.

b) Biotic Components: These include all living organisms categorized based on their role in energy flow.

ii) Producers (Autotrophs)

• Mainly green plants, algae, and photosynthetic bacteria
• Capture solar energy and convert it into chemical energy via photosynthesis
• Form the first trophic level

ii) Consumers (Heterotrophs)

They depend on producers or other consumers for food.

• Primary Consumers: Herbivores (deer, rabbit, goat, grasshopper)
• Secondary Consumers: Small carnivores (frog, small fish)
• Tertiary Consumers: Large carnivores (snake, fox)
• Top Carnivores: Apex predators (lion, tiger, eagle)

iii) Decomposers (Saprotrophs)

• Bacteria and fungi
• Break down dead plants and animals into nutrients
• Essential for nutrient cycling and soil fertility

iv) Detritivores: Earthworms, termites, millipedes. Feed on decomposing matter and help fragmentation Together, these components create the food chain, food web, and trophic levels.

Functions of an Ecosystem 

Ecosystems perform crucial ecological functions:

• Energy Flow: Movement of energy through trophic levels from producers → consumers → decomposers.
• Nutrient Cycling (Biogeochemical Cycles): Recycling of essential nutrients: Carbon cycle, Nitrogen cycle, Phosphorus cycle, Water cycle. These maintain ecosystem productivity.
• Food Chain and Food Web Formation: Organisms interact through feeding relationships, maintaining ecological balance.
• Ecological Regulation: Ecosystems regulate: Climate, Water purification, Soil formation, Population balance
• Productivity: Ecosystems have: Primary productivity (plants). Secondary productivity (animals). Decomposition rate Productivity determines the energy available for life processes.

Energy Flow in an Ecosystem: Energy flow is the most fundamental process of an ecosystem. It describes how energy moves from the sun through living organisms.

i) Characteristics of Energy Flow

• Unidirectional: Sun → Producers → Consumers → Decomposers
• Non-cyclic: Unlike nutrients, energy cannot be recycled
• Loss as Heat: At every trophic level, energy decreases (2nd law of thermodynamics)

ii) Steps in Energy Flow

• Solar Energy Input: Sunlight is the primary source. Only 1–3% of solar energy is captured by plants
• Primary Production: Plants convert light energy into chemical energy (glucose) via photosynthesis. This is the basis of all ecosystem energy.
• Energy Transfer Through Trophic Levels: Energy flows through feeding levels:
  • • Trophic Level 1: Producers
    • Trophic Level 2: Herbivores
    • Trophic Level 3: Carnivores
    • Trophic Level 4: Top predators

iii) The 10% Law (Lindeman’s Rule): Only 10% of energy is transferred from one trophic level to the next.
Example: Plants → 1000 units, Herbivores → 100 units, Carnivores → 10 units, Top carnivores → 1 unit. This explains why food chains are short and why top predators are fewer.

Types of Energy Flow Models: i) Linear Food Chain Flow, ii) Food Web Flow, iii) Ecological Pyramid (Pyramid of Energy); Always upright because energy decreases at higher levels.

Role of Decomposers

• Break down organic waste
• Release nutrients back into the soil
• Complete the cycle of matter
• Support primary producers

Without decomposers, ecosystem s would collapse.

Types of ecosystem: Ecosystems are broadly classified based on their origin, location, and environmental conditions. They may be natural or artificial, terrestrial or aquatic, and large or small.

The major types are:

A) Natural Ecosystems: These ecosystems develop without human interference and operate through natural processes such as energy flow, nutrient cycling, and species interactions.

a) Terrestrial Ecosystems: Found on land; influenced mainly by climate, soil, and vegetation.

• i) Forest Ecosystems
  • Dense vegetation, high biodiversity
  • Types: tropical, temperate, deciduous, coniferous
  • High productivity and complex food webs

• ii) Grassland Ecosystems
• Dominated by grasses
• Found in temperate and tropical regions
• Examples: savannas, prairies
• Support large herbivores (deer, buffalo, antelope)

• iii) Desert Ecosystems
• Extremely low rainfall, high temperature
• Sparse vegetation (cacti, succulents)
• Animal adaptations (nocturnal, water conservation)

• iv) Mountain Ecosystems
• High altitude, low temperature
• Vegetation varies with elevation
• Examples: Himalayan ecosystem, Alps ecosystem

b) Aquatic Ecosystems: Found in water bodies; influenced by salinity, depth, and water flow.

i) Freshwater Ecosystems: Low salinity (<1%).
Types:

• Ponds and Lakes – stagnated water; zonation present
• Rivers and Streams – flowing water; high oxygen content
• Wetlands – marshes, swamps; highly productive ecosystems

ii) Marine Ecosystems: High salinity (~3.5%).
Includes:

• Oceans and seas
• Coral reefs (high biodiversity)
• Estuaries (mix of fresh and saltwater)
• Coastal ecosystems (mangroves, lagoons)

Marine ecosystems are the largest ecosystems on Earth, covering ~71% of the planet’s surface.

b) Artificial (Man-Made) Ecosystems

Created and maintained by humans for specific purposes.

Examples:

• Agricultural fields / Croplands
• Gardens and parks
• Aquariums
• Zoos
• Dams and reservoirs
• Terraced farms

These ecosystems have low biodiversity and depend on human management (fertilizers, irrigation, feeding, etc.).

c) Micro-Ecosystems

These are very small ecosystems. Examples:

• Tree hole ecosystem
• A patch of soil
• A decaying log
• A puddle of water

They are small but complete systems with their own producers, consumers, and decomposers.

Major Global Ecosystems (Biomes): Ecosystems grouped by climate, vegetation, and animal life.

Major biomes include: Tropical Rainforest

• Savanna
• Desert
• Temperate Grassland
• Temperate Forest
• Taiga (Coniferous Forest)
• Tundra

Biomes represent the largest ecological units on Earth.

Important facts

• Ecosystem concept was given by A.G. Tansley in 1935.
• Marine ecosystem is the largest ecosystem on Earth Covers ~71% of Earth’s surface.
• Freshwater ecosystems contain less than 1% salt.
• Forest ecosystem has the highest biomass among terrestrial ecosystems.
• Desert ecosystems have the least rainfall and lowest biodiversity.
• Wetlands are the most productive ecosystems after tropical rainforests.
• Artificial ecosystems have low biodiversity and depend on human input. Examples: Croplands, aquariums, gardens.
• Biomes are the largest ecological units Examples: Tundra, Savanna, Rainforest.
• Estuaries are the most nutrient-rich aquatic ecosystems (Where rivers meet sea).
• Grasslands support large herbivores (bison, deer, antelope).
• Freshwater lakes have thermal stratification (epilimnion, hypolimnion layers).
• The Antarctic ecosystem is the coldest and driest ecosystem.
• Mangroves = Coastal ecosystems with halophytic plants.
• Tundra = No trees; permafrost permanently frozen soil.
• Taiga (Coniferous forest) = Largest continuous forest biome.
• Savanna = Tropical grassland with scattered trees.
• Ponds = Smallest complete ecosystems.
• Amazon rainforest = World’s largest forest ecosystem.