Concept and Structure of Ecosystem
An ecosystem is a functional unit of nature where living organisms interact with each other and with their physical environment, forming a dynamic system of energy flow and nutrient cycling.
Concept of Ecosystem
Introduced by A.G. Tansley (1935), it highlights interdependence between organisms and their environment, maintaining balance through energy flow and nutrient cycling.
Example: A forest ecosystem includes trees, animals, microbes, sunlight, and rainfall interacting as one unit.
Components of an Ecosystem
Ecosystems consist of biotic (living) and abiotic (non-living) components, both essential for maintaining ecological balance.
Abiotic Components
Include physical factors like sunlight, rainfall, temperature, and soil; and chemical factors such as gases and nutrients.
Example: In aquatic systems, dissolved oxygen affects species diversity.
Biotic Components
Include producers (plants), consumers (animals), and decomposers (fungi, bacteria) responsible for energy transfer and nutrient recycling.
Structure of an Ecosystem
Defined by species composition, energy flow, food chains and webs, nutrient cycling, and ecological pyramids.
Types of Ecosystems
Natural (forest, desert, ocean, pond) and artificial (aquariums, farmlands, urban parks) sustain ecological interactions.
Example: The Sundarbans mangrove ecosystem balances tidal flows and biodiversity.
Functional Aspects
Energy flow, decomposition, nutrient cycling, succession, and homeostasis maintain stability and productivity.
Biotic and Abiotic Components
Ecosystems function through intricate interactions between biotic (living) and abiotic (non-living) components. Together, they regulate energy flow, nutrient cycling, and ecological balance essential for sustaining life on Earth.
Biotic Components
Living elements forming the biological foundation of ecosystems.
Producers
Autotrophs converting solar energy into biomass via photosynthesis.
Producers, also known as autotrophs convert sunlight into chemical energy via photosynthesis
Diatoms and green algae form base of aquatic food webs, supporting larger organisms.
Terrestrial plants, trees and grasses fix carbon, release oxygen, sustaining terrestrial life.
Consumers
Heterotrophs relying on other organisms for food and energy.
Primary Consumers
Herbivores feeding directly on producers like plants or algae.
Secondary Consumers
Carnivores or omnivores feeding on herbivores for energy.
Apex Predators
Top predators with no natural enemies, maintaining food chain balance.
Decomposers
Fungi, bacteria, and detritivores recycling nutrients back to soil.
Break down dead organic matter, recycling nutrients back into soil and water.
Fungi and bacteria secrete enzymes that decompose complex molecules into simpler compounds.
Detritivores like earthworms shred litter, enhancing microbial decomposition and soil fertility.
Abiotic Components
Physical and chemical environmental factors influencing life processes.
Sunlight
Primary energy source for photosynthesis.
Water
Essential for metabolism and habitat formation.
Soil & Minerals
Provide nutrients and anchorage for plants.
Air & Gases
Support respiration and photosynthesis processes.
Temperature
Controls metabolic rates and species distribution.
Climate
Regulates weather patterns and ecosystem diversity.
Topography
Shapes habitats through elevation and slope.
Nutrients
Essential chemical elements cycling through ecosystems.
Species Interactions: The Web of Ecological Relationships
Species interactions form the foundation of ecological balance, influencing population dynamics, resource use, and ecosystem structure. These interactions can be positive, negative, or neutral, shaping how species coexist and evolve in nature.
Competition
Occurs when species vie for limited resources like food, space, or light, affecting population size and survival.
Example: Grasses and herbs in meadows compete for sunlight and soil nutrients.
Intraspecific Competition
Occurs within members of the same species competing for identical resources, regulating population density and promoting natural selection.
Example: Male deer competing for territory or mates during the breeding season.
Interspecific Competition
Takes place between different species utilizing similar ecological niches, leading to niche differentiation or exclusion.
Example: Lions and hyenas in the African savanna competing for prey.
Mutualism
Both species benefit through cooperation that enhances survival or reproduction.
Example: Bees pollinating flowers — bees gain nectar, plants achieve pollination.
Symbiosis
A long-term association between different species, which can be beneficial, harmful, or neutral.
Example: Lichens — a symbiosis between algae and fungi forming a stable ecological unit.
Amensalism
One species is harmed while the other remains unaffected, often through chemical dominance.
Example: Penicillium mold releases antibiotics that kill nearby bacteria.
Commensalism
One species benefits while the other is unaffected, often aiding mobility or habitat use.
Example: Cattle egrets feeding on insects stirred by grazing cattle.
Parasitism
One organism (parasite) benefits at the expense of another (host), often causing disease.
Example: Malarial parasites (Plasmodium) living in human blood cells.
Neutralism
Two species coexist in the same habitat without directly affecting each other.
Example: A spider and a frog sharing the same forest but using different niches.
Functions of Ecosystem
Ecosystem functions refer to the natural processes and interactions through which energy flows, nutrients cycle, and life sustains itself. These functions ensure ecological stability and support all living organisms on Earth.
Production Function
Creation of biomass through photosynthesis and nutrient assimilation by producers like plants, algae, and bacteria.
Example: Grasslands produce vast biomass supporting grazers like deer.
Productivity
Measures the rate of biomass generation in an ecosystem, showing energy transfer efficiency.
Example: Tropical rainforests and coral reefs show the highest productivity.
Gross Primary Productivity (GPP)
Total energy captured by producers through photosynthesis, representing potential energy before losses.
Example: Paddy fields show high GPP during monsoon due to sunlight and nutrients.
Net Primary Productivity (NPP)
Energy available to consumers after subtracting respiration losses (NPP = GPP – Respiration).
Example: Amazon forests and Sundarbans mangroves exhibit high NPP.
Regulatory Functions
Maintain ecological balance by regulating climate, gases, and nutrient flows.
Example: Forests regulate CO₂–O₂ balance; wetlands purify water and control floods.
Nutrient Cycling
Recycling of vital elements like carbon, nitrogen, and phosphorus through decomposition and uptake.
Example: Decomposers release nutrients vital for Gangetic Plains crops.
Climate and Gas Regulation
Forests absorb CO₂, influence rainfall, and reduce greenhouse effects.
Example: Himalayan forests regulate temperature and monsoon patterns.
Information Functions
Provide genetic, cultural, and scientific knowledge for research and education.
Example: Western Ghats aid discovery of medicinal plants used in Ayurveda.
Habitat and Support Functions
Provide shelter and breeding grounds for diverse species.
Example: Coral reefs sustain fish, crustaceans, and sea turtles.
Cultural and Recreational Functions
Hold aesthetic, spiritual, and tourism value.
Example: Ecotourism in Jim Corbett and Kerala backwaters supports conservation and livelihoods.
Nutrient Recycling in Ecosystems
Nutrient recycling is the continuous movement and reuse of essential elements within ecosystems, ensuring balance and sustainability of life. It connects the biotic and abiotic components through biogeochemical cycles — water, carbon, oxygen, nitrogen, sulphur, and phosphorus — that sustain ecosystem productivity and stability.
1. Water Recycling
Water circulates through evaporation, condensation, precipitation, and transpiration. Plants absorb groundwater and return moisture to the air.
Example: Western Ghats forests enhance rainfall and sustain rivers like the Godavari and Cauvery.
2. Carbon Recycling
Carbon cycles between air, water, soil, and organisms through photosynthesis and respiration. Oceans act as major carbon sinks.
Example: Mangroves in the Sundarbans store vast “blue carbon,” reducing global warming.
3. Oxygen Recycling
Oxygen cycles via photosynthesis and respiration. Plants and phytoplankton release O₂, while organisms use it for respiration.
Example: Forests in North-East India and Indian Ocean phytoplankton maintain oxygen balance.
4. Nitrogen Recycling
Nitrogen cycles through fixation, nitrification, and denitrification. Bacteria like Rhizobium convert N₂ into usable forms.
Example: Legume farming in Punjab enriches soil through symbiotic nitrogen fixation.
5. Sulphur Recycling
Sulphur moves through air, soil, and organisms. Volcanoes and microbes release and transform sulphur compounds for plant use.
Example: Andaman volcanic soils rich in sulphur support unique tropical vegetation.
6. Phosphorus Recycling
Phosphorus originates from weathered rocks as phosphates absorbed by plants and recycled via decomposition and sediments.
Example: Chilika Lake’s productivity is sustained by phosphorus-rich river sediments supporting plankton growth.
Food Chains – Basic Concept and Classification
Food chains represent the fundamental pathway of energy flow and nutrient transfer within an ecosystem. They describe how energy captured by producers passes through consumers and decomposers, maintaining ecological balance. Each organism occupies a specific trophic level, forming a link in this continuous energy flow.
Basic Concept
The foundation of every food chain lies in solar energy harnessed by green plants through photosynthesis. Producers form the first trophic level, followed by herbivores, carnivores, and finally decomposers that recycle nutrients back to the soil.
Energy transfer between levels is only about 10% efficient (the 10% law), limiting trophic levels and ecosystem productivity.
1. Grazing Food Chain (GFC)
Begins with green plants or phytoplankton as producers, consumed by herbivores and then carnivores. Represents direct use of solar energy through photosynthesis.
Example: Grass → Grasshopper → Frog → Snake → Hawk.
Dominates both terrestrial and aquatic ecosystems as the primary energy route.
2. Detritus Food Chain (DFC)
Starts with dead organic matter like leaves or remains, consumed by detritivores and decomposed by microbes. Nutrients released are reused by producers.
Example: Leaf litter → Earthworm → Frog → Snake → Eagle.
Plays a vital role in forest floors, mangroves, and sediments, ensuring nutrient recycling.
3. Parasitic Food Chain (PFC)
Energy flows from larger organisms to parasites and further to hyperparasites. Though less visible, such chains help regulate populations.
Example: Tree → Bird → Lice → Mites.
Often overlaps with other chains, forming complex food webs that sustain ecosystem balance.
Interconnection: Food Webs
Multiple food chains interconnect to form webs, providing stability and resilience. A diverse food web ensures no single species collapse affects the entire system.
Food Webs – Basic Concept and Classification
Food webs represent the complex network of feeding interactions within an ecosystem, showing how multiple food chains interconnect. Unlike simple linear food chains, they illustrate realistic energy and matter flow through various trophic levels—producers, consumers, and decomposers—highlighting ecological stability, resilience, and interdependence.
Basic Concept
A food web integrates multiple food chains into a single interconnected system. One organism may occupy different trophic levels—for example, omnivores like bears feed on both plants and animals, linking diverse chains.
This networked structure increases stability and allows ecosystems to adapt to environmental changes.
1. Interaction Food Webs
Depict direct feeding relationships among species, showing predator-prey and plant-herbivore links.
Example: In a forest, deer feed on shrubs and tigers prey on deer, forming part of an interaction web.
Helps identify keystone species whose removal could destabilize entire ecosystems.
2. Connectance Food Webs
Focus on the proportion of possible feeding links realized within an ecosystem, indicating network complexity.
Example: Coral reef ecosystems show high connectance due to numerous predator-prey interactions.
Greater connectance ensures stronger resilience and multiple alternate energy pathways.
3. Energy Flow Food Webs
Quantify energy transfer between trophic levels, highlighting efficiency and losses at each stage.
Example: In grasslands, 10% of plant energy passes to herbivores, and only 1% to top carnivores.
Essential for assessing productivity and managing ecosystem energy dynamics.
4. Fossil Food Webs
Reconstruct ancient ecosystems using fossils, isotopes, and paleoecological data to trace past interactions.
Example: Mesozoic marine fossils reveal predator-prey patterns that shaped modern biodiversity.
Provide insights into evolutionary dynamics and extinction events.
5. Functional Food Webs
Group species by ecological roles—such as decomposers, herbivores, or predators—rather than identity.
Example: Soil-based webs link decomposers, fungi, and detritivores recycling nutrients for fertility.
Highlight the functional cycling of energy and matter within ecosystems.
Advantages of Food Webs over Food Chains
Complexity & Realism: Represent real-world feeding networks, not linear chains.
Ecosystem Stability: Provide alternative energy paths when species decline.
Keystone Detection: Identify critical species maintaining balance.
Energy Analysis: Trace multiple energy routes for productivity studies.
Conservation Insight: Guide ecosystem restoration and biodiversity management.
Ecological Pyramids
Ecological pyramids are graphical representations that depict quantitative relationships among organisms at different trophic levels. They show how energy, biomass, or number of individuals is distributed from producers to top consumers, offering insights into ecosystem structure and energy flow.
1. Pyramid of Number
Basic Concept: Shows the number of individual organisms at each trophic level — numerous producers at the base, fewer herbivores, and even fewer carnivores at the top. It indicates population size but not biomass.
Characteristics:
- Reflects population count, not energy or size.
- Usually upright where producers outnumber consumers.
- Simple but may not represent stability accurately.
Example: Grass → Grasshopper → Frog → Snake → Hawk (upright pyramid).
Possibility of Inversion: A single tree may support many insects and parasites, forming an inverted pyramid.
2. Pyramid of Biomass
Basic Concept: Represents the total dry weight of living organisms (biomass) at each trophic level, showing organic matter flow through food chains.
Characteristics:
- Reflects total living material available as food.
- Usually upright in terrestrial ecosystems.
- Better indicator of stored energy than numbers.
Example: Forest: Trees → Deer → Tiger (upright pyramid).
Possibility of Inversion: In ponds, phytoplankton biomass is less than zooplankton — inverted pyramid.
3. Pyramid of Energy
Basic Concept: Depicts the flow of energy through trophic levels over time (kcal/m²/year). Energy decreases at each level due to heat loss, following the second law of thermodynamics.
Characteristics:
- Always upright as energy transfer is inefficient (~10%).
- Most realistic measure of ecosystem productivity.
- Highlights loss through respiration and decomposition.
Example: Grass → Rabbit → Fox → Hawk (upright pyramid).
Possibility of Inversion: Impossible — energy flows in one direction only.
Homeostasis of Ecosystems
Homeostasis in ecosystems refers to the natural balance and self-regulation that maintain stability among living organisms and their environment. It ensures that despite disturbances like climate variations or species loss, ecosystems can recover and continue functioning efficiently.
Concept of Ecosystem Homeostasis
Ecosystem homeostasis represents the dynamic equilibrium maintained through feedback mechanisms regulating population sizes, nutrient cycling, and energy flow. It enables ecosystems to adapt to changes while sustaining productivity.
Role of Producers, Consumers, and Decomposers
Producers capture solar energy, consumers regulate populations, and decomposers recycle nutrients—collectively maintaining energy and matter balance.
Example: Grassland plants, herbivores, and decomposers sustaining nutrient flow across trophic levels.
Feedback Mechanisms
Feedback loops maintain stability—negative feedback restores balance, while positive feedback establishes new equilibrium.
Example: Predator-prey relationships regulating population size.
Nutrient Cycling and Energy Flow
Continuous nutrient recycling and one-way energy flow ensure resilience and productivity in ecosystems.
Example: Forest litter decomposition enriching soil nutrients.
Population Regulation
Natural controls like predation, disease, and competition maintain population equilibrium and prevent overuse of resources.
Example: Zooplankton adjusting to phytoplankton abundance in aquatic ecosystems.
Climate and Abiotic Factors
Temperature, light, moisture, and pH influence homeostasis. Species adapt and adjust productivity to changing abiotic conditions.
Example: Mangroves maintaining salinity balance in coastal habitats.
Ecological Succession and Stability
Succession restores equilibrium after disturbances, leading to stable climax communities over time.
Example: Recolonization of burnt forests by grasses and shrubs.
Resilience and Resistance
Resilience allows recovery from stress; resistance enables ecosystems to withstand disturbances.
Example: Coral reefs regaining stability post-bleaching through coral regrowth.
Human Impacts on Homeostasis
Human actions like deforestation, pollution, and climate change disrupt natural feedbacks and weaken resilience.
Example: Fertilizer-induced eutrophication in water bodies.
Restoration and Sustainable Management
Conservation and ecological restoration promote self-regulation and biodiversity stability.
Example: Reforestation in Western Ghats restoring hydrological balance.
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