A food chain is the path that energy and nutrients take through an ecosystem as one living thing eats another, starting with plants that capture sunlight and ending with the animals and microbes that consume and recycle them. Many such chains overlap and interlock into a food web, and in India the pattern runs from the grass-chital-tiger link in a Terai forest to the algae-fish-kingfisher link in a village pond. Last reviewed on 3 November 2026, this explainer walks through the building blocks, the flow of energy, the Indian examples and the ways pollution and invasive species can break the links.
School textbooks usually draw a food chain as a neat line of arrows: grass, grasshopper, frog, snake, eagle. Real nature is messier. Almost every animal eats several kinds of food and is eaten by several predators, so the real picture is a tangled web. Understanding both the simple chain and the complex web helps explain why removing or adding a single species can ripple through an entire ecosystem.
Quick Facts
| Food chain | A linear sequence showing who eats whom and how energy passes along |
|---|---|
| Food web | A network of many interconnected food chains in one ecosystem |
| Starting point | Producers, mainly green plants, algae and some bacteria, that capture solar energy |
| Main groups | Producers, primary, secondary and tertiary consumers, and decomposers |
| Energy rule | Roughly 10 percent of energy passes from one trophic level to the next |
| Typical chain length | Usually three to five links because energy runs out |
| Two main types | Grazing food chain and detritus food chain |
| Indian examples | Grassland, pond, Sundarbans mangrove, coastal sea and Himalayan meadow chains |
Key Takeaways
- A food chain traces the single path of energy from producers through consumers to decomposers, while a food web shows how many chains connect.
- Energy flows one way through an ecosystem and shrinks at every step, with roughly a tenth passing to the next trophic level, so top predators are always few.
- Grazing food chains begin with living plants, while detritus food chains begin with dead matter and dominate in forests, mangroves and many wetlands.
- Decomposers such as fungi and bacteria close the loop by returning nutrients to the soil and water, so the web can start again.
- Toxins like DDT and mercury can build up along the chain, becoming most concentrated in top predators through biomagnification.
- Invasive species such as water hyacinth, lantana and African catfish can disrupt local food webs by outcompeting, eating or poisoning native species.
What is a food chain and why does it matter?
A food chain is a simple sequence that shows how food energy moves from one organism to the next, and it matters because it explains who depends on whom in nature. Every living thing needs energy, and the original source of nearly all that energy on Earth is the Sun.
The chain begins with organisms that make their own food, then moves to those that eat them, then to those that eat the eaters. At each step some energy is used for living and lost as heat, so only a part is passed up. Food chains matter because they show the flow of energy and matter in a form that is easy to follow, and because they reveal dependencies. If a link is removed, creatures above it may starve and creatures below it may multiply out of control.
Who are the producers, consumers and decomposers?
Producers are organisms that make their own food from sunlight, consumers are organisms that eat other organisms, and decomposers are fungi, bacteria and other organisms that break down dead matter. These three groups form the basic roles in every ecosystem.
Producers, also called autotrophs, include grasses, trees, aquatic plants, algae and phytoplankton. They carry out photosynthesis, using sunlight, water and carbon dioxide to build sugars. Consumers, or heterotrophs, are divided by what they eat. Herbivores such as chital, blackbuck and elephants eat plants, carnivores such as tigers and leopards eat other animals, and omnivores such as sloth bears and crows eat both. Decomposers, including mushrooms, moulds and soil bacteria, feed on dead plants, animal waste and carcasses, and in doing so release minerals that producers can use again. Without them, forests would pile up with dead matter and nutrients would be locked away.
Scavengers such as vultures and jackals and detritivores such as earthworms, termites and dung beetles sit between consumers and decomposers, helping speed the breakdown of dead material.
What are trophic levels?
Trophic levels are the feeding steps in a food chain, counted from the producers upward, and they show an organism’s position in the flow of energy. Producers occupy the first level, herbivores the second, and carnivores the third and beyond.
| Trophic level | Role | Indian example |
|---|---|---|
| First | Producer | Grasses of the Terai, phytoplankton in a pond |
| Second | Primary consumer (herbivore) | Hog deer, blackbuck, grasshopper, zooplankton, tadpoles |
| Third | Secondary consumer (carnivore) | Frog, small fish, jackal, mongoose |
| Fourth | Tertiary consumer | Snake, large fish, wolf, leopard |
| Top | Apex predator | Tiger, crocodile, eagle, snow leopard |
| All levels | Decomposers | Fungi, bacteria, earthworms, termites |
An animal can occupy more than one trophic level. A crow that eats seeds is a primary consumer, but when it eats insects it is a secondary consumer. This flexibility is one reason the real picture is a web, not a line.
How does energy flow through a food chain?
Energy flows through a food chain in one direction, from the Sun to producers to consumers, and a large share is lost as heat at every step. It does not recycle, which is the key difference from nutrients, which are used again and again.
Producers capture only a small fraction of the sunlight that reaches them. When a deer eats grass, much of the energy in the grass goes into the deer’s movement, body heat and maintenance, and part of the plant is never eaten or digested. Only a fraction becomes new deer tissue available to a tiger. This is why ecologists speak of a pyramid of energy that narrows steeply upward.
What is the 10 percent rule?
The 10 percent rule is a rough guideline stating that only about a tenth of the energy at one trophic level is passed to the next. It was popularised from the work of American ecologist Raymond Lindeman in the early 1940s.
The real figure varies widely with the ecosystem and the organisms, often from a few percent to above twenty, so it is best treated as a rule of thumb. It nevertheless explains an important fact: because so much energy is lost at every step, there is far less energy available for top predators than for herbivores. A forest can support thousands of insects, hundreds of deer and only a few tigers over the same area. It also explains why food chains are short. After four or five links, too little energy is left to support another level.
The same reasoning gives pyramids of numbers and of biomass, which usually, though not always, narrow upward as well. A single large tree can host many insects, which gives an inverted pyramid of numbers in some forests, and phytoplankton in the sea may be eaten so quickly that the biomass of zooplankton at a moment exceeds that of the algae. These exceptions are interesting, but the energy pyramid always narrows.
What is the difference between grazing and detritus food chains?
A grazing food chain starts with living green plants eaten by herbivores, while a detritus food chain starts with dead organic matter that is eaten by detritivores and decomposers. Both operate in almost every ecosystem, but their relative importance varies.
The grazing chain is the one most people picture: grass, deer, tiger. In open grasslands and in the sunlit surface layer of oceans and lakes, it carries a large share of the energy. The detritus chain is the hidden half. In a forest, most leaves are never eaten by herbivores; they fall, are broken up by termites, millipedes and earthworms, and are decomposed by fungi and bacteria. Those organisms are themselves eaten by beetles, lizards, birds and so on, and this feeds back into the predator chains.
The Sundarbans offers a good Indian example. The mangroves drop vast amounts of leaf litter into tidal water, where bacteria, fungi and small crustaceans use it, and in turn support crabs, fish, prawns and the larger predators. This detritus-based web is one reason mangroves are such productive nurseries for aquatic life.
What does a food web look like in an Indian grassland?
A food web in an Indian grassland links grasses and herbs to insects and grazing mammals, then to predators such as jackals, wolves, raptors and big cats, with decomposers recycling everything. Grasslands such as the Terai, the Deccan plains and the semi-arid scrub of Gujarat and Rajasthan each have their own versions.
In the Terai grasslands of Kaziranga and Dudhwa, tall grasses feed one-horned rhinoceros, swamp deer, hog deer and elephants, and grasshoppers and other insects feed on the same plants. These herbivores are in turn eaten by tigers, leopards and other predators, while insects are eaten by birds, lizards and frogs, and snakes feed on the frogs and rodents, with eagles and owls hunting snakes and rodents alike. In the drier plains, grass is eaten by blackbuck and insects, rodents are hunted by harriers and foxes, and wolves and jackals take the larger prey. Dung beetles roll away dung, mixing nutrients into the soil, and vultures and jackals clean carcasses.
The practical lesson is that any grassland is only as healthy as its base. If grazing by livestock or invasion by woody plants reduces the grass, the effects move up the web to the blackbuck, the wolf and the raptors.
How does a pond food web work in India?
A pond food web works by passing energy from microscopic algae and water plants through tiny animals and fish to birds and larger predators, with bottom-dwelling decomposers recycling the waste. A village pond or tank is a miniature ecosystem, and it is a good place to see the web in action.
The producers are phytoplankton, floating plants such as duckweed and lotus, and rooted plants such as hydrilla. Zooplankton, insect larvae, snails and tadpoles graze on them. Small fish such as minnows eat zooplankton and larvae, and in turn are eaten by larger fish, frogs, snakes, kingfishers, herons and otters. Dead plants and animals sink to the bottom, where bacteria, worms and snails break them down and release nutrients.
A short pond chain might be: phytoplankton, zooplankton, small fish, large fish, kingfisher. Indian carps like rohu, catla and mrigal occupy different layers of the water, feeding at the surface, middle and bottom, which is one reason they are raised together in aquaculture: each uses a different part of the food web.
What is bioaccumulation and biomagnification?
Bioaccumulation is the build-up of a substance in the body of a living thing over time, and biomagnification is the increase in its concentration at each higher level of the food chain. They matter because many pollutants do not break down and are not easily excreted.
Persistent substances such as the pesticide DDT, other organochlorines and heavy metals like mercury can be taken up by small organisms. Each predator eats many contaminated prey, so the chemical concentrates in its tissues, and top predators end up with the highest doses. Fish-eating birds, river dolphins, crocodiles and humans who eat large fish are at the top of this pollution ladder.
The classic worldwide case was DDT thinning the eggshells of raptors, and similar concerns have been raised in India about pesticide residues in rivers, fish, milk and even human tissue. The vulture crisis from diclofenac is a related example of a toxin moving along a food chain, though the poison there was passed directly from treated cattle carcasses to the scavengers rather than being slowly magnified. Reducing persistent chemicals, treating wastewater and regulating pesticides all help break the cycle.
How do invasive species disrupt native food webs?
Invasive species disrupt native food webs by outcompeting local producers, eating or displacing native consumers, or changing the habitat so that the original web can no longer function. Because food webs depend on the particular species present, a newcomer with no natural enemies can reshape them.
India has several well-known cases. Water hyacinth, a floating plant from South America, can cover lakes and ponds, blocking sunlight and cutting oxygen, which crowds out native water plants and the fish and invertebrates that depend on them. Lantana, a shrub introduced as an ornamental, forms dense thickets in many forests and reduces the grasses and herbs that herbivores feed on, in effect weakening the base of the grazing chain. Prosopis juliflora, a mesquite introduced to dry areas, has spread across scrub and grasslands, including parts of Gujarat’s Banni grassland, and replaces native vegetation. In waterbodies, the African catfish and exotic fish such as tilapia, which have been introduced or have escaped from aquaculture, can prey on or outcompete native fish, shortening or reshaping aquatic chains.
The key difference between native and invasive species in a web is the evolutionary history. Native species have co-evolved with their neighbours, so predators, prey, parasites and competitors balance one another. An invader arrives without that history and can break the balance. Prevention, early detection and removal are far cheaper than clean-up after an invader has established.
Why do food webs matter for biodiversity and people?
Food webs matter because they keep populations in balance, sustain fisheries and farms, and deliver services such as pest control and nutrient cycling that people rely on. The stronger and more diverse the web, the better it can absorb shocks.
Diverse webs tend to be more stable because there are alternative pathways: if one prey species declines, predators can switch to another. Simplified webs, such as those in monocultures, are fragile. Indian farmers benefit directly from natural food webs, since frogs, spiders, birds and insect-eating beetles control crop pests, and vultures, jackals and dung beetles handle waste. When pesticides kill the natural enemies of pests, farmers can end up with worse pest problems.
Fisheries, too, depend on food webs. The oil sardine and mackerel catches along India’s west coast ride on blooms of plankton, and changes in ocean temperature or nutrient supply can ripple up the web to affect fish landings. Understanding the chain helps with sustainable management.
Bottom Line
A food chain is a single thread, and a food web is the whole fabric. Energy enters from the Sun, shrinks as it climbs, and is recycled by decomposers. In India, from Terai grasslands and mangroves to village ponds and coastal seas, protecting the base of the web, keeping toxins out of it and stopping invaders from unravelling it are the best ways to keep ecosystems in balance.
Frequently Asked Questions
What is the difference between a food chain and a food web?
A food chain is a single linear path showing who eats whom, while a food web is a network of many interconnected food chains in an ecosystem. Real ecosystems are webs because most animals eat and are eaten by several species.
What are the three main groups in a food chain?
The three main groups are producers, which make food from sunlight, consumers, which eat other organisms, and decomposers, which break down dead matter. Together they move energy and recycle nutrients.
What is the 10 percent rule in ecology?
It is a rough guideline that only about a tenth of the energy at one trophic level passes to the next, with the rest lost mainly as heat. This is why food chains are short and top predators are few.
What are grazing and detritus food chains?
A grazing food chain starts with living plants eaten by herbivores, while a detritus food chain starts with dead organic matter eaten by detritivores and decomposers. Forests and mangroves rely heavily on detritus chains.
What is biomagnification?
Biomagnification is the rise in concentration of a persistent toxin, such as DDT or mercury, at each higher level of the food chain. It means top predators carry the heaviest load.
How do invasive species affect food webs in India?
Invasive species like water hyacinth, lantana and African catfish can outcompete or prey on native species and alter habitats, which breaks links in the native food web. Because they lack natural enemies, they can spread fast and reduce biodiversity.
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