Q.The introduction of alien species usually enhances biodiversity by adding stability to native ecosystems.
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Invasive Alien Species and Biodiversity Loss
An alien (exotic) species is one introduced — deliberately or accidentally — into an area outside its natural range. Most introductions go nowhere. But some alien species find the new environment so favourable, with none of the predators, parasites, or competitors that kept them in check back home, that their population explodes. When that happens, the alien turns invasive, and it becomes one of the major recognised causes of biodiversity loss worldwide — alongside habitat loss, over-exploitation, and co-extinction.
How An Invasion Causes Decline
An invasive alien species drives down native biodiversity in a few overlapping ways: it out-competes native species for food, light, or space; it may directly prey on native species that never evolved defences against it; and it can alter the habitat itself so thoroughly that native species can no longer survive there at all. The damage compounds — a successful invader keeps spreading and keeps displacing natives for as long as it remains established.
Well-Documented Examples
- Nile perch, introduced into Lake Victoria (East Africa) as a food fish, is directly implicated in the extinction of an estimated 200-plus species of the cichlid fish that were native to the lake — one of the most cited case studies of invasion-driven mass extinction.
- Water hyacinth (Eichhornia crassipes), introduced to India as an ornamental plant, spreads explosively across ponds, lakes and canals, choking them, blocking sunlight to submerged native plants, and depleting dissolved oxygen for aquatic life. …
Introduced alien species often lack natural checks in the new habitat and outcompete native species, so they reduce rather than enhance native biodiversity, which makes the statement false. …
Alien species introduced from elsewhere often lack natural predators/competitors in the new habitat, allowing them to outcompete and displace native species, causing biodiversity loss rather than gain.
Alien species invasions are recognised as one of the major causes of the ongoing loss of biodiversity globally. When a non-native species is introduced (deliberately or accidentally) into a new region, it may multiply rapidly (because natural checks like predators, parasites and competitors from its native range are absent) and outcompete indigenous species for resources such as light, nutrients and space, sometimes driving native species to lo …
- CBSE 2026Set ANNUAL1 markMCQQ.African catfish brought for aquaculture purpose is posing a threat to the native fishes in our river :(a) Clarias(b) Oriza(c) Albacar(d) Rospo
›Reveal solutionSolution
The African catfish, Clarias gariepinus, introduced for aquaculture, is an invasive alien species that threatens native Indian fish.
Clarias gariepinus (African magur/catfish) was introduced into India for aquaculture because of its fast growth and hardiness. However, it turned out to be a highly predatory and invasive alien species — it preys on and outcompetes native fish species (like the indigenous Clarias batrachus), disrupting local aquatic ecosystems. Because of this threat to nati …
- CBSE 2025Set ANNUAL1 markQ.The introduction of alien species usually enhances biodiversity by adding stability to native ecosystems.
›Reveal solutionSolution
Alien species introduced from elsewhere often lack natural predators/competitors in the new habitat, allowing them to outcompete and displace native species, causing biodiversity loss rather than gain.
Alien species invasions are recognised as one of the major causes of the ongoing loss of biodiversity globally. When a non-native species is introduced (deliberately or accidentally) into a new region, it may multiply rapidly (because natural checks like predators, parasites and competitors from its native range are absent) and outcompete indigenous species for resources such as light, nutrients and space, sometimes driving native species to lo …
- CBSE 2024Set E1 markMCQQ.Which of the following plants is referred to as 'Terror of Bengal'?(a) Water hyacinth(b) Bamboo(c) Lantana(d) Parthenium
›Reveal solutionSolution
The 'Terror of Bengal' is water hyacinth (Eichhornia crassipes).
Water hyacinth (Eichhornia crassipes) is an alien (introduced) aquatic weed that grows abundantly in waterbodies, choking them, depleting oxygen and killing aquatic life. Because of the devastation it caused to waterbodies, it earned the name 'Terror of …
- CBSE 2024Set E1 markMCQQ.What was the reason for extinction of more than 200 species of Cichlid fish in Lake Victoria?(a) Co-extinction(b) Alien species invasion(c) Overexploitation(d) Habitat loss
›Reveal solutionSolution
The introduced Nile perch — an alien predator — drove more than 200 native cichlid fish species of Lake Victoria to extinction.
When the predatory Nile perch was introduced into Lake Victoria in East Africa, it preyed heavily on the native cichlid fishes. This alien (exotic) species invasion led to the extinction of more than 200 species of these ecologically unique cichl …
- CBSE 2024Set D1 markQ.Write True or False: Clarias gariepinus reared for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.
›Reveal solutionSolution
The statement is True — Clarias gariepinus, introduced for aquaculture in India, has become a serious threat to native/indigenous catfish species.
The African catfish, Clarias gariepinus, was introduced into India for commercial aquaculture purposes because of its fast growth rate and adaptability. However, being a voracious, highly adaptable predator, it escaped into natural water bodies (rivers and ponds).
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- CBSE 2020Set ANNUAL1 markMCQQ.Select the cause of extinction of Cichlid fish in lake Victoria of East Africa.(a) Habitat loss and fragmentation(b) Over-exploitation(c) Alien species invasions(d) Co-extinctions
›Reveal solutionSolution
The Nile perch, an alien predatory fish introduced into Lake Victoria, wiped out the native cichlid fish population — a classic case of extinction caused by alien species invasion.
The introduction of the predatory Nile perch (an alien/exotic species) into Lake Victoria in East Africa is a well-known ecological example of how alien species invasions can drive native species to extinction — it eventually led to the extinction of the lake's more than 200 endemic species of cichlid fish. This is distinct from habitat loss/fragmentation (destruction of natural habitat), over-exploitation (excessive harvesting, e.g., of Steller's sea cow or the …
- CBSE 2020Set ANNUAL1 markMCQQ.Which one of the following is regarded as 'terror of Bengal'?(a) Bryophyllum(b) Water hyacinth(c) Strobilanthus kunthiana(d) Banana
›Reveal solutionSolution
Water hyacinth is the classic invasive alien species famously called the "terror of Bengal" for choking Indian water bodies.
Water hyacinth (Eichhornia crassipes), a free-floating aquatic plant native to South America, was introduced into India as an ornamental plant but escaped and became one of the world's most notorious invasive alien species. It reproduces and spreads extremely rapidly (both vegetatively via stolons and via seeds), forming dense floating mats that cover the entire surface of ponds, lakes, canals and other water bodies. This unchecked growth blocks sunlight from reaching submerged plants, depletes dissolved oxygen (harming fish and other aquatic life), obstructs waterways/irrigation and navigation, and displaces native aquatic biodiversity — its extensive damage in West Bengal's …
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