Alien Species Invasion (Nile Perch, Lantana, Parthenium, Clarias)
Biology · Biodiversity and Conservation · NEET
Alien species invasion is the third cause in the Evil Quartet of biodiversity loss. When a species from outside is introduced into a new area (by accident or on purpose), some of them turn invasive and cause the decline or extinction of the native (indigenous) species. Memory hook: "NLPC" - Nile perch, Lantana, Parthenium, Clarias - these four NCERT names win you the mark.
The four NCERT examples of alien species invasion split into fish (Nile perch, Clarias gariepinus) and invasive weeds (Parthenium, Lantana, water hyacinth). All are non-native species introduced accidentally or deliberately, causing native species to decline or go extinct.
Your doubts, answered
What exactly is an 'alien species' in NCERT?
An alien species is a species introduced into an area where it does not naturally live. It comes from outside that region. NCERT says these are introduced either unintentionally (by accident) or deliberately (on purpose, for example for farming). Most stay harmless, but SOME turn invasive and harm the native species. So 'alien' just means 'not native to that place'.
Why did the Nile perch cause so much damage in Lake Victoria?
The Nile perch is a large predatory fish that was introduced into Lake Victoria in East Africa. It ate and out-competed the native fish. NCERT states this led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish in the lake. Remember the number: MORE THAN 200 cichlid species. NTA loves this exact figure.
Is Clarias gariepinus an example of alien invasion or over-exploitation?
Alien species invasion. Clarias gariepinus is the African catfish, illegally introduced for aquaculture. It threatens our native (indigenous) catfishes in Indian rivers. Because it was BROUGHT IN from outside and harms native fish, it is alien invasion - NOT over-exploitation (which means humans harvesting too much). The NEET 2026 paper tested exactly this trap with the Yamuna river.
Which examples are plants and which are animals?
Animals (fish): Nile perch and Clarias gariepinus (African catfish). Plants (invasive weeds): carrot grass (Parthenium), Lantana, and water hyacinth (Eichhornia). Do not mix these up - NEET often gives you a name and asks its category. Fish = Nile perch and Clarias; weeds = Parthenium, Lantana, water hyacinth.
Is alien invasion the most important cause of extinction?
No. Among the Evil Quartet, NCERT clearly says HABITAT LOSS AND FRAGMENTATION is the most important cause. Alien species invasion is a real cause but it is NOT ranked first. This is a very common NTA trap - if a question asks for the 'most important' cause, the answer is habitat loss, not alien invasion.
⚠️ The NEET trap ✗ Clarias gariepinus declining native fish in the Yamuna = over-exploitation (because fish are being harmed). ✓ It is ALIEN SPECIES INVASION. Clarias is an introduced (foreign) catfish. Over-exploitation means humans harvesting a species too much; here the harm comes from an introduced species out-competing natives. 🧠 If a NON-NATIVE species is INTRODUCED and harms natives, it is always alien invasion - never over-exploitation.
Real NEET questions
NEET 2026
Decline in the population of Indian native fishes due to introduction of Clarias gariepinus in river Yamuna can be categorised as
A · Co-extinction
B · Habitat fragmentation
C · Over exploitation
D · Alien species invasion ✓
Solution: Clarias gariepinus (the African catfish) is an introduced alien species. The decline of native fishes after its introduction is a classic case of alien species invasion, one of the Evil Quartet. It is not co-extinction (needs an obligate associated species), not habitat fragmentation, and not over-exploitation (which means human harvesting). NCERT Ch 13, p.223: 'The recent illegal introduction of the African catfish Clarias gariepinus for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.'
NEET 2016 · 2023
Which of the following is correctly matched?
A · Aerenchyma – Opuntia
B · Age pyramid – Biome
C · Parthenium hysterophorus – Threat to Biodiversity ✓
D · Stratification – Population
Solution: Parthenium (carrot grass) is named in NCERT as an invasive alien weed that threatens native species - one of the Evil Quartet causes of biodiversity loss - so this pairing is correct. The other options are wrong pairings from other chapters (aerenchyma belongs to hydrophytes, not the desert cactus Opuntia). NCERT Ch 13, p.223: 'invasive weed species like carrot grass (Parthenium), Lantana and water hyacinth (Eicchornia).'
NEET 2025
Match List I with List II: A. The Evil Quartet, B. Ex situ conservation, C. Lantana camara, D. Dodo — with I. Cryopreservation, II. Alien species invasion, III. Causes of biodiversity losses, IV. Extinction.
A · A-III, B-IV, C-II, D-I
B · A-III, B-II, C-IV, D-I
C · A-III, B-II, C-I, D-IV
D · A-III, B-I, C-II, D-IV ✓
Solution: The Evil Quartet is the sobriquet for the four major causes of biodiversity losses (A-III). Ex situ conservation uses cryopreservation of gametes (B-I). Lantana camara is an invasive alien weed species (C-II). The dodo of Mauritius is a classic recent extinction (D-IV). Only option (d) matches all four correctly.
Solved Biodiversity and Conservation NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the introduction of a non-native species into an area where some of them turn invasive and cause the decline or extinction of native species. It is the third member of the Evil Quartet.
What are the four NCERT examples of alien species invasion?
Nile perch (Lake Victoria, extinguished 200+ cichlid species), carrot grass (Parthenium), Lantana, and water hyacinth (Eichhornia) as invasive weeds, and the African catfish Clarias gariepinus threatening native Indian catfishes.
How many cichlid fish species did the Nile perch wipe out?
More than 200 species of cichlid fish in Lake Victoria became extinct. This exact number is a favourite NEET fact.
What is the scientific name of water hyacinth and carrot grass?
Water hyacinth is Eichhornia; carrot grass is Parthenium (Parthenium hysterophorus). Both are invasive alien weeds named in NCERT.
Is alien invasion or habitat loss the biggest cause of extinction?
Habitat loss and fragmentation is the most important cause per NCERT. Alien species invasion is one of the four causes but not ranked first - a frequent NEET trap.
