Invasive alien species

Topic: Biodiversity and its Conservation · NCERT: Class 11, Ch 14 "Biodiversity and Conservation"

Meaning

Invasive alien species (IAS) are exotic species (species brought into a place where they do not grow or live naturally) that spread fast and harm native plants, animals, ecosystems or people's livelihoods. They matter because they are a "hidden" driver of biodiversity loss. Invasive species played a part in about 60% of recorded extinctions and cost the world over US$423 billion a year (IPBES Invasive Alien Species Assessment, 2023).

Explanation

How a species gets into a new place

• Exotic species means any species brought into a habitat where it does not occur naturally.
• People bring it in two ways:
• On purpose: for gardens or fish farms.

• By accident: carried in ships or mixed in with grain.

• Not every exotic species becomes invasive. It becomes an invasive alien species only when it spreads fast and causes harm.

How an invasive species takes over

• It arrives with no natural enemies:
• The new place has no predators (animals that eat it) and no diseases that attack it.

• So nothing keeps its numbers in check.

• It grows and breeds faster than native species:

• It spreads over large areas in a short time.

• It takes the resources native species need:

• It takes over light, water, food and space.

• Native species get less, so their numbers fall.

• Result: the habitat changes. Grassland can turn into thicket, a lake surface can get covered, and native fish can be eaten.

Types of invasive species in India

Species	Type	Harm it does
Lantana camara	Shrub	Stops grass and tree seedlings from growing
Prosopis juliflora	Thorny tree	Turns grassland into thicket and reduces fodder (animal feed)
Water hyacinth	Floating water plant	Covers the water surface and cuts oxygen for fish
Parthenium (congress grass)	Weed	Harms crops and causes allergies
Mikania	Climbing vine	Smothers (covers and chokes) trees
African catfish	Fish	Eats native fish

Why islands suffer most

• Island species evolved with few predators around them.
• So they have little defence when a new species arrives.
• This is why native island species are the most at risk from introduced species.

Its place among the drivers of biodiversity loss

• The IPBES (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services) Global Assessment 2019 ranks five direct drivers of loss [2]: 1. Changes in land and sea use 2. Direct exploitation of organisms (hunting, fishing, logging) 3. Climate change 4. Pollution 5. Invasive alien species

• Invasive species are ranked fifth of the five [2]. Even so, they played a part in about 60% of recorded extinctions (IPBES 2023).

Where it occurs

• India:
• Lantana camara: forests across India, including tiger reserves.
• Prosopis juliflora: Banni grasslands, Kachchh (Gujarat).
• Water hyacinth: lakes, ponds and canals.
• Parthenium: farmland and wasteland.
• Mikania: forests of the North-East and the Western Ghats.

• African catfish: rivers and wetlands.

• World:

• Hawaii (Pacific Ocean): Class 11 NCERT uses it as the example of native island species threatened by introduced species.
• Globally: invasive species cost the world over US$423 billion a year (IPBES 2023).

Don't confuse with

• Exotic species vs invasive alien species: every species brought in from outside is exotic. It counts as invasive only when it spreads fast and causes harm. All invasive aliens are exotic, but not all exotics are invasive.
• Native species: these occur naturally in a place. Invasive species are the outsiders that push native species out.
• Endemic species: these are found only in one region and nowhere else. They are often the victims of invasives, especially on islands such as Hawaii.
• Habitat loss: this is the first and biggest driver in IPBES 2019, while invasive species come fifth [2]. Do not mix up the order.

Prelims Hooks

• Prosopis juliflora invasion → Banni grasslands, Kachchh, Gujarat.
• Mikania (a climbing vine) → forests of the North-East and Western Ghats.
• IPBES 2019 driver ranking: land and sea use change > direct exploitation > climate change > pollution > invasive alien species. Invasive species come fifth, i.e. last [2].
• IPBES Invasive Alien Species Assessment (2023): invasive species played a part in about 60% of recorded extinctions and cost over US$423 billion a year.
• Class 11 NCERT example of island species threatened by introduced species: Hawaii (Pacific Ocean).
• Trap: Parthenium is also called congress grass. It is a weed of farmland and wasteland, not a water plant. Water hyacinth is the floating water plant.

Mains Points

• Invasive species as a hidden driver (GS-III):
• Lantana in tiger reserves, Prosopis in Banni and water hyacinth in wetlands reduce native fodder, water and habitat.
• This hurts wildlife and also the herders and fishers who depend on these places.

• Invasives played a part in about 60% of recorded extinctions and cost over US$423 billion a year (IPBES 2023).

• Policy response:

• Early detection: find new invaders before they spread.
• Uprooting campaigns: for example, clearing Lantana from forests and Prosopis from grasslands.

• Controls on deliberate introductions: check species brought in for gardens and fish farms, such as African catfish, before they are released.

• Islands and fragile ecosystems need special care: species there evolved with few predators and have little defence, as Hawaii shows. In India, wetlands and grasslands such as Banni need targeted restoration (bringing the habitat back to its natural state).

Related concepts

• Loss of biodiversity
• Habitat loss
• Exotic species
• Poaching
• Overfishing
• Extinction
• IPBES
• Living Planet Report

Read more

• Loss of biodiversity: drivers and evidence