Maarg Manthan · Topic 3.8

Endemic Species, Keystone Species, Indicator Species, Invasive Species

Environment & Ecology › Population Ecology and Species Interactions · Topic 3.8

Four kinds of species are often asked together. An endemic species is restricted to a particular geographic region and found nowhere else, such as the Nilgiri tahr and the lion-tailed macaque in the Western Ghats. A keystone species has a disproportionately large effect on its ecosystem relative to its numbers, and its loss changes the community greatly; the term was coined by Robert Paine in 1969 after his study of the starfish Pisaster. An indicator species is sensitive to environmental change and shows the condition of an ecosystem, like lichens for air quality. An invasive alien species is a non-native species that spreads rapidly, outcompetes natives and harms biodiversity, economy or health, such as Lantana camara, water hyacinth, Parthenium and Prosopis juliflora in India.

5 min read · UPSC Prelims · Environment & Ecology · Population Ecology and Species Interactions

At a Glance

Endemic Found only in one region
Keystone Big effect, small numbers
Indicator Shows environmental health
Invasive Alien that spreads
Term keystone by Robert Paine, 1969
Exam link UPSC Prelims, Environment & Ecology: Population Ecology and Species Interactions

Where Does It Fit?

This topic follows the account of ecotones. It explains four species categories that appear in many Prelims questions and links with the later macros on biodiversity and conservation. Previous topic: Ecotone. Next topic: Allopatric and Sympatric Speciation.

What Are Endemic and Keystone Species?

Category	Meaning and examples
Endemic species	Confined to a specific area, often islands, mountains or biodiversity hotspots. India examples: Nilgiri tahr, lion-tailed macaque, Malabar civet, Nilgiri laughingthrush, Kashmir stag (hangul, endemic to Kashmir), pygmy hog (Assam), Andaman wild pig
Why endemics matter	They are vulnerable to extinction because of small ranges, and they define hotspots. Over 30 percent of Indian flowering plants are endemic
Keystone species	A species whose impact on the community is much larger than its biomass. Robert Paine removed the starfish Pisaster from rocky shores in 1969, and mussels took over and diversity fell
Examples of keystone species	Tigers and wolves (top predators), elephants (create clearings and disperse seeds), sea otters (control urchins that eat kelp), fig trees (feed many animals in the lean season), beavers, bats and bees (pollinators), mangrove trees
Keystone versus dominant	A dominant species has influence from high numbers. A keystone species has influence from its role
Keystone role types	Predators, mutualists such as pollinators, engineers and prey
Loss effect	Trophic cascade and loss of other species

What Are Indicator and Invasive Species?

Indicator species: lichens (air pollution), frogs and amphibians (water and habitat quality), stonefly and mayfly larvae (clean streams), tubifex worms (organic pollution), coliform bacteria (faecal pollution), and corals (ocean temperature)
Invasive alien species: alien species that establish in new areas and spread, harming natives
Plants in India: Lantana camara, Parthenium hysterophorus (carrot grass), Eichhornia crassipes (water hyacinth), Prosopis juliflora, Mikania micrantha (mile-a-minute), Chromolaena odorata, Ageratum
Animals: African catfish (Clarias gariepinus), Nile tilapia, red-eared slider turtle and giant African snail
World examples: cane toad in Australia, Nile perch in Lake Victoria, zebra mussel in North America, Burmese python in Florida, rabbits in Australia
Why successful: no natural enemies, high reproduction, wide tolerance, human help
Impacts: loss of native species, change in habitat, damage to farming and fisheries, health problems, high control cost
Control: prevention, early detection, mechanical removal, biological control and awareness

What Else Should You Remember?

Invasive alien species: a leading cause of species loss, especially on islands, along with habitat loss
IUCN: maintains a database of the 100 worst invasive species
CBD: Convention on Biological Diversity asks parties to control invasive species, as in Article 8(h)
India’s law: the Biological Diversity Act, 2002 mentions regulating invasive species, and the Wildlife (Protection) Amendment Act, 2022 added provisions on invasive alien species
Wildlife Amendment Act 2022: empowers the Central Government to regulate or prohibit import and spread of invasive alien species
Lantana: introduced in India as an ornamental plant in the British period, now covers vast forest area
Water hyacinth: blocks lakes and lowers oxygen, called the terror of Bengal
Prosopis juliflora: spreads in dry areas and affects grassland
Mikania: smothers forest in north-east India and Kerala
Ballast water: ships carry species across oceans
Pet trade: release of exotic pets
Aquaculture: introduced fish can escape
Climate change: helps invaders to spread
Eradication example: rats were removed from some islands to protect birds
Indian endemic hotspots: Western Ghats, Himalaya, Indo-Burma and Sundaland
Amphibians: India has over 400 species, many endemic to the Western Ghats
Bioindicators: used for water quality in the Ganga
Link: types are summarised in Types of Species
Link to loss: invasion as a threat is in Causes of Biodiversity Loss
Link to hotspots: endemism defines Biodiversity Hotspots
Caution: the same plant can be useful in one place and a weed in another

Why Does It Matter for the Exam?

Endemic examples: Nilgiri tahr, lion-tailed macaque
Keystone: Paine, Pisaster
Indicators: lichens, frogs
Current affairs link: Wildlife Amendment Act 2022 and invasive species
Common errors: listing a native species as invasive or confusing keystone with dominant

As an analytical point, endemic species are the first to disappear when habitats shrink, keystone species decide how an ecosystem works, indicators give a cheap health check, and invasive species are an expanding threat. Management must address all four.

Why Is This Topic Important?

Endemic Only here
Keystone Big role
Invasive Alien threat

What Came Next?

The next topic covers allopatric and sympatric speciation. Next topic: Allopatric and Sympatric Speciation.

Key People and Terms

Endemism Restriction to a region
Keystone species Disproportionate effect species
Bioindicator Species showing conditions
Invasive alien species Harmful spreading alien
Trophic cascade Chain effect of predator
IAS Invasive alien species

Exam Corner

Points to Remember

Keystone term: Robert Paine, 1969, starfish.
Lichens are air pollution indicators.
Water hyacinth: terror of Bengal.
Lantana: introduced as ornamental.
Wildlife Act amended 2022 for invasive species.

Do Not Confuse With

Endemic and native Only in one region versus natural to a region
Keystone and dominant Role versus numbers
Invasive and alien Harmful spreader versus any introduced species

Memory Hook

Endemic: only here. Keystone: arch’s top stone. Indicator: canary in the mine. Invasive: the unwelcome spreader.

Mains Angle

Questions ask for definitions and Indian examples. These points help.

Types Four
Threat Invasives
Policy Laws

A Question You May Face

An original practice question, not a past paper question.

“Explain endemic, keystone, indicator and invasive alien species with examples and discuss the threat posed by invasive species in India.”

How to Answer

Define Four types.
Examples Indian.
Threat Invasives.
Policy Laws.

GS Relevance

Prelims: definitions with Indian examples, invasive plants and animals, laws. GS Paper 3: biodiversity.

Frequently Asked Questions

What is an endemic species?

An endemic species is one that is native to and restricted to a particular geographical region, and is found nowhere else in the world. Examples in India are the Nilgiri tahr and lion-tailed macaque of the Western Ghats, the hangul of Kashmir and the pygmy hog of Assam. Because of their small ranges, endemics are at high risk of extinction.

What is a keystone species?

A keystone species is one whose effect on its community is much greater than expected from its abundance, so that its removal causes major changes. The term was coined by Robert Paine in 1969 from his experiments with the starfish Pisaster. Tigers, elephants, sea otters and fig trees are examples.

What are indicator species?

Indicator species, or bioindicators, are organisms that are sensitive to changes in their environment and whose presence, absence or condition shows the health of an ecosystem. Lichens indicate clean air, frogs and stonefly larvae indicate clean water, and coliform bacteria indicate faecal pollution.

What is an invasive alien species?

An invasive alien species is a non-native species that has been introduced to a new area, establishes itself, spreads quickly and causes harm to native biodiversity, the economy or human health. Examples in India are Lantana camara, water hyacinth, Parthenium and Prosopis juliflora among plants, and the African catfish among animals.

Which Indian law was amended in 2022 to address invasive species?

The Wildlife (Protection) Amendment Act, 2022 added provisions that allow the Central Government to regulate or prohibit the import, trade, possession and spread of invasive alien species, which was a major change because the earlier Wildlife Protection Act, 1972 did not deal with them directly.

PYQ Practice — Statement Analysis

1 The lion-tailed macaque is endemic to the Western Ghats.

True

Found nowhere else.

2 The term keystone species was coined by Robert Paine.

True

In 1969.

3 Water hyacinth is a native Indian plant.

False

It is an invasive alien species.

4 Lichens are indicators of water pollution.