Species Adaptations, Extinction and Invasives

A recurring question in this cluster asks candidates to place a species' IUCN Red List category correctly, in the exact order from Extinct down to Least Concern, and a second recurring one asks which committee, Gadgil or Kasturirangan, recommended the larger Ecologically Sensitive Area in the Western Ghats. Both look like recall questions but are really precision traps: examiners swap adjacent categories, or swap which committee's number was bigger, betting that aspirants remember the topic but not the specific figure attached to it.

The sibling note Indian Wildlife and Biodiversity Hotspots covers the biodiversity hotspot definition, its two-part criteria, and India's four hotspots (Western Ghats and Sri Lanka, Himalaya, Indo-Burma, Sundaland) in depth. This note covers different ground entirely: how species physically adapt to extreme habitats, the IUCN Red List's extinction-risk framework, named invasive alien species and their damage in India, and the Gadgil versus Kasturirangan policy debate over how much of the Western Ghats should actually be protected.

Species adaptations

An adaptation is any morphological, physiological or behavioural trait that lets an organism survive and reproduce in its specific habitat, and UPSC tests this through named, verifiable examples rather than the general concept. Two habitat extremes recur most: deserts and high altitude.

Desert adaptations centre on water conservation rather than heat avoidance alone. The kangaroo rat of the Arizona desert never drinks water in its life: it meets its entire water requirement through internal oxidation of fat (metabolic water) and produces highly concentrated urine to minimise loss, while a thick coat limits evaporative water loss through the skin and it stays inside a comparatively cool, humid burrow through the heat of the day. The camel shows a parallel but distinct strategy, storing fat (not water) in its hump, which yields metabolic water when oxidised, and tolerating a several-degree daily swing in its own body temperature (heterothermy) so it does not need to sweat away water simply to stay at a fixed internal temperature. Desert lizards and snakes solve the same problem behaviourally rather than physiologically: they bask in the sun during the cooler early morning hours and burrow into the sand during the hottest part of the afternoon to escape peak heat, timing their activity around temperature rather than resisting it.

High-altitude adaptation works through the respiratory and circulatory systems responding to low atmospheric oxygen (low partial pressure of oxygen, or low pO2). The body compensates by increasing red blood cell production, so more haemoglobin is available to carry the scarcer oxygen, and by increasing the breathing rate, so more air (and therefore more oxygen) passes through the lungs per minute. These two responses work together and are the standard textbook answer whenever a question describes a person or animal acclimatising to a mountain environment.

This is deliberately distinct from the site's other Environment notes: Plant and Animal Classification Basics covers animal behaviour in the sense of communication and mutualism (the honeybee's waggle dance, fungus-farming ants), and Ecology and Ecosystem Functions covers plant-animal interactions built around pollination and seed dispersal. Neither covers the physiological survival adaptations above, which is this chapter's own ground.

The IUCN Red List categories

The IUCN Red List sorts every assessed species into one of nine categories, in a strict hierarchy of extinction risk, and UPSC likes to test the exact order and exact boundary between adjacent categories, not just the concept of "endangered species" in the abstract.

• Extinct (EX): there is no reasonable doubt that the last individual of the species has died.
• Extinct in the Wild (EW): the species survives only in cultivation, in captivity, or as a naturalised population well outside its past range, with no known wild population remaining in its native habitat.
• Critically Endangered (CR): faces an extremely high risk of extinction in the wild, the highest risk category for a species that is not yet extinct.
• Endangered (EN): faces a very high risk of extinction in the wild, one step below Critically Endangered.
• Vulnerable (VU): faces a high risk of extinction in the wild, one step below Endangered.
• Near Threatened (NT): does not currently qualify as Critically Endangered, Endangered or Vulnerable, but is close to qualifying, or is likely to qualify, for one of those categories in the near future.
• Least Concern (LC): does not qualify for any of the categories above; this covers widespread and abundant species and is the most common category by number of assessed species.
• Data Deficient (DD): there is inadequate information to make a direct or indirect assessment of extinction risk; this is not itself a threat category, it simply means more research is needed.
• Not Evaluated (NE): the species has not yet been assessed against the criteria at all.

Critically Endangered, Endangered and Vulnerable together are termed "threatened", the category UPSC most often means when a question simply says a species is "under threat" without naming a specific IUCN category. A frequent trap is treating Near Threatened as itself a threatened category; it is explicitly not one, it is a watch-list category one step below the threatened tier. Another is assuming Data Deficient means "safe" or "not a concern," when it only means the assessment could not be completed with the available evidence.

Invasive alien species

An invasive alien species is a non-native organism, introduced deliberately or accidentally, that establishes itself and causes demonstrable ecological or economic harm in its new range. India carries several well-documented cases, each tested through its specific introduction story and specific damage, not as an interchangeable list of "bad plants."

Lantana camara, a flowering shrub, was brought to India as an ornamental plant in the early 1800s. Over roughly two centuries, the originally introduced varieties hybridised into a complex able to grow as a climbing vine, a dense thicket, or a scrambling shrub, which is part of why it has proved so hard to eradicate. A 2020 study found it now occupies about 154,000 sq km of forest, more than 40% of India's tiger range by area, concentrated in the Shivalik Hills, Central India's fragmented deciduous forests, and the southern Western Ghats. Where it dominates, it outcompetes native undergrowth for space and light, alters soil nutrient cycling, and reduces the native forage available to wild herbivores; its leaves can trigger allergic reactions on animals' muzzles, and heavy feeding on it has been linked to diarrhoea, liver failure and death in livestock and wildlife. It is listed among the world's worst invasive species globally.

Parthenium hysterophorus, commonly called congress grass or carrot grass, is native to the American subtropics and reached India as a contaminant in imported grain shipments during the 1950s; the first case of parthenium-linked dermatitis in India was documented at Pune in 1968. It has since spread across much of the country and is now the single commonest cause of plant-linked contact dermatitis in India, responsible for close to 40% of patients seen at Indian contact dermatitis clinics, alongside allergic rhinitis in exposed populations and dermatitis, hair loss, diarrhoea and organ damage recorded in livestock that graze on it. Ecologically, it is strongly allelopathic: it releases substances that suppress the germination of other plants, so areas it dominates often support almost no other vegetation at all.

Water hyacinth (Eichhornia crassipes), a free-floating aquatic plant native to South America, was introduced to India in the early 19th century for its ornamental flowers. It spread so aggressively, especially across Bengal's water bodies, that it earned the nickname "terror of Bengal." It reproduces vegetatively through stolons and can double its population within about two weeks under favourable conditions, forming dense surface mats that block sunlight from reaching submerged plants and organisms; the eventual decomposition of that biomass depletes dissolved oxygen, lowers pH and raises carbon dioxide and hydrogen sulphide levels in the water, a combination that drives fish kills and broader biodiversity loss in the water body it colonises. It remains listed in the Global Invasive Species Database as one of the world's most problematic invasive plants.

The pattern across all three is worth holding onto directly: each was introduced deliberately, for an ordinary and often ornamental or agricultural reason, and each caused disproportionate ecological harm only after establishing itself, the standard shape of an invasive alien species problem.

Gadgil versus Kasturirangan: two views on the Western Ghats

This is the specific policy history UPSC tests under this chapter's own alias, and it turns on how much of the Western Ghats each committee wanted protected, and why the two numbers differ so much.

The Western Ghats Ecology Expert Panel (WGEEP), chaired by ecologist Madhav Gadgil and commonly called the Gadgil Committee, was constituted by the Union Ministry of Environment and Forests and submitted its report on 31 August 2011. It recommended that roughly 64% of the entire Western Ghats (the full range spans about 1.64 lakh sq km across six states) be declared an Ecologically Sensitive Area, graded into three tiers, Ecologically Sensitive Zones 1, 2 and 3, by decreasing fragility, with the strictest restrictions (on mining, large dams, thermal power plants and similar activities) applied to the most sensitive zone. It also proposed a new authority, the Western Ghats Ecology Authority, to oversee this regime, and took what is generally described as a bottom-up, environment-first approach. State governments resisted it strongly, arguing it was impractical: applying strict, blanket ecological restrictions across almost two-thirds of the entire range, uniformly, was seen as a serious threat to mining, hydropower, plantation agriculture and other livelihoods across the six states the range touches, without enough granular distinction between genuinely pristine forest and land that was already inhabited or cultivated.

In response to that pushback, the ministry constituted a second body, the High Level Working Group (HLWG), chaired by space scientist K. Kasturirangan, on 17 August 2012, specifically to review the Gadgil report, and it submitted its own report in April 2013. It took a narrower and more development-accommodating approach: rather than grading the whole range by fragility, it first split the Western Ghats into a "cultural" landscape (existing habitations, farms and plantations) and a "natural" landscape, and then recommended Ecologically Sensitive Area status only for a large share of the natural landscape, arriving at a final figure of about 37% of the total Western Ghats area, roughly 59,940 to 60,000 sq km, well under Gadgil's 64%. Within that area, it identified specific villages across the six states, more than 4,000 in total, as falling inside the proposed ESA. It banned the most damaging activities outright inside that zone, mining, quarrying, thermal power plants and red-category industries, while explicitly trying to keep existing agriculture and habitation outside the restricted area.

The Kasturirangan report still drew real opposition, especially from Kerala, where villages containing plantations and other non-forest, already-inhabited land were nonetheless mapped inside the proposed ESA boundary, creating confusion and protest among residents who depended on that land for their livelihood. More than a decade on, the underlying disagreement remains unresolved: the Union government has issued several successive draft notifications attempting to formally declare a Western Ghats Eco-Sensitive Area (the most recent proposing roughly 56,825 sq km, close to the Kasturirangan figure), but as of 2026 no version has been finalised, because the six Western Ghats states still have not reached consensus on the exact boundary.

The one-line summary worth keeping in mind for the exam: Gadgil (2011) wanted a bigger area (about 64%) under strict, tiered protection, driven primarily by ecological criteria; Kasturirangan (2013), reviewing that report after state pushback, recommended a smaller area (about 37%) by separating already-inhabited "cultural" land out first, trying to balance conservation against development and livelihood concerns.

Why this is tested

This chapter rewards knowing the specific number attached to a specific name, not the general shape of the topic. The IUCN category questions almost always hinge on ordering, whether Near Threatened counts as "threatened" (it does not) or whether a species one notch apart in the hierarchy has been swapped in a statement. The invasive species questions test the specific introduction story, ornamental water hyacinth versus contaminant-grain Parthenium versus ornamental Lantana, since these are easy to confuse when studied as an undifferentiated list. The Gadgil versus Kasturirangan question is the single most repeated trap in this cluster: examiners bank on aspirants remembering that "one committee wanted more protection than the other" without remembering which one, so fix the direction firmly, Gadgil's number is the larger one, and Kasturirangan's revision came later and was smaller.

Quick revision points

• Desert adaptations: kangaroo rat survives on metabolic water and concentrated urine; camel stores fat (not water) in its hump and tolerates daily body-temperature swings (heterothermy); desert lizards bask at dawn and burrow through peak afternoon heat.
• High-altitude adaptation: low pO2 is compensated by increased red blood cell production and increased breathing rate.
• IUCN Red List order: Extinct, Extinct in the Wild, Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern, plus Data Deficient and Not Evaluated outside the risk gradient.
• Critically Endangered, Endangered, Vulnerable together = "threatened"; Near Threatened is one step below that tier, not part of it.
• Lantana camara: ornamental introduction, early 1800s; now over 40% of India's tiger range by forest area.
• Parthenium hysterophorus: arrived as a 1950s grain-shipment contaminant; first Indian dermatitis case recorded at Pune, 1968; now the leading cause of plant-linked contact dermatitis in India.
• Water hyacinth: ornamental introduction, early 19th century; "terror of Bengal"; can double its population in about two weeks; causes oxygen depletion and fish kills as it decomposes.
• Gadgil Committee (WGEEP, submitted 31 August 2011): recommended about 64% of the Western Ghats as Ecologically Sensitive Area, in three tiered zones (ESZ 1, 2, 3).
• Kasturirangan Committee (HLWG, constituted 17 August 2012, submitted April 2013): recommended about 37% (roughly 60,000 sq km) as ESA, after separating out already-inhabited "cultural" landscape; still unimplemented as of 2026 for lack of state consensus.

Try a few questions now to see whether you can hold the Gadgil and Kasturirangan numbers apart under pressure.