13.1 1. Biodiversity — Definition & The Three Levels
Immense diversity (heterogeneity) exists not only at the species level but at ALL levels of biological organisation — ranging from macromolecules within cells to biomes.
BIODIVERSITY is the term popularised by the sociobiologist EDWARD WILSON to describe the combined diversity at all the levels of biological organisation.
Learn the name. "Who popularised the term biodiversity?" is asked almost every year.
The three important components (levels) of biodiversity
| Level | What it means | NCERT's examples — memorise these exactly |
|---|
| 1. GENETIC diversity |
Diversity shown by a SINGLE species at the genetic level, over its distributional range |
• Rauwolfia vomitoria — a medicinal plant growing in different Himalayan ranges — shows genetic variation in the potency and concentration of the active chemical RESERPINE that it produces.
• India has more than 50,000 genetically different strains of RICE.
• India has 1,000 varieties of MANGO. |
| 2. SPECIES diversity |
Diversity at the species level — the number of species in an ecological community |
The WESTERN GHATS have a greater AMPHIBIAN species diversity than the Eastern Ghats. |
| 3. ECOLOGICAL diversity |
Diversity at the ecosystem level |
INDIA — with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries and alpine meadows — has a greater ecosystem diversity than a Scandinavian country like NORWAY. |
Genes within a species
(Rauwolfia, rice, mango)→
Species within a community
(Western Ghats amphibians)→
Ecosystems within a region
(India vs Norway)
Trap: "Genetic diversity" is within ONE species. If the question says "different species of amphibians", that is SPECIES diversity, not genetic.
13.2 2. How Many Species Are There? — The Global & Indian Number Bank
Global species numbers
| Statement | Number |
|---|
| IUCN (2004) — total plant + animal species described so far | slightly more than 1.5 million |
| Robert May's conservative, scientifically sound estimate of global species diversity | about 7 MILLION |
| Extreme (unreliable) estimates range | 20 to 50 million |
| Of described species, ANIMALS | more than 70 per cent |
| Of described species, PLANTS (algae, fungi, bryophytes, gymnosperms, angiosperms) | no more than 22 per cent |
| Among animals, INSECTS — the most species-rich taxonomic group | 70 per cent of all animals |
THE KILLER ONE-LINER: Out of every 10 animals on this planet, 7 are INSECTS.
THE OTHER ONE: The number of FUNGI species in the world is MORE than the COMBINED total of the species of fishes + amphibians + reptiles + mammals.
Why prokaryotes are under-counted
- Conventional taxonomic methods are NOT suitable for identifying microbial species.
- Many prokaryotes are NOT CULTURABLE under laboratory conditions.
- If biochemical or molecular criteria were applied, their diversity would rise to "biblical proportions".
India's share
| Statement | Number |
|---|
| India's share of the world's LAND area | only 2.4 per cent |
| India's share of global SPECIES diversity | an impressive 8.1 per cent |
| India is one of the world's | 12 MEGA-DIVERSITY COUNTRIES |
| Plant species recorded from India | nearly 45,000 |
| Animal species recorded from India | twice as many — nearly 90,000 |
| If only 22 per cent of species have been recorded, India still has yet to discover… | more than 1,00,000 plant species and more than 3,00,000 animal species |
Mnemonic: "Small land (2.4%), big life (8.1%)."
How do ecologists ESTIMATE the total number of species? (Exercise Q2)
Species inventories are more complete in TEMPERATE than in TROPICAL countries, yet an overwhelmingly large proportion of undiscovered species live in the tropics. So biologists:
Take an exhaustively studied group of INSECTS→
Make a STATISTICAL comparison of its temperate vs tropical species richness→
EXTRAPOLATE that ratio to other groups of animals and plants→
Arrive at a gross estimate of global species diversity
13.3 3. Pattern 1 — Latitudinal Gradients
THE RULE: Species diversity DECREASES as we move AWAY from the equator TOWARDS the poles.
With very few exceptions, TROPICS (latitudinal range of 23.5° N to 23.5° S) harbour MORE species than temperate or polar areas.
The bird gradient — memorise the four numbers
| Place | Latitude | Bird species |
|---|
| Colombia | near the equator | nearly 1,400 |
| India | much land in tropical latitudes | more than 1,200 |
| New York | 41° N | 105 |
| Greenland | 71° N | only 56 |
The plant gradient: a forest in a tropical region like ECUADOR has up to 10 TIMES as many species of VASCULAR PLANTS as a forest of equal area in a temperate region like the MIDWEST of the USA.
The Amazonian rain forest — the greatest biodiversity on Earth
| Group | Number of species |
|---|
| Plants | more than 40,000 |
| Fishes | 3,000 |
| Birds | 1,300 |
| Mammals | 427 |
| Amphibians | 427 |
| Reptiles | 378 |
| Invertebrates | more than 1,25,000 |
| Insects waiting to be discovered | at least 2 MILLION |
Memory hook: mammals and amphibians are BOTH 427. That coincidence is your anchor — build the rest around it.
The THREE hypotheses for tropical richness (Exercise Q3) — "TIME, CONSTANCY, ENERGY"
| Hypothesis | The argument |
|---|
(a) TIME
Speciation is a function of time |
Unlike temperate regions — which were subjected to frequent GLACIATIONS in the past — tropical latitudes have remained relatively UNDISTURBED for millions of years. They therefore had a long evolutionary time for species diversification. |
(b) CONSTANCY
Less seasonal, more predictable |
Tropical environments, unlike temperate ones, are LESS SEASONAL, relatively more CONSTANT and PREDICTABLE. Such constant environments promote NICHE SPECIALISATION, which leads to greater species diversity. |
(c) ENERGY
More solar energy |
There is more SOLAR ENERGY available in the tropics, which contributes to HIGHER PRODUCTIVITY — and this in turn might contribute INDIRECTLY to greater diversity. |
Note the hedge: the energy hypothesis is stated as contributing INDIRECTLY. Examiners love the word "indirectly" here.
13.4 4. Pattern 2 — The Species–Area Relationship (THE FORMULA)
Alexander von Humboldt — during his pioneering and extensive explorations in the SOUTH AMERICAN JUNGLES — observed that within a region species richness INCREASED with increasing explored AREA, but only UP TO A LIMIT.
Plot species richness (S) vs area (A)→
Curve is a RECTANGULAR HYPERBOLA→
Convert both axes to a LOGARITHMIC scale→
The relationship becomes a STRAIGHT LINE
THE EQUATION — write it exactly:
log S = log C + Z log A
S = Species richness
A = Area
Z = Slope of the line (also called the REGRESSION COEFFICIENT)
C = Y-intercept
(In non-log form: S = C·AZ)
The Z values — three numbers, three contexts
| Context | Z value | NCERT's examples |
|---|
| SMALL areas — within a region |
0.1 to 0.2 |
Amazingly similar regardless of the taxonomic group or the region — whether it is plants in Britain, birds in California, or molluscs in New York state. |
| VERY LARGE areas — entire continents |
0.6 to 1.2
(the slope is much STEEPER) |
— |
| Frugivorous (fruit-eating) birds and mammals in the tropical forests of different continents |
1.15 |
The single most-tested specific Z value. |
Which taxa did Humboldt-style analyses cover? Angiosperm plants, birds, bats, freshwater fishes — a wide variety of taxa, all giving the same rectangular hyperbola.
Significance of the slope (Exercise Q4): Z tells you HOW FAST species richness rises with area. A small Z (0.1–0.2) means richness climbs slowly — you are sampling within one region, so you keep meeting the same species pool. A large Z (0.6–1.2) means richness climbs steeply — across continents, each new area brings an entirely different species pool. That the small-area Z is so consistent across taxa and continents is what makes the relationship a genuine ecological law, not an accident.
13.5 5. The Importance of Species Diversity — Tilman & the Rivet Popper
Does the number of species in a community really matter to the functioning of an ecosystem? Ecologists have not been able to give a definitive answer — but the evidence points one way.
The core belief: Communities with MORE species tend to be MORE STABLE than those with fewer species.
What does STABILITY actually mean? (three conditions)
| # | A stable community… |
|---|
| 1 | does NOT show much variation in PRODUCTIVITY from year to year |
| 2 | is either RESISTANT or RESILIENT to occasional DISTURBANCES (natural or man-made) |
| 3 | is RESISTANT to INVASIONS by ALIEN species |
Mnemonic: "Steady, Sturdy, Sealed." Steady productivity · Sturdy against disturbance · Sealed against aliens.
David Tilman's outdoor-plot experiments
Tilman ran long-term ecosystem experiments using OUTDOOR PLOTS. His findings:
- Plots with MORE SPECIES showed LESS year-to-year VARIATION in total BIOMASS.
- Increased diversity contributed to HIGHER PRODUCTIVITY.
Two results, two different variables: more species → less variation AND more productivity. Questions often swap them. Learn both.
Paul Ehrlich's RIVET POPPER HYPOTHESIS
| In the analogy | In reality |
|---|
| The AIRPLANE | The ECOSYSTEM |
| The thousands of RIVETS holding it together | The SPECIES |
| A PASSENGER popping a rivet to take home | A species driven to EXTINCTION by humans |
| Rivets on the WINGS | KEY species — losing them is a serious threat |
| Rivets on the SEATS or WINDOWS | Less critical species — losing a few is survivable |
Passengers start popping rivets→
Initially flight safety is NOT affected→
As more rivets are removed, the plane becomes DANGEROUSLY WEAK→
WHICH rivet is popped is critical — WING rivets matter far more than SEAT rivets
NCERT's conclusion: Rich biodiversity is not only essential for ecosystem health but IMPERATIVE for the very SURVIVAL OF THE HUMAN RACE on this planet.
13.6 6. Loss of Biodiversity — The Sixth Extinction
It is doubtful whether any new species are being added (through speciation) to the Earth's treasury — but there is no doubt about the continuing losses. The accusing finger points clearly at human activities.
The extinction number bank
| Statement | Number |
|---|
| Native bird species lost to the colonisation of tropical Pacific Islands by humans | more than 2,000 |
| IUCN Red List (2004) — species extinct in the last 500 years | 784 |
| → of which vertebrates | 338 |
| → of which invertebrates | 359 |
| → of which plants | 87 |
| Species that disappeared in the last 20 years alone | 27 |
| Species currently facing the threat of extinction worldwide | 15,500 |
Check the arithmetic: 338 + 359 + 87 = 784. Note that invertebrates (359) OUTNUMBER vertebrates (338) — a favourite trick option.
Recent extinctions — species and their homes
| Species | Region |
|---|
| Dodo | Mauritius |
| Quagga | Africa |
| Thylacine | Australia |
| Steller's Sea Cow | Russia |
| Three subspecies of TIGER | Bali, Javan, Caspian |
Extinctions are NOT random
Careful analysis shows that extinctions across taxa are not random — some groups are more vulnerable. NCERT singles out AMPHIBIANS.
| Group | % of all species facing the threat of extinction |
|---|
| Amphibians | 32% ← highest |
| Gymnosperms | 31% |
| Mammals | 23% |
| Birds | 12% ← lowest |
Mnemonic — descending order: A > G > M > B → 32, 31, 23, 12. ("Amphibians Get Massacred Badly.")
THE SIXTH EXTINCTION
Current species extinction rates are estimated to be 100 to 1,000 TIMES FASTER than in pre-human times — and our activities are responsible.
Ecologists warn that if the present trends continue, NEARLY HALF OF ALL THE SPECIES ON EARTH might be wiped out within the next 100 YEARS.
Consequences of biodiversity loss in a region (three)
- Decline in plant PRODUCTION
- Lowered RESISTANCE to environmental perturbations such as drought
- Increased VARIABILITY in certain ecosystem processes — plant productivity, water use, and pest and disease cycles
13.7 7. Causes of Biodiversity Loss — THE EVIL QUARTET
Mnemonic: "Humans Over-Ate Creation" → H-O-A-C
Habitat loss and fragmentation · Over-exploitation · Alien species invasions · Co-extinctions
1. HABITAT LOSS AND FRAGMENTATION — the MOST IMPORTANT cause
- This is the most important cause driving animals and plants to extinction.
- Most dramatic example: the TROPICAL RAIN FORESTS — once covering more than 14 per cent of the earth's land surface, they now cover no more than 6 per cent.
- The Amazon rain forest — so huge it is called the 'LUNGS OF THE PLANET' — harbours probably millions of species and is being cut and cleared for cultivating SOYA BEANS or for conversion to grasslands for raising BEEF CATTLE.
- Besides total loss, the DEGRADATION of many habitats by POLLUTION also threatens the survival of many species.
- When large habitats are broken up into small FRAGMENTS, mammals and birds requiring LARGE TERRITORIES, and certain animals with MIGRATORY habits, are badly affected — leading to population declines.
14% of land surface→ tropical rain forests →
now no more than 6%
2. OVER-EXPLOITATION
- Humans have always depended on nature, but when 'NEED' turns to 'GREED', it leads to over-exploitation.
- Many species extinctions in the last 500 years — the STELLER'S SEA COW and the PASSENGER PIGEON — were due to over-exploitation by humans.
- Presently many MARINE FISH populations around the world are over-harvested, endangering the continued existence of some commercially important species.
3. ALIEN SPECIES INVASIONS
| Invader | Where | Damage |
|---|
| Nile perch |
Introduced into LAKE VICTORIA, east Africa |
Led eventually to the extinction of an ecologically unique assemblage of MORE THAN 200 SPECIES of CICHLID FISH in the lake |
| Carrot grass (Parthenium), Lantana, Water hyacinth (Eichhornia) |
India |
Invasive WEED species causing environmental damage and posing a threat to native species |
| African catfish (Clarias gariepinus) |
Illegally introduced into Indian rivers for AQUACULTURE |
Posing a threat to the indigenous catfishes in our rivers |
Definition: alien species may be introduced unintentionally OR deliberately. Some turn invasive and cause decline or extinction of indigenous species.
4. CO-EXTINCTIONS
- When a species becomes extinct, the plant and animal species associated with it in an OBLIGATORY way also become extinct.
- Example 1: when a HOST FISH species becomes extinct, its unique assemblage of PARASITES also meets the same fate.
- Example 2: a CO-EVOLVED PLANT–POLLINATOR MUTUALISM — the extinction of one invariably leads to the extinction of the other.
Cross-link to Ch 11: the fig–wasp one-to-one mutualism and the Ophrys–bee system are exactly the kind of relationships that would produce co-extinction.
13.8 8. Why Should We Conserve Biodiversity? — Three Categories
Mnemonic: "Nature's Bounty and Ethics" → N-B-E
Narrowly utilitarian · Broadly utilitarian · Ethical
1. NARROWLY UTILITARIAN — direct economic benefits
| Benefit | Examples |
|---|
| Food | cereals, pulses, fruits |
| Materials | firewood, fibre, construction material |
| Industrial products | tannins, lubricants, dyes, resins, perfumes |
| Medicines | products of medicinal importance |
- More than 25 per cent of the drugs currently sold in the market worldwide are derived from PLANTS.
- 25,000 species of plants contribute to the traditional medicines used by native peoples around the world.
- BIOPROSPECTING = exploring molecular, genetic and species-level diversity for products of economic importance. Nations endowed with rich biodiversity can expect to reap enormous benefits from it.
2. BROADLY UTILITARIAN — ecosystem services
| Service | Detail |
|---|
| Oxygen | The fast-dwindling AMAZON forest is estimated to produce, through photosynthesis, 20 PER CENT of the total oxygen in the earth's atmosphere |
| Pollination | Without it, plants cannot give us fruits or seeds. Provided by BEES, BUMBLEBEES, BIRDS and BATS |
| Intangible / aesthetic | The aesthetic pleasures — walking through thick woods, watching spring flowers in full bloom, waking up to a bulbul's song. Can we put a price tag on them? |
3. ETHICAL
Every species has an INTRINSIC VALUE, even if it may not be of current or any economic value to us. We have a MORAL DUTY to care for their well-being and to pass on our biological legacy in good order to future generations.
Flood & soil-erosion control by biotic components (Exercise Q8)
- Roots BIND soil particles together, preventing erosion by wind and water.
- The canopy INTERCEPTS rainfall, reducing the force with which drops strike the soil.
- Litter and humus INCREASE INFILTRATION and the soil's water-holding capacity.
- Vegetation SLOWS surface run-off, so water percolates instead of rushing off as flood.
- Deforestation therefore directly increases flooding, siltation and soil erosion.
13.9 9. How Do We Conserve Biodiversity? — In Situ vs Ex Situ
| Feature | IN SITU (on site) | EX SITU (off site) |
|---|
| Where | In the natural habitat | Outside the natural habitat |
| What is protected | The WHOLE ECOSYSTEM — so biodiversity at all levels is protected | Individual threatened species, given special care |
| Slogan | "Save the entire FOREST to save the TIGER" | "Take it out and protect it" |
| Examples | Biodiversity hotspots, biosphere reserves, national parks, wildlife sanctuaries, sacred groves | Zoological parks, botanical gardens, wildlife safari parks, cryopreservation, in vitro fertilisation, tissue culture, seed banks |
IN SITU — Biodiversity Hotspots
Conservationists identified regions with (a) very high levels of SPECIES RICHNESS and (b) a high degree of ENDEMISM — species confined to that region and not found anywhere else — for maximum protection. These are biodiversity hotspots.
| Fact | Number |
|---|
| Hotspots identified initially | 25 |
| Subsequently added | 9 more |
| TOTAL hotspots in the world | 34 |
| Land area they cover, all put together | LESS THAN 2 per cent of the earth's land area |
| Reduction in ongoing mass extinctions from strict protection of hotspots | by almost 30 PER CENT |
Hotspots are also regions of ACCELERATED HABITAT LOSS. That is precisely why they are urgent.
THE THREE INDIAN HOTSPOTS — mnemonic "We Indians Have":
(i) Western Ghats and Sri Lanka
(ii) Indo-Burma
(iii) Himalaya
IN SITU — India's legally protected areas
14 Biosphere Reserves|
90 National Parks|
448 Wildlife Sanctuaries
IN SITU — SACRED GROVES (Exercise Q7)
India has a history of religious and cultural traditions that emphasised protection of nature. In many cultures, tracts of forest were set aside, and all the trees and wildlife within were VENERATED and given TOTAL PROTECTION.
| Where sacred groves are found | Region |
|---|
| Khasi and Jaintia Hills | Meghalaya |
| Aravalli Hills | Rajasthan |
| Western Ghat regions | Karnataka and Maharashtra |
| Sarguja, Chanda and Bastar areas | Madhya Pradesh |
In MEGHALAYA, the sacred groves are the LAST REFUGES for a large number of RARE and THREATENED PLANTS.
Their role: community-driven, culturally enforced IN SITU conservation — the whole habitat is protected, not just a species.
EX SITU — the modern toolkit
| Method | What it does |
|---|
| Zoological parks, botanical gardens, wildlife safari parks | Threatened plants and animals are taken out of their natural habitat and placed in a special setting with protection and special care. Many animals extinct in the wild continue to be maintained in zoological parks. |
| CRYOPRESERVATION | Gametes of threatened species preserved in viable and fertile condition for long periods |
| IN VITRO fertilisation | Eggs can be fertilised in vitro |
| TISSUE CULTURE | Plants can be propagated using tissue culture methods |
| SEED BANKS | Seeds of different genetic strains of commercially important plants kept for long periods |
Mnemonic for the modern ex situ toolkit: "C-I-T-S" — Cryopreservation · In vitro fertilisation · Tissue culture · Seed banks.
International conservation efforts
Biodiversity knows no political boundaries — its conservation is therefore a collective responsibility of all nations.
| Year | Event | Outcome |
|---|
| 1992 |
The EARTH SUMMIT, held in RIO DE JANEIRO |
Called upon all nations to take appropriate measures for the conservation of biodiversity and the sustainable utilisation of its benefits |
| 2002 |
The WORLD SUMMIT ON SUSTAINABLE DEVELOPMENT, held in JOHANNESBURG, SOUTH AFRICA |
190 COUNTRIES pledged their commitment to achieve, by 2010, a significant reduction in the current rate of biodiversity loss at global, regional and local levels |
Do not mix these up: Rio = 1992. Johannesburg = 2002, 190 countries, 2010 target.
13.10 10. Cheat Sheet — Every Number, Name & Exercise Answer
THE FORMULA
log S = log C + Z log A
S = species richness · A = area · Z = slope of the line = regression coefficient · C = Y-intercept
Small areas: Z = 0.1–0.2 · Continents: Z = 0.6–1.2 · Frugivorous birds & mammals: Z = 1.15
THE PEOPLE
| Name | What they did |
|---|
| Edward Wilson | Sociobiologist who popularised the term BIODIVERSITY |
| Alexander von Humboldt | Observed the species–area relationship during explorations of the South American jungles |
| Robert May | Conservative global species estimate: about 7 million |
| David Tilman | Outdoor-plot experiments: more species → less year-to-year variation in biomass AND higher productivity |
| Paul Ehrlich | The RIVET POPPER hypothesis |
THE FULL NUMBER BANK
| Category | Numbers |
|---|
| Global species | Described (IUCN 2004): >1.5 million · Robert May's estimate: 7 million · Extreme estimates: 20–50 million |
| Composition | Animals >70% · Plants ≤22% · Insects = 70% of animals (7 of every 10 animals) · Fungi > fishes + amphibians + reptiles + mammals combined |
| India | Land area 2.4% · Species share 8.1% · One of 12 mega-diversity countries · 45,000 plants · 90,000 animals · yet to find: >1,00,000 plants, >3,00,000 animals |
| Latitude | Tropics = 23.5° N to 23.5° S · Colombia 1,400 birds · India >1,200 · New York (41° N) 105 · Greenland (71° N) 56 · Ecuador forest = 10× the vascular plants of a Midwest-USA forest |
| Amazon | Plants >40,000 · Fishes 3,000 · Birds 1,300 · Mammals 427 · Amphibians 427 · Reptiles 378 · Invertebrates >1,25,000 · Undiscovered insects ≥2 million · Produces 20% of atmospheric oxygen · Called the 'lungs of the planet' |
| Extinction | Pacific Island birds lost: >2,000 · IUCN 2004: 784 = 338 vertebrates + 359 invertebrates + 87 plants (in 500 years) · Last 20 years: 27 species · Currently threatened: 15,500 · Rate: 100–1,000× faster than pre-human · Half of all species could go in 100 years |
| % facing extinction | Amphibians 32% > Gymnosperms 31% > Mammals 23% > Birds 12% |
| Habitat loss | Tropical rain forests: once >14% of land surface → now ≤6% |
| Alien invasion | Nile perch in Lake Victoria wiped out >200 species of cichlid fish |
| Medicine | >25% of drugs sold worldwide come from plants · 25,000 plant species used in traditional medicine |
| Hotspots | 25 + 9 = 34 · cover <2% of land · strict protection could cut mass extinctions by ~30% · 3 in India |
| India's protected areas | 14 biosphere reserves · 90 national parks · 448 wildlife sanctuaries |
| Summits | Rio de Janeiro 1992 (Earth Summit) · Johannesburg 2002 (World Summit on Sustainable Development, 190 countries, 2010 target) |
EXERCISE ANSWER KEY
| Q | Answer in one line |
|---|
| 1. Three components of biodiversity | Genetic, Species and Ecological diversity |
| 2. How ecologists estimate total species | Statistical comparison of temperate vs tropical species richness of an exhaustively studied insect group, then extrapolate the ratio to other taxa |
| 3. Three hypotheses for tropical richness | TIME (undisturbed by glaciations, long evolutionary time) · CONSTANCY (less seasonal, predictable → niche specialisation) · ENERGY (more solar energy → higher productivity → indirectly more diversity) |
| 4. Significance of the slope of regression | Z shows how fast richness rises with area. It is 0.1–0.2 within a region regardless of taxon, but 0.6–1.2 across continents. The consistency of the small-area Z is what makes it a real ecological law. |
| 5. Major causes of species loss | The EVIL QUARTET — habitat loss and fragmentation, over-exploitation, alien species invasions, co-extinctions |
| 6. Importance of biodiversity for ecosystem functioning | Stability (steady productivity, resistance/resilience to disturbance, resistance to invasion) · Tilman (more species → less biomass variation and higher productivity) · Rivet Popper (loss of key species threatens the whole system) |
| 7. Sacred groves and their role | Tracts of forest set aside, with all trees and wildlife venerated and given TOTAL protection. Found in Khasi & Jaintia Hills (Meghalaya), Aravalli Hills (Rajasthan), Western Ghats (Karnataka & Maharashtra), Sarguja, Chanda & Bastar (MP). In Meghalaya they are the last refuges of many rare and threatened plants. They are community-driven IN SITU conservation. |
| 8. Flood and soil-erosion control | Roots bind soil · canopy intercepts rain · litter increases infiltration · vegetation slows run-off so water percolates instead of flooding |
| 9. Why animals (72%) diversified more than plants (22%) | Greater MOTILITY — animals can escape adverse conditions and colonise new habitats · Complex, sensitive NERVOUS SYSTEMS to perceive and respond to the environment · Rigid EXOSKELETON in arthropods, giving protection and support · better overall adaptability |
| 10. A species we deliberately want extinct | YES — disease-causing pathogens. The SMALLPOX VIRUS was deliberately eradicated worldwide through vaccination. Justification: human welfare — it caused enormous suffering and death, and its removal harms no ecosystem service. |