Why Losing One Pollinator Can Wipe Out a Plant Too

From the microbes in soil to the tigers of the Sundarbans, the variety of life keeps ecosystems productive and stable, supplies food, medicine and fibre, and pollinates crops.

This lesson covers what biodiversity is and how it is distributed, why it is being lost, how it is conserved, and the tools used to protect it.

Biodiversity is the variety of life at every level — genetic, species and ecological diversity — and it is richest in the tropics, falls towards the poles, and rises with the size of the area studied.

Levels of biodiversity:

- Genetic diversity — variation within a species, such as the many varieties of rice and mango grown in India
- Species diversity — the variety of species in an area; the Western Ghats hold more amphibian species than the Eastern Ghats
- Ecological diversity — the variety of ecosystems, such as deserts, rainforests, mangroves, coral reefs, wetlands and alpine meadows in India

Patterns of biodiversity:

- Latitudinal gradient — diversity generally decreases from the equator towards the poles, so tropical forests hold far more species than temperate ones
- Tropical richness is linked to a long, relatively undisturbed evolutionary history, a less seasonal and more predictable climate, and more solar energy
- Species-area relationship — species richness rises with area up to a limit:

$$\log S=\log C+Z\log A$$

where S is species richness, A is area, C is the intercept and Z is the slope, usually between 0.1 and 0.2 for smaller regions and much steeper when whole continents are compared.

An everyday example. A monsoon trek in the Western Ghats can reveal a remarkable variety of frogs, orchids and butterflies within a few kilometres.

The substance. India is one of the world's megadiverse countries — its range of habitats, from deserts to rainforests, gives it an unusually large share of species for its land area.

Biodiversity is lost mainly through habitat loss and fragmentation, over-exploitation, invasion by alien species and co-extinctions.

Causes of biodiversity loss:

- Habitat loss and fragmentation — clearing forests and breaking large habitats into small patches
- Over-exploitation — excessive hunting, fishing and harvesting; Steller's sea cow and the passenger pigeon were lost this way
- Alien species invasions — the Nile perch introduced into Lake Victoria wiped out many native cichlid fish, and weeds such as Lantana and water hyacinth threaten native plants in India
- Co-extinctions — when a species dies out, species that depend on it vanish too, such as a parasite whose only host disappears or a plant whose specialist pollinator is lost

Recently extinct species. The dodo of Mauritius, the quagga of Africa, the thylacine of Australia, Steller's sea cow of Russia, and the Bali, Javan and Caspian subspecies of tiger.

An everyday example. Lantana bushes spreading along forest edges in many Indian states crowd out native shrubs and the animals that feed on them.

The substance. Habitat loss is the most important cause of extinction — a species cannot survive without a place to live, so it affects far more species than hunting alone.

In-situ conservation protects species in their natural habitats, while ex-situ conservation protects them outside those habitats, in zoos, botanical gardens, seed banks and through cryopreservation.

In-situ (on-site) conservation:

- Protected areas — national parks, wildlife sanctuaries and biosphere reserves protect entire ecosystems
- Sacred groves — forest patches protected by communities for religious reasons, in the Khasi and Jaintia Hills of Meghalaya, the Aravalli Hills of Rajasthan, the Western Ghats of Karnataka and Maharashtra, and the Sarguja, Chanda and Bastar areas of central India

Ex-situ (off-site) conservation:

- Zoological parks, botanical gardens and wildlife safari parks — care for threatened animals and plants and support captive breeding
- Seed banks — store seeds of crop varieties and wild plants for long periods
- Cryopreservation — gametes and embryos stored in liquid nitrogen at -196 °C

An everyday example. Sacred groves in Meghalaya still shelter rare trees and orchids that have disappeared from the cleared land around them.

The substance. Ex-situ conservation is a backup, not a replacement — captive animals and stored seeds cannot keep evolving with their ecosystems the way wild populations do.

Hotspots mark highly threatened regions rich in endemic species, the Red Data Book records species by their risk of extinction, Ramsar sites are internationally important wetlands, and international conventions commit countries to protect biodiversity.

Biodiversity hotspots:

- Regions with very high species richness and endemism — species found nowhere else — that have lost much of their original habitat
- India includes parts of the Western Ghats and Sri Lanka, Indo-Burma, Himalaya and Sundaland hotspots

Red Data Book:

- A record of threatened species maintained by the IUCN (International Union for Conservation of Nature)
- Categories include extinct, extinct in the wild, critically endangered, endangered, vulnerable, near threatened and least concern

Ramsar sites:

- Wetlands designated as internationally important under the Ramsar Convention
- Indian examples include Chilika Lake in Odisha, Keoladeo National Park in Rajasthan and Loktak Lake in Manipur

International conventions:

- Convention on Biological Diversity (CBD) — countries agree to conserve biodiversity, use it sustainably and share its benefits fairly
- CITES — regulates international trade in endangered wild animals and plants

An everyday example. Large flocks of migratory birds that winter at Chilika Lake depend on the wetland protection that Ramsar designation supports.

The substance. Endemism, not species numbers alone, makes a hotspot — losing an endemic species there means losing it from the entire planet.