Chapter Notes

Biodiversity

Biodiversity, a term popularized by sociobiologist Edward Wilson, describes the immense variety of life on Earth. This diversity, or heterogeneity, exists at all levels of biological organization, from the molecules inside cells to entire biomes.

The three most important levels of biodiversity are:

• Genetic diversity: This refers to the variation of genes within a single species. For example, the medicinal plant Rauwolfia vomitoria found in different parts of the Himalayas shows genetic diversity in the potency and concentration of the chemical reserpine it produces. India has over 50,000 genetically different strains of rice and 1,000 varieties of mango.
• Species diversity: This is the variety of different species within a region. For instance, the Western Ghats have a greater diversity of amphibian species than the Eastern Ghats.
• Ecological diversity: This refers to the variety of ecosystems. India, with its deserts, rain forests, mangroves, coral reefs, wetlands, and alpine meadows, has a greater ecological diversity than a Scandinavian country like Norway.

This rich diversity has taken millions of years of evolution to develop. However, if the current rate of species loss continues, we could lose this wealth in less than two centuries.

How Many Species are there on Earth and How Many in India?

According to the International Union for Conservation of Nature and Natural Resources (IUCN) (2004), the total number of plant and animal species described so far is slightly more than 1.5 million. However, this is only a fraction of the total species on Earth, as many have yet to be discovered.

A conservative and scientifically sound estimate by Robert May places the global species diversity at about 7 million.

Key facts about global species distribution:

• More than 70% of all recorded species are animals.
• Plants (including algae, fungi, bryophytes, gymnosperms, and angiosperms) make up no more than 22% of the total.
• Among animals, insects are the most species-rich group, accounting for over 70% of the total. This means 7 out of every 10 animals on the planet are insects.
• The number of fungi species is greater than the combined total of all fish, amphibian, reptile, and mammal species.
• Estimates for prokaryotic species are uncertain because conventional identification methods are unsuitable, but their diversity could be in the millions.

India's Biodiversity:

• India has only 2.4% of the world's land area but holds an impressive 8.1% of the global species diversity.
• This makes India one of the 12 mega diversity countries in the world.
• Nearly 45,000 species of plants and twice as many (around 90,000) species of animals have been recorded from India.
• If we apply Robert May's global estimates, there are likely more than $1,00,000$ plant species and more than $3,00,000$ animal species in India yet to be discovered.

Patterns of Biodiversity

Biodiversity is not evenly distributed across the globe. It follows certain patterns.

Latitudinal gradients

The most well-known pattern is the increase in species diversity as one moves from the poles towards the equator. Tropical regions (latitudinal range of $23.5^{\circ} \mathrm{N}$ to $23.5^{\circ} \mathrm{S}$) have more species than temperate or polar areas.

• Colombia (near the equator) has nearly 1,400 bird species.
• New York (at $41^{\circ} \mathrm{N}$) has 105 bird species.
• Greenland (at $71^{\circ} \mathrm{N}$) has only 56 bird species.
• The Amazonian rain forest in South America has the greatest biodiversity on Earth, with over 40,000 plant species, 3,000 fish species, 1,300 bird species, and millions of insect species.

Hypotheses for higher tropical biodiversity:

1. Longer Evolutionary Time: Tropical latitudes have remained relatively undisturbed for millions of years, unlike temperate regions which experienced frequent glaciations. This long, stable period allowed for more time for species diversification.
2. Constant Environment: Tropical environments are less seasonal and more predictable. This promotes niche specialisation and leads to greater species diversity.
3. More Solar Energy: The tropics receive more solar energy, which leads to higher productivity. This higher productivity can support a greater diversity of life.

Species-Area relationships

The German naturalist Alexander von Humboldt observed that within a region, species richness increases with increasing explored area, but only up to a certain limit. This relationship, when plotted, forms a rectangular hyperbola.

On a logarithmic scale, this relationship is a straight line described by the equation: $\log \mathrm{S}=\log \mathrm{C}+\mathrm{Z} \log \mathrm{A}$ Where:

• $\mathrm{S}$ = Species richness
• $\mathrm{A}$ = Area
• $\mathrm{Z}$ = Slope of the line (regression coefficient)
• $\mathrm{C}$ = Y-intercept

The value of Z (slope) is significant:

• For small areas, the Z value typically lies in the range of 0.1 to 0.2, regardless of the taxonomic group or region.
• For very large areas, like entire continents, the slope is much steeper, with Z values in the range of 0.6 to 1.2. A steeper slope indicates that species richness increases more rapidly with an increase in area.

The importance of Species Diversity to the Ecosystem

Ecologists believe that communities with more species are generally more stable than those with fewer species.

A stable community has the following characteristics:

• It does not show too much year-to-year variation in productivity.
• It is resistant or resilient to occasional disturbances (natural or man-made).
• It is resistant to invasions by alien species.

David Tilman's long-term ecosystem experiments showed that:

• Plots with more species showed less year-to-year variation in total biomass.
• Increased diversity contributed to higher productivity.

• An airplane represents the ecosystem.
• The rivets holding the airplane together represent species.
• If every passenger starts taking a rivet home (causing a species to become extinct), the plane (ecosystem) may not be affected initially.
• However, as more rivets are removed, the plane becomes dangerously weak.
• Furthermore, removing a rivet from the wing (key species) is a more serious threat to flight safety than removing a rivet from a seat or window. Key species are those that drive major ecosystem functions.

Loss of Biodiversity

The biological wealth of our planet is declining rapidly due to human activities. The IUCN Red List (2004) documents the extinction of 784 species in the last 500 years.

Examples of recent extinctions:

• Dodo (Mauritius)
• Quagga (Africa)
• Thylacine (Australia)
• Steller's Sea Cow (Russia)
• Three subspecies of tiger (Bali, Javan, Caspian)

Currently, more than 15,500 species worldwide are facing the threat of extinction.

• 12% of all bird species
• 23% of all mammal species
• 32% of all amphibian species
• 31% of all gymnosperm species

The Sixth Extinction

Fossil records show five previous episodes of mass extinction in Earth's history. The current wave of extinction is called the Sixth Extinction. It is different from previous episodes because the current extinction rates are estimated to be 100 to 1,000 times faster than in pre-human times, and human activities are the primary cause.

Consequences of biodiversity loss:

• Decline in plant production.
• Lowered resistance to environmental disturbances like drought.
• Increased variability in ecosystem processes like plant productivity, water use, and pest/disease cycles.

Causes of biodiversity losses: ‘The Evil Quartet’

There are four major causes for the accelerated rates of species extinction:

1. Habitat loss and fragmentation: This is the most important cause. Tropical rain forests, which once covered 14% of the Earth's land, now cover no more than 6%. They are being cleared for agriculture (e.g., cultivating soya beans) or for raising livestock. Breaking up large habitats into small fragments badly affects animals requiring large territories or those with migratory habits.
2. Over-exploitation: When human need turns to greed, it leads to the over-harvesting of natural resources. The extinction of Steller's sea cow and the passenger pigeon was due to over-exploitation. Many marine fish populations are now over-harvested.
3. Alien species invasions: When new species are introduced into an ecosystem, they can become invasive and cause the decline or extinction of native species.
   • The introduction of the Nile perch into Lake Victoria in East Africa led to the extinction of over 200 species of native cichlid fish.
   • Invasive weeds in India like carrot grass (Parthenium), Lantana, and water hyacinth (Eicchornia) threaten native species.
   • The illegal introduction of the African catfish (Clarias gariepinus) is a threat to indigenous catfishes in Indian rivers.
4. Co-extinctions: When one species becomes extinct, other species that depend on it in an obligatory way also become extinct. For example, when a host fish species becomes extinct, its unique parasites also vanish. Similarly, in a coevolved plant-pollinator relationship, the extinction of one leads to the extinction of the other.

Biodiversity Conservation

Why Should We Conserve Biodiversity?

There are three main categories of reasons for conserving biodiversity:

1. Narrowly utilitarian: These are the direct economic benefits humans derive from nature.

   • Food: cereals, pulses, fruits.
   • Resources: firewood, fibre, construction material.
   • Industrial products: tannins, lubricants, dyes, resins, perfumes.
   • Medicines: More than 25% of drugs sold worldwide are derived from plants.
   • Bioprospecting: Exploring molecular, genetic, and species-level diversity for products of economic importance.

2. Broadly utilitarian: This refers to the essential services that ecosystems provide.

   • Oxygen Production: The Amazon forest is estimated to produce 20% of the total oxygen in the Earth's atmosphere through photosynthesis.
   • Pollination: Bees, bumblebees, birds, and bats provide pollination services without which we wouldn't have fruits or seeds.
   • Aesthetic Value: The intangible benefits we get from nature, such as the pleasure of walking through a forest or listening to birdsong.

3. Ethical: This argument relates to our moral duty.

   • Every species has an intrinsic value, even if it has no direct economic value to us.
   • We have a moral responsibility to care for all living organisms and pass on our biological legacy to future generations.

How do we conserve Biodiversity?

There are two main approaches to conservation:

In situ (on site) conservation

This approach involves conserving and protecting the entire ecosystem to protect its biodiversity at all levels. We save the whole forest to save the tiger.

• Biodiversity hotspots: These are regions with very high levels of species richness and a high degree of endemism (species found only in that region and nowhere else). There are now 34 biodiversity hotspots in the world. Protecting these hotspots could reduce the ongoing mass extinctions by almost 30%.
• Three hotspots cover India's high biodiversity regions: Western Ghats and Sri Lanka, Indo-Burma, and Himalaya.
• Protected Areas in India: Ecologically unique and biodiversity-rich regions are legally protected as:
  • 14 Biosphere Reserves
  • 90 National Parks
  • 448 Wildlife Sanctuaries
• Sacred Groves: These are tracts of forest set aside and given total protection due to religious and cultural traditions. They are found in places like the Khasi and Jaintia Hills in Meghalaya and the Aravalli Hills of Rajasthan. They serve as refuges for rare and threatened plants.

Ex situ (off site) conservation

In this approach, threatened animals and plants are taken from their natural habitat and placed in special settings where they can be protected and cared for.

• Facilities: Zoological parks, botanical gardens, and wildlife safari parks.
• Advanced Techniques:
  • Cryopreservation: Preserving gametes of threatened species in a viable and fertile condition for long periods at very low temperatures.
  • In vitro fertilisation: Fertilising eggs outside the body.
  • Tissue culture: Propagating plants using small tissue samples.
  • Seed banks: Storing seeds of different genetic strains of commercially important plants for long periods.

International Efforts for Conservation

• The Earth Summit (Convention on Biological Diversity): Held in Rio de Janeiro in 1992, it called upon all nations to take measures for biodiversity conservation and the sustainable use of its benefits.
• The World Summit on Sustainable Development: Held in Johannesburg, South Africa, in 2002, where 190 countries pledged to significantly reduce the rate of biodiversity loss by 2010.