Biodiversity

The living world exhibits an astonishing array of diversity and complexity. This variety extends from the microscopic level of macromolecules within cells to the grand scale of biomes. The term Biodiversity, popularized by sociobiologist Edward Wilson, refers to the combined diversity present at all levels of biological organization.

Key levels of biological diversity are:

1. Genetic diversity: The diversity of genes within a single species. A species with high genetic diversity (variation in alleles) is better able to adapt to environmental changes. Example: The medicinal plant Rauwolfia vomitoria shows genetic variation in the potency and concentration of the chemical reserpine it produces across different Himalayan ranges. India boasts over 50,000 genetically distinct strains of rice and 1,000 varieties of mango.
2. Species diversity: The variety of different species in a specific area. This includes both species richness (number of species) and species evenness (relative abundance of species). Example: The Western Ghats in India have a greater diversity of amphibian species compared to the Eastern Ghats.
3. Ecological diversity: The variety of different types of ecosystems within a geographical region. Example: India, with its diverse landscapes including deserts, rainforests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows, exhibits much greater ecosystem diversity than a country like Norway, which has a more uniform landscape.

This vast biological diversity has accumulated over millions of years of evolution. However, at current rates of species loss, a significant portion of this diversity could be lost within a few centuries. Biodiversity and its conservation have become critical international environmental issues as awareness grows about their importance for human survival and well-being.

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How Many Species Are There On Earth And How Many In India?

While the International Union for Conservation of Nature (IUCN) (2004) reported just over 1.5 million described species of plants and animals, the total number of species on Earth is likely much higher, with many yet to be discovered and described. Estimates for the total global species diversity vary widely (from 20 to 50 million), but a more conservative and widely accepted estimate by Robert May places the total number at about 7 million.

Currently available data shows interesting patterns:

• Animals constitute over 70% of all recorded species, while plants (including algae, fungi, bryophytes, gymnosperms, and angiosperms) make up about 22%.
• Among animals, insects are the most diverse group, accounting for over 70% of all animal species (7 out of every 10 animals on Earth are insects).
• The number of fungal species globally is greater than the combined number of species of fishes, amphibians, reptiles, and mammals.

These estimates typically do not include prokaryotes (bacteria and archaea) because conventional taxonomic methods are not well-suited for them, and many are not culturable. If molecular criteria were used, the diversity of prokaryotes alone could be in the millions.

India, despite having only 2.4% of the world's land area, is home to about 8.1% of the global species diversity, making it one of the 12 mega-diversity countries of the world. Approximately 45,000 species of plants and twice as many species of animals have been recorded in India so far.

Applying Robert May's estimate (only 22% of global species described), India is estimated to have over 100,000 plant species and over 300,000 animal species yet to be discovered and described. The process of cataloguing this vast biological wealth is a challenge due to the required trained personnel and time. Furthermore, many species are facing extinction even before they are discovered.

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Patterns Of Biodiversity

Species diversity is not uniform across the globe but shows distinct patterns:

1. Latitudinal gradients: Species diversity generally decreases as one moves away from the equator towards the poles. Tropical regions ($23.5^\circ$ N to $23.5^\circ$ S) typically have much higher species richness than temperate or polar regions.
   • Example: Colombia (near the equator) has ~1,400 bird species, while New York ($41^\circ$ N) has 105, and Greenland ($71^\circ$ N) has only 56. India, being largely in the tropics, has over 1,200 bird species.
   • A tropical forest can have significantly more plant species than an equivalent area in a temperate forest. The Amazon rainforest in South America is the most biodiverse region on Earth, home to millions of species across various taxa.
   Hypotheses for higher tropical diversity: (a) Time: Tropics, unlike temperate regions affected by past glaciations, have been relatively undisturbed for millions of years, providing more evolutionary time for speciation. (b) Stable environment: Tropical climates are less seasonal and more constant, promoting niche specialization and potentially leading to greater species diversity. (c) Higher productivity: Greater solar energy in the tropics leads to higher primary productivity, which could indirectly support higher species richness.
2. Species-Area relationships: As observed by Alexander von Humboldt, within a region, species richness increases with increasing explored area, but only up to a certain limit. The relationship between species richness (S) and area (A) is typically a rectangular hyperbola.
   On a logarithmic scale, the relationship is a straight line described by the equation: $\log S = \log C + Z \log A$, where S is species richness, A is area, Z is the slope of the line (regression coefficient), and C is the Y-intercept.
   • For smaller areas, the Z value typically ranges between 0.1 and 0.2, regardless of the taxonomic group or region.
   • However, for very large areas (like entire continents), the slope (Z value) is steeper, ranging from 0.6 to 1.2. For frugivorous birds and mammals across different continents, Z is about 1.15. Steeper slopes imply that exploring larger areas yields a much higher number of new species.

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The Importance Of Species Diversity To The Ecosystem

Does the number of species in a community affect the functioning of an ecosystem? While a definitive answer is debated, ecologists generally believe that higher species diversity contributes to ecosystem stability and health.

A stable community is thought to show:

• Less year-to-year variation in productivity.
• Resistance or resilience to occasional natural or man-made disturbances.
• Resistance to invasion by alien species.

David Tilman's experiments with outdoor plots showed that increased species richness led to less year-to-year variation in total biomass and higher productivity. This suggests that greater biodiversity contributes to ecosystem stability and productivity.

Biodiversity is not only crucial for ecosystem health but also essential for human survival. The loss of species raises questions about its impact on ecosystem function and human quality of life. The 'rivet popper hypothesis' by Paul Ehrlich uses an analogy of an airplane (ecosystem) with rivets (species) to illustrate that while the loss of a few species might not immediately cause noticeable problems, the cumulative loss weakens the system, and the loss of key species (like rivets on wings) can have severe consequences.

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Loss Of Biodiversity

While speciation adds new species over long timescales, species are currently being lost at an alarming rate due to human activities. The IUCN Red List (2004) documented the extinction of 784 species in the last 500 years, including birds, mammals, and plants. Examples of recent extinctions include the dodo, quagga, thylacine, and Steller’s Sea Cow. Some taxonomic groups, like amphibians, appear more vulnerable.

Globally, over 15,500 species are currently threatened with extinction (e.g., 12% of bird species, 23% of mammals, 32% of amphibians, 31% of gymnosperms face extinction threat).

Earth's history includes five episodes of mass extinction, but the current 'Sixth Extinction' is different due to its speed. Current extinction rates are estimated to be 100 to 1,000 times faster than pre-human times, driven by human activities. Ecologists warn that nearly half of all species could be extinct within the next century if current trends continue.

Loss of biodiversity can lead to a decline in plant production, reduced ecosystem resilience to environmental disturbances (like drought), and increased variability in ecosystem processes (like plant productivity, water use, pest/disease cycles).

Major causes of biodiversity losses ('The Evil Quartet'):

1. Habitat loss and fragmentation: The most significant driver of extinction. Tropical rainforests, once covering 14% of Earth's land, now cover only 6% and are rapidly disappearing due to deforestation for agriculture (soybean, cattle grazing). Habitat degradation by pollution also contributes. Fragmentation breaks large habitats into small, isolated pieces, negatively affecting species requiring large territories or with migratory habits.
2. Over-exploitation: Excessive harvesting of natural resources driven by human greed beyond sustainable levels. Examples: extinction of Steller’s sea cow and passenger pigeon due to overexploitation. Many commercially important marine fish populations are currently overharvested.
3. Alien species invasions: Introduction of non-native (alien) species (accidentally or deliberately) into an area. Some alien species become invasive, outcompeting or preying on native species, leading to their decline or extinction. Examples: Nile perch causing extinction of cichlid fish in Lake Victoria, invasive weeds like Parthenium, Lantana, water hyacinth (Eichhornia) in India, illegal introduction of African catfish threatening native Indian catfishes.
4. Co-extinctions: The extinction of a species leading to the extinction of other species that are obligatorily associated with it. Example: Extinction of a host fish species leads to the extinction of its specific parasites. Extinction of a plant species can lead to the extinction of its specific pollinator species in a co-evolved mutualism.

Biodiversity Conservation

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Why Should We Conserve Biodiversity?

Conserving biodiversity is essential for numerous reasons, often grouped into three categories:

1. Narrowly utilitarian: Direct economic benefits derived from biodiversity.
   • Food (cereals, pulses, fruits).
   • Fuelwood, fiber, construction material.
   • Industrial products (tannins, lubricants, dyes, resins, perfumes).
   • Products of medicinal importance: Over 25% of modern medicines are derived from plants. 25,000 plant species contribute to traditional medicines. Many more potentially useful medicinal plants may exist in tropical forests.
   Bioprospecting (exploring biodiversity for commercially valuable products) holds significant economic potential for biodiversity-rich nations.
2. Broadly utilitarian: The large-scale benefits provided by biodiversity through ecosystem services, which are crucial for planetary and human health.
   • Oxygen production: The Amazon rainforest is estimated to produce 20% of Earth's atmospheric oxygen through photosynthesis.
   • Pollination: Ecosystems provide pollinators (bees, birds, bats) essential for the production of fruits and seeds from many plants.
   • Climate regulation, flood control, soil formation, nutrient cycling, aesthetic value (enjoyment of nature).
3. Ethical: Our moral and spiritual obligations to other species.
   • Every species has an intrinsic value, independent of its usefulness to humans.
   • We share the planet with millions of other species and have a moral duty to ensure their well-being.
   • It is our ethical responsibility to protect our biological legacy and pass it on to future generations in a healthy state.

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How Do We Conserve Biodiversity?

Biodiversity conservation strategies aim to protect species and their habitats. The two main approaches are *in situ* and *ex situ* conservation.

1. In situ (On-site) conservation: Protecting species in their natural habitats. This approach conserves the entire ecosystem and all its biodiversity levels.
   • Given limited resources, conservation efforts often focus on biodiversity hotspots: regions with high levels of species richness and a high degree of endemism (species found nowhere else). These are also areas facing accelerated habitat loss.
   • Initially 25 hotspots were identified, now totalling 34 globally.
   • Three hotspots in India: Western Ghats and Sri Lanka, Indo-Burma, and Himalaya. These areas, despite covering less than 2% of Earth's land, could significantly reduce mass extinctions if strictly protected.
   • In India, ecologically rich regions are legally protected as Biosphere Reserves (14), National Parks (90), and Wildlife Sanctuaries (448).
   • India also has a tradition of protecting nature through Sacred Groves: tracts of forest set aside and protected based on religious/cultural beliefs. Examples: Khasi and Jaintia Hills (Meghalaya), Aravalli Hills (Rajasthan), Western Ghats (Karnataka/Maharashtra), Sarguja, Chanda, Bastar (Madhya Pradesh). Sacred groves often serve as last refuges for rare and threatened plants.
2. Ex situ (Off-site) conservation: Protecting threatened species by taking them out of their natural habitats and placing them in special settings for protection and care.
   • Examples: Zoological parks (for animals), Botanical gardens (for plants), and Wildlife Safari parks. These serve as refuges for species that might be extinct in the wild.
   • Modern ex situ techniques include Cryopreservation: preserving gametes (sperms, eggs) of threatened species in viable condition at very low temperatures for long periods.
   • In vitro fertilisation: Fertilizing eggs outside the body to create embryos.
   • Tissue culture: Propagating plants from cells or tissues in a lab.
   • Seed banks: Storing seeds of different genetic strains of commercially important plants for long-term preservation.

Biodiversity conservation is a global responsibility, transcending political boundaries. The 1992 Earth Summit in Rio de Janeiro called for international action on biodiversity conservation and sustainable use. The 2002 World Summit on Sustainable Development aimed for a significant reduction in biodiversity loss rates by 2010.

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