Biodiversity

Biodiversity refers to the variety of life on Earth at all its levels, encompassing genetic, species, and ecosystem diversity. It has taken millions of years of evolution to accumulate this rich variety, but human activities are causing rapid losses.

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

Globally, around 1.5 million species have been described, but estimates of total species range widely, possibly from 20 to 50 million, with a more accepted scientific estimate around 7 million. Most species are animals (over 70%), with insects being the most diverse group. Fungi species outnumber all vertebrate species combined. India, despite having only 2.4% of the world's land area, is one of the 12 mega-diverse countries, harboring about 8.1% of global species diversity, with an estimated 100,000 plant species and over 300,000 animal species yet to be discovered. The diversity of prokaryotes is largely unknown due to limitations in traditional taxonomic methods.

Patterns Of Biodiversity

Species diversity is not uniformly distributed across the globe. Key patterns include:

• Latitudinal Gradients: Species richness generally decreases from the equator towards the poles. Tropical regions (between 23.5° N and 23.5° S) have significantly higher species diversity than temperate or polar regions. Hypotheses for this include longer evolutionary time in the tropics (less affected by past glaciations), more stable and predictable environments promoting niche specialization, and greater solar energy availability contributing to higher productivity.
• Species-Area Relationships: Within a region, species richness increases with explored area, following a rectangular hyperbola. On a logarithmic scale, this relationship is linear ($log S = log C + Z log A$), with a slope (Z) typically between 0.1 and 0.2, regardless of the taxonomic group or region. For larger areas like continents, the slope becomes steeper (Z ≈ 0.6 to 1.2).

The Importance Of Species Diversity To The Ecosystem

While the exact relationship is complex, greater species diversity generally leads to more stable ecosystems. Stable communities exhibit less variation in productivity over time, are more resistant to disturbances (like drought or invasions by alien species), and are more resilient. The 'rivet popper hypothesis' suggests that ecosystems function like an airplane, with species as rivets. Removing a few rivets might not immediately affect safety, but losing key species (like rivets on wings) can critically destabilize the ecosystem.

Loss Of Biodiversity

Biodiversity is declining rapidly, primarily due to human activities. The current extinction rate is estimated to be 100-1000 times higher than in pre-human times. Almost 700 species have gone extinct in the last 500 years, and over 15,500 species worldwide are threatened. Amphibians appear particularly vulnerable.

The major causes of biodiversity loss (The 'Evil Quartet') are:

• Habitat Loss and Fragmentation: Destruction of habitats, especially tropical rainforests (now covering only 6% of land), for agriculture (soybeans, cattle ranching) and urban development. Fragmentation isolates populations, affecting migratory species and those needing large territories.
• Over-exploitation: Unsustainable harvesting of natural resources driven by human greed, leading to the extinction of species like the passenger pigeon and over-harvesting of marine fish.
• Alien Species Invasions: Introduction of non-native species can disrupt ecosystems and lead to the extinction of indigenous species (e.g., Nile perch in Lake Victoria, Parthenium weed in India).
• Co-extinctions: The extinction of one species leads to the extinction of other species dependent on it (e.g., host fish and its parasites, or plant-pollinator mutualisms).

Biodiversity Conservation

Conserving biodiversity is crucial for ecosystem health and human survival. Reasons for conservation are broadly categorized:

Why Should We Conserve Biodiversity?

• Narrowly Utilitarian: Direct economic benefits derived from nature, including food, firewood, fiber, construction materials, industrial products (tannins, dyes), and medicinal resources (over 25% of current drugs are from plants; traditional medicine uses thousands of plant species). Bioprospecting aims to discover new products from biodiversity.
• Broadly Utilitarian: Ecosystem services provided by biodiversity, such as oxygen production by forests (Amazon rainforest produces ~20% of global oxygen), pollination by animals (bees, bats, birds), aesthetic pleasures (walking in forests, enjoying nature), and regulation of climate and water cycles.
• Ethical: A moral obligation to protect all species, recognizing their intrinsic value regardless of their economic utility to humans. We must preserve our biological legacy for future generations.

How Do We Conserve Biodiversity?

Conservation strategies include both in situ and ex situ approaches:

• In Situ Conservation (On-site): Protecting species within their natural habitats and ecosystems. This involves conserving entire ecosystems, which implicitly protects all species within them. Key strategies include:
  • Biodiversity Hotspots: Regions with high species richness and high endemism (species found nowhere else), which are also under threat from habitat loss. Identifying and strictly protecting these hotspots (e.g., Western Ghats-Sri Lanka, Himalayas, Indo-Burma in India) can significantly reduce extinction rates.
  • Protected Areas: Legally protected regions like Biosphere Reserves, National Parks, and Wildlife Sanctuaries. India has 14 biosphere reserves, 90 national parks, and 448 wildlife sanctuaries.
  • Sacred Groves: Forest patches protected by cultural traditions, serving as refuges for rare and threatened species (found in regions like Meghalaya, Rajasthan, Karnataka, Maharashtra).
• Ex Situ Conservation (Off-site): Protecting species outside their natural habitats, usually for threatened or endangered species. Methods include:
  • Zoological parks and botanical gardens.
  • Wildlife safari parks.
  • Cryopreservation: Preserving gametes (sperm, eggs) at very low temperatures (-196°C).
  • In vitro fertilization and tissue culture techniques for propagation.
  • Seed banks: Storing seeds of commercially important plants for long-term preservation.

International cooperation is essential, as biodiversity transcends political boundaries. The Convention on Biological Diversity (Earth Summit, Rio de Janeiro, 1992) and the World Summit on Sustainable Development (Johannesburg, 2002) aimed to reduce biodiversity loss globally.

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