BIODIVERSITY AND CONSERVATION

BIODIVERSITY

The Earth exhibits an enormous diversity of life. This rich variety fascinates and astonishes, with examples like over 20,000 species of ants, 300,000 species of beetles, 28,000 species of fishes, and nearly 20,000 species of orchids.

Ecologists and evolutionary biologists study this diversity, posing questions such as why there are so many species, if such diversity always existed, how it diversified, its importance to the biosphere, how the biosphere would function with less diversity, and how humans benefit from it.

Biodiversity, a term popularized by sociobiologist Edward Wilson, describes the combined diversity at all levels of biological organisation. These levels include:

Levels of Biological Organisation

• Genetic diversity: High diversity within a single species over its distributional range.
  • Example: The medicinal plant Rauwolfia vomitoria shows genetic variation in the potency and concentration of reserpine across Himalayan ranges. India has over 50,000 genetically different strains of rice and 1,000 varieties of mango.
• Species diversity: Diversity at the species level.
  • Example: The Western Ghats have greater amphibian species diversity than the Eastern Ghats.
• Ecological diversity: Diversity at the ecosystem level.
  • Example: India, with its deserts, rainforests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows, has greater ecosystem diversity compared to a Scandinavian country like Norway.

It has taken millions of years of evolution to accumulate this diversity. However, this wealth could be lost in less than two centuries if current species loss rates continue. Biodiversity and its conservation are vital environmental issues of international concern due to their critical importance for human survival and well-being.

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

While discovered and named species are recorded, determining the total number of species on Earth is challenging.

• Recorded Species: According to the International Union for Conservation of Nature and Natural Resources (IUCN) (2004), slightly more than 1.5 million plant and animal species have been described so far.
• Estimates for Undiscovered Species: Estimates vary widely, with many being educated guesses. Species inventories are more complete in temperate regions than in tropical ones.
  • Considering most undiscovered species are in the tropics, biologists extrapolate from exhaustively studied insect groups.
  • Robert May’s conservative and scientifically sound estimate places the global species diversity at about 7 million. Extreme estimates range from 20 to 50 million.

Aspects of Earth’s Biodiversity (Based on Current Inventories)

• Animals: More than 70 percent of all recorded species.
  • Insects: The most species-rich taxonomic group among animals, making up more than 70 percent of the total (7 out of every 10 animals).
• Plants: (Including algae, fungi, bryophytes, gymnosperms, and angiosperms) comprise no more than 22 percent of the total.
• Fungi: The number of fungi species in the world is more than the combined total of fishes, amphibians, reptiles, and mammals.

Prokaryotes are not included in these estimates because conventional taxonomic methods are unsuitable for identifying microbial species, and many cannot be cultured in laboratories. If biochemical or molecular criteria were used, their diversity could run into millions.

India’s Biodiversity

India has only 2.4 percent of the world’s land area, but its share of global species diversity is an impressive 8.1 percent, making it one of the 12 mega diversity countries.

• Recorded Species in India: Nearly 45,000 species of plants and twice as many animals.
• Estimated Undiscovered Species (based on May’s global estimate): Probably more than 100,000 plant species and more than 300,000 animal species are yet to be discovered and described in India.
• Challenge: Completing this inventory requires immense trained manpower (taxonomists) and time. A large fraction of these species faces extinction even before discovery, likened to “Nature’s biological library burning” before its books are cataloged.

Patterns of Biodiversity

Latitudinal gradients

The diversity of plants and animals is not uniform globally, showing an uneven distribution.

• General Pattern: Species diversity decreases as we move away from the equator towards the poles.
• Tropics (23.5° N to 23.5° S): Harbour more species than temperate or polar areas.
  • Examples:
    • Colombia (near the equator) has nearly 1,400 species of birds, while New York (41° N) has 105, and Greenland (71° N) has only 56 species.
    • India, largely in tropical latitudes, has more than 1,200 species of birds.
    • A tropical forest (e.g., Ecuador) can have up to 10 times as many species of vascular plants as a temperate forest of equal area (e.g., Midwest USA).
  • Amazonian Rain Forest (South America): Possesses the greatest biodiversity on Earth.
    • Home to >40,000 plant species, 3,000 fishes, 1,300 birds, 427 mammals, 427 amphibians, 378 reptiles, and >125,000 invertebrates.
    • Scientists estimate at least 2 million insect species might be undiscovered in these forests.

Hypotheses for Greater Tropical Biodiversity

Ecologists and evolutionary biologists propose several reasons for the high diversity in the tropics:

• (a) Evolutionary Time: Tropical latitudes have remained relatively undisturbed for millions of years, unlike temperate regions subjected to frequent glaciations. This has provided a long evolutionary time for species diversification.
• (b) Constant Environment: Tropical environments are less seasonal, more constant, and predictable than temperate ones. Such stability promotes niche specialisation, leading to greater species diversity.
• (c) Solar Energy/Productivity: There is more solar energy available in the tropics, which contributes to higher productivity, potentially contributing indirectly to greater diversity.

Species-Area relationships

Alexander von Humboldt observed that within a region, species richness increased with increasing explored area, but only up to a limit.

• Graphical Representation: The relationship between species richness and area for a wide variety of taxa (plants, birds, bats, freshwater fishes) is a rectangular hyperbola.
• Logarithmic Scale: On a logarithmic scale, the relationship becomes a straight line.
  • Equation: log S = log C + Z log A
    • S = Species richness
    • A = Area
    • Z = Slope of the line (regression coefficient)
    • C = Y-intercept
• Value of Z:
  • For small areas, regardless of taxonomic group or region (e.g., plants in Britain, birds in California, molluscs in New York state), the value of Z lies in the range of 0.1 to 0.2.
  • For very large areas (e.g., entire continents), the slope of the line is much steeper, with Z values in the range of 0.6 to 1.2.
  • Example: For frugivorous (fruit-eating) birds and mammals in tropical forests across different continents, the slope is found to be 1.15.

The importance of Species Diversity to the Ecosystem

Ecologists have long believed that communities with more species generally tend to be more stable than those with fewer species.

Attributes of a Stable Community

A stable biological community should exhibit:

• Minimal Variation: Not too much variation in productivity from year to year.
• Resistance/Resilience: Resistance or resilience to occasional disturbances (natural or man-made).
• Resistance to Invasions: Resistance to invasions by alien species.

David Tilman’s long-term ecosystem experiments provided tentative answers:

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

Rich biodiversity is not only essential for ecosystem health but imperative for the very survival of the human race.

The ‘Rivet Popper Hypothesis’

Stanford ecologist Paul Ehrlich used the ‘rivet popper hypothesis’ to illustrate the importance of species diversity:

• Airplane: Represents the ecosystem.
• Rivets: Represent species.
• Popping a rivet (causing species extinction): Initially, it may not affect flight safety (proper ecosystem functioning).
• Cumulative Effect: As more and more rivets are removed, the plane becomes dangerously weak over time.
• Key Species: The loss of rivets on the wings (key species that drive major ecosystem functions) is a more serious threat to flight safety than the loss of a few rivets on seats or windows.

Loss of Biodiversity

The biological wealth of our planet is declining rapidly, primarily due to human activities.

• Historical Examples: Colonization of tropical Pacific Islands by humans led to the extinction of over 2,000 species of native birds.
• Recent Extinctions: The IUCN Red List (2004) documents the extinction of 784 species (338 vertebrates, 359 invertebrates, 87 plants) in the last 500 years.
  • Examples: Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller’s Sea Cow (Russia), and three subspecies of tiger (Bali, Javan, Caspian).
  • 27 species disappeared in the last twenty years alone.
  • Extinctions are not random; amphibians appear more vulnerable.

Threatened Species

• More than 15,500 species worldwide are facing the threat of extinction.
• Currently, 12% of all bird species, 23% of all mammal species, 32% of all amphibian species, and 31% of all gymnosperm species face this threat.

Mass Extinctions

• Earth’s history shows five previous episodes of mass extinction of species, occurring before humans.
• The current ‘Sixth Extinction’ differs significantly because the current species extinction rates are estimated to be 100 to 1,000 times faster than in pre-human times, with human activities being responsible for these accelerated rates.
• Ecologists warn that if current trends continue, nearly half of all species on Earth might be wiped out within the next 100 years.

Consequences of Biodiversity Loss in a Region

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

Causes of Biodiversity Losses: The ‘Evil Quartet’

The accelerated rates of species extinctions are largely due to human activities, categorized into four major causes:

• (i) Habitat loss and fragmentation: This is the most important cause driving species to extinction.
  • Tropical rain forests: Once covered >14% of Earth’s land surface, now less than 6% and are rapidly being destroyed.
  • The Amazon rain forest, known as the ‘lungs of the planet’, is being cleared for soybean cultivation or conversion to grasslands for beef cattle.
  • Habitat degradation by pollution also threatens species survival.
  • Fragmentation: Large habitats broken into small fragments due to human activities badly affect mammals and birds requiring large territories, and migratory animals, leading to population declines.
• (ii) Over-exploitation: When human ‘need’ turns into ‘greed’, leading to over-exploitation of natural resources.
  • Examples: Extinction of Steller’s sea cow and passenger pigeon were due to overexploitation.
  • Currently, many marine fish populations worldwide are over-harvested, endangering commercially important species.
• (iii) Alien species invasions: Introduced unintentionally or deliberately, some alien species become invasive and cause the decline or extinction of indigenous species.
  • Examples:
    • The Nile perch introduced into Lake Victoria led to the extinction of over 200 species of cichlid fish.
    • Invasive weed species like carrot grass (Parthenium), Lantana, and water hyacinth (Eicchornia) cause environmental damage and threaten native species.
    • The illegal introduction of the African catfish (Clarias gariepinus) for aquaculture poses a threat to indigenous catfishes in Indian rivers.
• (iv) Co-extinctions: When a species becomes extinct, the plant and animal species obligatorily associated with it also become extinct.
  • Examples:
    • Extinction of a host fish species leads to the extinction of its unique assemblage of parasites.
    • In a coevolved plant-pollinator mutualism, the extinction of one invariably leads to the extinction of the other.

BIODIVERSITY CONSERVATION

Why Should We Conserve Biodiversity?

Reasons for conserving biodiversity are grouped into three categories:

• (i) Narrowly utilitarian: Focuses on direct economic benefits humans derive from nature.
  • Products: Food (cereals, pulses, fruits), firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes), and medicinal products.
  • More than 25% of drugs sold worldwide are plant-derived, and 25,000 plant species contribute to traditional medicines.
  • Bioprospecting: Exploring molecular, genetic, and species-level diversity for economic products, offering enormous benefits to biodiversity-rich nations.
• (ii) Broadly utilitarian: Highlights biodiversity’s major role in providing ecosystem services.
  • Oxygen Production: The Amazon forest is estimated to produce 20% of the Earth’s total oxygen through photosynthesis.
  • Pollination: Ecosystems provide vital pollination services through pollinators like bees, bumblebees, birds, and bats, essential for fruit and seed production.
  • Intangible Benefits: Aesthetic pleasures such as walking through woods, watching flowers, or listening to bird songs.
• (iii) Ethical: Relates to the moral obligation to other species with whom we share the planet.
  • Every species has an intrinsic value, regardless of its current or future economic value to humans.
  • Humans have a moral duty to care for the well-being of species and pass on Earth’s biological legacy in good order to future generations.

How do we conserve Biodiversity?

Biodiversity conservation employs two main approaches:

In situ (on site) conservation

This approach involves protecting the entire ecosystem to conserve biodiversity at all levels. For example, saving an entire forest to protect the tiger.

• Biodiversity Hotspots: To maximize protection amidst limited resources, conservationists identified ‘biodiversity hotspots’ – regions with very high levels of species richness and a high degree of endemism (species confined to that region).
  • Initially 25, now 34 biodiversity hotspots globally.
  • These hotspots are also regions of accelerated habitat loss.
  • Three hotspots cover India’s high biodiversity regions: Western Ghats and Sri Lanka, Indo-Burma, and Himalaya.
  • Though these hotspots cover less than 2% of Earth’s land area, their strict protection could reduce ongoing mass extinctions by almost 30%.
• In-situ Conservation Efforts in India (Legally Protected Areas):
  • 14 biosphere reserves
  • 90 national parks
  • 448 wildlife sanctuaries
• Sacred Groves: India has a history of religious and cultural traditions emphasizing nature protection. Tracts of forest set aside and given total protection, with trees and wildlife venerated.
  • Locations: Khasi and Jaintia Hills (Meghalaya), Aravalli Hills (Rajasthan), Western Ghat regions (Karnataka and Maharashtra), and Sarguja, Chanda, and Bastar areas (Madhya Pradesh).
  • In Meghalaya, sacred groves serve as the last refuges for many rare and threatened plants.

Ex situ (off site) conservation

This approach involves taking threatened animals and plants out of their natural habitats and placing them in special settings for protection and care.

• Facilities: Zoological parks, botanical gardens, and wildlife safari parks serve this purpose. Many animals extinct in the wild are maintained in zoological parks.
• Advanced Techniques: Ex situ conservation has advanced beyond simple enclosures.
  • Cryopreservation techniques: Gametes of threatened species can be preserved in viable and fertile conditions for long periods.
  • In vitro fertilisation: Eggs can be fertilized in laboratories.
  • Tissue culture methods: Plants can be propagated.
  • Seed banks: Seeds of different genetic strains of commercially important plants can be kept for long periods.

International Cooperation

Biodiversity conservation transcends political boundaries, making it a collective responsibility.

• The Convention on Biological Diversity (‘The Earth Summit’) (Rio de Janeiro, 1992): Called upon all nations to take appropriate measures for biodiversity conservation and sustainable utilization of its benefits.
• The World Summit on Sustainable Development (Johannesburg, 2002): 190 countries pledged to achieve a significant reduction in the rate of biodiversity loss at global, regional, and local levels by 2010.