Biodiversity and Conservation Biology Notes - Levels, Patterns, Loss, Conservation, Hotspots and Protected Areas

Biodiversity is the diversity of biological organization ranging from cellular macromolecules to biomes. Edward Wilson popularized the term ‘biodiversity’.

Levels of Biodiversity

1. Genetic diversity: Diversity shown by a single species at the genetic level. For example, Rauwolfia vomitoria (Himalaya) shows genetic variation in the potency and concentration of the chemical reserpine. India has more than 50,000 different strains of rice and 1,000 varieties of mango.
2. Species diversity: Diversity at the species level. For example, the Western Ghats have greater amphibian species than the Eastern Ghats.
3. Ecological diversity: Diversity at the ecosystem level. For example, in India, deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows are seen.

Number of Species on Earth (Global Species Diversity)

• According to IUCN (2004), more than 1.5 million species have been described so far.
• According to Robert May’s Global estimate, about 7 million species would exist on Earth (considering species to be discovered in the tropics, i.e., only 22% of total species have been recorded so far).
• Animals are more diverse (above 70%) than plants, including Plantae and Fungi (22%).
• Among animals, insects are the most species-rich group (70%, i.e., out of every 10 animals, 7 are insects).
• The number of fungi species is more than the combined total of species of fishes, amphibians, reptiles, and mammals.
• India has only 2.4% of the world’s land area but has 8.1% of the species diversity. India is one of the 12 mega-diversity countries of the world. Nearly 45,000 plant species and twice as many animals have been recorded from India.
• Applying May’s global estimates, India would have more than 100,000 plant species and 300,000 animal species. Biologists are not sure about the total number of prokaryotic species because:
  • Conventional taxonomic methods are not suitable for identifying microbial species.
  • In laboratories, many species cannot be cultured.

Patterns of Biodiversity

Latitudinal Gradients

• Species diversity decreases from the equator to the poles.
• Tropics (latitudinal range of 23.5° N to 23.5° S) have more species than temperate or polar areas.
• For example, the number of bird species in different latitudes:
  • Colombia (near equator): about 1,400 species.
  • India (in tropics): over 1,200 species.
  • New York (41° N): 105 species.
  • Greenland (71° N): 56 species.
• The tropical forest region like Ecuador has up to 10 times the number of vascular plant species compared to a temperate forest region like the Midwest of the USA.
• Tropical Amazonian rainforest (South America) has the greatest biodiversity on Earth, containing:
  • Over 40,000 species of plants.
  • 3,000 species of fishes.
  • 1,300 species of birds.
  • 427 species of mammals.
  • 427 species of amphibians.
  • 378 species of reptiles.
  • Over 125,000 species of invertebrates.
• Biodiversity (species richness) is highest in the tropics because:
  • Tropics had more evolutionary time.
  • Relatively constant environment (less seasonal).
  • They receive more solar energy, which contributes to greater productivity.

Species-Area Relationship

• According to Alexander von Humboldt’s study in South American jungles, within a region, species richness increases with increasing explored area, but only up to a limit. The relation between species richness and area gives a rectangular hyperbola.
• The equation is: S = CA^z, where:
  • S = Species richness
  • A = Area
  • C = Y-intercept
  • Z = Slope of the line (regression coefficient)
• On a logarithmic scale, the relationship is a straight line described by the equation: Log S = log C + Z log A.
• Generally, for small areas, the Z value is 0.1 to 0.2. For large areas (e.g., entire continents), the slope is steeper (Z value: 0.6 to 1.2). For example, for frugivorous birds and mammals in tropical forests of different continents, the Z value is 1.15.

Importance of Species Diversity

• According to David Tilman, plots with more species show less year-to-year variation in total biomass.
• Increased diversity contributes to higher productivity, essential for ecosystem health and the survival of the human race.
• ‘Rivet Popper Hypothesis’: Proposed by Stanford ecologist Paul Ehrlich, it uses an analogy to understand the importance of biodiversity. In an airplane (ecosystem), all parts are joined with many rivets (species). If passengers pop a rivet (extinction of a species), it may not affect flight safety (functioning of the ecosystem). But as more rivets are removed, the plane becomes dangerously weak. Loss of rivets on the wings (key species that drive major ecosystem functions) is more dangerous than loss of a few rivets on seats or windows.

Loss of Biodiversity

• IUCN Red List (2004) reports that 784 species (338 vertebrates, 359 invertebrates, and 87 plants) have gone extinct in the last 500 years. Examples include Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Stellar’s Sea Cow (Russia), and three subspecies of tiger (Bali, Javan, Caspian).
• 27 species have disappeared in the last 20 years.
• More than 15,500 species are currently facing the threat of extinction.
• 12% of birds, 23% of mammals, 32% of amphibians, and 31% of gymnosperm species face the threat of extinction.
• The current extinction rate is 100–1000 times faster than in pre-human times. If this trend continues, nearly 50% of species might be extinct within the next 100 years.

Impacts of Loss of Biodiversity

• Decline in plant production.
• Environmental perturbations such as drought.
• Increased variability in ecosystem processes such as plant productivity, water use, and pest and disease cycles.

Causes of Biodiversity Losses (‘The Evil Quartet')

1. Habitat Loss and Fragmentation: The most important cause.
   • Tropical rainforests have reduced from 14% to 6% of Earth’s surface.
   • Thousands of hectares of rainforests are lost within hours.
   • The Amazon rainforest is being cut for cultivating soybeans or converting to grasslands for cattle.
   • Fragmentation severely affects animals requiring large territories and migratory animals.
2. Over-exploitation: Species like Stellar’s Sea Cow and Passenger Pigeon went extinct due to over-exploitation.
3. Alien Species Invasions: Alien species cause decline or extinction of indigenous species.
   • Nile Perch introduced in Lake Victoria (East Africa) caused the extinction of over 200 species of cichlid fish.
   • Invasive weeds like Parthenium (carrot grass), Lantana, and Eichhornia (water hyacinth) have damaged native species.
   • Illegal introduction of the African Catfish (Clarias gariepinus) for aquaculture threatens indigenous catfishes in rivers.
4. Co-extinction: When a species becomes extinct, associated species also go extinct.
   • Extinction of parasites when their host goes extinct.
   • In co-evolved plant-pollinator mutualism, extinction of one causes extinction of the other.

Biodiversity Conservation

There are three categories of reasons for conservation.

Narrowly Utilitarian Arguments

• Humans derive economic benefits from nature, such as food, firewood, fibre, construction material, industrial products (tannins, lubricants, dyes, resins, perfumes), and medicines.
• More than 25% of drugs are derived from plants.
• 25,000 species of plants have medicinal value.

Broadly Utilitarian Arguments

Biodiversity provides many ecosystem services, for example:

• The Amazon forest (‘lung of the planet’) produces 20% of total O₂ in the Earth’s atmosphere.
• Pollination through bees, bumblebees, birds, and bats.
• Aesthetic pleasures.

Ethical Arguments

• Every species has an intrinsic value. We have a moral duty to care for their well-being.

Biodiversity conservation is two types: In situ (on site) conservation and Ex situ (off site) conservation.

Types of Biodiversity Conservation

1. In Situ Conservation (On Site)

It is the conservation of genetic resources within natural or human-made ecosystems in which they occur. Examples include protected areas such as National Parks, Sanctuaries, Biosphere Reserves, cultural landscapes, and natural monuments.

• National Park: Strictly reserved for the welfare of wildlife, where private ownership, cultivation, and grazing are prohibited. Example: Eravikulam National Park in Kerala.
• Sanctuary: Protection is given only to animals. Collection of timber, minor forest products, and private ownership are allowed if they do not harm animals. Example: Periyar Wildlife Sanctuary in Kerala.
• Biosphere Reserves: Areas of land or coastal ecosystems for conservation and sustainable use.
• Sacred Forests (Sacred Groves): Forest fragments communally protected based on religious beliefs. Examples:
  • Sacred groves in Khasi and Jaintia Hills in Meghalaya.
  • Aravalli Hills of Rajasthan.
  • Western Ghat regions of Karnataka and Maharashtra.
  • Sarguja, Chanda, and Bastar areas (Madhya Pradesh).

India has 14 Biosphere Reserves, 90 National Parks, and 448 wildlife sanctuaries.

2. Ex Situ Conservation (Off Site)

It is the conservation of organisms outside their habitats. Examples include genetic resource centres, zoological parks, wildlife safari parks, botanical gardens, gene banks, and cryopreservation.

Hotspots

• These are regions with very high species richness, a high degree of endemism (species confined to a specific region), but are most threatened.
• There are 34 hotspots in the world.
• Three hotspots cover India’s biodiversity regions: Western Ghats & Sri Lanka, Indo-Burma, and Himalaya.
• All hotspots together cover only less than 2% of the Earth’s land area, but their species richness is extremely high. Protection of hotspots has reduced ongoing extinctions by 30%.

International Efforts for Conserving Biodiversity

• The Earth Summit or Convention on Biological Diversity (Rio de Janeiro, 1992) had three objectives:
  1. Conservation of biodiversity.
  2. Sustainable use of biodiversity.
  3. Sharing of benefits arising from genetic resources.
• The World Summit on Sustainable Development (Johannesburg, South Africa, 2002): 190 countries pledged to reduce the current rate of biodiversity loss.