Chapter 13: Biodiversity and its Conservation

Introduction

Biodiversity refers to the totality of genes, species, and ecosystems of a region. In our biosphere, immense diversity (or heterogeneity) exists not only at the species level but at all levels of biological organisation ranging from macromolecules within cells to biomes. The term biodiversity was popularized by the sociobiologist Edward Wilson.

Levels of Biodiversity

1. Genetic diversity: A single species might show high diversity at the genetic level over its distributional range. The genetic variation shown by the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges might be in terms of the potency and concentration of the active chemical (reserpine) that the plant produces. India has more than 50,000 genetically different strains of rice and 1,000 varieties of mango.
2. Species diversity: The diversity at the species level. For example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.
3. Ecological diversity: At the ecosystem level, India, with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows has a greater ecosystem diversity than a Scandinavian country like Norway.

Global Species Diversity

According to the IUCN (2004), the total number of plant and animal species described so far is slightly more than 1.5 million. Current estimates put the global species diversity at about 7 million (Robert May’s estimate).

• More than 70% of all the species recorded are animals, while plants comprise no more than 22%.
• Among animals, insects are the most species-rich taxonomic group, making up more than 70% of the total (out of every 10 animals on this planet, 7 are insects).

Patterns of Biodiversity

1. Latitudinal gradients: Species diversity decreases as we move away from the equator towards the poles. Tropics (latitudinal range of 23.5° N to 23.5° S) harbour more species than temperate or polar areas. Reasons for high tropical diversity:
   • Speciation is generally a function of time. Temperate regions were subjected to frequent glaciations, while tropical latitudes have remained relatively undisturbed for millions of years.
   • Tropical environments are less seasonal, relatively more constant and predictable, which promotes niche specialisation and leads to a greater species diversity.
   • There is more solar energy available in the tropics, leading to higher productivity and consequently greater diversity.
2. Species-Area relationships: Alexander von Humboldt observed that within a region, species richness increased with increasing explored area, but only up to a limit. On a logarithmic scale, the relationship is a straight line described by the equation: $$ \log S = \log C + Z \log A $$ Where \(S = \text{Species richness}\), \(A = \text{Area}\), \(Z = \text{slope of the line (regression coefficient)}\), \(C = \text{Y-intercept}\).

The Importance of Species Diversity

Ecologists believe that communities with more species tend to be more stable than those with less species. A stable community shouldn’t show too much variation in productivity from year to year; it must be resistant or resilient to occasional disturbances and also resistant to invasions by alien species (David Tilman’s long-term ecosystem experiments). Paul Ehrlich’s Rivet Popper Hypothesis: In an airplane (ecosystem), all parts are joined by thousands of rivets (species). If passengers start popping rivets (causing a species to become extinct), it may not affect flight safety initially (proper ecosystem functioning), but as more rivets are removed, the plane becomes dangerously weak. Loss of rivets on the wings (key species) is obviously a more serious threat than loss of a few rivets on the seats inside.

Loss of Biodiversity

The biological wealth of our planet has been declining rapidly. The IUCN Red List (2004) documents the extinction of 784 species in the last 500 years (including the Dodo, Quagga, Thylacine, Steller’s Sea Cow, and 3 subspecies of tiger). Presently, 12% of birds, 23% of mammals, 32% of amphibians, and 31% of gymnosperms face the threat of extinction. Amphibians appear more vulnerable to extinction.

The “Evil Quartet” (Causes of Biodiversity Loss)

1. Habitat loss and fragmentation: The most important cause driving animals and plants to extinction (e.g., clearing of Amazon rainforests). When large habitats are broken into small fragments due to various human activities, mammals and birds requiring large territories are badly affected.
2. Over-exploitation: Many species extinctions in the last 500 years (Steller’s sea cow, passenger pigeon) were due to overexploitation by humans.
3. Alien species invasions: When alien species are introduced unintentionally or deliberately for whatever purpose, some of them turn invasive and cause decline or extinction of indigenous species (e.g., Nile perch introduced into Lake Victoria in east Africa led eventually to the extinction of an ecologically unique assemblage of more than 200 species of cichlid fish).
4. Co-extinctions: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct (e.g., host plant and its specific pollinator).

Biodiversity Conservation

Why should we conserve biodiversity?

1. Narrowly utilitarian: Humans derive countless direct economic benefits from nature (food, firewood, fibre, construction material, industrial products, and a host of medicinally useful plants).
2. Broadly utilitarian: Biodiversity plays a major role in many ecosystem services that nature provides (e.g., oxygen production through photosynthesis, pollination without which plants cannot give us fruits or seeds, aesthetic pleasure).
3. Ethical: Every species has an intrinsic value, even if it may not be of current or any economic value to us. We have a moral duty to care for their well-being.

How do we conserve biodiversity?

1. In situ (on-site) conservation: Conserving the entire ecosystem to protect its species.
   • Biodiversity hotspots: Regions with very high levels of species richness and high degree of endemism (species confined to that region and not found anywhere else). Initially 25 hotspots were identified globally; now there are 34 (e.g., Western Ghats and Sri Lanka, Indo-Burma, and Himalaya cover India’s high biodiversity regions).
   • Protected areas: National parks, wildlife sanctuaries, and biosphere reserves. India has 14 biosphere reserves, 90 national parks, and 448 wildlife sanctuaries.
   • Sacred groves: Tracts of forest are set aside, and all the trees and wildlife within are venerated and given total protection (e.g., Khasi and Jaintia Hills in Meghalaya).
2. Ex situ (off-site) conservation: Taking threatened animals and plants out of their natural habitat and placing them in special settings for protection and special care.
   • Zoological parks, botanical gardens, and wildlife safari parks.
   • Advances allow gametes of threatened species to be preserved in viable and fertile condition for long periods using cryopreservation techniques at \(-196^{\circ} \text{C}\). Eggs can be fertilized in vitro, and plants can be propagated using tissue culture. Seeds of different genetic strains can be kept in seed banks.

International Conventions:

• The Earth Summit: Held in Rio de Janeiro in 1992, calling upon nations to take appropriate measures for conservation.
• The World Summit on Sustainable Development: Held in 2002 in Johannesburg, South Africa, where 190 countries pledged their commitment to significantly reduce the rate of biodiversity loss by 2010.

Competency Based Questions

Q1. According to the foundational Species-Area relationship (\(S = CA^Z\)), an ecologist surveying bird richness over heavily restricted areas mathematically charts a gentle linear slope accurately representing a \(Z\)-value equal to \(0.1\). Extending this survey to encompass all known avian species completely across the entire massive continent of Asia causes the surveyed regression line to steepen. Predict the universally expected numerical range for this newly observed continental biological regression \(Z\)-value.

(A) Exactly \(0\)
(B) \(0.1\) to \(0.2\)
(C) \(0.6\) to \(1.2\)
(D) Exactly \(4.0\)

Q2. Robert May placed the global biological species estimate at approximately 7 million. Based on records published by the IUCN (2004), how many total species have been formally classified and described scientifically worldwide to date?

Q3. To mitigate the “Evil Quartet” factor driving co-extinctions caused by physical habitat fragmentation, conservationists established contiguous forested land “bridges” connecting two isolated wildlife sanctuaries. Biologically, what are these structural bridges formally called?

Q4. A specialized botanical garden stores cryopreserved active genetic pollen and viable wild plant seeds collected from endangered native orchids inside liquid nitrogen tanks at \(-196^{\circ}\text{C}\). Categorize what formal type of biodiversity conservation this biological facility represents.

Q5. State the primary biological goal underlying the creation of designated sacred groves located within the Khasi and Jaintia Hills of Meghalaya.