Biodiversity and Conservation Notes

Biodiversity

An alien visiting Earth would be amazed by the diversity of life. Humans are also constantly astonished by the variety of living organisms. There are 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 seek to understand the significance of this diversity, questioning why there are so many species, whether this diversity has always existed, how diversification occurred, its importance to the biosphere, and how humans benefit from it.

13.1 Biodiversity

Biodiversity refers to the immense diversity or heterogeneity within our biosphere, existing at all levels of biological organization, from macromolecules to biomes. Edward Wilson popularized the term to describe the combined diversity at all levels.

The most important levels are:

(i) Genetic Diversity: A single species can exhibit high diversity at the genetic level across its distribution range. For example, the medicinal plant Rauwolfia vomitoria shows genetic variation in the potency and concentration of the chemical reserpine it produces in different Himalayan ranges. India has over 50,000 genetically different strains of rice and 1,000 varieties of mango.
(ii) Species Diversity: Diversity at the species level. The Western Ghats have greater amphibian species diversity than the Eastern Ghats.
(iii) Ecological Diversity: Diversity at the ecosystem level. India, with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows, has greater ecosystem diversity than a country like Norway.

This rich diversity has accumulated over millions of years of evolution, but it 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.

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

While we know the number of species recorded and named, estimating the total number of species on Earth is challenging. 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. However, many species are yet to be discovered and described.

Estimates vary widely. Species inventories are more complete in temperate regions than in the tropics. Biologists extrapolate temperate-tropical species richness ratios from exhaustively studied insect groups to other groups to estimate the total number of species. Some estimates range from 20 to 50 million, but Robert May's conservative estimate places global species diversity at about 7 million.

Earth’s Biodiversity

Based on current species inventories:

More than 70% of all recorded species are animals.
Plants (including algae, fungi, bryophytes, gymnosperms, and angiosperms) comprise no more than 22% of the total.
Insects are the most species-rich taxonomic group among animals, making up more than 70% of the total. Thus, 7 out of every 10 animals are insects.
The number of fungi species exceeds the combined total of fish, amphibian, reptile, and mammal species.

These estimates do not include prokaryotes due to the unsuitability of conventional taxonomic methods for identifying microbial species. Many microbial species are also not culturable under laboratory conditions. Using biochemical or molecular criteria could lead to millions of prokaryotic species.

Although India has only 2.4% of the world’s land area, it contributes 8.1% of global species diversity, making it one of the 12 mega-diversity countries. Nearly 45,000 plant species and twice as many animal species have been recorded in India.

If May’s global estimates are accurate, only 22% of the total species have been recorded so far. Applying this to India suggests there are potentially more than 100,000 plant species and 300,000 animal species yet to be discovered and described. Completing this inventory would require immense manpower and time. Many of these species face extinction before they can be discovered.

13.1.2 Patterns of Biodiversity

(i) Latitudinal Gradients

Species diversity is not uniform worldwide but shows an uneven distribution. A well-known pattern is the latitudinal gradient in diversity.

In general, species diversity decreases as we move from the equator towards the poles. Tropics (23.5° N to 23.5° S) harbor more species than temperate or polar areas.

Examples:

Colombia (near the equator) has nearly 1,400 bird species.
New York (41° N) has 105 bird species.
Greenland (71° N) has only 56 bird species.
India, in tropical latitudes, has over 1,200 bird species.
A tropical forest in Ecuador can have up to 10 times as many vascular plant species as a temperate forest in the Midwest USA.
The Amazonian rain forest has the greatest biodiversity, with over 40,000 plant species, 3,000 fish species, 1,300 bird species, 427 mammal species, 427 amphibian species, 378 reptile species, and over 125,000 invertebrate species. Scientists estimate at least two million insect species remain undiscovered there.

Why do the tropics have greater biological diversity?

(a) Time for Speciation: Tropical latitudes have remained relatively undisturbed for millions of years, allowing a longer evolutionary time for species diversification, unlike temperate regions subjected to frequent glaciations.
(b) Constant Environment: Tropical environments are less seasonal, more constant, and more predictable, promoting niche specialization and greater species diversity.
(c) Solar Energy: More solar energy in the tropics contributes to higher productivity, indirectly supporting greater diversity.

(ii) Species-Area Relationships

Alexander von Humboldt observed that species richness increased with increasing explored area, but only up to a limit. The relationship between species richness (S) and area (A) is 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:

$S$ = Species richness
$A$ = Area
$Z$ = Slope of the line (regression coefficient)
$C$ = Y-intercept

The value of $Z$ typically ranges from 0.1 to 0.2, regardless of the taxonomic group or region (e.g., plants in Britain, birds in California, mollusks in New York). However, for very large areas like entire continents, the slope of the line is much steeper ( $Z$ values range from 0.6 to 1.2). For frugivorous birds and mammals in tropical forests, the slope is around 1.15. Steeper slopes indicate a more rapid increase in species richness with area.

13.1.3 The Importance of Species Diversity to the Ecosystem

Ecologists have long debated whether the number of species in a community affects ecosystem functioning. It was believed that communities with more species tend to be more stable.

Stability in a biological community implies:

Not showing significant variation in productivity from year to year.
Resistance or resilience to occasional disturbances.
Resistance to invasions by alien species.

David Tilman’s long-term ecosystem experiments showed that plots with more species had less year-to-year variation in total biomass and increased diversity contributed to higher productivity.

Rich biodiversity is essential for ecosystem health and human survival. The loss of species can have significant consequences. Paul Ehrlich’s ‘rivet popper hypothesis’ illustrates this: in an airplane (ecosystem), each rivet represents a species. Removing rivets (species extinction) may not initially affect the flight (ecosystem functioning), but as more rivets are removed, the plane becomes dangerously weak. Losing rivets on the wings (key species) is more critical than losing rivets on seats (less critical species).

13.1.4 Loss of Biodiversity

While new species addition (speciation) is doubtful, species losses are evident. Human activities are the primary cause. Colonization of tropical Pacific Islands led to the extinction of over 2,000 native bird species.

The IUCN Red List (2004) documents the extinction of 784 species (338 vertebrates, 359 invertebrates, and 87 plants) in the last 500 years. Recent extinctions include the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller’s Sea Cow (Russia), and three tiger subspecies (Bali, Javan, Caspian). The last twenty years saw the disappearance of 27 species.

Some groups, like amphibians, are more vulnerable to extinction. Over 15,500 species worldwide face the threat of extinction. Currently, 12% of bird species, 23% of mammal species, 32% of amphibian species, and 31% of gymnosperm species face extinction threats.

Past mass extinction events have occurred before humans, but the current ‘Sixth Extinction’ is happening 100 to 1,000 times faster due to human activities. Ecologists warn that nearly half of all species could be wiped out within the next 100 years if present trends continue.

Loss of biodiversity can lead to:

Decline in plant production.
Lowered resistance to environmental disturbances like drought.
Increased variability in ecosystem processes.

Causes of Biodiversity Losses

The accelerated rates of species extinction are due to human activities, summarized as ‘The Evil Quartet’:

Habitat Loss and Fragmentation: The most important cause. Tropical rain forests, once covering over 14% of the Earth’s land surface, now cover no more than 6% and are rapidly being destroyed. The Amazon rain forest is being cleared for soya bean cultivation or to create grasslands for beef cattle. Pollution also degrades habitats. Fragmentation affects mammals and birds requiring large territories and migratory animals, leading to population declines.
Over-exploitation: When ‘need’ turns to ‘greed,’ it leads to over-exploitation of natural resources. The Steller’s sea cow and passenger pigeon extinctions resulted from overexploitation. Many marine fish populations are overharvested.
Alien Species Invasions: Alien species, whether introduced intentionally or unintentionally, can become invasive and cause the decline or extinction of native species. The Nile perch introduction into Lake Victoria led to the extinction of over 200 cichlid fish species. Invasive weeds like carrot grass (Parthenium), Lantana, and water hyacinth (Eicchornia) also cause environmental damage. The introduction of the African catfish Clarias gariepinus threatens indigenous catfishes.
Co-extinctions: When a species becomes extinct, species associated with it in an obligatory manner also become extinct. For example, the extinction of a host fish species leads to the extinction of its unique parasites. Similarly, the extinction of one partner in a coevolved plant-pollinator mutualism leads to the extinction of the other.

13.2 Biodiversity Conservation

13.2.1 Why Should We Conserve Biodiversity?

Reasons for conservation can be grouped into narrowly utilitarian, broadly utilitarian, and ethical categories.

Narrowly Utilitarian: Humans derive direct economic benefits from nature, including food, firewood, fiber, construction material, industrial products, and medicinal products. Over 25% of drugs are derived from plants, and 25,000 plant species contribute to traditional medicines. ‘Bioprospecting’ can lead to enormous benefits for nations with rich biodiversity.
Broadly Utilitarian: Biodiversity plays a major role in ecosystem services. The Amazon forest produces an estimated 20% of the Earth’s atmospheric oxygen through photosynthesis. Pollination by bees, bumblebees, birds, and bats is another vital ecosystem service. There are also intangible benefits like aesthetic pleasures.
Ethical: Every species has an intrinsic value, even if it lacks current economic value. We have a moral duty to care for their well-being and pass on our biological legacy to future generations.

13.2.2 How do we conserve Biodiversity?

Conservation can be in situ (on-site) or ex situ (off-site).

In situ Conservation: Protecting the whole ecosystem to save all its biodiversity. This involves saving the entire forest to save the tiger, for example. Many nations find it unrealistic to conserve all their biological wealth due to conflicts between development and conservation. Conservationists have identified ‘biodiversity hotspots’ for maximum protection – regions with high species richness and endemism. Initially, 25 hotspots were identified, and later 9 more were added, bringing the total to 34. These hotspots, covering less than 2% of the Earth’s land area, harbor a high number of species. Strict protection of these hotspots could reduce ongoing mass extinctions by nearly 30%. India has 3 hotspots: Western Ghats and Sri Lanka, Indo-Burma, and Himalaya. Ecologically unique and biodiversity-rich regions in India are legally protected as biosphere reserves (14), national parks (90), and wildlife sanctuaries (448). Sacred groves also play a role in conservation.
Ex situ Conservation: Removing threatened animals and plants from their natural habitat and placing them in special settings where they can be protected and given special care. Zoological parks, botanical gardens, and wildlife safari parks serve this purpose. Gametes of threatened species can be preserved using cryopreservation, 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.

Biodiversity conservation is a collective responsibility. The Convention on Biological Diversity (‘The Earth Summit’) in Rio de Janeiro in 1992 called on all nations to take measures for conservation and sustainable use of biodiversity. The World Summit on Sustainable Development in 2002 pledged to achieve a significant reduction in the current rate of biodiversity loss by 2010.