2.1. BIODIVERSITY MEANING
Biodiversity is a combination of two words, Bio (life) and diversity (variety).
Biodiversity is formally defined by the Convention on Biological Diversity (CBD) as: “the variability among living organisms from all sources including, among others, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems”.
In simple terms, biodiversity is the number and variety of organisms found within a specified geographic region. It refers to the varieties of plants, animals and micro-organisms, the genes they contain and the ecosystems they form. It relates to the variability among living organisms on the earth, including the variability within and between the species and that within and between the ecosystems.
According to the IUCN (2004), the total number of plant and animal species described so far is slightly more than 1.5 million, but there is no clear idea of how many species are yet to be discovered and described.
Some extreme estimates range from 20 to 50 million, but a more conservative and scientifically sound estimate made by Robert May places the global species diversity at about 7 million.
2.1.1. BIODIVERSITY OF INDIA
With only 2.4% of the world’s land area, its share of the global species diversity is an impressive 8.1 per cent
This includes 45,500 recorded species of plants and 91,000 recorded species of animals.
There is diversity of ecological habitats like forests, grassland, wetlands, coastal and marine ecosystems, and desert ecosystems.
India is considered one of the world’s 17 “megadiverse” countries in terms of biodiversity.
India has four global biodiversity hot spots (Eastern Himalaya, Indo-Burma, Western Ghats and Sri Lanka, and Sundaland).
The megadiverse countries are a group of countries that harbor the majority of the Earth's species and are therefore considered extremely biodiverse. Conservation International identified 17 megadiverse countries in 1998. Together, these 17 countries harbour more than 70% of the earth's species. All megadiverse countries are located in, or partially in, tropical or subtropical regions. All are located in, or partially in, tropical or subtropical regions.
The identified Megadiverse Countries are: United States of America, Mexico, Colombia, Ecuador, Peru, Venezuela, Brazil, Democratic Republic of Congo, South Africa, Madagascar, India, Malaysia, Indonesia, Philippines, Papua New Guinea, China and Australia.
The principle criterion is endemism, first at the species level and then at higher taxonomic levels such as genus and family. To qualify as a Megadiverse Country, a country must:
1. Have at least 5000 of the world’s plants as endemics.
2. Have marine ecosystems within its borders.
Despite endemism being the main criterion, thresholds for the criteria are flexible and countries have been considered individually based on all criteria.
2.2. LEVELS OF BIODIVERSITY
Biodiversity can be discussed at three levels: Genetic diversity, Species diversity and Ecosystem diversity.
2.2.1. GENETIC DIVERSITY
Genetic biodiversity refers to the variation of genes within species.
Groups of individual organisms having certain similarities in their physical characteristics are called species.
Human beings genetically belong to the homo-sapiens group and also differ in their characteristics such as height, colour, physical appearance, etc., considerably. This is due to genetic diversity.
The genetic diversity is essential for a healthy breeding of population of species.
2.2.2. SPECIES DIVERSITY
This refers to the variety of species.
It relates to the number of species in a defined area.
The diversity of species can be measured through its richness, abundance and types. Some areas are richer in species than others. Areas rich in species diversity are called hotspots of diversity.
2.2.3. ECOSYSTEM DIVERSITY
The broad differences between ecosystem types and the diversity of habitats and ecological processes occurring within each ecosystem type constitute the ecosystem diversity.
The boundaries of communities (associations of species) and ecosystems are not very rigidly defined.
Thus, the demarcation of ecosystem boundaries is difficult and complex.
2.3. PATTERNS OF BIODIVERSITY
Biodiversity as we have today is the result of 2.5-3.5 billion years of evolution It is consistently richer in the tropics. The distribution of biodiversity can be discussed as under Latitudinal gradients: Tropical forests are very rich in bio-diversity. As one approaches the Polar Regions, one finds larger and larger populations of fewer and fewer species. With very few exceptions, tropics (latitudinal range of 23.5° N to 23.5° S) harbour more species than temperate or polar areas.
Forest in a tropical region like Ecuador has up to 10 times as many species of vascular plants as a forest of equal area in a temperate region like the Midwest of the USA. Decline in richness with latitude may be faster in the Northern than in the Southern Hemisphere and the peaks in richness may not lie actually at the Equator itself but some distance away.
Species-Area relationships: Within a region species richness increases with increasing explored area, but only up to a limit. In fact, the relation between species richness and area for a wide variety of taxa (angiosperm plants, birds, bats, freshwater fishes) turns out to be a rectangular hyperbola. It implies that even if area is increased further the richness of species will tend to become constant.
What is so special about tropics that might account for their greater biological diversity?
Various hypotheses have been given. Some important ones are:
Speciation is generally a function of time, unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for species diversification.
Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.
2.4. MEASUREMENT OF BIODIVERSITY
Scientists use different biodiversity indices to measure diversity, and no single one will always be appropriate. The two main factors taken into account when measuring diversity are richness and evenness.
Species richness: It is the number of different species represented in an ecological community, landscape or region.
Species evenness: Evenness is a measure of the relative abundance of the different species making up the richness of an area.
For example, there might be two different fields for wildflowers. The sample from the first field consists of 300 daisies, 335 dandelions and 365 buttercups. The sample from the second field comprises 20 daisies, 49 dandelions and 931 buttercups. Both samples have the same richness (3 species) and the same total number of individuals (1000). However, the first sample has more evenness than the second. This is because the total number of individuals in the sample is quite evenly distributed between the three species. In the second sample, most of the individuals are buttercups, with only a few daisies and dandelions present. Sample 2 is therefore considered to be less diverse than sample 1.
Many diversity indices have been developed that combine different measures of biodiversity. One is called the Simpson’s Index, which takes into account both species richness, and an evenness of abundance among the species present.
Diversity may be measured at different scales. These are three indices used by ecologists:
1. Alpha diversity refers to diversity within a particular area, community or ecosystem, and is measured by counting the number of taxa(usually species) within the ecosystem.
2. Beta diversity is species diversity between ecosystems; this involves comparing the number of taxa that are unique to each of the ecosystems.
3. Gamma diversity is a measurement of the overall diversity for different ecosystems within a region.
The more diverse an ecosystem, better are the chances for the species to survive through adversities and attacks, and consequently, is more productive. Hence, the loss of species would decrease the ability of the system to maintain itself. Just like a species with a high genetic diversity, an ecosystem with high biodiversity may have a greater chance of adapting to environmental change. In other words, the more the variety of species in an ecosystem, the more stable the ecosystem is likely to be.
2.5. IMPORTANCE OF BIODIVERSITY
Biodiversity has contributed in many ways to the development of human culture and, in turn, human communities have played a major role in shaping the diversity of nature at the genetic, species and ecological levels. Biodiversity plays the following roles:
2.5.1. ECOLOGICAL ROLES
Species of many kinds perform some or the other functions in an ecosystem. Every organism, besides extracting its needs, also contributes something useful to other organisms.
Species capture and store energy, produce and decompose organic materials, help to cycle water and nutrients throughout the ecosystem, fix atmospheric gases and help regulate the climate.
Thus, they help in soil formation, reducing pollution, protection of land, water and air resources.
These functions are important for ecosystem function and human survival.
2.5.2. ECONOMIC ROLE
Biodiversity is an important resource in day-to-day life. One important part of biodiversity is ‘crop diversity’, which is also called agro-biodiversity. Biodiversity is seen as a reservoir of resources to be drawn upon for the manufacture of food, pharmaceutical, and cosmetic products. This concept of biological resources is responsible for the deterioration of biodiversity. Some of the important economic commodities that biodiversity supplies to humankind are: food crops, livestock, forests, fish, medicinal resources, etc.
2.5.3. SCIENTIFIC ROLE
Biodiversity is important because each species can give us some clue as to how life evolved and will continue to evolve. Biodiversity also helps in understanding how life functions and the role of each species in sustaining ecosystems of which we are also a species.
2.5.4. SOCIAL/CULTURAL SERVICES
Diversity of nature provides us aesthetic pleasure. It provides us recreational avenues and rich biological diversity encourages tourism in the region. Many communities and cultures have co-evolved with the surroundings and the resources provided by a biologically diverse environment. Hence, it performs an important social role as well. Important services which it provides are:
Recreation and Relaxation
Tourism especially eco-tourism
Art, Design and Inspiration
Spiritual experiences and a sense of place
It is our ethical responsibility to consider that each and every species along with us have an intrinsic right to exist. Hence, it is morally wrong to voluntarily cause the extinction of any species. The level of biodiversity is a good indicator of the state of our relationships with other living species.
2.6. LOSS OF BIODIVERSITY
The biological wealth of the planet has been declining rapidly.
The colonisation of tropical Pacific Islands by humans is said to have led to the extinction of more than 2,000 species of native birds.
The IUCN Red List (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.
Some examples of recent extinctions include the dodo (Mauritius), quagga (Africa), thylacine (Australia), Steller’s Sea Cow (Russia) and three subspecies (Bali, Javan, Caspian) of tiger.
The last twenty years alone have witnessed the disappearance of 27 species.
2.6.1. CAUSES OF BIODIVERSITY LOSSES
1. Natural causes like floods, earthquakes and other natural disasters.
2. Habitat loss and fragmentation:
This is the most important cause driving animals and plants to extinction. The most dramatic examples of habitat loss come from tropical rain forests. Once covering more than 14 per cent of the earth’s land surface, these rain forests now cover no more than 6 per cent.
Besides total loss, the degradation of many habitats by pollution also threatens the survival of many species. When large habitats are broken up into small fragments due to various human activities, mammals and birds requiring large territories and certain animals with migratory habits are badly affected, leading to decline of population.
Habitat loss is caused by deforestation, over-population, pollution, global warming etc.
3. Over-exploitation: Over-hunting, over-fishing or over-collecting of a species can quickly lead to its decline. Changing consumption patterns
of humans is often cited as the key reason for this unsustainable exploitation of natural resources. Many species extinctions in the last 500 years
(Steller’s sea cow, passenger pigeon) were due to overexploitation by humans.
4. Alien species invasions: When alien species are introduced unintentionally or deliberately for any purpose, some of them turn invasive, and cause decline or extinction of indigenous species.
5. Co-extinctions: When a species becomes extinct, the plant and animal species associated with it in an obligatory way also become extinct. When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate.
6. Global climate change: Both climate variability and climate change cause biodiversity loss. Species and populations may be lost permanently, if they are not provided with enough time to adapt to changing climatic conditions.
7. Hunting and Poaching: Because of this, not only the particular species become prone to extinction but also the other species dependent on that species.
2.6.2. EXTINCTION EVENT
Extinction is every day. Mass extinction is not. An extinction event (or mass extinction) is a widespread and rapid decrease in biodiversity of earth. It occurs when the prevailing rate of extinction far exceeds the background or natural rate of extinction. This rate is measured normally in number of species going extinct over a given period of time. The opposite of extinction is speciation- the rate at which new species are formed, which contributes to the biodiversity. There is little evidence of a total decline in biodiversity in recent or pre-human history. In fact, the total number of species on earth has been steadily increasing. This implies average speciation rates are similar to or higher than average extinction rates. In fact, extinction events are important starting point of speciation activities as new and dormant species flourish due to wiping out of competition. Domination and spread of Dinosaurs during Jurassic period is considered as a consequence of Permian extinction event.
More than 90% of all organisms that have ever lived on Earth are extinct. As new species evolve to fit ever changing ecological niches, older species fade away. But the rate of extinction is far from constant. Extinction events are recorded through mass disappearance of fossil records, especially for marine organisms, whose fossils are better preserved. Scientists have recognised several mass extinction events in past 500 million years, out of which five are considered to the major ones. These are:
1. End Ordovician-Silurian EE (450-440 million years): During the Ordovician, most life was in the sea, so it was sea creatures such as trilobites, brachiopods and graptolites that were drastically reduced in number.
2. Late Devonian EE (375 my): Trilobites were the most diverse and abundant species. They were almost wiped out in this phase. The likely culprit was the newly evolved land plants that emerged, covering the planet during the Devonian period. Their deep roots stirred up the earth, releasing nutrients into the ocean. This might have triggered algal blooms which sucked oxygen out of the water, suffocating bottom dwellers like the trilobites.
3. Permian-Triassic EE (250 my): The Permian mass extinction has been nicknamed The Great Dying, since a staggering 96% of species died out. All life on Earth today is descended from the 4% of species that survived. A cataclysmic eruption near Siberia blasted CO2 into the atmosphere. Methanogenic bacteria responded by belching out methane, a potent greenhouse gas. Global temperatures surged while oceans acidified and stagnated, belching poisonous hydrogen sulfide. Rocks after this period record no coral reefs or coal deposits.
4. Triassic-Jurassic EE (200 my): Estimated 80% species were lost during this phase. No definite cause has been found. Climate change, flood basalt eruptions and an asteroid impact have all been blamed for this loss of life.
5. Cretaceous-Tertiary EE (66 my): The Cretaceous-Tertiary mass extinction - also known as the K/T extinction - is famed for the death of the dinosaurs. However, many other organisms perished at the end of the Cretaceous including the ammonites (which were most abundant marine organisms), many flowering plants and the last of the pterosaurs.
General Causes of mass extinctions of past:
Change in chemical composition of atmosphere and hydrosphere (such as loss of oxygen)
Flood basalt events (volcanic eruptions) and releasing of trapped gases
Temperature changes- global warming or cooling
Cosmic factors such as asteroid impact
Sea level change
Asteroid impact or volcanism lead to debris in atmosphere, which blocks sunlight for long duration
During this period, greenhouse gases such as methane also collect in atmosphere – as soon as debris clears, there is fast paced rise in temperature.
Present Mass Extinction phase
It is estimated that the extinction rate today is at least 100 times the background or natural rate. Scientists believe that we have entered the age of sixth mass extinction, caused almost entirely due to anthropogenic activities. According to studies, about 300 terrestrial vertebrates have gone extinct in the past 500 years and about 16-33% of all species are either endangered or threatened. Most vulnerable to extinction today are amphibians (41% of all amphibians, 26% of mammals and 13% of birds face extinction).
Modern causes of extinction:
Land development and habitat destruction
Anthropogenic emissions into land and water
2.7. BIODIVERSITY CONSERVATION
Biodiversity is important for human existence. All forms of life are so closely interlinked that disturbance in one gives rise to imbalance in the others. If species of plants and animals become endangered, they cause degradation in the environment, which may threaten human being’s own existence.
There are two approaches in biodiversity conservation:
1. In situ conservation: It is the approach of protecting
an endangered plant or animal species in its natural habitat, either by protecting or cleaning up the habitat itself, or by defending the species from predators. Some methods under it are:
2. Ex-situ conservation: In this approach, threatened animals and plants are taken out from their natural habitat and placed in special setting where they can be protected and given special care.
Zoological parks, botanical gardens and wildlife safari parks serve this purpose.
In recent years ex situ conservation has advanced beyond keeping threatened species in enclosures.
Now gametes of threatened species can be preserved in viable and fertile condition for long periods using cryopreservation techniques, eggs can be fertilised in vitro, and plants can be propagated using tissue culture methods.
Seeds of different genetic strains of commercially important plants can be kept for long periods in seed banks.
There is an increasing consciousness of the fact that such conservation with sustainable use is possible only with the involvement and cooperation of local communities and individuals. For this, the development of institutional structures at local levels is necessary. The critical issue is not merely the conservation of species nor the habitat but the continuation of process of conservation. The world conservation strategy1 has suggested the
following steps for biodiversity conservation:
1. Efforts should be made to preserve the species that are endangered.
2. Prevention of extinction requires proper planning and management.
3. Varieties of food crops, forage plants, timber trees, livestock, animals and their wild relatives should be preserved;
4. Each country should identify habitats of wild relatives and ensure their protection.
5. Habitats where species feed, breed, rest and nurse their young should be safeguarded and protected.
6. International trade in wild plants and animals should be regulated.
The International Union of Conservation of Nature and Natural Resources (IUCN) has classified the species of plants and animals into various categories for the purpose of their conservation which are as follows:
The A to E criteria are:
Declining population (past, present and/or projected)
Geographic range size, and fragmentation, decline or fluctuations
Small population size and fragmentation, decline, or fluctuations
Very small population or very restricted distribution
Quantitative analysis of extinction risk
(e.g., Population Viability Analysis)
A taxon is Extinct when there is no reasonable doubt that the last individual has died.
EXTINCT IN THE WILD (EW)
A taxon is Extinct in the Wild when it is known only to survive in cultivation, in captivity or as a naturalized population (or populations) well outside the past range.
CRITICALLY ENDANGERED (CR)
A taxon is Critically Endangered when the best available evidence indicates that it meets any of the criteria A to E for Critically Endangered, and it is therefore considered to be facing an extremely high risk of extinction in the wild.
A taxon is Endangered when the best available evidence indicates that it meets any of the criteria A to E for Endangered, and it is therefore considered to be facing a very high risk of extinction in the wild.
A taxon is Vulnerable when the best available evidence indicates that it meets any of the criteria A to E for Vulnerable, and it is therefore considered to be facing a high risk of extinction in the wild.
NEAR THREATENED (NT)
A taxon is Near Threatened when it has been evaluated against the criteria but does not qualify for Critically Endangered, Endangered or Vulnerable now, but is close to qualifying for or is likely to qualify for a threatened category in the near future.
LEAST CONCERN (LC)
A taxon is Least Concern when it has been evaluated against the criteria and does not qualify for Critically Endangered, Endangered, Vulnerable or Near Threatened. Widespread and abundant taxa are included in this category.
DATA DEFICIENT (DD)
A taxon is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of extinction based on its distribution and/or population status.
NOT EVALUATED (NE)
A taxon is Not Evaluated when it has not yet been evaluated against the criteria.
2.8. BIODIVERSITY HOTSPOT
The concept of biodiversity hotspots was given by Norman Myers. A biodiversity hotspot is a biogeographic region with a significant reservoir of biodiversity that is threatened with destruction. These hot spots which cover less than 2% of the world’s land area are found to have about 50% of the terrestrial biodiversity. Criteria for determining hot-spots:
Contain at least 1,500 species of vascular plants (> 0.5 percent of the world's total) as endemics (species found nowhere else on Earth).
Degree of threat, which is measured in terms of Habitat loss: Have lost at least 70 percent of its original habitat.
There are 35 such hot spots of biodiversity on a global level.
Plants: The hotspots hold at least 150,000 endemic plant species, 50 percent of the world’s total vascular plants.
Vertebrates: Overall, 11,980 mammals, birds, reptiles and amphibians are endemic to the hotspots (42 percent of all terrestrial vertebrates), while a total of 22,022 vertebrate species occur in the hotpots (77 percent of the world's total). In addition, there are more than 3,400 freshwater fish species endemic to the hotspots, which is likely to be an underestimate.
Vegetation: The biodiversity hotspots once stretched across 15.7 percent of the Earth’s land surface, however 86 percent of the hotspots’ original habitat has already been destroyed. Today, the intact remnants of the hotspots now cover only 2.3 percent of the Earth’s land surface.
1. Cape Floristic Region
2. Coastal Forests of Eastern Africa
3. Eastern Afromontane
4. Guinean Forests of West Africa
5. Horn of Africa
6. Madagascar and the Indian Ocean Islands
8. Succulent Karoo
9. East Melanesian Islands
13. Mountains of Southwest China
14. New Caledonia
15. New Zealand
18. Southwest Australia
19. Forests of Eastern Australia (new)
22. Western Ghats and Sri Lanka
III. Europe and Central Asia
25. Mediterranean Basin
26. Mountains of Central Asia
IV. North and Central America
27. California Floristic Province
28. Caribbean Islands
29. Madrean Pine-Oak Woodlands
V. South America
31. Atlantic Forest
33. Chilean Winter Rainfall-Valdivian Forests
35. Tropical Andes
Out of these, four are present in India. These are:
1. Himalaya: Includes the entire Indian Himalayan region (and that falling in Pakistan, Tibet, Nepal, Bhutan, China and Myanmar)
2. Indo-Burma: Includes entire North-eastern India, except Assam and Andaman group of Islands (and Myanmar, Thailand, Vietnam, Laos, Cambodia and southern China)
3. Sundalands: Includes Nicobar group of Islands (and Indonesia, Malaysia, Singapore, Brunei, Philippines)
4. Western Ghats and Sri Lanka: Includes entire Western Ghats (and Sri Lanka)
Conservation International’s ranking of the world’s 10 most threatened forested hotspots, listed by percentage of remaining original habitat:
Indo-Burma (southern Asia)
New Caledonia (Pacific Islands)
Atlantic Forest (South America)
Mountains of Southwest China
California Floristic Province(U.S. and Mexico)
Coastal Forests of Eastern Africa
Madagascar & Indian Ocean Islands
Eastern Afromontane (Africa)
2.9. UPSC QUESTIONS RELATED TO ABOVE TOPICS
1. What is biodiversity? Why should it be preserved? (UPSC 1992/40 Marks)
2. What do you understand by Ecological Balance? Why is this balance necessary? What is being done in India today to maintain this balance? (UPSC 1987/15 Marks)
3. Deforestation contributes to the accumulation of carbon dioxide in the atmosphere in different ways. What are these processes? Explain. (IFS 2011/10 Marks)
4. What is biodiversity? How have human activities in recent decades affected biodiversity? (IFS 2012/10 Marks).