Environmental Studies

Module 4. Biodiversity and its conservation

Lesson 15
HOT-SPOTS OF BIODIVERSITY AND THREATS TO BIODIVERSITY

15.1 Hotspots of Biodiversity

The most remarkable places/ areas on earth are also the most threatened ones, and many of them have been reduced to less than 10 percent of their original vegetation. These places/ areas are called hotspots of biodiversity for preservation. Hotspots are the main areas of focus for biodiversity conservation. These are the areas that are extremely rich in biodiversity, have high level of endemism, and are under constant threat of species extinctions and habit destruction.

Recently, Norman Myers and a team of scientists have brought out updated lists of 25 hotspots (Myers et. al. 2000). These identified hotspots of biodiversity are

Caribbean, California Floristic Province and Mesoamereca in North and Central America; Tropical Andes, Choco-Darien-Western Ecuador, Atlantic Forest, Brazilian Cerrado and Central Chile in South America; Caucasus and Mediterranean Basin in Europe and Central Asia; Madgascar and Indian Ocean Islands, Eastern Arc Mountains and Coastal Forests, Guinean Forests of West Africa, Cape Floristic Region and Succulent Karoo in Africa; Mountains of Southwest China, Indo-Burma and Western Ghats of India in Mainland Asia; and Philippines, Sundaland, Wallacea, Southwest Australia, Newzeland, New Calenonia and Pollynesia and Micronesia in Asia Pacific region..

The two hotspots of biodiversity that extend into India.

The two hotspots that extend into India are the:

1. Indo-Burma and Western Ghat
2. Sri Lanka.

15.1.1 Indo-Burma

The Indo-Burma hotspot covers about 2 million square kilometres of tropical Asia east of the Indian subcontinent. The hotspot includes all of Cambodia, Vietnam and Laos, and nearly the entire areas of Thailand, Myanmar and Bhutan, as well as part of Nepal, far eastern India and extreme southern China. In addition, it covers several offshore Islands including Mainan Islands in the South China Sea, and the Andaman and Nicobar Islands in the Indian Ocean. Today, it is estimated that about 1,00,000 square kilometres or 5% of the original extent of the habitat is in pristine condition.

The entire hotspot was originally covered with broad-leaf forests; but, today, only fragments remain. In these fragments, a wide variety of ecosystems is represented including deciduous, wet evergreen dry evergreen and montane forests. Also, there are patches of shrublands, woodlands and scattered heath forests. The hotspot has the world’s highest diversity of freshwater turtle species. Moreover, the hotspot is still revealing its biological treasures, for example, three large mammal species have been discovered in recent years.

15.1.2 Western ghats and Sri Lanka

The hotspot encompasses the montane forests in the south-western parts of India and on the neighbouring Island of Sri Lanka. Although the two forest blocks are separated from each other by about 400 kilometres of land and water, yet they are similar enough that they can be grouped into a single hotspot. Though the entire extent of the hotspot was originally about 1,82,500 square kilometres; but, due to tremendous population pressure, now only 12,445 square kilometres or 6.8% is in pristine condition.

The Western Ghat Mountains stretch from India’s southern tip of Gujarat in the North, and run parallel to the country’s western coast. They cover an area of about 1,60,000 square kilometres. The western slopes of the mountains receive heavy annual rainfall, whereas the eastern slopes are drier. The wet tropical south-western zone of Sri Lanka is remarkably similar to the Western Ghats because of the repeated appearance and disappearance of a land bridge between them over many thousands of years.

The predominant vegetation of the entire hotspot includes deciduous and tropical rain forests, montane forests and grasslands, as well as scrup forests in lower, drier areas. The hotspot is home to a diverse and endemic assemblage of plants, reptiles and amphibians. The important populations include Asian elephants, Indian tigers and the endangered lion-tailed macaque.

15.2 Threats to Biodiversity

Human actions have caused extinctions (elimination of species) over a long time, not just in recent decades. The earliest humans probably caused extinctions through hunting; with the invention of fire, humans began to change habitats over large areas; with the development of agriculture and the rise of civilization, rapid deforestation and other habitat changes took place; as new areas were explored, the introduction of exotic species became an important cause of extinction; later, in the twentieth century, with the introduction of industrial chemicals and emissions, pesticides, etc. into the environment, pollution has become an increasingly significant cause of extinction.

Human actions poses threats to biodiversity through:

15.2.1 Habitat loss and degradation

Habitat loss and degradation are the major proximate causes of species extinction, affecting 89% of all threatened birds, 83% of mammals and 91% of all threatened plants assessed globally. The main causes of habitat loss are agricultural activities, harvesting or extraction (including mining, fishing, logging, etc.) and development of human settlements, industry and associated infrastructure.

Habitat destruction inevitably results from the expansion of human populations and human activities. The ever-expanding human settlements have been causing destruction of natural ecosystems to meet their requirements of food, space, shelter, etc. The greatest destruction of biological communities has occurred during the last 150 years during which the human population went from just one billion in 1850 to 6.2 billion in 2002, and will reach an estimated 7.8 billion in 2025. In many countries, particularly Islands and where human population density is high, most of the original habitat has already been destroyed.

15.2.2 Habitat fragmentation

It is a process where a large, continuous area of habitat is both reduced in area and divided into two or more fragments. Habitat fragmentation may take place due to the development of roads, towers, canals, fields, industries, etc. in an original large habitat. The fragments thus divide populations into isolated groups that not only limit the potential of species for dispersal and colonization but also reduce the foraging ability of animals. These isolated, small, scattered populations are increasingly vulnerable to inbreeding depression, high infant mortality and susceptible to environmental hardships, and consequently, in the end, possible extinction.

15.2.3 Genetic assimilation

Some rare and endangered species are threatened by genetic assimilation because they crossbreed with closely related species that are more numerous or more vigorous. Opportunistic plants or animals that are introduced into a new habitat by human actions may genetically overwhelm local populations. For example, hatchery-raised trout introduced into lakes or streams may genetically dilute indigenous stocks.

15.2.4 Pollution

Environmental pollution is the most subtle form of habitat degradation. The most common causes of which are pesticides, industrial effluents and emissions, and emission from automobiles. Toxic pollutants can have disastrous effects on local populations of organisms. Pesticides linked declines of fish-eating birds and falcons was well documented in the 1970s. Mysterious, widespread deaths of thousands of seals on both sides of Atlantic in recent years are linked to an accumulation of chemicals such as DDT, PCB’s and dioxins. Lead poisoning is another major cause of mortality for many species of wildlife.

15.2.5 Poaching

Poaching is another insidious threat that has emerged in recent decades as one of the primary reasons for the decline in number of species. Poaching pressures, however, are unevenly distributed since certain selected species are more heavily targeted that others are. Despite legal protection in many countries, products from endangered species are widely traded within and between nations.

Wildlife is sold for live specimens, folk medicines, furs, hides, skin (or leather) and other products such as ivory, antlers and horns amounting to millions of dollars each year. Developing countries in Asia, Africa and Latin America with the richest biodiversity in the world are the main source of wild animal and animal products, while Europe, North America and some Wealthy Asian countries are the principal importers.

15.2.6 Introduction of exotic species

Organisms introduced into habitats where they are not native are termed as exotics. They can be thought of us biological pollutants and are considered to be among the most damaging agents of habitat alteration and degradation in the world. Inducing species intentionally or unintentionally (accidentally) from one habitat into another where they have never been before is a very risky business. Freed from the parasites, pathogens, predators and competitors that normally keep their numbers in check, exotics often exhibit explosive population growth that crowds out native species. Their aggressive invasion might be considered a kind of ecological cancer. Introductions of exotic species have caused especially severe problems on Islands.

The above mentioned causes of biodiversity loss due to human actions, however, are poverty, macroeconomic policies, international trade factors, policy failures, poor environmental laws/ weak enforcement, unsustainable development projects and lack of local control over resources. Population pressures and accompanying increases in the collection of fuel wood and fodder, and grazing in forests by local communities too take their toll on the forests, and consequently its biodiversity.

15.3 Important Terms in Biodiversity

(i) Endangered species
(ii) Vulnerable species
(iii) Rare species
(iv) Threatened species

15.3.1 Endangered species

The species that are considered in imminent danger of extinction and whose survival is unlikely if factors causing their decline continue to operate. These are species whose numbers have been reduced to a critical level or whose habitats have been so drastically reduced that they are in immediate danger of extinction.

15.3.2 Vulnerable species

The species that are under threat such that they may have to be classified as endangered in the near future if causal factors continue to operate. These include species whose populations have been seriously depleted and whose ultimate security is not assured, as well as those species whose populations are still abundant but are under threat throughout their range.

15.3.3 Rare species

These are species with small total population size in the world. In their distribution, they are usually localized within restricted habitats or geographical area or are thinly scattered over an extensive range. It is necessary to mention here that a species that is rare is not necessarily in danger of becoming extinct; some species, like the whooping crane, are naturally rare. However, rarity does raise concerns about the possibility of extinction. Rare species, thus, are not at present endangered and vulnerable but are at risks.

15.3.4 Threatened species

The term ‘threatened’ is used in the context of conservation of the species which are in any one of the above three categories. These are species that have declined significantly in total numbers and may be on the verge of extinction in certain localities.

At present, 1672 species of animals are listed in these four categories worldwide (Table 4.10). Information is sketchier about plants, because numerous plant species grow only in poorly explored areas. Of 34,266 plants in the IUCN Red Database, 15780 are listed as threatened. As per IUCN estimates, there are 20,000 to 25,000 species of vascular plants (plants having a system for moving fluid, such as sap) that either have recently become extinct or are endangered, vulnerable or rare. Infact, the total number of species that are threatened is not yet known, because many areas, particularly in tropics, have not yet been explored for species diversity.

Table 15.1 Worldwide threatened species of animals

15.4 ‘Endangered and Endemic Species of India’

India ranks second in terms of the number of threatened mammals, while sixth in terms of countries with the most threatened birds. The numbers of threatened species of India by taxonomic group are shown in Table 4.11. Such a biological impoverishment of the country is a serious threat to sustainable advances in biological productivity as gene erosion also erodes the prospects for deriving full economic and ecological benefits from recent advances in molecular biology and genetic engineering.

Table 15.2 Threatened species of India by taxonomic group

According to the Red List of Threatened Animals, 18 animal species are critically endangered, 54 endangered and 143 are vulnerable, while 10 species are lower risk conservation dependent and 99 are lower risk near threatened. Amongst plants, 44 are critically endangered, 113 endangered and 87 vulnerable.

Some of the animal species that have been identified as endangered or threatened ones are Lion tailed macaque, Golden monkey, Himalayan brown beer, Tiger, Indian Lion, Great Indian one-horned rhinoceros, Indian antelope (or Blackbuck), Kashmir stag (or Hangul), Swamp deer (or Barasingha), Baleen whale, Mute swan, Great Indian bustard, Indian pied hornbill, Gharial.

Endemics are species that are found in a single locality/ area and nowhere else in the world. They, thus, have a value in their uniqueness. Areas of endemism containing several endemic species, genera or even families have generally been isolated for a long time, thus enabling the original species to evolve into new genetic entities better adopted to local area. Isolated mountain tops, valleys and large oceanic Islands are usually areas of endemism. Conservation of resources of these areas is very difficult as each area will pose its own peculiar problems.

The endemism of Indian biodiversity is quite high. About 33% of the country’s flora are endemic to the country and are concentrated mainly in the North-East, Western Ghats, North-West Himalaya and the Andaman and Nicobar Islands. Of the 49,219 plant species, 5,150 are endemic (not found elsewhere) and distributed into 141 genera under 47 families corresponding to about 30% of the world’s recorded flora, which means 30% of the world’s recorded flora are endemic to India. About 15,000 species of flowering plants (angiosperms) are known to occur in India, out of which 4,950 species of flowering plants had a birth in India. Of all these endemic plant species, 3,500 are found in the Himalayas and adjoining regions and 1,600 in the Western Ghats alone. Many deep and semi-isolated valleys are exceptionally rich in endemic plant species. Such as, in Sikkim, in an area of 7,298 square kilometer, of the 4,250 plant species, 2,550 (60%) are endemic.

India is particularly rich in floral wealth and endemism, not only in flowering plants but also in reptiles, amphibians, swallow-tailed butterflies, and some mammals. About 62% of the known amphibian species and nearly 50% of the lizards of the country are endemic with the majority occurring in the Western Ghats.
Endangered species of mammals, amphibians, reptiles and birds