Cause 1. Habitat Fragmentation:
Large areas rich in biodiversity have been reduced to small pockets. This is fragmentation which has occurred as agricultural fields, roads, and housing, industrial hydro-electric and other projects have come up in biodiversity-rich forested areas. Fragmentation of forests, for example, has severely affected the elephant population in India. This is one reason why these animals increasingly raid agricultural fields, leading to conflict between elephants and people.
Cause 2. Introduced Species:
Introduction of non-native species (also known as “alien” or “exotic species”), deliberately or accidentally, has been a major threat to biological diversity worldwide as the introduced species have often flourished at the cost of the local species. Weeds such as Parthenium hyderophorus, which came to India accidentally with a consignment of wheat from the United States, have spread over large forest areas at the expense of native species. The forest floor of several protected areas has been taken over by Lantana camara, a species brought to India from Mexico to serve as an ornamental . Indigenous (or native) species are being replaced by commercially useful exotics such as eucalyptus.
Cause 3. Overexploitation of Plant and Animal Species:
Many species have been overexploited by humans, sometimes to the point of extinction. Some species are overexploited for food and shelter. Marine fauna, in particular, is under great threat from overexploitation largely as a result of mechanised fishing and increasing international fishing operations in Indian waters.
Killing for precious commodities, such as ivory, and trapping of birds and mammals as collector’s items, curiosities and for rearing as pets, has threatened other species as well. Various reptiles and amphibians have been exploited for both skin and meat. The trade in live birds for falconry and as ornamental birds has also led to a decline in bird species in India. Excessive commercial demand from a rapidly expanding pharmaceutical industry, for which no collection regulations exist, affects medicinal plants of various taxa. Dioscorea deltoidea (yam), a species that grows in north-east India, is a major source of diosgenin used in the manufacture of contraceptive pills.
Cause 4. Pollution of Soil, Water and Atmosphere:
Pollution affects the functioning of ecosystems and may reduce or eliminate sensitive species. A long-term study in Keoladeo National Park in Rajasthan showed high levels of pesticide residues in Sarus Cranes. These toxic residues could lead to a high mortality rate among the cranes and eventually a decrease in their population.
Pesticides are responsible for the high mortality rates among birds of prey such as the Peregrine Falcon and the Osprey. Pesticides are known to persist in the body of animals and are passed on along the food chain to the next consumer causing further harm.
Water pollution also affects biodiversity. In India industrial effluents are destroying coral reefs and other marine life. About 40 tones of tar balls (by-products of petroleum refining) are deposited on Goa’s beaches every year. These tar balls are washed ashore during the monsoons. A thin film of oil spreads across the water surface reducing the penetration of sunlight. This affects the plant life found below by reducing their photosynthetic activity. The impermeable oil film also reduces the exchange of gases leading to disruption of respiration, thus killing of many aquatic organisms.
Cause 5. Global Climate Change:
Global warming, a side effect of air pollution, may play havoc with the world’s ecosystems in the coming decades. Many species that cannot adjust to warmer temperatures are likely to become extinct. Rare and isolated species will be most at risk, being most sensitive to any atmospheric change. Some habitats such as islands and coastal systems, which are at risk of flooding and submergence, will suffer particularly high losses of biodiversity.
Cause 6. Ignorance about Species and Ecosystems and Loss of Traditional Knowledge:
A species may be lost because we did not know it existed at a site that was developed. In some cases a species may be known locally but the knowledge may die out as traditional ways of life change. In India hundreds of tribal and other communities utilise biodiversity products in their everyday lives for many different purposes like food, fibre, antidotes against insect and snakebites, medicines, and for making hunting, fishing, and farm implements. The lifestyles of these communities are fast changing, and if their traditional knowledge is not recorded, understood and passed on, we are likely to lose it all.
Cause 7. Unplanned Development:
Large-scale development projects have contributed substantially to the loss forests. Between 1951 and 1980, over 5, 02,000 hectares of forests were diverted for river valley projects in India. For instance, the 11 dams constructed on the Periyar river in Kerala not only caused submergence of large tracts of forest but also gave rise to settlements and roads in the forest area.This badly fragmented the habitat , severely affecting the biodiversity. In Goa, for example, mining covers 500 sq km, or 14 per cent of the state’s total area and has destroyed the forest area.Coral reefs off Gujrat coast are another example of biodiversity loss.
Cause 8. Economic Systems and Policies:
Economic systems and policies that fail to value the environment and its resources contribute to the loss of biodiversity. Biologically diverse natural systems are most often undervalued in monetary terms and, as a result, are converted into agricultural lands or developed for housing or industrial activities that seemingly have more direct economic benefits. Wetlands in India, such as ponds in urban areas, are being converted for housing and commercial projects every day.
Cause 9. Inflexible or Inappropriate Legal and Institutional Systems:
Although laws to protect biodiversity exist, loss of biodiversity continues. This may be because rarely a cross-sectoral approach is adopted which combines ecological and economic realities. Over centralisation of planning hinders local participation which might have brought knowledge, insight and experience of the local environments into the planning process. Customary law (the traditional law of communities), which by and large promoted the sustainable use of biological resources, is being replaced by a less effective legal system.
Cause10. Some Agricultural and Forestry Practices:
Over the years farmers have bred and maintained a tremendous diversity of crops and livestock varieties. The broad genetic base provided insurance against pests, diseases and adverse climatic condition. But in the last few decades, prompted by the growing demand for food and by market forces, modern agriculture has moved towards fewer crop varieties which are high yielding and respond better to water, chemical fertilisers and pesticides. Indigenous breeds of cattle have been replaced by cross-breeds and exotics for their higher milk yields. Stability and diversity are thus being replaced by uniformity and productivity. Similarly forestry has also promoted monocultures, leading to substantial loss of biodiversity. In many parts of India commercial plantations of single species have replaced several other species. South India abounds in teak monocultures.
Cause 11. Unsustainable Natural Resource Consumption:
If the current demographic trend continues, human population will continue to grow for at least the next half century and probably longer, barring catastrophy. India’s population have crossed 1 billion in the year 2000 and will cross 1.4 billion by the year 2025. Growing population, as well as growing aspirations and consumption-oriented lifestyles is causing loss of biodiversity.
Cause 12. Inequities:
Inequities in the ownership, management and flow of benefits from the use and consumption of biological resources encourages unsustainable exploitation which leads to loss of biodiversity. Substantial areas in India significant for their biodiversity (expect in the north-east) are owned by the State or Centre as Reserved Forests, Protected Forests, National Parks and Sanctuaries.
Cause 13.Natural Calamities-like floods,forest fires ,volcanic eruptions,floods,draughts etc take a toll on plant and animal life and cause loss of biodiversity.