The present and projected losses of biodiversity have been termed a ‘crisis’ (Wilson, 1985).
The crisis is particularly more serious in developing countries like India. Serious losses of biodiversity are presently taking place all over the world.
It follows that the ‘bottom line’ is how much of biodiversity can we alter, or loose, before we threaten our own existence (Gaston and Spicer, 1998). The erosion of biodiversity may be attributed to the following factors.
Extinction of Species:
The list of animal and plants species that have become extinct or extinct in the wild (Table 7.5) is quite alarming. Since 1600 there have been over 1000 recorded extinctions of plant and animal species and about half of these extinctions took place between 1900 and 2000 (Smith et at 1993). Probably early humans were directly responsible for the extinction of many large mammals during the late Pleistocene and also indirectly responsible for the loss of many smaller ones (Martin 1984, Owen-Smith 1987). Colonization of tropical Pacific islands by prehistoric peoples led to large number of avian extinctions (Pimm et al, 1995).
However, our studies and data on extinctions are biased toward birds and mammals and also toward islands and some developed nations. Regarding invertebrate and plant extinctions we have little information. It is sometimes advocated that the current extinction rates are possibly 4 or 5 times more than the rates in the fossil record. The Red List of 2003 has more than 12 thousand species and the current extinction phase is effecting large mammals and birds and freshwater invertebrates. These changes call for rapid biodiversity assessment (RBA).
Human Population Growth and Urbanization:
According to World Resources Institute (1996), the world’s human population is estimated to about 5.7 billon and to be increasing by more than 86 million per annum. However, between 1800 and 2000 the rate has increased dramatically. This unprecedented human population growth led to increase in the number and sizes of the megacities in the world. A large portion of the world’s total population resides in about 25 megacities.
Though the world’s cities take up only 2% of the earth’s surface, they account for approximately 78% of carbon emission from human activities, 76% of industrial wood use and 60% of the water tapped for use by people (UNEP-IETC, 2000). Space created for expansion of cities or for conurbation has been through large-scale deforestations and use of agricultural land for human settlements.
These practices have created serious threats to biodiversity. It has been estimated that with the present rate of destruction of tropical forests, 20 to 25% of the world’s plant species would have been lost by the year 2000. According to another estimate, 90% of tropical forest area containing more than 500 varieties of plant species will be destroyed during the next 20 years.
Energy Consumption and Emissions:
It is estimated that from before the agricultural revolution to the present time, the total energy consumption by humans has multiplied about 7000 to 13000 fold (Ehrlich, 1995). The global commercial energy production in 1993 was 338 EJ (1EJ = 1018 J) or about 163 million barrels of oil, 40% greater than in 1973.
As this trend of energy consumption is further increasing year after year, we have more and more emissions of harmful gases to the troposphere. Global emissions of CO2 during 1992 were estimated at 26.4 Gt (1Gt = 109 t), of which about 85% was from industrial activity (World Resources Institute). The power generation activities and emissions of gases have adversely affected biodiversity both directly and indirectly.
Changes in Land-use Patterns:
According to Richards (1990), changes in land-use patterns during the past 300 years have caused about 19% reduction in forest cover, 8% reduction in grasslands and pastures and 500% increase in croplands. Expansion of modem agriculture and extensive and intensive aquaculture practices have also led to serious changes in land use over the past 50 years.
These changes have in turn caused severe losses of biodiversity in agricultural ecosystems. During green revolution a large number of wild crop varieties were replaced with a few hybrid species. This resulted in the small disappearance of our genetic resources of crop plants especially for wheat and rice. With the disappearance of the plants, the associated micro-organisms and fauna were also lost. Besides this, indiscriminate use of synthetic fertilizers and other chemicals reduced the microbial species diversity.
Habitat Degradation and Loss:
Habitat degradation and loss due to human activities and other disturbances are well known factors all over the world. The pattern of human disturbance may vary but it is causing unforeseen changes in all types of ecosystems and thus threatening the biodiversity. As a result of habitat degradation wild populations become more vulnerable to predators and diseases and fight for their existence. This is especially true for wildlife, which suffer due to habitat loss and fragmentation.
Pollution:
Some studies have shown a direct connection between economic growth and pollution and also between economic development and pollution. Pollution of air, water and soil and the presence of toxic and hazardous pollutants in different components of biosphere have created serious problems. As a result, our freshwater resources have suffered irreparably and many species of fish and aquatic birds and mammals have been threatened. Fish and birds are also killed by unregulated pesticide use.
In case of an electric power plant, only about 40% of the coal’s energy value is used to run turbines to produce electricity; the remaining 60% is low- grade energy which ordinarily becomes thermal pollution and harms all the aquatic communities and their natural food chains. Thus, environmental pollution is considered as one of the immediate causes affecting current levels of biodiversity (Mc Neely et al, 1995).
Global Climate Change:
As a result of global warming and other factors, a climate change is experienced. The potential environmental in applications of climate change are too many. As a result of climate change snow caps are receding, summer temperatures are rising and many coastal areas are going under water, besides many unnoticed changes in populations and ecosystem functioning.
It is estimated that the greenhouse effect is expected to threaten 400 species of mammals, 460 species of reptiles, 650 species of birds, 660 species of freshwater fish, and the tens of thousands species of invertebrates and plants in the United States (Sweeny). An increase in extinction rate of some of these species and changes in their migration patterns are predicted.
The global climate change is also going to affect crops fields, forests and coastal wetlands which are very rich in biodiversity. Due to pressure on account of environmental changes, 11046 species of plants and animals are facing high risk of extinction today (lUCN, 2000). In Oct.,2002 in Delhi 169 countries participated in UN conference and prepared Delhi declaration on climate change (Ddcc), which emphasizes on proper use of energy and ratification of Kyoto protocol by all the countries.
Introduction of Exotic Species:
Foreign species introductions are also considered one of the immediate causes affecting current levels of biodiversity. Although man has moved many species of plants and animals from one part of the globe to another and many of such species have established themselves in new environments but few studies have been made to assess the impact of exotic species on the local fauna and flora.
At a regional scale, new introductions may tend to increase biodiversity, but they also tend to homogenize biodiversity between regions (Gaston and spicer, 1998). In many cases exotic species outcompete or prey on the pre-existing biota. One of the most dramatic examples is of the brown tree snake Bioga irregularis, which since its introduction has caused high decline in the avifauna of the island of Guam (Pimm 1991). The indigenous fish fauna of India has suffered due to exotic species like common carp and the African cat fish, Clarias gariepinus, which has faster growth rate (NBFGR, AR 1999-2000).
Other Factors:
A number of other factors such as global trade and economic systems and policies that do not fully appreciate the value of natural resources have detrimental impacts on biodiversity. Illegal trade and poaching of wildlife products have reduced the populations of many wild animals such as African elephant, Asiatic lion, one homed rhinoceros and musk deer. Stuart Chapman recently commented ‘the Asian rhinos’ future hangs in the balance unless we reduce the persistent demand for its horn used in traditional Asian medicine as well as protect them from poaching’s’. Trade in medicinal plants has also played an adverse role.
It may be concluded that biodiversity is being destroyed mainly by human activities at alarming rates almost in all parts of the earth. If the present rate of loss of biodiversity continues, it is not surprising that many valuable species will become extinct even before they are described. The biodiversity loss results in ecological and environmental deteriorations.