Biodiversity loss has always existed as a natural process but threats to biodiversity arise when the rate of extinction exceeds the rate of speciation.
Biodiversity loss is primarily related with human interactions with natural resources.
In early phases of life, humans remained as one component of ecosystem but, very recently, humans have become a factor of ecosystem and started reshaping the biodiversity.
Now, biodiversity loss has become primarily human sourced phenomenon (Table 1.8).Humans have drastically disturbed the natural rate of extinction of species and speciation (Leemans, 2001). Factors that cause loss of biodiversity have exceeded the factors that cause gains in biodiversity (Figure 1.11). Rate of speciation has been adversely affected due to which many species have disappeared from the earth and many are facing varying degrees of threat of extinction.
Escalating human population is the root cause of biodiversity loss. Major threats to biodiversity not only emerge from ever-increasing human population but also multiplied by it. Deforestation, land use/cover changes, over-utilization of natural resources, poaching, pollution, etc., are some of the direct outcomes of increasing population leading to erosion or loss of biodiversity.
In 1951, India was characterized by about 361 million populations, but in the year 2001, it was threatened by 1,027 million populations (Table 1.9). Altogether population has increased by three times and is expected to increase upto 1,807 million by 2050, which would further increase the pressure on biodiversity.Typically, population and related threats are developed so rapidly and at such a large scale that species are not able to keep pace with these changes. Thus, species are not able to adapt genetically to these changes and are lost. Human uses resources as fuel wood, fodder, inputs in industries and converts natural landscape for agriculture and various other purposes, which eventually lead to loss of biodiversity.
In a developing country like India, the patterns and causes of habitat destruction, which is a prime cause of biodiversity loss, are linked to ever-increasing pressure of human population together with their domestic animals, associated with other developmental activities for the better living of mankind.
2. Habitat Destruction (Deforestation) and Fragmentation:
Habitat destruction and fragmentation are considered as prime reasons of the biodiversity loss and is generally called the deforestation. Although habitat may be degraded, modified or merely eliminated but it is more commonly devastated by human activities. Deforestation is, generally, of two types: decrease of forest land, i.e., conversion of forest land into other land uses and decrease in the tree density due to cutting of selective tree species. Large tracts of forests are now converted into other land uses. This process is more common throughout the world, especially in developing countries like India.
In tropical Asia, 65 per cent of the total forests have been destroyed with particularly high rate of destruction reported for Bangladesh (96%), Sri Lanka (86%) and India (78%). Altogether, India has recorded increase in net forest cover in recent past but natural forests have decreased.
It is estimated that after independence, India has lost 4,696 million hectares of forest land, while 0.07 million hectares of forest land have been illegally encroached upon, 4.37 million hectares has been subjected to cultivation, 0.52 million hectares given to river valley projects, 0.14 million hectares to industries and townships, 0.16 million hectares for transmission lines and roads and rest for miscellaneous purposes (MoEF, 1999).
Presently, remaining forest cover is under severe pressure particularly in Himalaya, Central Indian uplands and Western Ghats. Clearance of forests up to limited extent does not render the species vulnerable, nor decrease the number of its members but devastation upto greater extent poses vulnerability to biodiversity and further to ecosystem (Joshi and Joshi, 2004).
Besides, massive destruction of forests that formerly occupied wide unbroken areas are now often divided into pieces usually called fragmentation of habitat by roads, field, farms, houses, industries, power lines and a broad range of human activities.
Basically, habitat fragmentation is a process in which a large continuous area is, both, reduced in area and divided into fragments that aggravate the problem in many ways as under:
1. Fragments limit the dispersal and development of species.
2. Fragments prevent the natural migration of species which may lead to starvation of these species and degradation of these habitats.
3. Fragments often change the micro-climate at fragment edge resulting high wind speed and lower humidity. Each of these can have a severe impact on species such as change in micro-climate, frequent fires in forests and in this process many of species are eliminated.
3. Overuse of Natural Resources:
The hunting and harvesting of wild plants and animals is needed for survival of man. As long as the human population was small and methods of collection were primitive, people could harvest the plants and animals in sustainable manner.
Now, as humans become more numerous and widespread, they start killing species faster than those species can replace themselves, either through reproduction or immigration from elsewhere. Increased human population has led to almost complete depletion of large animals from many biological communities leaving habitat ’empty’.
The illegal killing and smuggling of wildlife is rampant in almost all parts of the world. In India, killing of elephants to obtain their tusk and tiger to obtain their multiple benefits has taken place. Poaching of male elephant for tusk leads to imbalance in the sex ratio to their population.
The one-horned rhino is poached for its horn, which is supposed to have some aphrodisiac property. Earlier this animal was found in Tarai regions of Uttar Pradesh, Assam and Bengal but now confined to only one or two pockets of country. Their number has also decreased to about two to four hundred. Similarly, the musk dear, formerly widespread throughout the Himalayan sub-alpine forests and alpine scrub, is now confined within a quarter of its former range in India.
This animal is killed for a special gland or musk pod, which is found in abdominal region of male. Today, musk fetches around 40,000 to 60,000 US dollars in the international market and about 2,000 male musk deer are killed to obtain one kilogram of musk (Joshi and Joshi, 2004).
4. Impact of Non-native/Exotic Species:
Species introduced by humans have exterminated the native species by competing with them, preying upon them or destroying their habitat. These introduced species may displace native species through competition for limited natural resources; they may push them on the verge of extinction or they may alter the habitat so that many native species are no longer able to persist.
The introduction of exotic species into some areas has had devastating impacts on the native biodiversity. Native species, most vulnerable to impact of exotic species introduction, are those which have evolved in isolation from high level of competition and predation. The majority of recent extinct species inhabited small isolated oceanic islands.
Important examples of this is Doda, which were early target of sailors for much needed protein but many more fight-less bird species were victims of species introduced by man, accidentally and deliberately. Researchers have demonstrated that 22 species and sub-species of reptiles and amphibians have disappeared worldwide due to alien animals. Alien species are significant threat affecting 350 (30% of all threatened) birds and 361 (15% of all threatened species) of plants species (Simaon, 2001).
5. Climate Change:
Climate change is a significant driving force behind the loss of genes, species, speciation and critical ecosystem’s services.
There are some close relations between climate change and biodiversity, as under:
1. Due to global warming, ecosystems generally shift northward or upward in altitude, but in some cases they will run out of space, as 1°C change in temperature corresponds to 100 kilometers change in latitude. Hence, average shift in habitat condition by the year 2100 will be in the order of 140 to 580 km (CPCB, 2002).
2. High temperature trigger earlier flowering. This could affect interaction with other species that depend on flowering plants. For example, alteration of distribution and growing season of upland could adversely impact pollinators.
3. Climate change is affecting species already threatened by multiple threats across the globe—habitat fragmentation due to colonization, logging, agricultural and mining, etc., are all contributing to further destruction of terrestrial habitats.
4. Coral reef mortality increases and erosion is accelerated due to increasing temperature. In 1998, 16 per cent of the world’s corals died due to higher temperature. Increased level of CO2 adversely impacts the coral building process (calcification). Scientists estimate calcification could decline 17-35 per cent below pre-industrial level by 2100.
5. Sea level rise due to global warming would result in disappearance of low-lying areas and further to extinctions of island species.
6. In equatorial regions, growth of plants will be disturbed. Many species that are very sensitive and cannot adapt to rapid climate change process will disappear. Photosynthesis process will increase in temperate regions that will result in greening of these regions. Plant growth will increase.
7. Loss of biodiversity in equatorial region and development in temperate region is taking place due to global climate change leading to food cycle changes at local and global levels.
6. Natural Calamities:
Natural calamities such as floods, cyclones, landslides and avalanches, volcanism, etc., are also responsible for depletion of biological diversity. For example, during the monsoon season in 1998 and also many times after 1998, entire Kaziranga National Park in Assam was heavily flooded which led to the death of 28 rhinos, 70-85 deer, 8 bears and 3 elephants and many plant species were also lost.
7. Energy Resources:
Development and utilization of various forms of energy resources, e.g., fossil fuel (crude oil, coal and natural gas), biomass energy, nuclear energy, hydroelectricity and other non-conventional energy sources has direct implications on biodiversity. Development of these energy sources modifies natural habitat and alters the evolutionary process (Table 1.10).
Development and utilization of fossil fuel accelerates global climatic change and associated disturbances like air pollution, particularly when coupled with human population growth and eventually leads to the loss of biodiversity. Development of biomass energy requires vast stretches of land to be under agricultural land.
This results in conversion of natural landscapes in agricultural land. Also, it leads to monoculture and destroys the diversity of that landscape which is the loss of biodiversity. Development of hydroelectricity necessitates water storage in highlands, due to which large areas under forests and grasslands submerged under water. This results in modification of natural habitat and ultimately in loss of biodiversity. Similarly, other modes of energy sources affect the biodiversity.