Bed 2nd Year What do you mean by Threats to Biodiversity
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Bed 2nd Year What do you understand by Biodiversity
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Threats to Biodiversity
The following types of species tend to disappear in due course of time:
(i) Species with a very narrow geographical range.
(ii) Species with only one or a few populations.
(iii) Species in which pollution size is small.
(iv) Species with low population density.
(v) Species that need a large home range.
(vi) Species that have large body sizes.
(vii) Species with low rates of population increase.
(viii) Species that are not effective dispersers.
(ix) Species that migrate.
(x) Species with little genetic variability.
(xi) Species with specialized niche requirements.
(xii) Species that are characteristically found in stable environments,
(xii) Species that form permanent or temporary aggregation.
(xiii) Species that are hunted or harvested by people.
To highlight the legal status of rare species for purpose of conservation, IUCN (1984, 1988) has established the following five main conservation categories:
- Extinct. Species that are no longer known to exist in the wild. The search of localities where they were once found and of other possible sites have failed to detect the species.
- Endangered. Species have a high likelihood of going extinct in the near future.
- Vulnerable. Species that may become endangered in the near future because populations of the species are decreasing in size throughout their range. (Bed 2nd Year What do you mean by Threats to Biodiversity)
- Rare. Species that have a small total number of individuals are often due to limited geographical ranges or low population densities. (Bed 2nd Year What do you mean by Threats to Biodiversity)
- Insufficiently known. Species that probably belong to one of the conservation categories but are not sufficiently well known to be assigned to a specific category. (Bed 2nd Year What do you mean by Threats to Biodiversity)
Mace and Lande (1991) have proposed a three-level system of classification based on the probability of extinction.
- Critical. Species with a 50% or greater probability of extinction within years of 2 generations whichever is longer.
- Endangered. Species with a 20% probability of extinction within 20 years of 10 generations.
- Vulnerable. Species with a 10% probability of extinction within 100 years.
Causes of Threats to Biodiversity Human activity is the major threat to biodiversity and the following are the chief causes of extinction of species caused by man to fulfill its needs:
(1) Habitat Loss,
(2) Habitat Fragmentation,
(3) Habitat Degradation and Pollution,
(4) Introduction of Exotic Species,
(5) Disease, and
The details of these points have been given in the following paragraphs:
- Habitat Loss. The primary cause of the loss of biodiversity is not direct human exploitation but habitat destruction that inevitably results from the expansion of human populations and human activities. The greatest destruction of biological communities has occurred during the last 150 years during which the human population went from 1 billion in 1850 to 2 billion in 1930, to 5.3 billion in 1990, and will reach an estimated 6.5 billion by the year 2005. Habitat loss is the primary threat to the majority of vertebrates currently facing extinction. In many countries, particularly on Islands and where human population density is high, most of the original habitat has been destroyed. More than 50% of the wildlife habitat has been destroyed in 49 out of 61 old world tropical countries (IUCN, UNEP 1986) in 1 tropical Asia, fully 65% of the wildlife habitat has been lost, with particularly high rates of destruction in Bangladesh (94%), Hong Kong (95%), Sir Lanka (95%), Vietnam (80%) and India (80%).
In many cases, the factors causing habitat destruction are the large industrial and commercial activities, associated with a global economy, such as mining, cattle ranching, commercial fishing, forestry, plantation, agriculture, manufacturing, and dam construction, initiated with the goal of making a profit. Huge amounts of habitat are lost each year as the world’s forests are cut down. Rain forests, tropical dry forests, wetlands, mangroves, and grassland are threatened habitats and lead to desertification.
- Habitat Fragmentation. Habitat that formation occupied Wide areas is now often divided up into pieces by roads, fields, towns, canals, power lines, etc. Habitat fragmentation is the process where large, continuous areas of habitat are both, reduced in area and divided into two or more fragments. When a habitat is destroyed there is often a patchwork of habitat treatments left behind. These fragments are often isolated from one another by a highly modified or degraded landscape. Habitat fragments differ from the original habitat in two ways, and second, the center of each habitat fragment is closer to an edge. Habitat fragmentation may limit the potential of species for dispersal and colonization. It also reduces the foraging ability of animals. Habitat fragmentation causes such edge effects as microclimatic changes in light, temperature, wind, etc.
- Habitat Degradation and Pollution. Some activities may not affect by such habitat degradation. For example, physical degradation of forest habitat by uncontrolled ground fires, might not kill the trees, but the rich perennial wild plant community and insect fauna on the forest floor would be affected. Boating and diving in coral reef areas degrade the fragile species most common causes of which are pesticides, industrial chemicals and w emissions from factories and automobiles, and sediment deposits from hillsides. Effects of pesticide pollution, water pollution, and air pollution environment are well known. The problem of acid rains and global climate is also well known and of global concern.
- Introduction of Exotic Species. Habitat destruction, fragmentation, and degradation have obvious harmful effects on biodiversity. But even if biological communities are intact, significant losses can be taking place due to changes caused by human activities. Three such changes are the introduction of exotic species, increased levels of diseases, and excessive exploitation, of particular species by people. The three chief factors responsible for introduced. of exotic species are European colonization, horticulture, and agriculture accidental transport. The great majority of the exotic species do not been established in the introduced new places. However, some of the species are al to establish in the new areas. Such successful exotic species may kill or eat native species to the point of extinction, or may so alter the habitat that many natives are no longer able to persist. The effect of exotic species is maximum on islands. Disease-causing microorganisms, if introduced to new virgin areas may cause epidemics and native species are eliminated completely.
- Disease. Human activities may increase the incidence of disease in wild species. The extent of the disease increase when animals are confined to a nature reserve rather than being able to disperse over a large area. Also, animals are more prone to infection when they are under stress. Animals held in captivity are also more prone to higher levels of disease.
- Over Exploitation. The increasing human population has escalated the use of natural resources. Methods of harvesting have been dramatically modified to have maximum gains. In traditional societies, there existed some controls to prevent over-exploiting in several ways. In contrast to this, in much of the world, today resources are exploited as rapidly as possible. Overexploitation of resources also occurs when a commercial market develops for a previously unexploited or locally used species. The best example trades in furs. Overexploitation threatens about one-third of the endangered vertebrates in the world, as well as other species, Growing rural poverty, increasingly efficient methods of harvesting, and the globalization of the economy, combine to exploit species to the point of extinction. Even if a species is not completely eliminated by over-exploitation the population size may become so low that the species is unable to recover.
- Shifting or Jhum Cultivation. Some rural people destroy biological communities and hunt endangered species because they are poor and have no land of their own. In many countries, there is extreme inequality in the distribution of wealth; with the majority of wealth (money, good farmland, timber resources, etc.) owned by a small percentage of the population. The local poor people with a traditional way of life in rural areas have often established a local system of rights to natural resources. These local people are quite distinct from settlers who have arrived more recently and are not closely linked to the land. In fact, tropical areas of the world have had particularly a long association with slips, since the tropics have been free of glaciations and are particularly amendable to human settlement. People have lived in every terrestrial ecosystem sands of years as hunters, fishermen gatherers, and farmers. (Bed 2nd Year What do you mean by Threats to Biodiversity)