"When the last individual of a race of living beings breathes no more, another heaven and another earth must pass before such a one can be again."William Beebe, Naturalist.
Biodiversity is most often thought of as the variety of organisms on earth. Yet it also includes two other factors: ecological diversity - the variety of ecosystems and ecological communities. And genetic diversity - the range of genetic differences found within and between species.
All three aspects are crucial for the success and development of life on earth. Since environmental conditions at every level are constantly changing, only diversity can ensure that some individuals and species will be able to adapt to the changes.
And all three have profound value for human beings. The value of biodiversity lies not just in our direct use of nature's vast range of products, from foods and medicines to fibres and materials. Biodiversity also guarantees a permanent source of new genetic materials for future breeding programmes.
Through ecosystems it delivers a vast range of environmental services from regulation of local climate to prevention of flooding and erosion. Not least biodiversity is one of the main sources of nature's perennial aesthetic appeal.
The rise of diversity
The history of life on earth has, to a large extent, been a story of increasing complexity. Though the fossil record may have obliterated traces of the earliest life forms, the number of families seems to have risen sharply in the Cambrian and Ordovician ages (about 543-443 million years ago). It then levelled out until the end of the Permian (about 248 million years ago), when the largest ever mass extinction wiped out more than 90 per cent of species on earth. There have been five massive episodes of extinction, but extinction is a normal facet of evolution: the average species in the fossil record lasts no more than five to ten million years.
No one knows the true scope of biodiversity on earth. Most estimates put the total number of species of plants and animals at somewhere between 10 and 30 million, with some convergence around the figure of 14 million. However, only around 1.7 million species - a small share of the total - have been identified and categorized, while even fewer have actually been studied. Of the known species, three-fifths are insects.
Diversity is not evenly distributed around the earth. The tropics, both wet and dry, along with tropical and sub-tropical coral reefs, have much higher levels of biodiversity compared to temperate areas. Britain, for instance, has 80 species of breeding birds for every 10,000 square kilometres of territory, while the Gambia in West Africa has 269 species for the same area, Indonesia has 271, and tiny Costa Rica 350.
The sixth extinction
Life on earth is currently undergoing a sixth mass extinction event. Its extent is only vaguely known - species are only recorded as extinct after there is no reasonable doubt that the last individual has died.
The known figures are alarming enough. Over the past 500 years 785 species have become extinct in the wild, while a further 65 are found only in captivity or under cultivation. Over 200 of the known extinctions have occurred since 1800, 50 times greater than the natural background rate for extinctions [based on the fossil record, the background rate is one extinction per one million species per year]. Current estimates of extinctions projected to occur over the next quarter century are 100 to 1,000 times the background rate.
In September 2007, the World Conservation Union (IUCN) in its annual report of endangered species, flagged the continued loss of biodiversity as a cause of major concern. Of the 41,415 species on the IUCN Red List, 16,306 of them are threatened with extinction, listed as critically endangered, endangered or threatened.
The list is grim reading. One in four mammals face extinction, along with one in eight birds, one third of all amphibians and 70% of the world's assessed plants.
Heading for the finality of extinction include:
- Close to 1,100 species of mammals, one-quarter of the total;
- 1,221 species of birds, 12.4% of the total number of 9,821 (another 812 species are considered near threatened). Of Europe's 514 species, more than 270 are threatened with extinction.
- 1,808 amphibians, 30% of the total;
- Over 2,000 species of freshwater fish, 20% of the total number identified. If totalled by continent, then nearly 40% of US freshwater fauna are at risk, 42% of Europe's and 33% of Australia's.
- 8,447 higher plant species (trees, flowering plants, etc.), representing 70% of those evaluated.
"The IUCN Red List shows that the invaluable efforts made so far to protect species are not enough," pointed out IUCN Director-General Julia Marton-Lefèvre, "The rate of biodiversity loss is increasing and we need to act now to significantly reduce it and stave off this global extinction crisis."
Corals were added to the list for the first time in 2007, with five species endangered, including two corals found in the Galapagos Islands, a protected reserve. The continued rise in ocean temperature triggered by climate change and El Niño has been identified as the main causes. Ocean warming also threatens 10 species of seaweeds, with 6 of them already classified as possibly extinct.
Gorillas and orangutans face an increasingly uncertain future. Some 60% of the Western Lowland Gorilla population has been wiped out by the Ebola virus and the commercial bush meat trade. While on Borneo, the organutans' habitat is being decimated by illegal logging and conversion of forests to oil palm plantations.
Jane Smart, Head of IUCN's Species Conservation Programme underscored the importance of biodiversity: "our lives are inextricably linked with biodiversity and ultimately its protection is essential for our own survival."
These figures certainly underestimate the threat. The record is far better for Western countries with more biologists - the countries with the richest number of species are often those with the fewest scientists. Most extinctions must be occurring unseen among species that have not yet even been identified - among the countless insects, spiders, nematodes, molluscs and bacteria of cleared rainforest, or the largely unrecorded biota of the ocean floor.
The extinction of a species is of course the ultimate loss - but the process of local extinction has very serious consequences on local ecosystems, and effectively reduces people's chances of enjoying a glimpse of species - as the continued decline of songbirds in Britain illustrates.
Major threats
The principal threat to most species - land, aquatic and marine - is the loss or degradation of habitat due to human activities: conversion of natural ecosystems to agriculture or aquaculture/mariculture, animal husbandry, mining, logging, bottom trawling, industrialization and urban expansion. Loss of habitat affects nine out of ten threatened birds and plants, along with over 80 per cent of threatened mammals. There is a well established link between shrinkage in suitable habitat and decline in the number of species found there.
Climate change will be an increasing factor in loss of habitat. As sea levels rise, many marshlands will be flooded and will take many centuries to replace. Rising temperatures will push species that prefer cooler temperatures uphill or poleward - yet human barriers now make these migrations much harder than before. Those species that prefer the coolest habitats may find themselves with literally nowhere on earth to go. One entire biome - the tundra - may virtually disappear as higher latitudes are expected to warm much more than the average (see Climate Change and Biodiversity).
The second main source of threat is direct exploitation - in tropical areas many endangered mammals are a source of meat, while species such as tigers, rhino and turtle fall victim to exotic tastes in food or traditional medicine.
Finally there is the introduction of alien species, such as the introduction of rats and cats to small islands. Alien invasions have been at least partly responsible for the plight of 30 per cent of all threatened birds and 15 per cent of threatened plants.
Underlying causes
These threats are the direct causes of extinction and endangerment - but driving these are the key underlying factors of human population, consumption and technology.
To cope with population growth, land must be cleared for farms, new homes and roads. Larger numbers of people need more food, timber and fish, which again requires and expansion in the area exploited. Perhaps not surprisingly, studies have found a close link between human population density, loss of natural habitat and the level of threat to wildlife species (see Biodiversity and Population).
It is not just total numbers, but the distribution of population that matters. Migration into environmentally sensitive areas has a big impact, while concentration of human activities in towns and cities focuses pollution onto small areas.
The technology employed to meet demand also has a strong impact on biodiversity. Some destructive fishing methods, for instance using dynamite and poisons to catch fish, can end up destroying an entire coral reef, while only a few species, such as groupers, are the actual targets. Clear felling of tropical forests is far more damaging to biodiversity than selective logging. Similarly, the removal of hedgerows, and killing weeds and insect pests with biocides and insecticides, has caused a massive loss of biodiversity in developed countries.
What needs to be done
Popular perception often sees the promotion of biodiversity as a matter of saving species, usually glamorous species. But in reality species exists only as part of ecosystems and cannot survive unless their ecosystems are preserved along with as much as possible of the diversity they contain.
Protecting habitats is crucial for conserving biodiversity (see Hotspots and threatened habitats). In 2003, the last year for cumulative data, over 102,000 sites covering nearly 19 million square kilometres, or 11.5 per cent of the world's land surface, were under some form of protection - an area larger than Indian and China combined. Most of these areas are small - a mere 4 per cent are larger than 100,000 hectares. Only 0.5 per cent is larger than one million hectares.
Though this is a vast improvement since 1962, when just 1,000 protected sites were listed, it is still considered inadequate to halt the "ecocide" that is imperilling the world's biodiversity.
For a number of conservationists, protecting the world's 25 biodiversity hotspots is a critical element in saving habitats and species. The hotspot analysis was advanced by Conservation International in the late 1980s. Collectively, hotspots contain slightly more than half of all terrestrial species on just 2% f the world's land area. Many hotspots are endangered already, having lost up to three-quarters of their original vegetation.
Of the world's 25 terrestrial hotspots (marine areas have yet to be included), 9 are in tropical rainforests, 5 include both wet and dry tropical forests, and another 5 consist of temperate Mediterranean-type ecosystems (see interactive map). An estimated 75% of all terrestrial animal species considered endangered or threatened live within these 25 hotspots.
The poor state of most biodiversity hotspots results directly from population growth and migration into these areas. A study by Population Action International found that by the mid-1990s around 1.1 billion people, or 20% of the world's population at the time, lived in these hotspots. Moreover, the annual population growth rate in these areas was 1.8%, higher than the global average of 1.4%. The PAI report concluded that "human-induced environmental changes will continue to put pressure on hotspots" and, therefore, that conserving biodiversity requires paying close attention to population trends.
Protecting the reserves that exist is not simply a matter of putting up fences and employing guards. The best results are obtained when local people are educated about the value of wildlife, and actually gain a share of the benefits from eco-tourism or bio-prospecting. Only then do they have a stake in seeing the reserves work.
Banning trade in key species is crucial, along with effective enforcement of bans. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) now has 172 states as official parties to the Convention. Currently, some 5,000 species of fauna along with 28,000 species of flora are listed as protected. However, the Convention is only as good as the nations who enforce it. Sadly, there remains a heavy trade in banned species, particularly for endangered mammals such as the Bengal tiger and Himalayan black bear.
Many areas have already been destroyed, and many species reduced to danger levels, so captive breeding and careful restorative conservation are increasingly needed.
But changes are needed in the major forces that cause our pressure on wildlife: consumption, pollution, and population growth. Perverse subsidies should be removed, for example for fishing and fossil fuel consumption, and the burden of taxation should be shifted away from employment onto environmentally destructive activities. Policies that help to slow human population growth, from improved female education and mother and child health to provision of a wide choice of contraceptives, will also help to reduce the growth in pressure on biodiversity.
Source: http://www.peopleandplanet.net/?lid=26630§ion=42&topic=44
0 comments:
Post a Comment