BIODIVERSITY
- species diversity
- ecosystem diversity
- genetic diversity
One textbook's definition is "variation of life at all levels of biological organization". For geneticists,biodiversity is the diversity of genes and organisms. They study processes such as mutations, gene transfer, and genome dynamics that generate evolution. Consistent with this, Wilcox also stated "genes are the ultimate source of biological organization at all levels of biological systems..."
A complex relationship exists among the different diversity levels. Identifying one level of diversity in a group of organisms does not necessarily indicate its relationship with other types of diversities. All types of diversity are broadly linked and a numerical study investigating the link between tetrapod (terrestrial vertebrates) taxonomic and ecological diversity shows a very close correlation between the two.
Distribution
Biodiversity is not evenly distributed. Flora and fauna diversity depends on climate, altitude, soils and the presence of other species. Diversity consistently measures higher in the tropics and in other localized regions such as Cape Floristic Province and lower in polar regions generally. In 2006 many species were formally classified as rare or endangered or threatened species; moreover, many scientists have estimated that millions more species are at risk which have not been formally recognized. About 40 percent of the 40,177 species assessed using the IUCN Red List criteria are now listed as threatened with extinction—a total of 16,119.
Even though biodiversity on land declines from the equator to the poles, this trend is unverified in aquatic ecosystems, especially in marine ecosystems. In addition, several cases demonstrate tremendous diversity in higher latitudes. Generally land biodiversity is up to 25 times greater than ocean biodiversity.
A biodiversity hotspot is a region with a high level of endemic species. Biodiversity is the result of 3.5 billion years of evolution. The origin of life has not been definitely established by science, however some evidence suggests that life may already have been well-established only a few hundred million years after the formation of the Earth. Until approximately 600 million years ago, all life consisted of archaea, bacteria, protozoans and similar single-celled organisms.
The history of biodiversity during the Phanerozoic (the last 540 million years), starts with rapid growth during the Cambrian explosion—a period during which nearly every phylum of multicellular organisms first appeared. Over the next 400 million years or so, global diversity showed little overall trend, but was marked by periodic, massive losses of diversity classified as mass extinction events. The worst was the Permo-Triassic extinction, 251 million years ago. Vertebrates took 30 million years to recover from this event.
The fossil record suggests that the last few million years featured the greatest biodiversity in history. However, not all scientists support this view, since there is considerable uncertainty as to how strongly the fossil record is biased by the greater availability and preservation of recent geologic sections. Corrected for sampling artifacts, modern biodiversity may not be much different from biodiversity 300 million years ago. Estimates of the present global macroscopic species diversity vary from 2 million to 100 million, with a best estimate of somewhere near 13–14 million, the vast majority arthropods. Diversity appears to increase continually in the absence of natural selection.
Most biologists agreed that the period since human emergence is part of a new mass extinction, named the Holocene extinction event, caused primarily by the impact humans are having on the environment. It has been argued that the present rate of extinction is sufficient to eliminate most species on the planet Earth within 100 years.
New species are regularly discovered (on average between 5–10,000 new species each year, most of them insects) and many, though discovered, are not yet classified (estimates are that nearly 90% of all arthropods are not yet classified). Most of the terrestrial diversity is found in tropical forests.
Human benefits
Agriculture
The reservoir of genetic traits present in wild varieties and traditionally grown landraces is extremely important in improving crop performance. Important crops, such as the potato, banana and coffee, are often derived from only a few genetic strains. Improvements in crop species over the last 250 years have been largely due to harnessing genes from wild varieties and species. Interbreeding crops strains with different beneficial traits has resulted in more than doubling crop production in the last 50 years as a result of the
Green Revolution.
Crop diversity is also necessary to help the system recover when the dominant cultivar is attacked by a disease or predator:
The Irish potato blight of 1846 was a major factor in the deaths of one million people and the emigration of another million. It was the result of planting only two potato varieties, both of which proved to be vulnerable.
When rice grassy stunt virus struck rice fields from Indonesia to India in the 1970s, 6,273 varieties were tested for resistance. Only one was resistant, an Indian variety, and known to science only since 1966. This variety formed a hybrid with other varieties and is now widely grown.
Coffee rust attacked coffee plantations in Sri Lanka, Brazil, and Central America in 1970. A resistant variety was found in Ethiopia. Although the diseases are themselves a form of biodiversity.
Monoculture was a contributing factor to several agricultural disasters, including the European wine industry collapse in the late 19th century, and the US Southern Corn Leaf Blight epidemic of 1970.
Higher biodiversity also limits the spread of certain diseases, because pathogens may have to adapt to infect different species.
Although about 80 percent of humans' food supply comes from just 20 kinds of plants, humans use at least 40,000 species. Many people depend on these species for their food, shelter, and clothing. Earth's surviving biodiversity provides as little-tapped resources for increasing the range of food and other products suitable for human use, although the present extinction rate shrinks that potential.
Human health
Biodiversity's relevance to human health is becoming an international political issue, as scientific evidence builds on the global health implications of biodiversity loss. This issue is closely linked with the issue of climate change, as many of the anticipated health risks of climate change are associated with changes in biodiversity (e.g. changes in populations and distribution of disease vectors, scarcity of fresh water, impacts on agricultural biodiversity and food resources etc.) Some of the health issues influenced by biodiversity include dietary health and nutrition security, infectious diseases, medical science and medicinal resources, social and psychological health. Biodiversity is also known to have an important role in reducing disaster risk, and in post-disaster relief and recovery efforts.
One of the key health issues associated with biodiversity is that of drug discovery and the availability of medicinal resources. A significant proportion of drugs are derived, directly or indirectly, from biological sources; At least 50% of the pharmaceutical compounds on the US market are derived from compounds found in plants, animals, and microorganisms, while about 80% of the world population depends on medicines from nature (used in either modern or traditional medical practice) for primary healthcare. Moreover, only a tiny proportion of the total diversity of wild species has been investigated for medical potential. Through the field of bionics, considerable advancement has occurred which would not have occurred without rich biodiversity. It has been argued, based on evidence from market analysis and biodiversity science, that the decline in output from the pharmaceutical sector since the mid-1980s can be attributed to a move away from natural product exploration ("bioprospecting") in favor of genomics and synthetic chemistry; meanwhile, natural products have a long history of supporting significant economic and health innovation. Marine ecosystems are of particular interest in this regard, although inappropriate bioprospecting has the potential to degrade ecosystems and increase biodiversity loss, as well as impacting the rights of the communities and states from which the resources are taken.
Business and Industry
A wide range of industrial materials derive directly from biological resources. These include building materials, fibers, dyes, rubber and oil. Further research into employing materials from other organisms is likely to improve product cost and quality. Biodiversity is also important to the security of resources such as water quantity and quality, timber, paper and fibre, food and medical resources. As a result, biodiversity loss is increasingly recognized as a significant risk factor in business development and a threat to long term economic sustainability. Case studies recently compiled by the World Resources Institute demonstrate some of these risks for specific industries.
Other services
Biodiversity provides many ecosystem services that are often not readily visible. It plays a part in regulating the chemistry of our atmosphere and water supply. Biodiversity is directly involved in water purification, recycling nutrients and providing fertile soils. Experiments with controlled environments have shown that humans cannot easily build ecosystems to support human needs; for example insect pollination cannot be mimicked, and that activity alone represents tens of billions of dollars in ecosystem services per year to humankind.
Ecosystem stability is also positively related to biodiversity, protecting them ecosystem services from disruption by extreme weather or human exploitation.
Leisure, cultural and aesthetic value
Many people derive value from biodiversity through leisure activities such as hiking, birdwatching or natural history study. Biodiversity has inspired musicians, painters, sculptors, writers and other artists. Many culture groups view themselves as an integral part of the natural world and show respect for other living organisms.
Popular activities such as gardening, fishkeeping and specimen collecting strongly depend on biodiversity. The number of species involved in such pursuits is in the tens of thousands, though the majority do not enter mainstream commerce.
The relationships between the original natural areas of these often exotic animals and plants and commercial collectors, suppliers, breeders, propagators and those who promote their understanding and enjoyment are complex and poorly understood. It seems clear, however, that the general public responds well to exposure to rare and unusual organisms—they recognize their inherent value at some level. A family outing to the botanical garden or zoo is as much an aesthetic and cultural experience as an educational one.
Philosophically it could be argued that biodiversity has intrinsic aesthetic and spiritual value to mankind in and of itself. This idea can be used as a counterweight to the notion that tropical forests and other ecological realms are only worthy of conservation because of the services they provide.
Number of species
Undiscovered and discovered species
According to the Global Taxonomy Initiative and the European Distributed Institute of Taxonomy, the total number of species for some phyla may be much higher as what we know currently:
10–30 million insects; (of some 0.9 we know today)
5–10 million bacteria;
1.5 million fungi; (of some 0.4 million we know today)
~1 million mites
The number of microbial species is not reliably known, but the Global Ocean Sampling Expedition dramatically increased the estimates of genetic diversity by identifying an enormous number of new genes from near-surface plankton samples at various marine locations, initially over the 2004-2006 period. The findings may eventually cause a significant change in the way science defines species and other taxonomic categories.
Due to the fact that we know but a portion of the organisms in the biosphere, we do not have a complete understanding of the workings of our environment. To make matters worse, we are wiping out these species at an unprecedented rate. This means that even before a species has had the chance of being discovered, studied and classified, it may already be extinct.
Species loss rates
During the last century, decreases in biodiversity have been increasingly observed. 30% of all natural species will be extinct by 2050. Of these, about one eighth of known plant species are threatened with extinction. Some estimates put the loss at up to 140,000 species per year (based on Species-area theory) and subject to discussion. This figure indicates unsustainable ecological practices, because only a small number of species evolve each year. Almost all scientists acknowledge that the rate of species loss is greater now than at any time in human history, with extinctions occurring at rates hundreds of times higher than background extinction rates.
Threats
Habitat destruction
Deforestation and increased road-building in the Amazon Rainforest are a significant concern because of increased human encroachment upon wild areas, increased resource extraction and further threats to biodiversity.
Most of the species extinctions from 1000 AD to 2000 AD are due to human activities, in particular destruction of plant and animal habitats. Extinction is being driven by human consumption of organic resources, especially related to tropical forest destruction. While most threatened species are not food species, their biomass is converted into human food when their habitat is transformed into pasture, cropland, and orchards. It is estimated that more than a third of biomass is tied up in humans, livestock and crop species. Factors contributing to habitat loss are: overpopulation, deforestation, pollution (air pollution, water pollution, soil contamination) and global warming or climate change.
The size of a habitat and the number of species it can support are systematically related. Physically larger species and those living at lower latitudes or in forests or oceans are more sensitive to reduction in habitat area. Conversion to trivial standardized ecosystems (e.g., monoculture following deforestation) effectively destroys habitat for the more diverse species that preceded the conversion. In some countries lack of property rights or access regulation to biotic resources necessarily leads to biodiversity loss (degradation costs having to be supported by the community).
A 2007 study conducted by the National Science Foundation found that biodiversity and genetic diversity are codependent—that diversity within a species is necessary to maintain diversity among species, and vice versa. "If any one type is removed from the system, the cycle can break down, and the community becomes dominated by a single species."
At present, the most threatened ecosystems are found in fresh water.
Genetic pollution
Endemic species can be threatened with extinction through the process of genetic pollution i.e. uncontrolled hybridization, introgression and genetic swamping which leads to homogenization or replacement of local genotypes as a result of either a numerical and/or fitness advantage of introduced plant or animal. Nonnative species can hybridize and introgress either through purposeful introduction by humans or through habitat modification, mixing previously isolated species. These phenomena can be especially detrimental for rare species coming into contact with more abundant ones. The abundant species can interbreed with the rare species, swamping its gene pool and creating hybrids, destroying native stock. This problem is not always apparent from morphological (outward appearance) observations alone. Some degree of gene flowis a normal adaptation process, and not all gene and genotype constellations can be preserved. However, hybridization with or without introgression may, nevertheless, threaten a rare species' existence.
Overexploitation
There is a whole history of overexploitation in the form of overhunting. The overkill hypothesis explains why the mega faunal extinctions occurred within a relatively short period of time. This can be traced with human migration. About 25% of world fisheries are now overexploited to the point where their current biomass is less than the level that maximizes their sustainable yield.
Hybridization, genetic pollution/erosion and food security
In agriculture and animal husbandry, the green revolution popularized the use of conventional hybridization to increase yield. Often hybridized breeds originated in developed countries and were further hybridized with local varieties in the developing world to create high yield strains resistant to local climate and diseases. Local governments and industry have been pushing hybridization. Formerly huge gene pools of various wild and indigenous breeds have collapsed causing widespread genetic erosion and genetic pollution. This has resulted in loss of genetic diversity and biodiversity as a whole.
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