Biodiversity: A Measure of the Health of Ecosystems

Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is one measure of the health of ecosystems. Life on Earth today consists of many millions of distinct biological species. The United Nations declared the year 2010 as the International Year of Biodiversity.
Biodiversity is not consistent across the Earth. In the terrestrial context for example, tropical regions are typically rich whereas polar regions support fewer species.
Rapid environmental changes typically cause extinctions.[1] 99.9 percent of species that have existed on Earth are now extinct.[2] Since life began on Earth, five major mass extinctions have led to large and sudden drops in Earthly biodiversity. The Phanerozoic eon (the last 540 million years) marked a rapid growth in biodiversity in the Cambrian explosion—a period during which nearly every phylum of multicellular organisms first appeared. The next 400 million years was distinguished by periodic, massive biodiversity losses classified as mass extinction events. The Permo-Triassic Extinction, 251 million years ago was the worst, devastating life in the sea and on land; vertebrate recovery took 30M years.[3]. The most recent, the Cretaceous–Tertiary extinction event, occurred 65 million years ago, and has attracted more attention than all others because it killed the nonavian dinosaurs.[4]
The period since the emergence of humans has displayed an ongoing reduction in biodiversity. Named the Holocene extinction, the reduction is caused primarily by human impacts, particularly the destruction of plant and animal habitat. In addition, human practices have caused a loss of genetic diversity. Biodiversity's impact on human health is a major international issue
Etymology
The term was used first by wildlife scientist and conservationist Raymond F. Dalesman in the 1968 lay book A Different Kind of Country[5] advocating conservation. The term was widely adopted only after more than a decade, when in the 1980s it came into common usage in science and environmental policy. Use of the term by Thomas Lovejoy, in the foreword to the book Conservation Biology,[6] introduced the term to the scientific community. Until then the term "natural diversity" was common, introduced by The Science Division of The Nature Conservancy in an important 1975 study, "The Preservation of Natural Diversity." By the early 1980s TNC's Science program and its head, Robert E. Jenkins,[7] Lovejoy and other leading conservation scientists at the time in America advocated the use of "biological diversity".
The term's contracted form biodiversity may have been coined by W.G. Rosen in 1985 while planning the National Forum on Biological Diversity organized by the National Research Council (NRC) which was to be held in 1986, and first appeared in a publication in 1988 when entomologist E. O. Wilson used it as the title of the proceedings[8] of that forum.[9]
Since this period both the term and the concept have achieved widespread use among biologists, environmentalists, political leaders, and concerned citizens. The term is sometimes used to reflect concern for the natural environment and nature conservation. This use has coincided with the expansion of concern over extinction observed in the last decades of the 20th century.
A similar concept in use in the United States is "natural heritage." Less scientific, it predates the others and is more accepted by the wider audience interested in conservation. Unlike biodiversity, it includes geology and landforms (geodiversity).

Definitions

A Sampling of fungi collected during summer 2008 in Northern Saskatchewan mixed woods, near LaRonge is an example regarding the species diversity of fungi. In this photo, there are also leaf lichens and mosses.
"Biological diversity" or "biodiversity" can have many interpretations and it is most commonly used to replace the more clearly defined and long established terms, species diversity and species richness. Biologists most often define biodiversity as the "totality of genes, species, and ecosystems of a region". An advantage of this definition is that it seems to describe most circumstances and presents a unified view of the traditional three levels at which biological variety has been identified:
• species diversity
• ecosystem diversity
• genetic diversity
But Professor Anthony Campbell at Cardiff University, UK and the Darwin Centre, Pembrokeshire, has defined a fourth, and critical one: Molecular Diversity[10]
This multilevel conception is consistent with the early use of "biological diversity" in Washington, D.C. and international conservation organizations in the late 1960s through 1970s, by Raymond F. Dasmann who apparently coined the term and Thomas E. Lovejoy who introduced it to the wider conservation and science communities. An explicit definition consistent with this interpretation was first given in a paper by Bruce A. Wilcox commissioned by the International Union for the Conservation of Nature and Natural Resources (IUCN) for the 1982 World National Parks Conference in Bali[11] Wilcox's definition was "Biological diversity is the variety of life forms...at all levels of biological systems (i.e., molecular, organismic, population, species and ecosystem)..." Subsequently, the 1992 United Nations Earth Summit in Rio de Janeiro defined "biological diversity" as "the variability among living organisms from all sources, including, 'inter alia', terrestrial, marine, and other aquatic ecosystems, and the ecological complexes of which they are part: this includes diversity within species, between species and of ecosystems". This definition is used in the United Nations Convention on Biological Diversity.
One textbook's definition is "variation of life at all levels of biological organization".[12][13] 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..."[11]
Linking biodiversity levels
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
Selection bias amongst researchers may contribute to biased empirical research for modern estimates of biodiversity. In 1768 Rev. Gilbert White succinctly observed of his Selborne, Hampshire "all nature is so full, that that district produces the most variety which is the most examined."[15]
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.[16]
Even though biodiversity on land declines from the equator to the poles, this trend is unverified in aquatic ecosystems, especially in marine ecosystems.[17] In addition, several cases demonstrate tremendous diversity in higher latitudes.[citation needed] Generally land biodiversity is up to 25 times greater than ocean biodiversity.[18]
A biodiversity hotspot is a region with a high level of endemic species. Hotspots were first named in 1988 by Dr. Norman Myers.[19][20] Dense human habitation tends to occur near hotspots. Most hotspots are located in the tropics and most of them are forests.[citation needed]
Brazil's Atlantic Forest is considered one such hotspot, containing roughly 20,000 plant species, 1,350 vertebrates, and millions of insects, about half of which occur nowhere else. The island of Madagascar, particularly the unique Madagascar dry deciduous forests and lowland rainforests, possess a high ratio of endemism. Since the island separated from mainland Africa 65 million years ago, many species and ecosystems have evolved independently.
Many regions of high biodiversity and/or endemism arise from specialized habitats which require unusual adaptations, for example alpine environments in high mountains, or Northern European peat bogs.
Evolution

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.[3]
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.[22] 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.[23] Diversity appears to increase continually in the absence of natural selection.[24]
Evolutionary diversification
The existence of a "global carrying capacity", limiting the amount of life that can live at once, is debated, as is the question of whether such a limit would also cap the number of species. While records of life in the sea shows a logistic pattern of growth, life on land (insects, plants and tetrapods)shows an exponential rise in diversity. As one author states, "Tetrapods have not yet invaded 64 per cent of potentially habitable modes, and it could be that without human influence the ecological and taxonomic diversity of tetrapods would continue to increase in an exponential fashion until most or all of the available ecospace is filled."[14]
On the other hand, changes through the Phanerozoic correlate much better with the hyperbolic model (widely used in population biology, demography and macrosociology, as well as fossil biodiversity) than with exponential and logistic models. The latter models imply that changes in diversity are guided by a first-order positive feedback (more ancestors, more descendants) and/or a negative feedback arising from resource limitation. Hyperbolic model implies a second-order positive feedback. The hyperbolic pattern of the world population growth arises from a second-order positive feedback between the population size and the rate of technological growth.[25] The hyperbolic character of biodiversity growth can be similarly accounted for by a feedback between diversity and community structure complexity. The similarity between the curves of biodiversity and human population probably comes from the fact that both are derived from the interference of the hyperbolic trend with cyclical and stochastic dynamics.[26]
Most biologists agree however 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.[27] It has been argued that the present rate of extinction is sufficient to eliminate most species on the planet Earth within 100 years.[28]
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).[23] Most of the terrestrial diversity is found in tropical forests.

Human benefits
Biodiversity supports a number of natural ecosystem processes and services.[29] Some ecosystem services that benefit society are air quality,[30] climate (e.g., CO2 sequestration), water purification, pollination, and prevention of erosion.[30]
Since the stone age, species loss has accelerated above the prior rate, driven by human activity. The exact rate is uncertain, but it has been estimated that species are now being lost at a rate approximately 100 times as fast as is typical in the fossil record, or perhaps as high as 10,000 times as fast.[31] Land is being transformed from wilderness into agricultural, mining, lumbering and urban areas for humans.
Non-material benefits include spiritual and aesthetic values, knowledge systems and the value of education.

Agriculture
The reservoir of genetic traits present in wild varieties and traditionally grown landraces is extremely important in improving crop performance.[citation needed] Important crops, such as the potato, banana and coffee, are often derived from only a few genetic strains.[citation needed] Improvements in crop species over the last 250 years have been largely due to harnessing genes from wild varieties and species.[citation needed] 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.[citation needed]
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.[32] Only one was resistant, an Indian variety, and known to science only since 1966.[32] This variety formed a hybrid with other varieties and is now widely grown.[32]
• Coffee rust attacked coffee plantations in Sri Lanka, Brazil, and Central America in 1970. A resistant variety was found in Ethiopia.[33] 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.[34]
Higher biodiversity also limits the spread of certain diseases, because pathogens may have to adapt to infect different species.[citation needed]
Although about 80 percent of humans' food supply comes from just 20 kinds of plants,[citation needed] humans use at least 40,000 species.[citation needed] Many people depend on these species for their food, shelter, and clothing.[citation needed] 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.[28]
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.[35][36][37] This issue is closely linked with the issue of climate change,[38] 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.[39] Biodiversity is also known to have an important role in reducing disaster risk, and in post-disaster relief and recovery efforts.[40][41]
One of the key health issues associated with biodiversity is that of drug discovery and the availability of medicinal resources.[42] 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.[36] 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.[43][44] Marine ecosystems are of particular interest in this regard,[45] 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.[46][47][48]
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.[49][50][51] 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.

Species loss rates
During the last century, decreases in biodiversity have been increasingly observed. 30% of all natural species will be extinct by 2050.[63] Of these, about one eighth of known plant species are threatened with extinction.[64] Some estimates put the loss at up to 140,000 species per year (based on Species-area theory) and subject to discussion.[65] This figure indicates unsustainable ecological practices, because only a small number of species evolve each year. Almost all scientists acknowledge [64] 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
Jared Diamond describes an "Evil Quartet" of habitat destruction, overkill, introduced species, and secondary extensions.[citation needed] Edward O. Wilson prefers the acronym HIPPO, standing for Habitat destruction, Invasive species, Pollution, Human Over Population, and Overharvesting.[66][67] The most authoritative classification in use today is IUCN’s Classification of Direct Threats[68] which has been adopted by most major international conservation organizations such as the US Nature Conservancy, the World Wildlife Fund, Conservation International, and Birdlife International. The massive growth in the human population through the 20th century has had more impact on biodiversity than any other single factor.[69] From 1950 to 2005, world population increased from 2.5 billion to 6.5 billion.[70]
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.
Main article: Habitat destruction
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.[71] 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.[72] It is estimated that more than a third of biomass[73] is tied up in humans, livestock and crop species. Factors contributing to habitat loss are: overpopulation, deforestation,[74] 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.[75] 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).[citation needed]
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."[76]
At present, the most threathened ecosystems are found in fresh water, according to the Millennium Ecosystem Assessment 2005, which was confirmed by the "Freshwater Animal Diversity Assessment", organised by the biodiversity platform, and the French Institut de recherche pour le développement (MNHNP).[77]
Invasive species
Barriers such as large rivers, seas, oceans, mountains and deserts encourage diversity by enabling independent evolution on either side of the barrier. So-called "super-species" have evolved to fill many habitat niches. Without the barriers such species would occupy those niches on a global basis, substantially reducing diversity. Humans have helped these species circumvent these barriers, valuing them for food and other purpose. This has occurred on a radically compressed time scale, unlike the eons that historically have been required for a species to extend its range.
Species introduced by humans to new areas are known as invasive or exotic species. In cases such as the zebra mussel, the invasion is inadvertent. In other cases, such as mongooses in Hawaii, the introduction is deliberate but ineffective (the rats the diurnal mongoose were supposed to kill are nocturnal!). In other cases, such as oil palms in Indonesia and Malaysia, the introduction produces substantial economic benefits, but the benefits are accompanied by costly unintended consequences. Finally, an introduced species may unintentionally injure a species that depends on the species it replaces. In Belgium, Prunus spinosa from Eastern Europe leafs much sooner than its West European counterparts, disrupting the feeding habits of the Thecla betulae butterfly (which feeds on the leaves).Introducing new species often leaves endemic and other local species unable to compete with the exotic species and unable to survive. The exotic organisms may be either predators, parasites, or may simply outcompete indigenous species for nutrients, water and light.
At present, several countries have already imported so many exotic species, that the own indigenous fauna/flora is greatly outnumbered. For example, in Belgium, only 5% of the indigenous trees remain.[78][79]
In 2004, an international team of scientists estimated that 10 percent of species would become extinct by 2050 because of global warming.[80] “We need to limit climate change or we wind up with a lot of species in trouble, possibly extinct,” said Dr. Lee Hannah, a co-author of the paper and chief climate change biologist at the Center for Applied Biodiversity Science at Conservation International.
Genetic pollution
Endemic species can be threatened with extinction[81] 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.[82] 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.[83][84]
Overexploitation
There is a whole history of overexploitation in the form of overhunting. The overkill hypothesis explains why the megafaunal extinctions occurred within a relatively short period of time. This can be traced with human migration.[85] 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.[86]
Joe Walston, director of the Wildlife Conservation Society’s Asian programs, called the illegal wildlife trade the “single largest threat” to biodiversity in Asia.[87] The international trade of endangered species is second only to drug trafficking.[88]
Hybridization, genetic pollution/erosion and food security
The Yecoro wheat (right) cultivar is sensitive to salinity, plants resulting from a hybrid cross with cultivar W4910 (left) show greater tolerance to high salinity
See also: Food Security and Genetic erosion
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.[89]
(GM organisms) have genetic material altered by genetic engineering procedures such as recombinant DNA technology. GM crops have become a common source for genetic pollution, not only of wild varieties but also of domesticated varieties derived from classical hybridization.[90][91][92][93][94]
Genetic erosion coupled with genetic pollution may be destroying unique genotypes, thereby creating a hidden crisis which could result in a severe threat to our food security. Diverse genetic material could cease to exist which would impact our ability to further hybridize food crops and livestock against more resistant diseases and climatic changes.[89]
Climate Change
The recent phenomenon of global warming is also considered to be a major threat to global biodiversity.[citation needed] For example coral reefs -which are biodiversity hotspots- will be lost in 20 to 40 years if global warming continues at the current trend

The Holocene extinction
Rates of decline in biodiversity in this sixth mass extinction match or exceed rates of loss in the five previous mass extinction events recorded in the fossil record.[96][97][98][99][100] Loss of biodiversity results in the loss of natural capital that supplies ecosystem goods and services. The economic value of 17 ecosystem services for the entire biosphere (calculated in 1997) has an estimated average value of US$ 33 trillion (1012) per year.[101]
Conservation
A schematic image illustrating the relationship between biodiversity, ecosystem services, human well-being, and poverty.[102] The illustration shows where conservation action, strategies and plans can influence the drivers of the current biodiversity crisis at local, regional, to global scales.

Conservation biology matured in the mid-20th century as ecologists, naturalists, and other scientists began to collectively research and address issues pertaining to global declines in biodiversity.[103][104][105] The conservation ethic differs from the preservationist ethic, originally led by John Muir, that seeks protected areas devoid of human exploitation or interference for profit.[104]
The conservation ethic advocates management of natural resources for the purpose of sustaining biodiversity in species, ecosystems, the evolutionary process, and human culture and society.[96][103][105][106][107]
Conservation biology is reforming around strategic plans that include principles, guidelines, and tools for the purpose of protecting biodiversity.[103][108][109] Conservation biology is crisis-oriented and multi-disciplinary, including ecology, social organization, education, and other disciplines outside of biology.[103][105] Preserving biodiversity is a global priority in strategic conservation plans that are designed to engage public policy and concerns affecting local, regional and global scales of communities, ecosystems, and cultures.[110] Action plans identify ways of sustaining human well-being, employing natural capital, market capital, and ecosystem service