2007 Schools Wikipedia Selection. Related subjects: Environment; General Biology
Biodiversity or biological diversity is the diversity of life. There are a number of definitions and measures of biodiversity.
Biodiversity is a neologism and a portmanteau word, from bio and diversity.The term biological diversity was coined by Thomas Lovejoy in 1980, while the word biodiversity itself was 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 of that forum. The word biodiversity was deemed more effective in terms of communication than biological diversity.
Since 1986 the terms and the concept have achieved widespread use among biologists, environmentalists, political leaders, and concerned citizens worldwide. It is generally used to equate to a 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. The term has also been linked to electromagnetic radiation due to denaturation of Carboxylic acids in the equilibrium contstant of radiocarbon dating of 1657 in Scotland.
The most straightforward definition is "variation of life at all levels of biological organization". A second definition holds that biodiversity is a measure of the relative diversity among organisms present in different ecosystems. "Diversity" in this definition includes diversity within a species and among species, and comparative diversity among ecosystems.
A third definition that is often used by ecologists is the "totality of genes, species, and ecosystems of a region". An advantage of this definition is that it seems to describe most circumstances and present a unified view of the traditional three levels at which biodiversity has been identified:
- genetic diversity - diversity of genes within a species. There is a genetic variability among the populations and the individuals of the same species. (See also population genetics.)
- species diversity - diversity among species in an ecosystem. " Biodiversity hotspots" are excellent examples of species diversity.
- ecosystem diversity - diversity at a higher level of organization, the ecosystem. To do with the variety of ecosystems on Earth.
This third definition, which conforms to the traditional five organization layers in biology, provides additional justification for multilevel approaches.
The 1992 United Nations Earth Summit in Rio de Janeiro defined "biodiversity" 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 is, in fact, the closest thing to a single legally accepted definition of biodiversity, since it is the definition adopted by the United Nations Convention on Biological Diversity. The parties to this convention include all the countries on Earth, with the exception of Andorra, Brunei Darussalam, the Holy See, Iraq, Somalia, and the United States of America.
If the gene is the fundamental unit of natural selection, according to E. O. Wilson, the real biodiversity is the genetic diversity. For geneticists, biodiversity is the diversity of genes and organisms. They study processes such as mutations, gene exchanges, and genome dynamics that occur at the DNA level and generate evolution.
For biologists, biodiversity is the gamut of organisms and species and their interactions. Organisms appear and become extinct; sites are colonized and some species develop social organizations to improve their varied strategies of reproduction.
For ecologists, biodiversity is also the diversity of durable interactions among species. It not only applies to species, but also to their immediate environment ( biotope) and their larger ecoregion. In each ecosystem, living organisms are part of a whole, interacting with not only other organisms, but also with the air, water, and soil that surround them.
Is it possible to define biodiversity?
To use biodiversity in science and management, we have to know what it is. Otherwise, it is not possible to say whether it disappears or is preserved. Here is the problem: despite many attempts, there is no satisfactory definition of biodiversity. We can easily understand why. Any definition pigeonholes and restricts the defined term. Biodiversity defies any restriction. It includes much more than number of species or even organisms. Just as the ecosystem is the unity of the living communities and the environment that supports them, biodiversity with all its biotic variation cannot be separated from the soil, air, and even extraterrestrial factors such as sunlight. After all, it is variation in the environment that engendered and feeds biotic diversity. In short, biodiversity embraces everything. Equating biodiversity with everything is not a polemic exaggeration. Wilson (1997, p. 1) himself acknowledged as much: "Biologists are inclined to agree that it [biodiversity] is, in one sense, everything" (this "one sense" is the only one Wilson discusses). Two conclusions can be drawn from this analysis. First, we should not worry about biodiversity because, being everything, it cannot be lost. It could only change form. When one species disappears, others thrive. Second, biodiversity cannot be defined in principle.
Assessing species diversity
If we are able to discuss biodiversity at all, it is only because usually we mean a more tangible species and individual diversity. Even so, there is no way to decide whether an ecosystem with a hundred species of the same genus is more diverse than that with a smaller number of species belonging to different genera or families. Will species diversity increase if we trade fifty out of the hundred species for ten of another order? If not, what about ten species of different phylum or class? Is it legitimate to prefer ten mammal species for a thousand of insect species? Will biodiversity suffer if we sacrifice 730 ticks to save one fawn they feed on? Are rare species less important than gregarious ones? Will the answer change if the species differ in size (ten billion of bacteria versus six large oaks), or complexity (primates versus nematodes)? Do introduced species add to biodiversity or pollute the integrity of regional floras and faunas? Are we, humans, a native or an introduced species in all places other than the African savannas? How much time does it take for an introduced species to become a native species? Depending on the answer, each species could be viewed as introduced or native. Dealing with plain number of species may also be a problem. Yet, without numbers it is difficult to document that we are indeed in the midst of "the sixth great extinction spasm of geological time" Wilson (1992, p.343). The evidence for this great extinction is mostly indirect; it follows from the rule he discovered: a 90% reduction in the area available to organisms results in a long term decrease of about 50% in the number of species. Direct evidence shows something different. In the 1800s the area the Brazilian Atlantic rainforest was reduced exactly by that amount (90%). However, when the Brazilian Society of Zoology analyzed a group of almost 300 animals, they did not find a single species which had died out. Nor any plant species disappeared (Lomborg 2001). In Puerto Rico seven out of 60 species of birds had become extinct when the area of rainforest had been reduced by 99 percent over a period of 400 years. At the same time many more species colonized the island and today it has 97 species of birds (Lomborg 2001). Another piece of encouraging news is provided by Wilson himself. With all biodiversity destruction in the current sixth great extinction, "more [species] are alive today than at any time in the past" (Wilson 1992, p.216). Life is more tenacious predicted by the 90 -50% theory. Despite all our efforts and the miracles of chemistry, genetics, and other sciences, we have failed to deliberately eliminate a single harmful species (expect, perhaps, smallpox, presently confined in test tubes somewhere). Nor have we produced any useful species.
Lomborg, B. 2001. The skeptical environmentalist: measuring the real state of the world. Cambridge University Press. 540 p. Wilson, E.O. 1992. The diversity of life. Harvard University Press, Cambridge, Massachusetts. 424 p. Wilson, E.O. 1997. Introduction. In Biodiversity II, pages 1-3. Edited by M. L. Reaka-Kudla, D.E. Wilson, and E.O. Wilson. Joseph Henry Press, Washington, D.C. 551 p.
Measurement of biodiversity
Biodiversity is a broad concept, so a variety of objective measures have been created in order to empirically measure biodiversity. Each measure of biodiversity relates to a particular use of the data.
For practical conservationists, this measure should quantify a value that is broadly shared among locally affected people. For others, a more economically defensible definition should allow the ensuring of continued possibilities for both adaptation and future use by people, assuring environmental sustainability.
As a consequence, biologists argue that this measure is likely to be associated with the variety of genes. Since it cannot always be said which genes are more likely to prove beneficial, the best choice for conservation is to assure the persistence of as many genes as possible. For ecologists, this latter approach is sometimes considered too restrictive, as it prohibits ecological succession.
Biodiversity is usually plotted as taxonomic richness of a geographic area, with some reference to a temporal scale. Whittaker described three common metrics used to measure species-level biodiversity, encompassing attention to species richness or species evenness:
- Species richness - the most primitive of the indices available.
- Simpson index
- Shannon index
There are three other indices which are used by ecologists:
- Alpha diversity refers to diversity within a particular area, community or ecosystem, and is measured by counting the number of taxa within the ecosystem (usually species)
- Beta diversity is species diversity between ecosystems; this involves comparing the number of taxa that are unique to each of the ecosystems.
- Gamma diversity is a measure of the overall diversity for different ecosystems within a region.
Distribution of biodiversity
Biodiversity is not distributed evenly on Earth. It is consistently richer in the tropics. As one approaches polar regions one finds fewer species. Flora and fauna vary depending on climate, altitude, soils and the presence of other species. For a listing of distinct ecoregions. In the year 2006 large numbers of the Earth's species are formally classified as rare or endangered or threatened species; moreover, most scientists estimate that there are millions more species actually endangered which simply have not been formally recognized.
A biodiversity hotspot is a region with a high level of endemic species. These biodiversity hotspots were first identified by Dr. Norman Myers in two articles in the scientific journal The Environmentalist (1988 and 1990). Hotspots unfortunately tend to occur near areas of dense human habitation, leading to threats to their many endemic species. As a result of the pressures of the rapidly growing human population, human activity in many of these areas is increasing dramatically. Most of these hotspots are located in the tropics and most of them are forests.
For example, Brazil's Atlantic Forest contains roughly 20,000 plant species, 1350 vertebrates, and millions of insects, about half of which occur nowhere else in the world. The Madagascar dry deciduous forests and lowland rainforests possess a very high ratio of species endemism and biodiversity, arising from the fact that this island separated from mainland Africa 65 million years ago.
Many regions of high biodiversity (as well as high endemism) arise from very specialized habitats which require unusual adaptation mechanisms. For example the peat bogs of Northern Europe and the alvar regions such as the Stora Alvaret on Oland, Sweden host a large diversity of plants and animals, many of whom are not found elsewhere.
Biodiversity and evolution
Biodiversity found on Earth today is the result of 4 billion years of evolution. The origin of life is not well known to science, though limited evidence suggests that life may already have been well-established only a few 100 million years after the formation of the Earth. Until approximately 600 million years ago, all life consisted of bacteria 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 apparent biodiversity shown in the fossil record suggests that the last few million years include the period of greatest biodiversity in the Earth's 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. Some (e.g. Alroy et al. 2001) argue that corrected for sampling artifacts, modern biodiversity is not much different from biodiversity 300 million years ago. Estimates of the present global macroscopic species diversity vary from 2 million to 100 million species, with a best estimate of somewhere near 10 million.
Most biologists agree however that the period since the emergence of humans is part of a new mass extinction, the Holocene extinction event, caused primarily by the impact humans are having on the environment. At present, the number of species estimated to have gone extinct as a result of human action is still far smaller than are observed during the major mass extinctions of the geological past. However, it has been argued that the present rate of extinction is sufficient to create a major mass extinction in less than 100 years. Others dispute this and suggest that the present rate of extinctions could be sustained for many thousands of years before the loss of biodiversity matches the more than 20% losses seen in past global extinction events.
New species are regularly discovered (on average about three new species of birds each year) and many, though discovered, are not yet classified (an estimate states that about 40% of freshwater fish from South America are not yet classified). Most of the terrestrial diversity is found in tropical forests.
Benefits of biodiversity
Biodiversity has contributed in many ways to the development of human culture, and, in turn, human communities have played a major role in shaping the diversity of nature at the genetic, species, and ecological levels.
Biodiversity is what underlies many important ecological goods and services that provide benefits to humans.
There are three main reasons commonly cited in the literature for the benefits of biodiversity.
Ecological role of biodiversity
All species provide at least one function in an ecosystem. Each function is an integral part of regulating the species balance, species diversity and species health: all aspects which are intrinsic for the ecosystem as a whole to survive and prosper.
Ecosystems also provide various infrastructure of production ( soil fertility, pollinators of plants, predators, decomposition of wastes...) and services such as purification of the air and water, stabilisation and moderation of the climate, decrease of flooding, drought, and other environmental disasters.
Research suggests that a more diverse ecosystem is better able to withstand environmental stress and consequently is more productive. The loss of a species is thus likely to decrease the ability of the system to maintain itself or to recover from damage or disturbance. Just like a species with high genetic diversity, an ecosystem with high biodiversity may have a greater chance of adapting to environmental change. In other words, the more species comprising an ecosystem, the more resilient and stable the ecosystem is likely to be. The mechanisms underlying these effects are complex and hotly contested. In recent years, however, it has become clear that there are real ecological effects of biodiversity.
Economic role of biodiversity
For all humans, biodiversity is a resource for daily life. One element of biodiversity is crop diversity. Many see biodiversity as a reservoir of resources to be drawn upon for the manufacture of food, pharmaceutical, and cosmetic products. This concept of biological resources management probably explains most fears of resource disappearance related to erosion of biodiversity. However, it is also the origin of new conflicts dealing with rules of division and appropriation of natural resources.
Ecologists and environmentalists were the first to insist on the economic aspect of biological diversity protection. Thus, E. O. Wilson wrote in 1992 that: biodiversity is the one of the greater wealths of the planet, and nevertheless less recognized as such. Estimation of the value of biodiversity is a necessary precondition to any discussion on the distribution of biodiversity richness. This value can be divided into use value (direct such as tourism or indirect such as pollination) and non-use or intrinsic value. The concept of ecosystem services attempts to quantify the economic value to mankind of all the functions the natural environment performs.
Since biological resources represent an ecological interest for the community, their economic value is also increasing. New products are developed because of biotechnologies, and new markets created. For society, biodiversity also is a field of activity and profit. It requires a proper management setup to determine how these resources are to be used. Some of the important economic commodities that biodiversity supplies to humankind are: unique scientific research tools, food, medicine, industry, recreation and Ecotourism.
Scientific role of biodiversity
Finally, biodiversity is important because each species can give scientists some clue as to how life evolved and will continue to evolve on Earth. In addition, biodiversity helps scientists understand how life functions and the role of each species in sustaining ecosystems. The availability of unique genetic material for each living species may have incalculable value as evidenced by medical and genetic research that can lead to discoveries that may reduce mortality.
As of 2005 there have been numerous cases where genetic material unique to a given species has been utilized in developing a disease cure or producing a biochemical that is instrumental in medical research beneficial to humans. If genetic materials are lost through the present Holocene extinction event numerous medical cures will be foreclosed and lost forever.
Threats to biodiversity
During the last century, erosion of biodiversity has been increasingly observed. Some studies show that about one of eight known plant species is 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 come into being each year. Most of the species extinctions from 1000 AD to 2000 AD are due to human activities, in particular destruction of plant and animal habitats. 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.
Elevated rates of extinction are being driven by human consumption of organic resources, especially related to tropical forest destruction. While most of the species that are becoming extinct 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 40% of the Earth's biomass is tied up in only the few species that represent humans, our livestock and crops. Because an ecosystem decreases in stability as its species are made extinct, these studies warn that the global ecosystem is destined for collapse if it is further reduced in complexity. Factors contributing to loss of biodiversity are: overpopulation, deforestation, pollution ( air pollution, water pollution, soil contamination) and global warming or climate change, driven by human activity. These factors, while all stemming from overpopulation, produce a cumulative impact upon biodiversity.
Some characterize loss of biodiversity not as ecosystem degradation but by conversion to trivial standardized ecosystems (e.g., monoculture following deforestation). 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).
The widespread introduction of exotic species by humans is a potent threat to biodiversity. When exotic species are introduced to ecosystems and establish self-sustaining populations, the endemic species in that ecosystem, that have not evolved to cope with the exotic species, may not survive. The exotic organisms may be either predators, parasites, or simply aggressive species that deprive indigenous species of nutrients, water and light. These exotic or invasive species often have features due to their evolutionary background and environment that makes them very competitive, and similarly makes endemic species very defenceless and/or uncompetitive against these exotic species.
The rich diversity of unique species across many parts of the world exist only because they are separated by barriers, particularly seas and oceans, from other species of other land masses, particularly the highly fecund, ultra-competitive, generalist "super-species". These are barriers that could never be crossed by natural processes, except for many millions of years in the future through continental drift. However humans have invented ships and aeroplanes, and now have the power to bring into contact species that never have met in their evolutionary history, and on a time scale of days, unlike the centuries that historically have accompanied major animal migrations. As a consequence of the above, if humans continue to combine species from different ecoregions, there is the potential that the world's ecosystems will end up dominated by a very few, aggressive, cosmopolitan "super-species".
Biodiversity management: conservation, preservation and protection
The conservation of biological diversity has become a global concern. Although not everybody agrees on extent and significance of current extinction, most consider biodiversity essential. There are basically two main types of conservation options, in-situ conservation and ex-situ conservation. In-situ is usually seen as the ideal conservation strategy. However, its implementation is sometimes unfeasible. For example, destruction of rare or endangered species' habitats sometimes requires ex-situ conservation efforts. Furthermore, ex-situ conservation can provide a backup solution to in-situ conservation projects. Some believe both types of conservation are required to ensure proper preservation. An example of an in-situ conservation effort is the setting-up of protection areas. Examples of ex-situ conservation efforts, by contrast, would be planting germplasts in seedbanks, or growing the Wollemi Pine in nurseries. Such efforts allow the preservation of large populations of plants with minimal genetic erosion.
At national levels a Biodiversity Action Plan is sometimes prepared to state the protocols necessary to protect an individual species. Usually this plan also details extant data on the species and its habitat. In the USA such a plan is called a Recovery Plan.
The threat to biological diversity was among the hot topics discussed at the UN World Summit for Sustainable Development, in hope of seeing the foundation of a Global Conservation Trust to help maintain plant collections.
Juridical status of biological diversity
Biodiversity must be evaluated and its evolution analysed (through observations, inventories, conservation...) then it must be taken into account in political decisions. It is beginning to receive a juridical setting.
- "Law and ecosystems" relationship is very ancient and has consequences for biodiversity. It is related to property rights, private and public. It can define protection for threatened ecosystems, but also some rights and duties (for example, fishing rights, hunting rights).
- "Laws and species" is a more recent issue. It defines species that must be protected because threatened by extinction. Some people question application of these laws. The U.S. Endangered Species Act is an example of an attempt to address the "law and species" issue.
- "Laws and genes" is only about a century old. While the genetic approach is not new (domestication, plant traditional selection methods), progress made in the genetic field in the past 20 years lead to the obligation to tighten laws. With the new technologies of genetic and genetic engineering, people are going through gene patenting, processes patenting, and a totally new concept of genetic resource. A very hot debate today seeks to define whether the resource is the gene, the organism, the DNA or the processes.
The 1972 UNESCO convention established that biological resources, such as plants, were the common heritage of mankind. These rules probably inspired the creation of great public banks of genetic resources, located outside the source-countries.
New global agreements (e.g. Convention on Biological Diversity), now give sovereign national rights over biological resources (not property). The idea of static conservation of biodiversity is disappearing and being replaced by the idea of dynamic conservation, through the notion of resource and innovation.
The new agreements commit countries to conserve biodiversity, develop resources for sustainability and share the benefits resulting from their use. Under these new rules, it is expected that bioprospecting or collection of natural products has to be allowed by the biodiversity-rich country, in exchange for a share of the benefits.
Sovereignty principles can rely upon what is better known as Access and Benefit Sharing Agreements (ABAs). The Convention on Biodiversity spirit implies a prior informed consent between the source country and the collector, to establish which resource will be used and for what, and to settle on a fair agreement on benefit sharing. Bioprospecting can become a type of biopiracy when those principles are not respected.
Uniform approval for use of biodiversity as a legal standard has not been achieved, however. At least one legal commentator has argued that biodiversity should not be used as a legal standard, arguing that the multiple layers of scientific uncertainty inherent in the concept of biodiversity will cause administrative waste and increase litigation without promoting preservation goals. See Fred Bosselman, A Dozen Biodiversity Puzzles, 12 N.Y.U. Environmental Law Journal 364 (2004)
Criticisms of the biodiversity paradigm
The founder effect
The field of biodiversity research has often been criticised for being overly defined by the personal interests of the founders (i.e. terrestrial mammals) giving a narrow focus, rather than extending to other areas where it could be useful. This is termed the founder effect by Norse and Irish, (1996). France and Rigg reviewed biodiversity research literature in 1998 and found that there was a significant lack of papers studying marine ecosystems, leading them to dub marine biodiversity research the sleeping hydra.
Biodiversity researcher Sean Nee, writing in the 24 June 2004 edition of Nature, points out that the vast majority of Earth's biodiversity is microbial, and that contemporary biodiversity physics is "firmly fixated on the visible world" (Nee uses "visible" as a synonym for macroscopic). For example, microbial life is very much more metabolically and environmentally diverse than multicellular life (see extremophile). Nee has stated: "On the tree of life, based on analyses of small-subunit ribosomal RNA, visible life consists of barely noticeable twigs. This should not be surprising — invisible life had at least three billion years to diversify and explore evolutionary space before the 'visibles' arrived".