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Biodiversity

Biodiversity

Biodiversity is the term applied to the variety of organisms that occupy a given region. This includes all organisms that live in the region, from microscopic protists to large mammals. The region can be a political unit such as a country, a geographic feature such as a mountain range, or the entire world.

The term "biodiversity" is a combination of two words, "biology" and "diversity." The union of these two words is fairly recent, being inspired by the growing realization that the number of species in the world is seriously declining. Used in this context, it has taken on a greater meaning than just the variety of species, having grown to include three closely related levels: genetic diversity, taxonomic diversity, and ecosystem diversity. Biodiversity is created by complex physical and biological environments (ecosystem diversity) that allow organisms to evolve specializations, and genetic barriers (genetic diversity) that allow them to speciate (taxonomic diversity).

The importance of biodiversity has been recognized by people of many cultures and backgrounds who understand the multitude of functions it serves for humans, from providing food to filtering waste. Threats to biodiversity include direct killing of species by hunting, contaminating the environment with toxins, and habitat loss . The loss of biodiversity through extinction must ultimately be overcome by drastic changes of human behavior. Otherwise, humans will destroy the very environment that supports them.

Levels of Biodiversity

Genetic Diversity.

The first level of biodiversity, genetic diversity, is the level at which we can most clearly observe the evolution of diversity. Genetic diversity includes the many kinds of genes that are available for given members of a species, such as a family, a population, or the entire species. This variety of genes allows the species to have many kinds of heritable traits that allow it to survive through changing environments.

For example, in a particularly cold winter, many individuals of a species may die from lack of insulation, but if the population as a whole has genetic diversity for a trait such as fat storage, then at least some members of the population will survive and the species will not become extinct. The next year, more offspring will have the valuable trait and the species will evolve to tolerate the cooler environment.

Species with little genetic diversity, such as farm hybrids (special breeds of crops or livestock that are all closely related), have limited ability to adapt to changing weather conditions or insect pests. Species lacking genetic diversity cannot adapt to a changing environment and may become extinct without help like the careful maintenance that goes into farm crops and animals.

At the opposite extreme, characteristics of genetically healthy populations are a high population size that includes many individuals that are unrelated to each other. Often, the existence of disjunct populations, those separated by some geographic barrier that only occasionally lets migrants through, ensures that there are always unrelated individuals.

Taxonomic Diversity.

The next level of biodiversity, taxonomic diversity, refers to the variety of individuals at a given hierarchical level in the scientific naming system. This could be the number of different species, genera, families, or kingdoms. For example, a cornfield may have hundreds of birds living in it, but they may represent only three species that are all in one family, meaning that there is low taxonomic diversity. A similar-sized area in a nearby forest may also have hundreds of birds living in it, but these birds may be from twenty different species that belong to eight families and three orders, representing a higher level of diversity. Around the world, crops and livestock typically consist of only one species. These monocultures support a low level of biodiversity.

Ecological Diversity.

Ecological diversity is the variety of habitat types that are available in a given area. These habitats can have different physical characteristics such as temperature and soil type, as well as different organisms inhabiting them. When the habitat with all its organisms and their complex interactions are considered together, it is termed an ecosystem. Ecosystem diversity is typically the level that is discussed in relation to biodiversity.

Beyond ecosystems is a division termed "landscape" that consists of all of the ecosystems in a defined region, such as a drainage basin. Biomes are groups of similar landscapes, such as all the mountain ranges in the world. Finally, the largest division is the biosphere, which refers to all life on Earth.

A mountain range is as an example of ecological diversity that illustrates the evolution and patterns of biodiversity. Because of the latitude of the range selected as an example here, the temperatures are warm and plants grow throughout the year. The topography and weather patterns typically make one side of the mountain moist while the other is dry, meaning that each side grows its own kinds of plants. There will also be variation in soil type, as the soils are made from dead plants, and variation in insects because many insects can eat only certain species of plants.

Soil type will determine what kind of ground-dwelling invertebrates and other decomposers can live there, as well as providing habitat for reptiles, amphibians, and small mammals that build their burrows in the soil and feed on the invertebrates. This kind of variation at the base of the food chain determines that there will be variation at all the higher levels as well, including predators.

Another major habitat characteristic is elevation. Higher elevation means colder temperatures and less oxygen, which also dictates that tougher, scrubbier plants will live near the top and that there will be less soil and fewer species at high elevations. Barriers that are inhospitable to some taxa, such as a mountaintop, a river, or a deep canyon, add complexity to the habitat that consequentially creates separate populations that do not communicate very often. These separated populations allow for greater genetic, and ultimately taxonomic, diversity.

From these examples we can make the generalization that biomes in warmer climates , with greater energy from primary producers and with more varied and complex habitat types, have a higher biodiversity than those without those traits. For example, a mountain range of the same overall characteristics at a higher latitude will have less soil and less energy because there is less primary production from the plants, which go dormant for much of the year. This will cause the overall number of species and biodiversity to be lower.

The Importance of Biodiversity

The value of biodiversity has been argued by many different people for a variety of reasons, but they all point to a unified ideal of conservation. Aldo Leopold is known as the father of environmental ethics in the United States. In books such as Sand County Almanac and Sketches Here and There (1949), he stressed that humans must change their role from consumer of the natural world to cohabitator of it. This change is needed to preserve biodiversity, which would ensure that natural resources are available for future generations.

The value of biodiversity is also recognized by various groups and organizations in modern society. They include waste managers who use wetlands to clean runoff; pharmacists who search for new drugs in rare species; a food industry that interbreeds wild species to improve domestic ones; a pet industry that imports and breeds rare animals; hobbyists who bird-watch, camp, and photograph in search of new species; hunters and fishermen who selectively harvest to eat and teach their families about the wilderness; scientists who use species to study evolution; and, finally, conservationists interested in preserving biodiversity not only for what it can do for them, but for its inherent value in that it lives and breathes as we do.

The Decline of Biodiversity

The decline of biodiversity is documented for prehistoric times and can be the result of natural events that may or may not be related to the fitness of the species that become extinct. A constant level of background extinction has always existed, but it is mass extinction events that cause concern about the future of biodiversity.

Extinction.

The largest extinction event recorded occurred 250 million years ago, when 95 percent of marine species died in response to an uplift of the species-rich continental shelf that was caused by plate tectonics . Another famous example of mass extinction is the impact of the Chicxulub meteorite, which is thought to have left a dense cloud over the sky worldwide for a decade, causing a decrease in primary production (plant activity) and a subsequent extinction of many taxa. This impact coincides with the end of the dinosaur age and probably contributed to the extinction of many of those lines.

Extinction rates at the beginning of the twenty-first century are undeniably higher than background rates, but the exact rate calculated depends on what method of calculation is employed. Using estimates from recent past extinction rates based on fossils, mammal extinctions were once one per two hundred years, and most recently were twenty species in the twentieth century. At the turn of the twenty-first century, the rate of bird extinction is 1,000 times the average over the past 2,000 years. Combining the two calculations provides an estimate of a 1 percent loss of species diversity over the twentieth century, a number much greater than any prehuman impact. Using habitat loss as a predictor of species loss, it is estimated that between 2 and 25 percent of biodiversity will be lost over the twenty-first century.

Causes of extinction.

Biodiversity decline can result from excessive hunting, environmental contamination, or habitat loss and there are a variety of ways to combat these sources of decline. Excessive hunting typically impacts large species that come into frequent contact with humans, usually because the humans are moving into the animal's habitat. These species are killed out of ignorance, because they are seen as a safety threat, or because they are desired for their fur or meat or as trophies. Many times these species are top predators, so their loss is felt throughout the food chain as populations of prey items go unchecked, which causes subsequent problems for the ecosystem and humans. The regulation of hunting, however, involves innumerable complications when impoverished people rely on hunting for their livelihood and when regulation is not well-funded.

Contamination of the air, land, and water results largely from the generation of energy and the use of machines such as the automobile. Power plants and cars produce huge amounts of pollution that have far-reaching impacts because the pollution is spread by wind and river to formerly pristine areas. Contamination of soils and waters also results from the use of pesticides and fertilizers associated with farming as well as from human waste generated in large urban centers. However, the major threat to bio-diversity is habitat loss. Human activities alter the environment to the degree that it can no longer sustain species where they once lived.

The solution to these problems must start with global recognition of the importance of conservation. Biodiversity will need to be maintained in those places where it still exists by creating and managing large protected areas. Some species will need to be helped along artificially by maintaining them in captivity and creating seed banks. Previously destroyed habitat will need to be restored by revegetating and repairing the damage that has been done. Management strategies will have to be created that allow for the conservation of land in concert with human goals. To support all of these strategies, a financial, legal, and political infrastructure will need to be created.

It is important to recognize that Earth's declining biodiversity is a serious global problem. It will be up to educators and future generations to stress the importance of conservation and find means to preserve biodiversity, the immense variety of organisms and interactions that support life on Earth.

see also Ecology; Habitat; Habitat Loss.

Jean K. Krejca

Bibliography

Becher, Anne. Biodiversity. Santa Barbara, CA: ABC-CLIO, 1998.

Begon, Michael, John L. Harper, and Colin R. Townsend. Ecology, 2nd ed. Cambridge, MA: Blackwell Scientific Publications, 1990.

Dunell, Lee. State of the Ark: An Atlas of Conservation in Action. London: Gaia Books, 1986.

Elredge, Niles. Life in the Balance: Humanity and the Biodiversity Crisis. Princeton, NJ: Princeton University Press, 1998.

Jeffries, Michael J. Biodiversity and Conservation. London: Routledge, 1997.

Leopold, Aldo. A Sand County Almanac and Sketches Here and There. New York: Oxford University Press, 1949.

Miller, G. Tyler, Jr. Environmental Science, 3rd ed. Belmont, CA: Wadsworth, 1991.

Rosenzweig, Michael L. Species Diversity in Space and Time. New York: Cambridge University Press, 1995.

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Biodiversity

BIODIVERSITY

The continued health of human societies depends upon a natural environment that is productive and contains a wide diversity of plant, animal, and microbe species. Life on the earth comprises at least 10 million species of plants, animals, and microbes, while in the United States there are an estimated 750,000 species, of which small organisms such as anthropods and microbes comprise 95 percent.

The sustainability of the forest ecosystems and other natural ecosystems are in danger from the expanding world population, which now totals more than 6 billion. With an estimated growth rate of 1.4 percent per year, it is projected to reach 12 billion by the year 2050. Further, due in large part to the growing human population and diverse human activities (supported in large part by fossil fuels), the current extinction rate of species ranges from approximately 1,000 to 10,000 times higher than natural extinction rates. This is alarming for several reasons. Foremost, biodiversity is essential for the sustainable functioning of agricultural, forest, and natural ecosystems upon which human survival and health depends. The loss of a key species (e.g., loss of a predator) creates an imbalance among the remaining species, and can sometimes result in the collapse of the entire ecosystem. Altering a habitat may also improve the environment for an infectious disease, like dengue.

Species diversity affects the quantity and quality of human food supply. For example, conserving pollinators and natural enemies of pests is essential for successful grain, fruit, and vegetable production. Improving food production decreases malnutrition. Yet, at present, the rapidly expanding human population is intensifying the need for increased food supplies. In the year 2000, more than 3 billion people were suffering from malnutritionthe largest number and proportion of people to date. Each year, between 6 million and 14 million people die from the effects of malnutrition.

In many parts of the world, especially in developing countries (e.g., in the Sahelian region of Africa), severe shortages of vitamin A are causing blindness and even death. Worldwide, approximately 250 million children are vitamin A deficient, and each year vitamin A deficiency causes approximately 2 million deaths and 3 million serious eye problems, including blindness.

Similarly, iron intake per person has been declining, especially in sub-Saharan Africa, South Asia, the People's Republic of China, and South America, because overall shortages of food result in inadequate nutrition. In 1998 more that 2 billion persons were sufficiently iron deficient to cause anemia in 1.2 billion people. An estimated 20 percent of the malnutrition deaths are attributed to severe anemia.

Malnutrition is also associated with parasitic infections that are found in areas were conditions of poverty and inadequate sanitation also exist. The health of malnourished individuals, especially children, is seriously affected by parasitic infections, because their presence reduces the availability of nutrients. Parasitic infections diminish appetites while increasing the loss of nutrients by causing diarrhea and dysentery. Hookworms, for instance, can suck as much as 30 milliliters of blood from an infected individual each day, lowering his or her resistance to other diseases. Because an estimated 5 to 20 percent of an individual's daily food intake is used by the body to offset the effects of parasitic illnesses, the overall nutritional status of a parasite-infected person is greatly diminished over time.

As a human population continues to expand and biodiversity declines, waste grows and its disposal becomes a major environmental problem. Each year the total quantity of waste produced by humans, livestock, and crops weighs about 38 billion tons worldwide. Numerous invertebrate animals and microbes function to degrade and recycle wastes. Their preservation in ecosystems is essential to maintain a healthy and productive environment.

Worldwide chemical waste and pollution are also major environmental problems. In the twenty-first century in the United States, 80,000 different chemicals are used and released into the soil, water, and air; worldwide, an estimated 100,000 chemicals are used. In the United States, more than 1,100 kilograms of chemicals per person are used each year; nearly 10 percent of these are known carcinogens. Each year nearly 3 billion kilograms of pesticides are applied worldwide. These toxic chemicals cause 26 million human poisonings annually, with about 220,000 deaths, and affect approximately 750,000 people with chronic diseases like cancer.

Approximately 75 percent by weight of the chemicals released into the environment can be degraded by biological organisms. Thus, species biodiversity helps provide continuous cleanup of contaminated sites (such as residue of pesticides in agriculture), and has a significant advantage over other techniques. Conserving beneficial natural enemies not only controls crop pests but also helps reduce the amount of pesticides applied.

In addition to degrading chemicals, some invertebrate and microbe species also degrade and recycle biological pollutants in water resources. Again, the biological pollution problem is particularly serious in developing nations. About 1.2 billion people in the world lack clean, safe water because most household and industrial wastes are dumped directly into rivers and lakes without treatment. This pollution contributes to the rapidly increasing incidence of diseases in humans. Waterborne infections account for 80 percent of all infectious diseases worldwide and 90 percent of all infectious diseases found in developing countries. A lack of sanitary conditions contributes to about 2 billion human infections of diarrhea, resulting in about 4 million deaths, per year, mostly among infants and young children.

Sometimes altering a natural habitat inadvertently leads to the spread of an infectious disease. Diseases like schistosomiasis that are associated with contaminated fresh water are expanding worldwide. In 1999 it was estimated that schistosomiasis caused 1 million deaths per year. The escalation of the incidence of this disease followed an increase in suitable habitats for the snail that serves as the intermediate host of the causative agent, Schistosoma mansoni. Thus, construction in 1968 of the Aswan High Dam in Egypt and its related irrigation systems was followed by an explosion in the prevalence of Schistosoma mansoni, which increased in the human population from 5 percent in 1968 to 77 percent in 1993.

Considered together, the natural biodiversity of plants, animals, and microbes functions in many ways to enhance the health and quality of life enjoyed by human society. In view of the likely continued growth in human population, and the resultant alteration of the earth's fragile natural ecosystem, greater efforts must be made to conserve biodiversity as a natural and essential treasure.

David Pimentel

(see also: Climate Change and Human Health; Demographic Trap, Drinking Water; Ecosystems; Endangered Species Act; Environmental Determinants of Health; Famine; Groundwater Contamination; Land Use; Municipal Solid Waste; Nutrition; Ocean Dumping; Pesticides; Pollution; Population Density; Population Growth; Sanitation; Species Extinction; Sustainable Development; Wastewater Treatment; Water Quality )

Bibliography

Heywood, V. H. (1995). Global Biodiversity Assessment. Cambridge, UK: Cambridge University Press.

Myers, N. (1994). "Global Biodiversity II: Losses." In Principles of Conservation Biology, eds. G. K. Meffe and C. R. Carroll. Sutherland, MA: Sinauer Associates.

Pimental, D. (1997). Techniques for Reducing Pesticides: Environmental and Economic Benefits. New York: John Wiley.

Pimental, D., and Pimentel, M. (1996). Food, Energy, and Society, revised edition. Niwot, CO: University Press of Colorado.

Pimental, D.; Tort, M.; D'Anna, L.; Krawic, A.; Berger, J.; Rossman, J.; Mugo, F.; Doon, N.; Shriberg, M.; Howard, E. S.; Lee, S.; and Talbot, J. (1998). "Ecology of Increasing Disease: Population Growth and Environmental Degradation." BioScience 48:817826.

Pimemtal, D.; Wilson, C.; McCullum, C.; Huang, R.; Dwen, P.; Flack, J.; Tran, Q.; Saltman, T.; and Cliff, B.(1997). "Economic and Environmental Benefits of Biodiversity." BioScience 47(11):747758.

Pimm, S. L.; Russell, G. J.; Gittleman, J. L; and Brooks, T. M. (1995). "The Future of Biodiversity." Science 269:347350.

Population Reference Bureau (1999). World Population Data Sheet. Washington, DC: Author.

World Health Organization (1992). Our Planet, Our Health: Report of the WHO Commission on Health and Environment. Geneva: Author.

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Biodiversity

Biodiversity

Biodiversity describes the variety of biological organisms in a given habitat , area, or ecosystem . It includes several components involving variation in species, ecosystems, and genetics.

Species diversity is perhaps what most people think of when they think of biodiversity. Species biodiversity describes the number of different species of plants, animals, fungi, protists, or bacteria within an area of interest. Although there are approximately 1.5 million named species globally, the large majority of species have yet to be studied or named, and there are likely to be as many as 10 million species on Earth.

Ecosystem diversity describes the variety of habitat types found within a given area. For example, there are numerous types of terrestrial (land-based) ecosystems in the United States, including forests, grasslands, wetlands , and deserts. There also are many types of aquatic (water-based) ecosystems, including lakes, rivers, estuaries , coral reefs, and intertidal habitats.

Genetic diversity describes genetic variation within species and represents a third component of biodiversity. Genetic variation allows species to adapt to changes in their environment. Species that are reduced to very small populations lose much of the gene pool and hence can lose much of this adaptability.

Aquatic Biodiversity

Aquatic biodiversity describes the diversity of species and ecosystems found in and around aquatic habitats such as rivers, lakes, and oceans. As with terrestrial ecosystems, aquatic biodiversity varies from region to region. Aquatic biodiversity is greatest in tropical latitudes. For example, an estimated 3,000 species of fish are found in the Amazon River alone. Coral reef habitats also have extremely high biodiversity; nearly a quarter of all known marine species are found in coral reefs. The Great Barrier Reef, off the coast of Australia, is the largest coral reef system in the world. It supports over 700 species of coral, in addition to 1,600 fish species and 4,000 species of mollusks .

In the Antarctic Ocean, on the other hand, only 120 fish species are found. These species possess special molecular, biochemical "antifreeze" properties to deal with the cold water temperatures. However, Antarctic habitats nonetheless support many unique aquatic groups, such as the albatross, penguin, and large numbers of marine mammals such as the whale and seal.*

Many fresh-water habitats also harbor a high proportion of unique species. This is due to the fact that, unlike oceans, fresh-water habitats often are isolated from one another, with natural barriers between them that are difficult to cross. This results in the evolution of distinct species in different fresh-water habitats. The preservation of fresh-water habitats therefore is particularly critical to conserving aquatic biodiversity.

The Value of Biodiversity

The value of biodiversity is an issue that has caused considerable debate, given that the preservation of habitats often conflicts with the desires of developers. Yet there are several reasons for valuing biodiversity.

First, biodiversity is essential to the functioning of ecosystems. Each species plays a unique role within an ecosystem, and every species is dependent on others for food, shelter, or other resources. The loss of a single species therefore can have profound effects for the ecosystem as a whole. Second, all species are potential sources of genetic variation for the development of new types of agricultural crops, as well as of medical drugs for treatment of human diseases. Third, biota (living organisms) have scientific and educational value. Finally, species have aesthetic and recreational valueconsider, for example, the popularity of activities such as snorkeling, scuba diving, and hiking.

Scientists have shown that habitats with greater biodiversity are more resilientthat is, they are better able to adjust to and recover from various disturbances. Because different species may perform overlapping functions in a biologically diverse ecosystem, a disturbance that affects one species may have lesser impact on the ecosystem as a whole. Habitats with little diversity are more vulnerable, because a disturbance affecting one species may cause the entire network of interactions to collapse.

Ecosystems approaches to natural resource management address interactions among species and among food webs , as well as the cycling of resources such as carbon, water, and nitrogen. These ecosystems approaches focus not on single species, but on the preservation of complex sets of interactions among species. Preservation of large, intact areas of habitat is necessary for the continued functioning of ecosystems.

Threats to Biodiversity

Aquatic biodiversity is threatened on many fronts. Fresh-water habitats support many of the most highly threatened animal groups. These include fish, mussels, amphibians , and crustaceans .

Fresh-water habitats are threatened by many factors, including pollution from industry, increased acidification, and agricultural runoff containing residues of fertilizers or pesticides . In addition, the building of dams destroys many river ecosystems. Development can harm aquatic habitats or remove them altogether, as when marshy areas are filled.

Aquatic ecosystems also are particularly fragile because the disturbance of a watershed can affect multiple components downstream, including rivers, lakes, estuaries, and oceans. Perhaps the largest threat to ocean biodiversity is overfishing. In addition to depleting commercial species of fish, bivalves, and crustaceans, many fishing methods cause the needless deaths of noncommercial fish species as well as numerous reptiles, birds, and marine mammals.

see also Amphibian Population Declines; Balancing Diverse Interests; Birds, Aquatic; Bivalves; Cephalopods; Corals and Coral Reefs; Crustaceans; Ecology, Fresh-Water; Ecology, Marine; Endangered Species Act; Estuaries; Fish; Fish and Wildlife Issues; Fisheries, Fresh-Water; Fisheries, Marine; Fishes, Cartilaginous; Instream Water Issues; Life in Extreme Water Environments; Life in Water; Marine Mammals; Oceans, Polar; Oceans, Tropical; Reptiles.

Jennifer Yeh

Bibliography

Byatt, Andrew, Alastair Fothergill, and Martha Holmes. The Blue Planet: A Natural History of the Oceans. New York: DK Publishers, 2001.

Gould, James L., and William T. Keeton, with Carol Grant Gould. Biological Science, 6th ed. New York: W. W. Norton & Co., 1996.

PHOTOGRAPHS OF ECOSYSTEMS

This encyclopedia contains photographs of several types of ecosystems. Entries with notable images include:

Entry Photograph

"Corals and coral reef

Coral Reefs"

"Desert Hydrology" desert

"Estuaries" estuary

"Forest Hydrology" forest

"Glaciers and snow and ice

Ice Sheets"

"Oceans, Polar" ocean

"Tides" intertidal

"Wetlands" wetland

* See "Marine Mammals" for photographs of a killer whale, manatee, elephant seal, and dolphin.

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Biodiversity

Biodiversity

Biodiversity is the sum total of life on Earth; the entire global complement of terrestrial, marine, and freshwater biomes and ecosystems , and the speciesplants, animals, fungi, and microorganismsthat live in them, including their behaviors, interactions, and ecological processes. Biodiversity is linked directly to the nonliving components of the planetatmosphere, oceans, freshwater systems, geological formations, and soilsforming one great, interdependent system, the biosphere.

Humankind's Relationship to Biodiversity

Humans depend entirely on this biodiversity and are an integral part of it. Directly or indirectly, be it from wild or domesticated components of biodiversity, humankind derives many goods critical to its sustenance, wellbeing, health, and enjoyment, such as food, medicine, building materials, and industrial products. Also, people enjoy many ecosystem services, including water regulation and supply, erosion control, soil formation, nutrient storage and cycling, pollination, pollution breakdown and absorption, climate stability, protection and recovery from natural disasters, and buffering against the spread of disease. These services, provided by nature free of charge, have an estimated value of $33 trillion per year.

Even though continued human welfare depends on it, our knowledge of biodiversity is seriously inadequate. As of 1998, scientists have described between 1.4 and 1.8 million species. However, later estimates indicate that the total number of species ranges between 5 and 30 million, and some scientists believe it may be higher than 100 million.

Clearly, much more work is needed to quantify and describe all biodiversity at three main levels: genetic diversity, or the variation of genes within species; species diversity, or the variety of species within a biome or ecosystem, measured in species richness, species abundance, and taxonomic diversity; and ecosystem diversity, or the broad differences between ecosystem structures and biome types, and the diversity of habitats and ecological processes occurring within each of them. Taxonomists and other scientists in fields such as zoology, botany, ecology, and genetics study biodiversity.

Threats to Biodiversity

Species are becoming extinct faster than scientists can discover them. The loss of biodiversity is an irreversible process: once a species becomes extinct its loss is permanent and irrevocable. Late-twentieth-century estimates cite the extinction rate between one thousand and ten thousand times greater than it would be naturally. This means that Earth is losing species at the fastest rate in the planet's 4.5 billion-year history and, unlike prior extinction episodes (such as the mass extinction of dinosaurs 65 million years ago), this extinction spasm is mainly the result of human activity and not of a cosmic event. If extinctions continue at the current rate, in the next one hundred years humankind runs the risk of losing half of the planet's biodiversity.

Most threats to biodiversity have to do with pressures on natural resources due to human activities. These include habitat destruction and conversion of natural ecosystems to agriculture; flooding for hydroelectric projects; large-scale extraction of natural resources such as mining and logging; excessive hunting and overfishing; pollution from agricultural pesticides, human waste, and industrial processes; and poorly planned urban and suburban sprawl.


WILSON, E. O. (1829)

U.S. evolutionary biologist and Pulitzer Prizewinning author. Wilson is the world's authority on ants and biodiversity and was an early advocate of studying the behavior of humans and other animals in the context of evolution and adaptation, socalled "sociobiology."


Conserving Biodiversity

Conserving biodiversity is an urgent matter of common concern and should be an integral part of the development process, as was outlined in the Convention on Biological Diversity. This global, comprehensive agreement was drafted at the 1992 Rio de Janeiro Earth Summit and signed by 160 nations to address all aspects of biological diversity. Its objectives include "the conservation of biodiversity, its sustainable use and the fair sharing of the benefits derived from the utilization of genetic resources."

One conservation strategy aimed at reaching this goal recognizes that biodiversity is not evenly distributed over the planet: certain regions have higher species richness (the number of species in an area) and endemism (the number of species in that area that occur nowhere else) than others. Ironically, many of these sensitive areas are also preferred by humans to inhabit, placing tremendous pressure on local biodiversity. These areas are called the "biodiversity hotspots"; twenty-five of them have been described thus far, including Madagascar, the tropical Andes, the Philippines, and the Atlantic forest of Brazil. Conservationists believe that urgent conservation efforts should be targeted at these regions. Equally important are the socalled wilderness areas: Amazonia, the Congo Basin, and Papua New Guinea. These areas are also high in biodiversity but are not so immediately threatened.

see also Biome; Conservation; Ecosystem; Endangered Species; Extinction; Invasive Species

Cristina G. Mittermeier and Russell A. Mittermeier

Bibliography

Costanza, Robert, et al. "The Value of the World's Ecosystem Services and Natural Capital." Nature 387, no. 15 (May 1997): 253260.

May, R. M. "How Many Species Are There on Earth?" Science 241 (1998): 14411449.

Mittermeier, Russell A., P. Robles Gil, and Cristina G. Mittermeier. Megadiversity: Earth's Biologically Wealthiest Countries. Mexico: Cemex, 1997.

. Hotspots: Earth's Biologically Richest and Most Endangered Terrestrial Ecorregions. Mexico: Cemex, 1999.

Stuart, S. Species: Unprecedented Extinction Rate, and It's Increasing. Gland, Switzerland: IUCN, 1999.

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Biodiversity

Biodiversity

The term biodiversity refers to the wide range of organismsplants and animalsthat exist within any given geographical region. That region may consist of a plot of land no more than a few square meters or yards, a whole continent, or the entire planet. Most commonly, discussions of biodiversity consider all the organisms that interact with each other in an extended geographical region, such as a tropical rain forest or a subtropical desert.

Concerns about biodiversity are relatively new. Only during the last quarter of the twentieth century did scientists begin to appreciate the vast number of organisms found on Earth and the complex ways in which they interact with each other and with their environments. Biologists have now discovered and named about 1.7 million distinct species of plants and animals. As many as 50 million species, however, are thought to exist.

Biodiversity in the tropics is of special interest since the richness of species found there is so great. According to some estimates, 90 percent of all plant, animal, and insect species exist in tropical regions. At the same time, surveys of organisms in the tropics have been very limited. Those studies that have been conducted provide only a hint of the range of life that may exist there. As an example, one study of a 108-square kilometer (42-square mile) reserve of dry forest in Costa Rica found about 700 plant species, 400 vertebrate species, and 13,000 species of insects. Included among the latter group were 3,140 species of moths and butterflies alone.

Human threats to biodiversity

One reason for the growing interest in biodiversity is the threat that human activities may pose for plant and animal species. As humans take over more land for agriculture, cities, highways, and other uses, natural habitats are seriously disrupted. Whole populations may be destroyed, upsetting the balance of nature that exists in an area. The loss of a single plant, for example, may result in the loss of animals that depend on that plant for food. The loss of those animals may, in turn, result in the loss of predators who prey on those animals.

As human populations grow, the threat to biodiversity will continue to grow with it. And as more people place greater stress on the natural environment, greater will be the loss of resources plant and animal communities need to survive.

Why is biodiversity important?

Maintaining biodiversity in a region and across the planet is important for a number of reasons. First, some people argue that all species

because they existhave a right to continue to exist in their own natural habitats, untouched by human development. Second, humans depend on many of the plants and animals that make up an ecological community. For example, one-quarter of all the prescription drugs in the United States contain ingredients obtained from plants. And third, humans themselves benefit from the interaction among organisms in a biologically diverse community: plants help clean the water and air, provide oxygen in the atmosphere, and control erosion. "Biodiversity," according to the biologist Peter Raven, "keeps the planet habitable and ecosystems functional."

Protection of threatened biodiversity

One of the great issues in environmental science today is how biodiversity can be preserved both in specific geographical regions and across the planet. One proposal that has been made involves the use of ecological reserves. Ecological reserves are protected areas established for the preservation of habitats of endangered species, threatened ecological communities, or representative examples of widespread communities. By the end of the 1990s, there were about 7,000 protected areas globally with an area of 651 million hectares (1.6 billion acres). Of this total, about 2,400 sites comprising 379 million hectares (936 million acres) were fully protected and could be considered to be true ecological reserves.

Ideally, the design of a national system of ecological reserves would provide for the longer-term protection of all native species and their natural communities including terrestrial (land-dwelling), freshwater, and marine (saltwater) systems. So far, however, no country has put in place a comprehensive system of ecological reserves to fully protect its natural biodiversity. Moreover, in many cases existing reserves are relatively small and are threatened by environmental change, illegal poaching of animals and plants, and tourism.

The World Conservation Union, World Resources Institute, and United Nations Environment Program are three important agencies whose purpose is to conserve and protect the world's biodiversity. These agencies have developed the Global Biodiversity Strategy, an international program to help protect plant and animal habitats for this and future generations. Because this program began only in the late 1970s, it is too early to evaluate its success. However, the existence of this comprehensive international effort is encouraging, as is the participation of most of Earth's countries, representing all stages of economic development.

[See also Ecosystem; Endangered species ]

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biodiversity

biodiversity (biological diversity) The existence of a wide variety of species (species diversity) or other taxa of plants, animals, and microorganisms in a natural community or habitat, or of communities within a particular environment (ecological diversity), or of genetic variation within a species (genetic diversity). The maintenance of a high level of biodiversity is important for the stability of ecosystems. Certain habitats, especially rainforests, have a rich species diversity, which is threatened by the continued destruction of habitats (see deforestation; desertification). Such ecosystems typically support large numbers of rare species, and population sizes of individual species tend to be small; they are therefore especially vulnerable to habitat destruction. Biodiversity in natural habitats also represents an important pool of species and genetic material of potential use to human societies. For example, wild plants continue to be used as a source of new drugs and other products, and the development of new strains and varieties of crop plants with increased disease resistance usually depends on incorporating genetic material from wild plants.

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Biodiversity

Biodiversity

Biodiversity exists at three interrelated levels: species diversity, genetic diversity, and community-level diversity. When we talk about plant biodiversity, we refer to the full range of plant species, the genetic variation found within those species, and the biological communities formed by those species. For vascular plants, biodiversity includes all species of ferns, gymnosperms , flowering plants, and related smaller groups such as clubmosses and horsetails. The genetic variation found within populations and among populations arises through the mutation of individual genes or chromosomes and is rearranged by genetic recombination during the sexual process. Genetic variation is important not only for the survival and evolution of species; it is also important to people for breeding improved crop plants with higher yields.

Biological diversity also refers to all biological communities, including temperate forests, tropical forests, grasslands, shrub lands, deserts, freshwater wetlands, and marine habitats. Each of these biological communities represents an adaptation of plants to particular regimes of climate, soil, and other aspects of the environment. This adaptation involves ecosystem interactions of each biological community with its physical and chemical environment. For example, the ability of a forest community to absorb rain water and slowly release the water into streams and the ability of a swamp to process and detoxify polluted water are both aspects of ecosystem-level biological diversity that are of central importance to human societies.

Measuring Biodiversity

Biological diversity can be measured in various ways, each of which captures some of the overall meaning of biological diversity. The most common method of measuring biological diversity is simply to count the number of species occurring in one particular place, such as a forest or a grassland. Since it is not possible to count every species of plant, insect, fungus, and microorganism, the usual procedure is to count certain types of organisms, such as birds, butterflies, all flowering plants, or just tree species. This type of local diversity of species is usually referred to as species richness or alpha diversity. A tropical rain forest might contain three hundred or more tree species in a square of forest measuring 400 meters on a side, whereas a temperate forest of equal area might contain only forty tree species. Biological diversity can also be measured in larger areas. For example the country of Colombia has more than fifty thousand species of higher plants, in contrast to sixteen hundred species for the United Kingdom and nearly sixteen thousand for Australia. This type of regional or large-scale diversity is referred to as gamma diversity.

Another way to measure biodiversity is to consider the number or percentage of a region's species that are endemic to that region. For example, of the United Kingdom's fifteen-hundred native plant species, only sixteen species or 1 percent are endemic. The overwhelming majority of the United Kingdom's plants can be found in other neighboring countries, such as Ireland, France, and Germany. In contrast, 14,074 of the 15,000 plant species of Australia are endemic and found in no other country.

Individual species can also be compared for their evolutionary uniqueness. Species that are not closely related to other species are generally considered to have greater value to overall biological diversity than species that have many close relatives. For example, the maidenhair tree, Ginkgo biloba, is the only species in its genus, and Ginkgo is the only genus in the gymnosperm family Ginkgoaceae. In contrast, the common dandelion, Taraxacum officinale, has many related species in the same genus and is a member of a large family, the Asteraceae, with twenty-five thousand species and eleven hundred genera. Using this approach, a species that was the only member of its genus and family would have greater biodiversity value than a species that had many relatives in the same genus and belonged to a family with many genera. In contrast, a few biologists would argue that a species in a large genus has greater value because this species has the greater potential to undergo further evolution than a species with no close relatives that may be an evolutionary dead end.

Extent of Diversity

There are around 250,000 living species of higher plants in the world today. Of these species, the overwhelming majority are flowering plants. Flowering plants are grouped into more than three hundred families, including such large and economically important families as the Poaceae, which contains the grasses and the cereal crops we depend on for food and animal fodder; the Fabaceae, which includes the beans and peas we need for protein in our diet; and the Rosaceae, which is important for fruit trees and ornamentals such as apples, pears, and roses.

Higher plants exhibit a great diversity of growth forms, leaf shapes and sizes, flower and fruit types, seed types, and particular adaptations for growing in different environments. Growth forms include trees, shrubs, annual herbs, perennial herbs, climbers, and aquatic plants.

Plant diversity is not equally distributed across the world's surface. Only a relatively few land plants are adapted to salt water, and these are found rooted in shallow waters. So the large oceanic expanses of the world are devoid of higher plants. On the land surface, the greatest diversity of plants is found in the tropical lowland and montane rain forests of the Americas, central Africa, and Southeast Asia. In such forests there is a great diversity of plant species in the form of trees, shrub, herbs, and climbers. There is also an abundance of epiphytes , in particular orchids and bromeliads, that perch on the branches of the trees. Illustrating this tropical diversity, there are only around thirty tree species in all of northern Canada, in contrast to more than one thousand tree species in just the southern countries of Central America.

There is also great species diversity in the temperate regions of the world that have mild, wet winters and dry, hot summers, such as the Mediterranean basin, the California region, central Chile, the cape region of South Africa, and southwest Australia. In such areas, many plants have adaptations to drought, such as succulent cacti, which store water in their stems, and annual plants that grow, reproduce, and die in one growing season.

Certain regions of the world are known as hot spots of biodiversity because of their high concentrations of species overall, their high percentages of species that are endemic, and the high degree of threat that those species face. In addition to rain forest areas and localities with Mediterranean climates, many of these are islands, such as the Caribbean Islands, Madagascar and nearby islands, New Caledonia, New Zealand, Sri Lanka, and the islands between New Guinea and peninsular Malaysia. Biodiversity hot spots encompass the entire range of 44 percent of the world's plant species, 25 percent of the bird species, 30 percent of the mammal species, 38 percent of the reptile species, and 54 percent of the amphibian species on only 1.4 percent of Earth's total land surface. The premier hot spot is the tropical Andes, in which 45,000 plant species, 1,666 bird species, 414 mammal species, 479 reptile species, and 830 amphibian species occur in the tropical forests and high-altitude grasslands that occupy less than 0.25 percent of Earth's land surface. This approach can also be applied to individual countries. In the United States hot spots for endangered species occur in the Hawaiian Islands, the southern Appalachian Mountains, the arid Southwest, and the coastal areas of the lower forty-eight states, particularly California, Texas, and Florida.

Threats to Biological Diversity

Biological diversity is being lost today at all levels, including genetic variation, species, and biological communities. The most serious threat is the extinction of species, because once a species is lost, it can never be regained. The loss of genetic variation is occurring in two different ways: when populations of a species are eliminated and when populations become smaller in size. This loss of populations is seen most immediately in the local extinction of species. In a study of a conservation area in Massachusetts, one-third of the native plant species present one hundred years ago could no longer be found today. They were not replaced by other native species, but there was an increase in the number of nonnative species. This park is now poorer in total species, and many species still present have fewer populations. Many species that were formerly listed as common now have only a few individuals left.

Biological diversity is most severely threatened when entire biological communities are lost. In many tropical countries of the world, the tropical rain forests that are so rich in species have been largely destroyed. Examples of countries with devastated forests are Madagascar (87 percent lost), Rwanda (84 percent), Vietnam (83 percent), and the Philippines (94 percent). With the loss of these communities comes the extinction of plant and animal species, the loss of genetic variation within remaining species, and the loss of the ecosystem services provided by these communities, such as flood control, soil erosion protection, and the production of wood and food. Other habitats almost completely destroyed include tropical deciduous forests, of which more than 98 percent have been destroyed in Central America, and temperate grasslands, which are readily converted to agriculture and ranching. In the United States, only around 560 acres of the tallgrass prairie of Illinois and Indiana remains undisturbed, only about one ten-thousandth of the original area. Wetlands including swamps, bogs, floodplains, and vernal pools are similarly suffering devastation. As these habitats are damaged by human activity and converted to other uses, the species they contain decline in abundance and eventually become extinct. Habitats that are restricted in area and contain high concentrations of endemic species are particularly vulnerable, such as the rain forests of Hawaii and isolated mountain peaks in the southwestern United States.

In general, the rate of extinction for plants has been lower than that for animals. To date, there are recorded extinctions of around four hundred plant species, about 0.2 percent of the total in contrast with around 2.1 percent of mammals and 1.3 percent of birds already extinct. The lower percentages of plants that are extinct are related in part to our ability to protect small populations of plants in nature reserves. In contrast, many animals have a greater need to migrate and have often been extensively exploited. At the turn of the twenty-first century, around 9 percent of plant species are in danger of extinction, a figure only slightly lower than that for birds (11 percent) and mammals (11 percent). The extinction rates for certain groups of plants are much higher than this average value. For example, 32 percent of gymnosperms and 33 percent of palms are threatened with global extinction in the wild due to the limited distribution of many species' specialized habitat requirements and the intensive collection of plants for horticulture.

Factors Threatening Species

Species are threatened with extinction primarily because of habitat destruction. Species are also driven to extinction when their habitat is degraded to the point where they can no longer exist. This might happen when a grassland is heavily grazed by domestic animals, a forest is repeatedly logged, or uncontrolled fires burn shrub land. Fully 81 percent of the endangered species of the United States are threatened by habitat degradation and loss. Species are also lost from habitats fragmented by human activity, when habitats are broken up into smaller pieces by roads, fences, power lines, residential areas, and ranches. The remaining fragments may be so altered in micro-climate, and so much more vulnerable to other human activities, that many plant species are no longer able to survive.

The second most significant threat to species diversity is competition and predation from exotic invasive species, which is a threat for 57 percent of the endangered plant species of the United States. In many cases, exotic species of animals such as cattle, sheep, goats, rabbits, and pigs selectively remove certain native plant species. For example, pigs introduced in Hawaii have removed all wild individuals of numerous plant species. Invasive exotic plants have often overwhelmed natural communities and outcompeted the native species. For example, in bottomland communities of the southern United States, Japanese honeysuckle plants have replaced the rich wildflower communities, and in the rangeland of the western United States European grasses outcompete native grasses and wildflowers. As a result, native species decline at the expense of the introduced species.

Overharvesting of plants, often for food, medicinal purposes, or by horticulturists, threatens 10 percent of the endangered plant species of the United States. A notable example is ginseng, an herb used in Asian medicine, which has been so overharvested throughout its range that only a small number of plants remain. Many rare wildflowers, such as orchids, have been so severely overcollected by gardeners that they are in danger of extinction in the wild. Information on the location of the last remaining plants is often kept secret to prevent the theft of these individuals.

Pollution threatens 7 percent of the plant species of the United States. Water pollution can alter the water chemistry so severely that aquatic plants cannot grow. Increased inputs of nitrogen and phosphorus compounds into the water from sewage and agricultural fertilizers can result in algal blooms that shade out and kill native plants. In the land environment air pollution in the form of smog, acid rain, and nitrogen deposition can cause plants to slow down in growth or die. In some cases, this death may be related to the decline and death of the sensitive soil fungi (mycorrhizae) that have mutualistic relations with plants, providing water and mineral nutrients and receiving carbohydrates in return. And lastly, about 1 percent of plant species is threatened by disease and parasites. While this number may not seem very great, some of the most important woody plants in the forests of North America, such as chestnuts, elms, and dogwoods, are in severe decline due to introduced diseases.

What Can Be Done?

The most important way to protect plant biological diversity is to establish protected areas that include high concentrations of species, particularly those species in danger of extinction or in decline. These protected areas may be established by governments, conservation organizations, or private individuals. Management plans must be developed and implemented, and these protected areas must be monitored to ensure they are meeting their goals. Many management plans for protected areas include some forms of public education, because public support is often crucial for the success of a park.

Where it is not possible to maintain plant species in the wild due to ongoing threats, plants can often be grown in botanical gardens or kept as stored seed samples in seed banks. Networks of botanical gardens and seed banks are making a concerted effort to increase their holdings of endangered species and species of potential agricultural and economic importance. The goal of many botanical gardens is to increase knowledge of plants, to educate the public concerning plants, and to return plants eventually to their natural habitats.

The diversity of plant species provides us with the agriculture crops that are our food, many of the medicines that keep us healthy, wood that is needed in construction, fodder that feeds our domestic animals, ornamental plants that enrich our gardens and homes, and even the oxygen that we breathe. People could not live without the diversity of plants, and many plant species will live in the wild only if we take care of them.

see also Asteraceae; Botanical Gardens and Arboreta; Endangered Species; Ginkgo; Human Impacts; Invasive Species; Rain Forests; Seed Preservation; Wetlands.

Richard B. Primack

Bibliography

Falk, D. A, C. I. Millar, and M. Olwell, eds. Restoring Diversity; Strategies for the Reintroduction of Endangered Plants. Washington, DC: Island Press, 1996.

Mittermeier, R. A., N. Myers, P. R. Gil, and C. G. Mittermeier. Hotspots: Earth's Richest and Most Endangered Terrestrial Ecoregions. Mexico City: Agrupacion Sierra Madre, SC, 1999.

Primack, R. A Primer of Conservation Biology. Sunderland, MA: Sinauer Associates, 2000.

Quammen, D. The Song of the Dodo: Island Biogeography in an Age of Extinctions. New York: Scribner, 1996.

Schneider, S. Laboratory Earth: The Planetary Gamble We Can't Afford to Lose. New York: Basic Books, 1998.

Stein, B. A., and S. R. Flack. Species Report Card: The State of U.S. Plants and Animals. Arlington, VA: The Nature Conservancy, 1997.

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biodiversity

biodiversity A portmanteau term, which gained popularity in the late 1980s, used to describe all aspects of biological diversity, especially including species richness, ecosystem complexity, and genetic variation.

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biodiversity

biodiversity A portmanteau term, which gained popularity in the late 1980s, that describes all aspects of biological diversity, especially including species richness, ecosystem complexity, and genetic variation.

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biodiversity

bi·o·di·ver·si·ty / ˌbīōdiˈvərsitē/ • n. the variety of life in the world or in a particular habitat or ecosystem.

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biodiversity

biodiversity: see biological diversity.

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biodiversity

biodiversitybanditti, bitty, chitty, city, committee, ditty, gritty, intercity, kitty, nitty-gritty, Pitti, pity, pretty, shitty, slitty, smriti, spitty, titty, vittae, witty •fifty, fifty-fifty, nifty, shifty, swiftie, thrifty •guilty, kiltie, silty •flinty, linty, minty, shinty •ballistae, Christie, Corpus Christi, misty, twisty, wristy •sixty •deity, gaiety (US gayety), laity, simultaneity, spontaneity •contemporaneity, corporeity, femineity, heterogeneity, homogeneity •anxiety, contrariety, dubiety, impiety, impropriety, inebriety, notoriety, piety, satiety, sobriety, ubiety, variety •moiety •acuity, ambiguity, annuity, assiduity, congruity, contiguity, continuity, exiguity, fatuity, fortuity, gratuity, ingenuity, perpetuity, perspicuity, promiscuity, suety, superfluity, tenuity, vacuity •rabbity •improbity, probity •acerbity • witchetty • crotchety •heredity •acidity, acridity, aridity, avidity, cupidity, flaccidity, fluidity, frigidity, humidity, hybridity, insipidity, intrepidity, limpidity, liquidity, lividity, lucidity, morbidity, placidity, putridity, quiddity, rabidity, rancidity, rapidity, rigidity, solidity, stolidity, stupidity, tepidity, timidity, torpidity, torridity, turgidity, validity, vapidity •commodity, oddity •immodesty, modesty •crudity, nudity •fecundity, jocundity, moribundity, profundity, rotundity, rubicundity •absurdity • difficulty • gadgety •majesty • fidgety • rackety •pernickety, rickety •biscuity •banality, duality, fatality, finality, ideality, legality, locality, modality, morality, natality, orality, reality, regality, rurality, tonality, totality, venality, vitality, vocality •fidelity •ability, agility, civility, debility, docility, edibility, facility, fertility, flexility, fragility, futility, gentility, hostility, humility, imbecility, infantility, juvenility, liability, mobility, nihility, nobility, nubility, puerility, senility, servility, stability, sterility, tactility, tranquillity (US tranquility), usability, utility, versatility, viability, virility, volatility •ringlety •equality, frivolity, jollity, polity, quality •credulity, garrulity, sedulity •nullity •amity, calamity •extremity • enmity •anonymity, dimity, equanimity, magnanimity, proximity, pseudonymity, pusillanimity, unanimity •comity •conformity, deformity, enormity, multiformity, uniformity •subcommittee • pepperminty •infirmity •Christianity, humanity, inanity, profanity, sanity, urbanity, vanity •amnesty •lenity, obscenity, serenity •indemnity, solemnity •mundanity • amenity •affinity, asininity, clandestinity, divinity, femininity, infinity, masculinity, salinity, trinity, vicinity, virginity •benignity, dignity, malignity •honesty •community, immunity, importunity, impunity, opportunity, unity •confraternity, eternity, fraternity, maternity, modernity, paternity, taciturnity •serendipity, snippety •uppity •angularity, barbarity, bipolarity, charity, circularity, clarity, complementarity, familiarity, granularity, hilarity, insularity, irregularity, jocularity, linearity, parity, particularity, peculiarity, polarity, popularity, regularity, secularity, similarity, singularity, solidarity, subsidiarity, unitarity, vernacularity, vulgarity •alacrity • sacristy •ambidexterity, asperity, austerity, celerity, dexterity, ferrety, posterity, prosperity, severity, sincerity, temerity, verity •celebrity • integrity • rarity •authority, inferiority, juniority, majority, minority, priority, seniority, sonority, sorority, superiority •mediocrity • sovereignty • salubrity •entirety •futurity, immaturity, impurity, maturity, obscurity, purity, security, surety •touristy •audacity, capacity, fugacity, loquacity, mendacity, opacity, perspicacity, pertinacity, pugnacity, rapacity, sagacity, sequacity, tenacity, veracity, vivacity, voracity •laxity •sparsity, varsity •necessity •complexity, perplexity •density, immensity, propensity, tensity •scarcity • obesity •felicity, toxicity •fixity, prolixity •benedicite, nicety •anfractuosity, animosity, atrocity, bellicosity, curiosity, fabulosity, ferocity, generosity, grandiosity, impecuniosity, impetuosity, jocosity, luminosity, monstrosity, nebulosity, pomposity, ponderosity, porosity, preciosity, precocity, reciprocity, religiosity, scrupulosity, sinuosity, sumptuosity, velocity, verbosity, virtuosity, viscosity •paucity • falsity • caducity • russety •adversity, biodiversity, diversity, perversity, university •sacrosanctity, sanctity •chastity •entity, identity •quantity • certainty •cavity, concavity, depravity, gravity •travesty • suavity •brevity, levity, longevity •velvety • naivety •activity, nativity •equity •antiquity, iniquity, obliquity, ubiquity •propinquity

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Biodiversity

Biodiversity


Biodiversity is an ecological notion that refers to the richness of biological types at a range of hierarchical levels, including: (1) genetic diversity within species , (2) the richness of species within communities, and (3) the richness of communities on landscapes. In the context of environmental studies, however, biodiversity usually refers to the richness of species in some geographic area, and how that richness may be endangered by human activities, especially through local or global extinction .

Extinction represents an irrevocable and highly regrettable loss of a portion of the biodiversity of Earth. Extinction can be a natural process, caused by: 1) random catastrophic events; 2) biological interactions such as competition , disease, and predation; 3) chronic stresses; or 4) frequent disturbance. However, with the recent ascendance of human activities as a dominant force behind environmental changes, there has been a dramatic increase in rates of extinction at local, regional, and even global levels.

The recent wave of anthropogenic extinctions includes such well-known cases as the dodo , passenger pigeon , great auk, and others. There are many other high-profile species that humans have brought to the brink of extinction, including the plains buffalo, whooping crane , eskimo curlew, ivory-billed woodpecker , and various marine mammals. Most of these instances were caused by an insatiable over-exploitation of species that were unable to sustain a high rate of mortality , often coupled with an intense disturbance of their habitat .

Beyond these tragic cases of extinction or endangerment of large, charismatic vertebrates, the earth's biota is experiencing an even more substantial loss of biodiversity caused by the loss of habitat. In part, this loss is due to the conversion of large areas of tropical ecosystems, particularly moist forest, to agricultural or otherwise ecologically degraded habitats. A large fraction of the biodiversity of tropical biomes is comprised of rare, endemic (i.e., with a local distribution) species. Consequently the conversion of tropical rain forest to habitats unsuitable for these specialized species inevitably causes the extinction of most of the locally endemic biota. Remarkably, the biodiversity of tropical forests is so large, particularly in insects, that most of it has not yet been identified taxonomically. We are therefore faced with the prospect of a mass extinction of perhaps millions of species before they have been recognized by science.

To date, about 1.7 million organisms have been identified and designated with a scientific name. About 6% of identified species live in boreal or polar latitudes, 59% in the temperate zones, and the remaining 35% in the tropics. The knowledge of the global richness of species is very incomplete, particularly in the tropics. If a conservative estimate is made of the number of unidentified tropical species, the fraction of global species that live in the tropics would increase to at least 86%.

Invertebrates comprise the largest number of described species, with insects making up the bulk of that total and beetles (Coleoptera ) comprising most of the insects. Biologists believe that there still is a tremendous number of undescribed species of insects in the tropics, possibly as many as another 30 million species. This remarkable conclusion has emerged from experiments conducted by the entomologist Terry Erwin, in which scientists "fogged" tropical forest canopies and then collected the "rain" of dead arthropods. This research suggests that: (1) a large fraction of the insect biodiversity of tropical forests is undescribed; (2) most insect species are confined to a single type of forest, or even to particular plant species, both of which are restricted in distribution; and (3) most tropical forest insects have a very limited dispersal ability.

The biodiversity and endemism of other tropical forest biota are better known than that of arthropods. For example, a plot of only 0.2 acres (0.1 ha) in an Ecuadorian forest had 365 species of vascular plants. The richness of woody plants in tropical rain forest can approach 300 species per hectare, compared with fewer than 1215 tree species in a typical temperate forest, and thirty to thirty-five species in the Great Smokies of the United States, the richest temperate forest in the world.

There have been few systematic studies of all of the biota of particular tropical communities. In one case, D. H. Janzen studied a savanna-like, 67-mi2 (108-km2) reserve of dry tropical forest in Costa Rica for several years. He estimated that the site had at least 700 plant species, 400 vertebrate species, and a remarkable 13,000 species of insect, including 3,140 species of moths and butterflies.

Why should one worry about the likelihood of extinction of so many rare species of tropical insects, or of many other rare species of plants and animals? There are three classes of reasons why extinctions are regrettable:

  1. There are important concerns in terms of the ethics of extinction. Central questions are whether humans have the "right" to act as the exterminator of unique and irrevocable species of wildlife and whether the human existence is somehow impoverished by the tragedy of extinction. These are philosophical issues that cannot be scientifically resolved, but it is certain that few people would applaud the extinction of unique species.
  2. There are utilitarian reasons. Humans must take advantage of other organisms in myriad ways for sustenance, medicine, shelter, and other purposes. If species become extinct, their unique services, be they biological, ecological, or otherwise, are no longer available for exploitation.
  3. The third class of reasons is ecological and involves the roles of species in maintaining the stability and integrity of ecosystems, i.e., in terms of preventing erosion and controlling nutrient cycling, productivity, trophic dynamics, and other aspects of ecosystem structure and function. Because we rarely have sufficient knowledge to evaluate the ecological "importance" of particular species, it is likely that an extraordinary number of species will disappear before their ecological roles are understood.

There are many cases where research on previously unexploited species of plants and animals has revealed the existence of products of great utility to humans, such as food or medicinals. One example is the rosy periwinkle (Catharantus roseus ), a plant native to Madagascar . During a screening of many plants for possible anti-cancer properties, an extract of rosy periwinkle was found to counteract the reproduction of cancer cells. Research identified the active ingredients as several alkaloids, which are now used to prepare the important anti-cancer drugs vincristine and vinblastine. This once obscure plant now allows treatment of several previously incurable cancers and is the basis of a multi-million-dollar economy.

Undoubtedly, there is a tremendous, undiscovered wealth of other biological products that are of potential use to humans. Many of these natural products are present in the biodiversity of tropical species that has not yet been "discovered" by taxonomists.

It is well known that extinction can be a natural process. In fact, most of the species that have ever lived on Earth are now extinct, having disappeared "naturally" for some reason or other. Perhaps they could not cope with changes in their inorganic or biotic environment , or they may have succumbed to some catastrophic event, such as a meteorite impact.

The rate of extinction has not been uniform over geological time. Long periods characterized by a slow and uniform rate of extinction have been punctuated by about nine catastrophic events of mass extinction. The most intense mass extinction occurred some 250 million years ago, when about 96% of marine species became extinct. Another example occurred 65 million years ago, when there were extinctions of many vertebrate species, including the reptilian orders Dinosauria and Pterosauria, but also of many plants and invertebrates, including about one half of the global fauna that existed then.

In modern times, however, humans are the dominant force causing extinction, mostly because of: (1) overharvesting; (2) effects of introduced predators, competitors, and diseases; and (3) habitat destruction. During the last 200 years, a global total of perhaps 100 species of mammals, 160 birds, and many other taxa are known to have become extinct through some human influence, in addition to untold numbers of undescribed, tropical species.

Even pre-industrial human societies caused extinctions. Stone-age humans are believed to have caused the extinctions of large-animal fauna in various places, by the unsustainable and insatiable hunting of vulnerable species in newly discovered islands and continents. Such events of mass extinction of large animals, co-incident with human colonization events, have occurred at various times during the last 1050,000 years in Madagascar, New Zealand, Australia , Tasmania, Hawaii, North and South America, and elsewhere.

In more recent times, overhunting has caused the extinction of other large, vulnerable species, for example the flightless dodo (Raphus cucullatus )of Mauritius. Some North American examples include Labrador duck (Camptorhynchus labradorium ), passenger pigeon (Ectopistes migratorius ), Carolina parakeet (Conuropsis carolinensis ), great auk (Pinguinus impennis ), and Steller's sea cow (Hydrodamalis stelleri ). Many other species have been brought to the brink of extinction by overhunting and loss of habitat. Some North American examples include eskimo curlew (Numenius borealis ), plains bison (Bison bison ), and a variety of marine mammals, including manatee (Trichechus manatus ), right whales (Eubalaena glacialis ), bowhead whale (Balaena mysticetus ), and blue whale (Balaenoptera musculus ).

Island biotas are especially prone to both natural and anthropogenic extinction. This syndrome can be illustrated by the case of the Hawaiian Islands ,an ancient volcanic archipelago in the Pacific Ocean, about 994 mi (1,600 km) from the nearest island group and 2,484 mi (4,000 km) from the nearest continental landmass. At the time of colonization by Polynesians, there were at least 68 endemic species of Hawaiian birds, out of a total richness of land birds of 86 species. Of the initial 68 endemics, 24 are now extinct and 29 are perilously endangered. Especially hard hit has been an endemic family, the Hawaiian honeycreepers (Drepanididae), of which 13 species are believed extinct, and 12 endangered. More than 50 alien species of birds have been introduced to the Hawaiian Islands, but this gain hardly compensates for the loss and endangerment of specifically evolved endemics. Similarly, the native flora of the islands is estimated to have been comprised of 1,7652,000 taxa of angiosperm plants, of which at least 94% were endemic. During the last two centuries, more than 100 native plants have become extinct, and the survival of at least an additional 500 taxa is threatened or endangered, some now being represented by only single individuals. The most important causes of extinction of Hawaiian biota have been the conversion of natural ecosystems to agricultural and urban landscapes, the introduction of alien predators, competitors, herbivores, and diseases, and to some extent, aboriginal over-hunting of some species of bird.

Overhunting has been an important cause of extinction, but in modern times habitat destruction is the most important reason for the event of mass extinction that Earth's biodiversity is now experiencing. As was noted previously, most of the global biodiversity is comprised of millions of as yet undescribed taxa of tropical insects and other organisms. Because of the extreme endemism of most tropical biota, it is likely that many species will become extinct as a result of the clearing of natural tropical habitats, especially forest, and its conversion to other types of habitat.

The amount and rate of deforestation in the tropics are increasing rapidly, in contrast to the situation at higher latitudes where forest cover is relatively stable. Between the mid 1960s and the mid 1980s there was little change (less than 2%) in the forest area of North America, but in Central America forest cover decreased by 17%, and in South America by 7% (but by a larger%age in equatorial countries of South America). The global rate of clearing of tropical rain forest in the mid 1980s was equivalent to 68% of that biome per year, a rate that if projected into the future would predict a biome half-life of only nine to 12 years. Some of the cleared forest will regenerate through secondary succession , which would ultimately produce another mature forest. Little is known, however, about the rate and biological character of succession in tropical rainforests, or how long it would take to restore a fully biodiverse ecosystem after disturbance.

The present rate of disturbance and conversion of tropical forest predicts grave consequences for global biodiversity. Because of a widespread awareness and concern about this important problem, much research and other activity has recently been directed towards the conservation and protection of tropical forests. As of 1985, several thousand sites, comprising more than 640,000 mi2 (1 million km), had received some sort of "protection" in low-latitude countries. Of course the operational effectiveness of the protected status varies greatly, depending on the commitment of governments to these issues. Important factors include: (1) political stability; (2) political priorities; (3) finances available to mount effective programs to control poaching of animals and lumber and to prevent other disturbances; (4) the support of local peoples and communities for biodiversity programs; (5) the willingness of relatively wealthy nations to provide a measure of debt relief to impoverished tropical countries and thereby reduce their short term need to liquidate natural resources in order to raise capital and provide employment; and (6) local population growth , which also generates extreme pressures to over exploit natural resources.

The biodiversity crisis is a very real and very important aspect of the global environmental crisis. All nations have a responsibility to maintain biodiversity within their own jurisdictions and to aid nations with less economic and scientific capability to maintain their biodiversity on behalf of the entire planet. The modern biodiversity crisis focuses on species-rich tropical ecosystems, but the developed nations of temperate latitudes also have a large stake in the outcome and will have to substantially subsidize global conservation activities if these are to be successful. Much needs to be done, but an encouraging level of activity in the conservation and protection of biodiversity is beginning in many countries, including an emerging commitment by many nations to the conservation of threatened ecosystems in the tropics.

[Bill Freedman Ph.D. ]


RESOURCES

BOOKS


Ehrlich, P. R., and A. H. Ehrlich. Extinction: The Causes and Consequences of the Disappearance of Species. New York: Ballantyne Books, 1981.

Freedman, B. Environmental Ecology. San Diego, CA: Academic Press, 1989.

Peters, R. L., and T. E. Lovejoy. Global Warming and Biological Diversity. New Haven, CT: Yale University Press, 1992.

Wilson, E. O. Biodiversity. Washington, DC: National Academy Press, 1988.

. Biophilia: The Human Bond With Other Species. Cambridge, MA: Harvard University Press, 1984.

PERIODICALS

Janzen, D. H. "Insect Diversity in a Costa Rican Dry Forest: Why Keep It, and How." Biological Journal of the Linnaean Society 30 (1987): 343356.

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Biodiversity

Biodiversity

Species richness of the biosphere

Why is biodiversity important?

Biodiversity and extinction

Protection of endangered biodiversity

Resources

Biodiversity is the total richness of biological variation. The scope of biodiversity is usually considered to range from the genetic variation of individual organisms within and among populations of a species, to different species occurring together in ecological communities. Biodiversity ranges from local to regional, state or provincial, national, continental, and ultimately to global.

Biodiversity at all scales is severely threatened by human activities; this is one of the most important aspects of the global environmental crisis. Humans have already caused permanent losses of biodiversity through the extinction of many species and extensive losses of distinctive, natural ecosystems. Ecologists predict that unless there are substantial changes in the ways that humans affect ecosystems, there will be much larger losses of biodiversity in the near future.

Species richness of the biosphere

About 1.7 million of Earths species have been identified and designated with a scientific name. About 5% of the identified species live in boreal or polar latitudes, about 60% in the temperate zones, and the remaining 35% in the tropics. However, the knowledge of Earths species is highly incomplete, especially for tropical countries. According to some estimates, there could be as many as 30-50 million species on Earth, with 90% of them occurring in tropical ecosystems. Tropical ecosystems are much richer in species than are those at higher latitudes.

Most of the described species on Earth are invertebrates, particularly insects, and most of the insects are beetles (order Coleoptera). Some biologists believe that beetles account for most of the undescribed tropical insects.

Studies conducted in tropical rainforest indicate that beetles account for most of the insect species and that most of the beetles have a local distribution and are found nowhere else. For example, the tree Luehea seemanii, has more than 1,100 species of beetle in its canopy, of which 15% are specific to that plant. The emerging conclusion from this and other descriptive research is that there is an enormous abundance of undescribed species of insects and other invertebrates living in tropical forests.

Compared with invertebrates, the numbers of species (that is, the species richness) of other groups of tropical-forest organisms are better known. Although it is extremely difficult to do so, the numbers of species of vascular plants have been described for a few tropical forests. For example: a plot of only 0.0004 sq mi (0.1 ha) in a moist forest in Ecuador had 365 species of vascular plants; there were 98 species of large trees in 0.006 sq mi (1.5 ha) of forest in Sarawak, Malaysia; there were 90 tree species in 0.0032 sq mi (0.8 ha) of forest in Papua New Guinea; 742 woody species occurred in 0.012 sq mi (3 ha) of forest in Sarawak, with 50% of the species recorded as single individuals; and more than 300 species of woody plants were discovered on a 2-sq mi (50-ha) area of forest in Panama. These tropical forests are much richer than temperate forests, stands of which typically support fewer than 12-15 species of trees. The Great Smokey Mountains of the eastern United States have some of the richest temperate forests in the world, and they typically contain 30-35 species, far fewer than tropical rainforests.

It is extraordinarily difficult to determine the numbers of birds in tropical forest because the dense foliage and darkness of the understory make it inconvenient to see small animals, even if they are brightly colored. As a result, few studies have been made of the birds of tropical rainforest. However, one study in Peru discovered 245 resident and 74 transient species in 0.4 sq mi (97 ha) of Amazonian forest. Another study of rainforest in French Guiana recorded 239 species of birds, and another found 151 species in a forest in Sumatra. In comparison, stands of temperate forest in North America typically support only 15-30 species of birds.

Almost no systematic surveys have been made of all of the species of tropical ecosystems. In one case, a 42 sq mi (108 sq km) reserve of dry forest in Costa Rica was estimated to support about 700 plant species, 400 vertebrate species, and 13,000 species of insects, including 3,140 species of moths and butterflies.

Why is biodiversity important?

Biodiversity is valuable for a number of reasons. Firstly, biodiversity has its own intrinsic value, regardless of its worth in terms of human needs. Because of its intrinsic merit, there are ethical considerations to any degradation of biodiversity. For example, do humans have the right to diminish or exterminate elements of biodiversity, all of which are unique and irretrievable? Is the human existence itself diminished by losses of biodiversity? Ethical issues cannot be resolved through science, but enlightened people would mourn any loss of species, or of natural ecosystems.

Secondly, humans have an absolute requirement for the products of other species. Because of this need, wild and domesticated species and their communities are exploited in many ways to provide food, materials, energy, and other goods and services. This fact can be illustrated in many ways. In the United States, for example, about one-quarter of prescription drugs have active ingredients obtained from higher plants, and these uses contribute about $14 billion per year to the U.S. economy, and $40 billion per year worldwide. Potentially, harvests of biodiversity can be conducted in ways that foster their renewal. Unfortunately, potentially renewable biodiversity resources are often harvested too intensively or inadequate attention is paid to regeneration, so the resource is degraded or becomes extinct.

Thirdly, biodiversity provides many ecological services that are directly or indirectly important to human welfare. Examples of these services include biological productivity, nutrient cycling, cleaning water and air of pollutants, control of erosion, provision of atmospheric oxygen, removal of carbon dioxide, and other functions related to the integrity of ecosystems.

There are many cases of the discovery, through research on previously unexploited plants and animals, of bio-products useful to humans as food, medicine, or for other purposes. Consider the case of the rosy periwinkle (Catharantus roseus ), a small plant native to the tropical island of Madagascar. During an extensive screening of wild plants for anti-cancer chemicals, an extract of rosy periwinkle was observed to inhibit the growth of cancerous cells. The active biochemicals are several alkaloids in foliage of the plant, which probably serve to deter herbivores. These natural substances are now used to prepare the drugs vincristine and vinblastine, which can be successfully used to treat childhood leukemia and a lymphatic cancer known as Hodgkins disease. In this case, a species of wild plant known only to a few botanists has proven to be of great benefit to humans by treating previously incurable diseases, in the process sustaining a large pharmaceutical economy. There is a tremendous undiscovered wealth of other biological products useful to humans in unexplored biodiversity.

Biodiversity and extinction

Extinction refers to the loss of some species or other taxonomic unit (e.g., subspecies, genus, family, etc.; each is known as a taxon), occurring over all of its range on Earth. The extinction of any species is an irrevocable loss of part of the biological richness of Earth, the only place in the universe known to support living creatures. Extinction can be a natural occurrence caused by an unpredictable catastrophe, chronic environmental stress, or ecological interactions such as competition, disease, or predation. However, there have been dramatic increases in extinction rates since humans have become Earths dominant large animal and the cause of global environmental change.

Extinction has always occurred naturally. Almost all species that have ever lived on Earth have become extinct. Perhaps they could not cope with changes occurring in their environment, such as climate changes, the intensity of predation, or disease. Alternatively, many extinctions may have occurred simultaneously as a result of unpredictable catastrophes. From the geological record it is known that species, families, and even phyla have appeared and disappeared over time. For example, numerous phyla of invertebrates proliferated during an evolutionary radiation occurring at the beginning of the Cambrian era about 570 million years ago, but most of these animals are now extinct. The 15-20 extinct phyla from that period are known from the Burgess Shale of British Columbia, and they represent unique experiments in invertebrate form and function. Similarly, entire divisions of plants have appeared, radiated, and disappeared, such as the seed ferns Pteridospermales, the cycad-like Cycadeoidea, and woody plants known as Cordaites. Of the 12 orders within the class Reptilia, only three survive today: crocodilians, turtles, and snakes/lizards. Clearly, the fossil record displays a great deal of evidence of natural extinctions.

Overall, the geological record suggests that there have been long periods of time characterized by uniform rates of extinction, but punctuated by about nine catastrophic episodes of mass extinction. The most intense extinction event occurred at the end of the Permian period some 245 million years ago, when 54% of marine families, 84% of genera, and 96% of species are estimated to have become extinct.

Another famous, apparently synchronous, extinction of vertebrate animals occurred about 65 million

KEY TERMS

Binomial The scientific name of organisms consists of two words, and is therefore a binomial. Humans, for example, are named Homo sapiens, which designates our genus as Homo, and our species within that genus as sapiens. Binomials are always latinized words, and are written in italics, or underlined.

Endangerment Refers to a situation in which a species is vulnerable to extinction or extirpation.

Endemic Refers to species with a relatively local distribution, sometimes occurring as small populations confined to a single place, such as an oceanic island. Endemic species are more vulnerable to extinction than are more widespread species.

Extinction The condition in which all members of a group of organisms have ceased to exist. Extirpation means that a species no longer occurs in a place or country, although it survives elsewhere.

Species diversity An indicator of biodiversity at the community level, which accommodates both the number of species present (i.e., richness) and their relative abundance. Ecologists consider species diversity to be a good indicator of biodiversity within communities, because it accommodates differences amongst species in rarity and commonness.

Species richness The number of species occurring in a community, a landscape, or some other defined area.

years ago at the end of the Cretaceous period. The most renowned extinctions were of the last of the reptilian dinosaurs and pterosaurs, but many plants and invertebrates also became extinct at that time. In total, perhaps 76% of species and 47% of genera became extinct in the end-of-Cretaceous crisis. One hypothesis to explain the cause of this mass extinction involves a meteorite impacting the Earth, causing huge quantities of fine dust to be spewed into the atmosphere, and resulting in a climatic deterioration that most large animals could not tolerate. However, some scientists believe that the extinctions of the last dinosaurs were more gradual.

However, humans have been responsible for almost all of Earths recent extinctions. These extinctions are occurring so quickly that they represent a modern mass extinction of similar intensity to those documented in the geological record. Examples of recent extinctions caused by humans include such well-known cases as the dodo, passenger pigeon, and great auk. Many other high-profile species have been taken to the brink of extinction, including the plains bison, whooping crane, right whale, and other marine mammals. These losses have been caused by insatiable overhunting and intense disturbance or conversion of natural habitats.

Beyond these well-known and tragic cases involving large animals, Earths biodiversity is experiencing an even larger loss. This ruin is mostly being caused by extensive conversions of tropical ecosystems, particularly rainforest, into agricultural habitats that sustain few of the original species. As was described previously, tropical ecosystems sustain extremely large numbers of species, most of which have restricted distributions. The conversion of tropical forest into other habitats inevitably causes the loss of most of the locally endemic biota. This is a great tragedy, and the lost species will never occur again.

The increased rate of extinction and endangerment of biodiversity during the past several centuries is best documented for vertebrates because, as noted previously, most invertebrate species, particularly insects, have not yet been described by scientists. During the last four centuries there have been more than 700 known extinctions globally, including about 100 species of mammals and 160 species of birds, all because of human influences.

Protection of endangered biodiversity

Biodiversity can be protected in ecological reserves, protected areas established for the conservation of natural values, usually the known habitat of endangered species, threatened ecosystems, or representative examples of widespread communities. The World Conservation Union, World Resources Institute, and United Nations Environment Program are three important agencies whose mandates center on the conservation of the worlds biodiversity. These agencies have developed the Global Biodiversity Strategy, an international program to help protect biodiversity. The broad objectives are to preserve biodiversity, maintain Earths ecological processes and life-support systems, and ensure that biodiversity resources are used in a sustainable manner. As such, the Global Biodiversity Strategy is a mechanism by which countries and peoples can initiate meaningful actions to protect biodiversity for the benefit of present and future generations of people, and also for its intrinsic value.

See also Biological community; Ecosystem.

Resources

BOOKS

Gaston, Kevin J. and John I. Spicer. Biodiversity: An Introduction. Boston: Blackwell Publishing,.

Hamblin, W.K., and Christiansen, E.H. Earths Dynamic Systems. 9th ed. Upper Saddle River: Prentice Hall, 2001.

Myers, Judith, and Dawn Bazely. Ecology and Control of Introduced Plants. Cambridge: Cambridge University Press, 2003.

Nebel, Bernard J., and Richard T. Wright. Environmental Science: Toward a Sustainable Future. 8th ed. Englewood Cliffs, NJ: Prentice Hall, 2002.

Novacek, Michael J. The Biodiversity Crisis: Losing What Counts. New York: The New Press, 2001.

Bill Freedman

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Biodiversity

Biodiversity

Introduction

Biodiversity is the number of distinct varieties or types within a group of living systems: distinct genes in a species, species in an ecosystem, or ecosystems in a biome. The term is often used to mean the total number of species living in a given ecosystem or on Earth as a whole. Climate change affects biodiversity primarily by shifting the boundaries of ecosystems, by altering the timing of seasonal events such as hatching and budding, and altering the temperature and chemical characteristics of lakes, rivers, and oceans. Atmospheric carbon dioxide (CO2), which is a main cause of global warming, also has direct effects on ecosystems, acidifying the oceans and encouraging the growth of some plants more than others. Such stresses inevitably cause extinctions, that is, loss of biodiversity.

Only evolution can create new species, and this occurs only over geologic time (usually millions of years). On human or historical time scales, extinction decreases biodiversity irreversibly. Some extinctions from climate change have already been recorded, although to date most have been caused by other human activities such as pollution, over-hunting, and deforestation. The rate of extinctions caused by climate change is predicted to be greater later in the twenty-first century than today.

Historical Background and Scientific Foundations

Context

The modern systematic classification of species was invented by Swedish naturalist Carl Linnaeus (1707– 1788) in the eighteenth century. In following decades, European naturalists scoured Earth looking for and classifying new species of plants and animals, greatly expanding scientific knowledge of just how diverse life on Earth is. Such knowledge was crucial to the development of evolutionary biology by Charles Darwin (1809–1882) and others in the mid-nineteenth century. Today, biologists estimate that there are more than 280,000 species of plants and over 1,250,000 species of animals (including insects). Nineteenth- and twentieth-century paleontology has shown that extinction is a normal process: over 99% of all species that have ever lived are now extinct. The typical lifespan of a species is between 1 and 10 million years.

Awareness that species biodiversity is a key feature of ecosystems was not common until the 1970s, however, when the term “biological diversity” first came into frequent use. The word “biodiversity,” a shortening of “biological diversity,” first appeared in print in 1988. In the 1990s and beyond, most biologists have agreed that human beings are causing the first mass extinction in 65 million years. This modern pulse of extinctions is sometimes called the Holocene extinction event. (The Holocene is the geological term for the era from 11,500 years ago to the present.)

Humans are causing extinctions through land development, destruction of rainforests, over-hunting and over-fishing, pollution, and other activities. Some of the more famous extinctions of recent times include the dodo bird, the passenger pigeon, and (announced in 2007) the baiji, a white river dolphin of China. Hunting has caused about 23% of known animal extinctions since 1600; the introduction of invasive species, 39%; and habitat destruction, 36%. These numbers are approximate because many of the species that are being destroyed are uncatalogued insects and plants living in rainforests. Estimates of how many extinctions have already occurred due to human activities range from several tens of thousands to over a million.

Although impacts by large asteroids have caused or at least contributed to some ancient mass extinctions, climate change has been the most common cause of natural mass extinction. Ancient climate changes were brought about by shifts in Earth's orbit, continental drift, volcanism, and other processes. Today's episode of climate change is unique in being caused by a single species, humans. Moreover, today's mass extinction is unique in that human beings, by taking action to mitigate (reduce the severity of) climate change, can influence the overall severity of the event.

Mechanisms by which Climate Change Affects Biodiversity

As warming continues, other forms of human pressure on biodiversity will continue and will be, in most cases, amplified by the effects of climate change. Although effects may vary from region to region, the overall effect of global warming is to cause the cooler zones of the world—the regions around the poles (especially the North Pole) and on mountains—to shrink. Shrinkage of habitat puts species at risk because smaller habitats support smaller populations, and smaller populations are always at higher risk of extinction.

Climate change also has many other effects on ecosystems. Some are not immediately obvious. For example, Lake Tanganyika in Africa, the world's second-largest and second-deepest lake, harbors at least 350 species of fish, most unique to its own waters. Lake Tanganyika is not typical of ecosystems most vulnerable to climate change: being near the equator it is likely to see less drastic warming than, say, the Arctic, while its large thermal mass (4,526 cubic mi of water; 18,900 cubic km) will resist temperature shifts and thus might be expected to moderate climate-change impacts on the lake ecosystem.

However, regional climate warming by 1.08°F (0.6°C), along with lessened wind speeds, has had rapid effects on Tanganyika's ecosystem. Warming of surface waters more than deep waters has decreased mixing between the two: warm water is less dense than cool water, so the bigger the temperature difference between the layers, the more stably the warm upper water floats on top of the cool deeper water. Since the deeper waters are more nutrient-rich, reduced mixing has meant that fewer planktonic organisms (tiny, floating organisms, both plants and animals) can thrive in the upper water, where energy from the sun is abundant but nutrients are poor. As of 2003, plankton density in Lake Tanganyika had declined to less than one third what it was 25 years before; algae density had declined by 30% from values 80 years before. Since plankton are the basis of the marine food chain, fish stocks declined along with the plankton: fish stocks in the lake were 30% smaller than they were 80 years earlier.

WORDS TO KNOW

: Well-defined terrestrial environment (e.g., desert, tundra, or tropical forest). The complex of living organisms found in an ecological region.

: Decoloration or whitening of coral from the loss, temporary or permanent, of symbiotic algae (zooxanthellae) living in the coral. The algae give corals their living color and, through photosynthesis, supply most of their food needs. High sea surface temperatures can cause coral bleaching.

: The period of time extending from the formation of Earth to the present.

: The Holocene is the geological period from 10,000 years ago to the present; the Holocene extinction is the worldwide mass extinction of animal and plant species being caused by human activity. Global warming may accelerate the ongoing Holocene extinction event, possibly driving a fourth of all terrestrial plant and animal species to extinction.

: The study of life in past geologic time.

: Measures the acidity of a solution. It is the negative log of the concentration of the hydrogen ions in a substance.

: Floating animal and plant life.

The reduction of water mixing due to climate warming has made other changes in the lake's chemistry: for one, oxygen dissolved from the air no longer mixes as well in deeper waters. As a result, the habitat has shrunk for some of the lake's endemic species, such as the snail Tiphobia horei, which in 1890 lived at depths down to 1,000 ft (300 m) but as of 2003 lived only down to 330 ft (100 m). The snail's habitat has thus shrunk by about two thirds, even though the lake itself has not shrunk and its bulk average temperature has changed only slightly.

Tanganyika surface plankton loss has been reflected in declining food-fish harvests from the lake (about 400,000 tons per year in 2003). Since Tanganyika supplies 25–40% of the protein needs of the four nations bounding the lake, such declines can have direct impacts on human populations as well as on biodiversity. Losses in biodiversity have not yet been measured directly in Tanganyika, but smaller populations will put some species at risk of extinction, especially as warming in the region continues to about 2.7°F (1.5°C), possibly higher, with even more drastic stabilization of the lake's waters and consequent effects on its ecosystem.

Slight changes in climate can lead to pressures on biodiversity by other mechanisms. For example, a 2006 study by J. Alan Pounds and colleagues found that global warming has almost certainly caused the recent extinction of about 67% of the 110 or so species of the Monteverde harlequin tree frog of the mountains of Costa Rica. The scientists saw the extinctions as validating the climate-linked epidemic hypothesis, according to which shifts in temperature, rainfall, and other climate variables make populations more vulnerable to disease and therefore to extinction. In the case of the Monteverde frogs, more frequent warm years shifted conditions toward the growth optimum of the Bactrachochytrium fungus, which infects the frogs. The researchers found that extinctions of the frogs consistently followed temperature peaks that were favorable to growth of the fungal disease.

Other effects are not strictly changes in climate, in the sense of temperature or precipitation, but chemical changes to air and water. Increased carbon dioxide (CO2) in theatmospherehas twomajor effectsthatare likelyto decrease biodiversity: 1) Heightened atmospheric CO2 causes increased levels of dissolved CO2 in the ocean. When CO2 dissolves in water, it produces a weak acid, carbonic acid. Rising atmospheric CO2 thus acidifies the oceans. 2) Green plants extract carbon from the air by breaking up CO2, constructing their tissues using the carbon, and releasing the oxygen. CO2 is plant food. Thus, increasing atmospheric CO2 tends to cause more rapid growth in most plant species, an effect called CO2 enrichment.

Acidification of the oceans by dissolved excess CO2 will impact biodiversity by making survival more difficult for organisms that form shells of calcium carbonate. This includes bivalves such as clams, mollusks such as periwinkles and conches, microscopic plankton species, and corals. Corals, which are also subject to bleaching in excessively warm waters, form large, shallow communities in tropical waters that have been compared to rainforests because of their high level of biodiversity. A typical large reef may support on the order of a million species of plants and animals.

Over the last two centuries, the average pH of the oceans has fallen by 0.1, corresponding to a rise in acidity and a 30% reduction in the number of carbonate ions (CO32–) available to shell-making organisms as building material. When carbonate ions fall below a certain level, corals have difficulty making their skeletons. This threshold may be reached if the atmospheric CO2 level, today about 375 parts per million, rises to over 500 parts per million, as may occur by the end of the twenty-first century.

Increasing atmospheric CO2 will also affect plant growth. Farmers today often add CO2 to the air inside greenhouses, because under indoor conditions, extra CO2 speeds plant growth and increases crop yields. Under outdoor conditions, however, the gain in yield is about half as much and the foods produced are significantly lower in protein and minerals. In the wild, rising CO2 will favor some species over others, depending on rooting depth, woodiness, and photosynthetic chemistry; this will impact biodiversity by altering competitive balances. The CO2 fertilization effect will be strongest in biomes where plant growth is limited by water availability, such as grasslands, savanna, and desert. The biodiversity impact of a 2.5-fold increase in CO2 would likely be only about a third as great on a boreal (northern pine) forest as on savanna or grassland, and half as great as on desert.

IN CONTEXT: PRESERVING BIODIVERSITY

“Reducing both loss of natural habitat and deforestation can have significant biodiversity, soil and water conservation benefits, and can be implemented in a socially and economically sustainable manner. Forestation and bioenergy plantations can lead to restoration of degraded land, manage water runoff, retain soil carbon and benefit rural economies, but could compete with land for food production and may be negative for biodiversity, if not properly designed.”

SOURCE:Metz, B., et al, eds. Climate Change 2007: Mitigation of Climate Change: Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Impacts and Issues

Global Patterns

Most plants require a specific range of temperature, moisture, and seasonal change to thrive; most animals require certain plants or other animals to thrive, and also have a limited range of tolerance for temperature and moisture. As climate warms, a typical ecosystem will tend to migrate away from areas where it was at the warm edge of its tolerance range and toward places where it was formerly at the cool edge. The most general effect of global climate change is thus to move ecological zones toward the poles and toward higher altitudes. For each 1.8°F (1°C) of warming, terrestrial (on-land) ecosystems typically shift poleward by 100 mi (160 km): for example, if climate warms by 5.4°F (3°C) by 2100, plant and animal communities in the Northern Hemisphere will migrate an average of 300 mi (480 km) northward—if they can—to stay in a suitable climate zone. This effect is observed, not only predicted.

In the Northern Hemisphere, terrestrial animal and plant ranges have been observed to shift northward, on average, by 3.8 mi (6.1 km) per decade over the last 50 years. In mountainous terrain, plant and animal ranges have shifted upward by 20 ft (6.1 m) over the same time period. Fragmentation of landscapes by human activity such as agriculture and city-building makes ecosystem migration more difficult today than during past climatic shifts, such as glacial periods. Species that fail to colonize new areas as the climate changes may go extinct.

Although climate change has so far been most intense in the Arctic and the West Antarctic Peninsula, where warming has been about twice the global average and dramatic effects such as retreating sea ice and melting tundra are readily visible, biodiversity is low in these regions compared to the tropics, where rainforests, coral reefs, and other particularly diverse communities are found. Thus, a smaller climate shift can have a greater impact on biodiversity in the tropics than a larger shift in boreal or temperate regions.

For marine ecosystems, changes in circulation patterns, ocean temperature, and ocean chemistry all influence biodiversity. For example, over the last 40 years or so, warm-water plankton species have shifted about 620 mi (1,000 km) in the North Atlantic due to warming.

Not all observed climate effects on biological systems are consistent with climate warming; a few are consistent with cooling. Also, some observed effects are consistent with natural climate shifts rather than those attributed to human-caused (anthropogenic) global warming. However, mathematical analysis shows that the very great majority of changes are consistent with warming trends, and that a combination of natural and anthropogenic climate changes describe observed changes in physical and biological systems better than either natural or anthropogenic changes alone. Anthropogenic changes have been added to or laid over those caused by natural processes, and are gradually becoming more dominant.

Future Impacts

The five main drivers of biodiversity change, ranked from most severe impact to least severe between now and 2100, are: 1) land-use changes (including deforestation);2) climate change; 3) nitrogen deposition (from fertilizer use); 4) biotic exchange (the introduction of invasive species); and 5) direct effects of increasing atmospheric CO2, apart from climate change.

The result of these combined, continuing, and growing pressures will be an irreversible loss of biodiversity in many parts of the world. However, many uncertainties remain. Ecologists do not understand the relationship between ecosystem structure and rapid climate change well enough to predict the exact effects of current climate changes on biomes. It is also unknown whether efforts to mitigate climate change will occur or succeed, and if so, to what extent.

Despite these uncertainties, scientists have estimated the likely impact that climate change will have on biodiversity. In 2004, Chris Thomas and colleagues published their study of an unbiased or representative sample of 1,103 animal and plant species. They found that climate change was likely to commit 15–37% of all species examined to extinction by 2050. “Committed to extinction” does not mean that a species would necessarily be extinct by that time, but that the population of each species would be so reduced that its species' extinction becomes highly likely. In many or most ecological regions, climate change will become the greatest threat to biodiversity by 2050. There are 5 to 15 million species of creatures on Earth (the large range arises from the difficulty of counting insect, bacterial, and fungal species). If only 15% of all species are committed to extinction by climate change—the lower end of the range given by Thomas and colleagues—then 750,000 to 2,250,000 million species will eventually become extinct as a result of global climate change.

Primary Source Connection

Human activities and the resulting global climate change have had, and will continue to have, a major impact on biodiversity across the globe. Biodiversity is the variety of all living organisms that exist in an ecosystem. This paper from the Intergovernmental Panel on Climate Change (IPCC) discusses the effect of human activity on biodiversity and possible adaptation and mitigation strategies.

The IPCC is a scientific panel that was founded by the United Nations in 1988 as part of the United Nations Environment Program and the U.N.'s World Meteorological Organization.

CLIMATE CHANGE AND BIODIVERSITY

At the global level, human activities have caused and will continue to cause a loss in biodiversity through, inter alia, land-use and land-cover change; soil and water pollution and degradation (including desertification), and air pollution; diversion of water to intensively managed ecosystems and urban systems; habitat fragmentation; selective exploitation of species; the introduction of non-native species; and stratospheric ozone depletion. The current rate of biodiversity loss is greater than the natural background rate of extinction. A critical question for this Technical Paper is how much might climate change (natural or human-induced) enhance or inhibit these losses in biodiversity?

Changes in climate exert additional pressure and have already begun to affect biodiversity . The atmospheric concentrations of greenhouse gases have increased since the pre-industrial era due to human activities, primarily the combustion of fossil fuels and land-use and land-cover change. These and natural forces have contributed to changes in the Earth's climate over the 20th century: Land and ocean surface temperatures have warmed, the spatial and temporal patterns of precipitation have changed, sea level has risen, and the frequency and intensity of El Niño events have increased. These changes, particularly the warmer regional temperatures, have affected the timing of reproduction in animals and plants and/or migration of animals, the length of the growing season, species distributions and population sizes, and the frequency of pest and disease outbreaks. Some coastal, high-latitude, and high-altitude ecosystems have also been affected by changes in regional climatic factors.

Climate change is projected to affect all aspects of biodiversity; however, the projected changes have to take into account the impacts from other past, present, and future human activities, including increasing atmospheric concentrations of carbon dioxide (CO2) . For the wide range of Intergovernmental Panel on Climate Change (IPCC) emissions scenarios, the Earth's mean surface temperature is projected to warm 1.4 to 5.8°C by the end of the 21st century, with land areas warming more than the oceans, and the high latitudes warming more than the tropics. The associated sea-level rise is projected to be 0.09 to 0.88 m. In general, precipitation is projected to increase in high-latitude and equatorial areas and decrease in the subtropics, with an increase in heavy precipitation events. Climate change is projected to affect individual organisms, populations, species distributions, and ecosystem composition and function both directly (e.g., through increases in temperature and changes in precipitation and in the case of marine and coastal ecosystems also changes in sea level and storm surges) and indirectly (e.g., through climate changing the intensity and frequency of disturbances such as wild-fires). Processes such as habitat loss, modification and fragmentation, and the introduction and spread of non-native species will affect the impacts of climate change. A realistic projection of the future state of the Earth's ecosystems would need to take into account human land- and water-use patterns, which will greatly affect the ability of organisms to respond to climate change via migration.

The general effect of projected human-induced climate change is that the habitats of many species will move pole-ward or upward from their current locations . Species will be affected differently by climate change: They will migrate at different rates through fragmented landscapes, and ecosystems dominated by long-lived species (e.g., long-lived trees) will often be slow to show evidence of change. Thus, the composition of most current ecosystems is likely to change, as species that make up an ecosystem are unlikely to shift together. The most rapid changes are expected where they are accelerated by changes in natural and anthropogenic non-climatic disturbance patterns.

Changes in the frequency, intensity, extent, and locations of disturbances will affect whether, how, and at which rate the existing ecosystems will be replaced by new plant and animal assemblages . Disturbances can increase the rate of species loss and create opportunities for the establishment of new species.

Globally by the year 2080, about 20% of coastal wetlands could be lost due to sea-level rise . The impact of sea-level rise on coastal ecosystems (e.g., mangrove/coastal wetlands, seagrasses) will vary regionally and will depend on erosion processes from the sea and depositional processes from land. Some mangroves in low-island coastal regions where sedimentation loads are high and erosion processes are low may not be particularly vulnerable to sea-level rise.

The risk of extinction will increase for many species that are already vulnerable . Species with limited climatic ranges and/or restricted habitat requirements and/or small populations are typically the most vulnerable to extinction, such as endemic mountain species and biota restricted to islands (e.g., birds), peninsulas (e.g., Cape Floral Kingdom), or coastal areas (e.g., mangroves, coastal wetlands, and coral reefs). In contrast, species with extensive, non-patchy ranges, long-range dispersal mechanisms, and large populations are at less risk of extinction. While there is little evidence to suggest that climate change will slow species losses, there is evidence it may increase species losses. In some regions there may be an increase in local biodiversity—usually as a result of species introductions, the long-term consequences of which are hard to foresee.

Where significant ecosystem disruption occurs (e.g., loss of dominant species or a high proportion of species, or much of the species redundancy), there may be losses in net ecosystem productivity (NEP) at least during the transition period . However, in many cases, loss of biodiversity from diverse and extensive ecosystems due to climate change does not necessarily imply loss of productivity as there is a degree of redundancy in most ecosystems; the contribution to production by a species that is lost from an ecosystem may be replaced by another species. Globally, the impacts of climate change on biodiversity and the subsequent effects on productivity have not been estimated.

Changes in biodiversity at ecosystem and landscape scale, in response to climate change and other pressures (e.g., changes in forest fires and deforestation), would further affect global and regional climate through changes in the uptake and release of greenhouse gases and changes in albedo and evapotranspiration. Similarly, structural changes in biological communities in the upper ocean could alter the uptake of CO2 by the ocean or the release of precursors for cloud condensation nuclei causing either positive or negative feedbacks on climate change.

Modeling the changes in biodiversity in response to climate change presents some significant challenges . The data and models needed to project the extent and nature of future ecosystem changes and changes in the geographical distribution of species are incomplete, meaning that these effects can only be partially quantified.

Impacts of climate change mitigation activities on biodiversity depend on the context, design, and implementation of these activities . Land-use, land-use change, and forestry activities (afforestation, reforestation, avoided deforestation, and improved forest, cropland, and grazing land management practices) and implementation of renewable energy sources (hydro-, wind-, and solar power and biofuels) may affect biodiversity depending upon site selection and management practices. For example, 1) afforestation and reforestation projects can have positive, neutral, or negative impacts depending on the level of biodiversity of the non-forest ecosystem being replaced, the scale one considers, and other design and implementation issues; 2) avoiding and reducing forest degradation in threatened/vulnerable forests that contain assemblages of species that are unusually diverse, globally rare, or unique to that region can provide substantial bio-diversity benefits along with the avoidance of carbon emissions; 3) large-scale bioenergy plantations that generate high yields would have adverse impacts on biodiversity where they replace systems with higher biological diversity, whereas small-scale plantations on degraded land or abandoned agricultural sites would have environmental benefits; and 4) increased efficiency in the generation and/or use of fossil-fuel-based energy can reduce fossil-fuel use and thereby reduce the impacts on biodiversity resulting from resource extraction, transportation (e.g., through shipping and pipelines), and combustion of fossil fuels.

Climate change adaptation activities can promote conservation and sustainable use of biodiversity and reduce the impact of changes in climate and climatic extremes on biodiversity . These include the establishment of a mosaic of interconnected terrestrial, freshwater, and marine multiple-use reserves designed to take into account projected changes in climate, and integrated land and water management activities that reduce non-climate pressures on biodiversity and hence make the systems less vulnerable to changes in climate. Some of these adaptation activities can also make people less vulnerable to climatic extremes.

The effectiveness of adaptation and mitigation activities can be enhanced when they are integrated with broader strategies designed to make development paths more sustainable . There are potential environmental and social synergies and tradeoffs between climate adaptation and mitigation activities (projects and policies), and the objectives of multilateral environmental agreements (e.g., the conservation and sustainable use objective of the Convention on Biological Diversity) as well as other aspects of sustainable development. These synergies and tradeoffs can be evaluated for the full range of potential activities—inter alia, energy and land-use, land-use change, and forestry projects and policies through the application of project, sectoral, and regional level environmental and social impact assessments—and can be compared against a set of criteria and indicators using a range of decision making frameworks. For this, current assessment methodologies, criteria, and indicators for evaluating the impact of mitigation and adaptation activities on biodiversity and other aspects of sustainable development will have to be adapted and further developed.

ipcc. “climate change and biodiversity.” 2001ipcc technical paper v. < HTTP://WWW.GRIDA.NO/CLIMATE/IPCC_TAR/BIODIV/PDF/BIO_ENG.PDF> (accessed november29, 2007).

See Also Endangered Species; Extinction.

BIBLIOGRAPHY

Books

Parry, M. L., et al, eds. Climate Change 2007: Impacts, Adaptation and Vulnerability: Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Periodicals

Araúo, Miguel B., and Carsten Rahbek. “How Does Climate Change Affect Biodiversity?” Science 313 (2006): 1,396–1,397.

Higgins, Paul A. T. “Biodiversity Loss Under Existing Land Use and Climate Change: An Illustration Using Northern South America.” Global Ecology and Biogeography 16 (2007): 197–204.

Jenkins, Martin. “Prospects for Biodiversity.” Science 302 (2003): 1,175–1,177.

Livingstone, Daniel A. “Global Climate Change Strikes a Tropical Lake.” Science 301 (2003): 468–469.

Pounds, J. Alan, et al. “Widespread Amphibian Extinctions from Epidemic Disease Driven by Global Warming.” Nature 439 (2006): 161–167.

Sala, Enric, and Nancy Knowlton. “Global Marine Biodiversity Trends.” Annual Review of Energy and the Environment 231 (2006): 93–122.

Sala, Osvaldo E., et al. “Global Biodiversity Scenarios for the Year 2100.” Science 287 (2000): 1,770–1,774.

Thomas, Chris D. “Extinction Risk from Climate Change.” Nature 427 (2004): 145–148.

Thuiller, Wilfried. “Climate Change and the Ecologist.” Nature 448 (2007): 550–552.

Willis, K. J., and H. J. B. Birks. “What Is Natural? The Need for a Long-Term Perspective in Biodiversity Conservation.” Science 314 (2006): 1,261–1,265.

Zimmer, Carl. “Predicting Oblivions: Are Existing Models Up to the Task.” Science 317 (2007): 892–893.

Web Sites

“Climate Change and Biodiversity.” Intergovernmental Panel on Climate Change, IPCC Technical Paper V. < http://www.ipcc.ch/pub/tpbiodiv.pdf> (accessed November 8, 2007).

Larry Gilman

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Biodiversity

Biodiversity

Introduction

Biodiversity is the number of distinct varieties or types within a group of living systems: distinct genes in a species, species in an ecosystem, or ecosystems in a biome. The term is often used to mean the total number of species living in a given ecosystem or on Earth as a whole. Biodiversity is created by speciation, that is, the evolutionary appearance of new species; it is diminished by extinction. Only evolution can create new species, and this occurs only over geologic time (usually millions of years). On human or historical timescales, extinction decreases biodiversity irreversibly.

Human beings have impacted biodiversity for thousands of years through activities such as hunting, pollution, and habitat destruction (swamp-draining, deforestation, plowing of prairies, and the like). Nor is human-caused extinction entirely a recent affair. There is evidence that a number of animal species in North America, Australia, and New Zealand became extinct tens of thousands of years ago after the arrival of the first human settlers. In the last century or so, however, extinction due to habitat destruction for expanding human populations and industrial activity has increased manyfold. Moreover, a new human-caused foe of biodiversity has begun to manifest, namely global climate change.

Climate change threatens biodiversity mostly by shifting the boundaries of ecosystems, changing the timing of seasonal events such as hatching and budding, and altering the temperature and chemical characteristics of lakes, rivers, and oceans. Atmospheric carbon dioxide (CO2), which is the main cause of global warming, also has direct affects on ecosystems, such as acidifying the oceans and encouraging the growth of some plants more than others. Such stresses inevitably cause extinctions, that is, loss of biodiversity. The rate of extinctions caused by climate change is predicted to be greater later in the twenty-first century than today.

Historical Background and Scientific Foundation

Context

The modern systematic classification of species was invented by Swedish naturalist Carl Linnaeus (1707–1788) in the eighteenth century. In following decades, European naturalists scoured Earth looking for and classifying new species of plant and animal, greatly expanding scientific knowledge of just how diverse life on Earth is. Such knowledge was crucial to the development of evolutionary biology by Charles Darwin (1809–1882) and others in the mid-nineteenth century. Today, biologists estimate that there are more than 280,000 species of plants and over 1,250,000 species of animals (including insects). Nineteenth- and twentieth-century paleontology has shown that extinction is a normal process: over 99% of all species that have ever lived are now extinct. The typical lifespan of a species is between 1 and 10 million years.

Awareness that species biodiversity is a key feature of ecosystems was not common until the 1970s, however, when the term “biological diversity” first came into frequent use. The word “biodiversity,” a shortening of “biological diversity,” first appeared in print in 1988. In the 1990s and beyond, most biologists have agreed that human beings are causing the first mass extinction in 65 million years. This modern pulse of extinctions is sometimes called the Holocene extinction event. (The Holocene is the geological term for the era from 11,500 years ago to the present.)

Humans are causing extinctions through land development, destruction of rain forests, over-hunting and over-fishing, pollution, and other activities. Some of the more famous extinctions of recent times include the dodo bird, the passenger pigeon, and (announced in 2007) the baiji, a white river dolphin of China. Hunting has caused about 23% of known animal extinctions since 1600; the introduction of invasive species, 39%; habitat destruction, 36%. These numbers are approximate because many of the species that are being destroyed are uncatalogued insects and plants living in rain forests. Estimates of how many extinctions have already occurred due to human activities range from several tens of thousands to over a million.

Although impacts by large asteroids have caused or at least contributed to some ancient mass extinctions, climate change has been the most common cause of natural mass extinction throughout Earth’s history. Ancient climate changes have been brought about by shifts in Earth’s orbit, continental drift, volcanism, and other processes. Today’s episode of climate change is unique in being caused by a single species, humans. Moreover, today’s ongoing mass extinction is unique in that human beings, by taking action to mitigate (reduce the severity of) climate change and to reduce the other impacts of human activity on biodiversity, can influence the overall severity of the event.

Case Study: How Climate Change Affects Biodiversity

As warming continues, other forms of human pressure on biodiversity will continue and will be, in most cases, amplified by the effects of climate change. Although effects may vary from region to region, the overall effect of global warming is to cause the cooler zones of the world—the regions around the poles (especially the North Pole) and on mountains—to shrink. Shrinkage of habitat puts species at risk because smaller habitats support smaller populations, and smaller populations are always at higher risk of extinction.

Climate change also has many other effects on ecosystems. Some are not immediately obvious. For example, Lake Tanganyika in Africa, the world’s second-largest and second-deepest lake, harbors at least 350 species of fish, most unique to its own waters. Lake Tanganyika is not typical of ecosystems most vulnerable to climate change. Being near the equator it is likely to see less drastic warming than, say, the Arctic, while its large thermal mass (4,526 cubic mi of water; 18,900 cubic km) will resist temperature shifts and thus might be expected to moderate climate-change impacts on the lake ecosystem.

However, regional climate warming by 1.08°F (0.6°C), along with lessened wind speeds, has had rapid effects on Tanganyika’s ecosystem. Warming of surface waters more than deep waters has decreased mixing between the two: Warm water is less dense than cool water, so the bigger the temperature difference between

WORDS TO KNOW

BIOME: A well-defined terrestrial environment (e.g., desert, tundra, or tropical forest) and the complex of living organisms found in that region.

DEFORESTATION: A reduction in the area of a forest resulting from human activity.

GEOLOGIC TIME: The period of time extending from the formation of the earth to the present.

PALEONTOLOGY: The study of life in past geologic time.

pH: The measure of the amount of dissolved hydrogen ions in solution.

PLANKTON: Floating animal and plant life.

the layers, the more stably the warm upper water floats on top of the cool deeper water. Since the deeper waters are more nutrient-rich, reduced mixing has meant that fewer planktonic organisms (tiny, floating organisms, both plants and animals) can thrive in the upper water, where energy from the sun is abundant but nutrients are poor. As of 2003, plankton density in Lake Tanganyika had declined to less than one third of what it was 25 years before; algae density had declined by 30% from values 80 years before. Since plankton are the basis of the marine food chain, fish stocks declined along with the plankton: Fish stocks in the lake were 30% smaller than they were 80 years earlier.

The reduction of water mixing due to climate warming has made other changes in the lake’s chemistry. For one, oxygen dissolved from the air no longer mixes as well in deeper waters. As a result, the habitat has shrunk for some of the lake’s endemic species, such as the snail Tiphobia horei, which in 1890 lived at depths down to 1,000 ft (300 m) but as of 2003 lived only down to 330 ft (100 m). The snail’s habitat has thus shrunk by about two thirds, even though the lake itself has not shrunk and its bulk average temperature has changed only slightly.

Tanganyika surface plankton loss has been reflected in declining food-fish harvests from the lake (about 400,000 tons per year in 2003). Since Tanganyika supplies 25-40% of the protein needs of the four nations bounding the lake, such declines can have direct impacts on human populations as well as on biodiversity. Losses in biodiversity have not yet been measured directly in Tanganyika, but smaller populations will put some species at risk of extinction, especially as warming in the region continues to about 2.7°F (1.5°C), possibly higher, with even more drastic stabilization of the lake’s waters and consequent effects on its ecosystem.

IN CONTEXT: WILDLIFE POPULATION DECLINE AND BIODIVERSITY LOSS, 1970–2005

In May 2008, the Zoological Society of London and World Wildlife Fund (WWF) released the results of a study indicating a dramatic decline in global wildlife populations during the last four decades. The data showed that reductions in populations of land-based species fell by 25%, marine by 28%, and freshwater species by 29% between 1970 and 2005. Biodiversity loss, in the form of extinction of about 1% of the world’s species each year, was also reported in what the foundation asserted was one of the “great extinction episodes” in Earth’s history.

The losses were attributed to pollution, climate change, urbanization, over-fishing, and hunting. The foundation and WWF based their conclusion on population estimates and other data related to 1,400 species tracked as part of its Living Planet index. Data were obtained from published sources in scientific journals.

Slight changes in climate can lead to pressures on biodiversity by other mechanisms. For example, a 2006 study by J. Alan Pounds and colleagues found that global warming has almost certainly caused the recent extinction of about 67% of the 110 or so species of the Monteverde harlequin tree frog of the mountains of Costa Rica. The scientists saw the extinctions as validating the climate-linked epidemic hypothesis, according to which shifts in temperature, rainfall, and other climate variables make populations more vulnerable to disease and therefore to extinction. In the case of the Monteverde frogs, more frequent warm years shifted conditions toward the growth optimum of the Bactrachochytrium fungus, which infects the frogs. The researchers found that extinctions of the frogs consistently followed temperature peaks that were favorable to growth of the fungal disease.

Other effects are not strictly changes in climate, in the sense of temperature or precipitation, but chemical changes to air and water. Increased carbon dioxide (CO2) in the atmosphere has two major effects that are likely to decrease biodiversity: 1) Heightened atmospheric CO2 causes increased levels of dissolved CO2 in the ocean. When CO2 dissolves in water, it produces a weak acid, carbonic acid. Rising atmospheric CO2 thus acidifies the oceans. 2) Green plants extract carbon from the air by breaking up CO2, constructing their tissues using the carbon, and releasing the oxygen. CO2 is plant food. Thus, increasing atmospheric CO2 tends to cause more rapid growth in most plant species, an effect called CO2 enrichment.

Acidification of the oceans by dissolved excess CO2 will impact biodiversity by making survival more difficult for organisms that form shells of calcium carbonate. This includes bivalves such as clams, mollusks such as periwinkles and conches, microscopic plankton species, and corals. Corals, which are also subject to bleaching in excessively warm waters, form large, shallow communitities in tropical waters that have been compared to rain forests because of their high level of biodiversity. A typical large reef may support on the order of a million species of plants and animals.

Over the last two centuries, the average pH of the oceans has fallen by 0.1, corresponding to a rise in acidity and a 30% reduction in the number of carbonate ions (CO32-) available to shell-making organisms as building material. When carbonate ions fall below a certain level, corals have difficulty making their skeletons. This threshold may be reached if the atmospheric CO2 level, today about 375 parts per million, rises to over 500 parts per million, as may occur by the end of the twenty-first century.

Increasing atmospheric CO2 will also affect plant growth. Farmers today often add CO2 to the air inside greenhouses, because under indoor conditions, extra CO2 speeds plant growth and increases crop yields. Under outdoor conditions, however, the gain in yield is about half as much and the foods produced are significantly lower in protein and minerals. In the wild, rising CO2will favor some species over others, depending on rooting depth, woodiness, and photosynthetic chemistry; this will impact biodiversity by altering competitive balances. The CO2 fertilization effect will be strongest in biomes where plant growth is limited by water availability, such as grasslands, savanna, and desert. The biodiversity impact of a 2.5-fold increase in CO2 would likely be only about a third as great on a boreal (northern pine) forest as on a savanna or grassland, and half as great as on a desert.

Impacts and Issues

Scientific studies estimate by that 2050 there will about 9 billion human beings on Earth. Industrial activity, pollution, hunting, settlement, introducing species to environments where they have not hitherto existed, and other human activities that decrease biodiversity will grow at least in proportion to population, maybe more. Biodiversity is already decreasing and will continue to do so, though the amount of decrease may be affected by human choices about behavior.

Although the future is always inherently uncertain to some extent, scientists have estimated the likely range of extinctions that will be seen by 2050. According to studies published in 2003, about 3.5% of the world’s bird species will be extinct by that time, about 350species; mammals and freshwater fish are likely to experience a somewhat higher rate of extinction. Destruction of tropical forest for wood products or for conversion to agricultural land will be one of the primary causes of extinction. Continued overfishing of the world’s fresh and ocean waters will cause top predator species to become rare or extinct.

The five main drivers of biodiversity change between now and 2100, ranked from most severe impact to least severe, are, apart from climate change, 1) land-use changes (including deforestation), 2) climate change, 3) nitrogen deposition (from fertilizer use), 4) biotic exchange (the introduction of invasive species), and 5) direct effects of increasing atmospheric CO2.

During this century and beyond, however, climate change is likely to play an increasing and perhaps eventually dominant role in reducing biodiversity. Most plants require a specific range of temperature, moisture, and seasonal change to thrive; most animals require certain plants or other animals to thrive, and also have a limited range of tolerance for temperature and moisture. As climate warms, a typical ecosystem will tend to migrate away from areas where it was at the warm edge of its tolerance range and toward places where it was formerly at the cool edge. The most general effect of global climate is thus to move ecological zones toward the poles and toward higher altitudes. For each 1.8°F (1°C) of warming, terrestrial (on-land) ecosystems typically shift pole-ward by 100 mi (160 km): For example, if climate warms

by 5.4°F (3°C) by 2100, plant and animal communities in the Northern Hemisphere will migrate an average of 300 mi (480 km) northward—if they can—to stay in a suitable climate zone. This effect is observed, not only predicted.

In the Northern Hemisphere, terrestrial animal and plant ranges have been observed to shift northward, on average, by 3.8 mi (6.1 km) per decade over the last 50 years. In mountainous terrain, plant and animal ranges have shifted upward by 20 ft (6.1 m) over the same time period. Fragmentation of landscapes by human activity such as agriculture and city-building makes ecosystem migration more difficult today than during past climatic shifts, such as glacial periods. Species that fail to colonize new areas as the climate changes may go extinct.

Although climate change has so far been most intense in the Arctic and the West Antarctic Peninsula, where warming has been about twice the global average and dramatic effects such as retreating sea ice and melting tundra are readily visible, biodiversity is low in these regions compared to the tropics, where rain forests, coral reefs, and other particularly diverse communities are found. Thus, a smaller climate shift can have a greater impact on biodiversity in the tropics than a larger shift in boreal or temperate regions.

For marine ecosystems, changes in circulation patterns, ocean temperature, and ocean chemistry all influence biodiversity. For example, over the last 40 years or so, warm-water plankton species have shifted about 620 mi (1,000 km) in the North Atlantic due to warming.

Not all observed climate effects on biological systems are consistent with climate warming; a few are consistent with cooling. Also, some observed effects are consistent with natural climate shifts rather than those attributed to human-caused (anthropogenic) global warming. However, mathematical analysis shows that the very great majority of changes are consistent with warming trends, and that a combination of natural and anthropogenic climate changes describe observed changes in physical and biological systems better than either natural or anthropogenic changes alone. Anthropogenic changes have been added to or laid over those caused by natural processes, and are gradually becoming more dominant.

Future Impacts

Irreversible loss of biodiversity in many parts of the world is likely in the near future and possibly beyond. However, many uncertainties remain. Ecologists do not understand the relationship between ecosystem structure and rapid climate change well enough to predict the exact effects of current climate changes on biomes. It is also unknown whether efforts to mitigate climate change and other human impacts on biodiversity will occur or succeed, and if so, to what extent. Parks, endangered-species laws, hunting bans, and similar conservation efforts have slowed the loss of biodiversity in some regions, especially for certain species of larger, more-easily-noticed animals.

Scientists have estimated the likely impact that climate change will have on biodiversity. In 2004, Chris Thomas and colleagues published their study of an unbiased or representative sample of 1,103 animal and plant species. They found that climate change was likely to commit 15–37% of all species examined to extinction by 2050. “Committed to extinction” does not mean that a species would necessarily be extinct by that time, but that the population of each species would be so reduced that its species’ extinction becomes highly likely. In many or most ecological regions, climate change will become the greatest threat to biodiversity by 2050. There are 5 to 15 million species of creatures on Earth (the large range arises from the difficulty of counting insect, bacterial, and fungal species). If only 15% of all species are committed to extinction by climate change—the lower end of the range given by Thomas and colleagues—then 750,000 to 2,250,000 million species will eventually become extinct as a result of global climate change.

Primary Source Connection

The following news article recognizes the United Nations’ involvement with the issue of climate change as gaining strength with international heads of government. The article acknowledges that recent U.N. meetings have made it hard for government officials to look away from the issue, provoking more countries to take the issue of global warming more seriously. Although obstacles such as convincing developing countries like India, China, and Brazil of the importance of decreasing CO2 emissions do exist, on the whole, going green is developing into an international agenda.

U.N. REVS UP OVER GLOBAL WARMING

The annual summertime retreat of the Arctic icecap, greater this year than perhaps at any time during the 20th century. The nightmare of intensifying storms in some areas and extended drought in others, already taking place in developing countries of South Asia and sub-Saharan Africa.

It is against this backdrop of almost daily news of what scientists describe as signs of advancing global warming that the United Nations holds Monday what may be the largest high-level international meeting ever on climate change.

The conference, called by UN Secretary-General Ban Ki Moon, kicks off what many experts and officials say will be the high week of a turning-point year in the global political response to the challenge of a warming planet.

More than 80 heads of state or government are expected among the representatives of better than 150 countries attending the UN session. Then on Thursday, President Bush will convene at the White House a gathering of leaders from the world’s top emitters of greenhouse gases.

In addition, the Clinton Global Initiative will host a forum in New York Wednesday, drawing business and international political leaders to promote grass-roots responses to global warming.

Over the past weekend, at a UN conference in Montreal, the governments of about 200 countries agreed to accelerate a treaty to phase out hydrochlorofluorocarbons.

Together, the meetings put climate change at the center of the global stage this week—and they will make it harder for leaders to drop the issue in the future, experts say. That may be especially true of Mr. Bush: He may be known internationally as the foot-dragging leader of a top emitter of fossil-fuel pollutants, but by endorsing Mr. Ban’s meeting and then calling for his own at the White House, he will be seen as committing to a path of no return on climate-change action.

The Monday UN meeting “is looking to be quite an extraordinary event in what is turning out to be a remarkable year in the international response to climate change,” says Richard Kinley, deputy executive director of the UN Framework Convention on Climate Change.

Typically, such international sessions draw environmental ministers, who may or may not attend with the full-fledged backing of their government. This time, many heads of state are involved, with the meeting coinciding with the opening of the UN General Assembly. Such high-level involvement suggests that the world has turned a corner in perception of the seriousness of the climate-change challenge, Mr. Kinley says.

“Increasingly, leaders are seeing this as an issue of national interest, and not just a question of responsibility. And the fact is that states are more apt to act when they see their interests at stake,” he says.

Other factors this year, he says, include what many experts describe as a “conclusive” report from an international group of scientists and officials finding evidence of global warming to be “unequivocal.” The Intergovernmental Panel on Climate Change concluded with what it termed near certainty that the warming taking place is the result of human activities.

“That doesn’t mean we won’t hear some unorthodox views” at the meeting, Kinley says. Czech Republic President Vaclav Klaus, for example, intends to portray the idea of man-made global warming as a “myth” that does not justify constrictive measures.

Yet other experts cite factors beyond scientific findings in global warming’s rise to the international spotlight. David Sandalow, a specialist in the political dimensions of climate issues at the Brookings Institution in Washington, spoke at a forum earlier this year on the “new political climate” around climate change and listed factors such as: the business community’s “astounding” rallying to the issue, the Democrats’ taking control of Congress, increased Republican support for action—starting with California Gov. Arnold Schwarzenegger (R)—and even the documentary featuring Al Gore, “An Inconvenient Truth.”

What UN experts hope for—and what Ban wants coming out of Monday’s meeting—is fresh momentum for action at the UN climate-change conference set for Bali, Indonesia, in December. The Bali conference will take up the crucial question of what kind of agreement should replace the Kyoto Protocol on reducing greenhouse-gas emissions, which expires in 2012.

“What I want… is a strong political commitment at the leaders’ level for the meeting in Bali,” Ban told reporters last week. “There must be no vacuum” after expiration of the Kyoto accord, “so we must address the challenge boldly.” That means reaching a replacement agreement by 2009 so national governments can act and implementation can begin in 2012, he says.

None of this means that the debates on climate change are over, or that global accord on measures for action will be easy to reach.

Many eyes will be focused on this week’s White House meeting to gauge just how committed the United States is to action—and what kind of action the Bush administration will accept. Some experts worry that the administration will stick to a preference for voluntary goals in emissions cuts rather than reduction commitments, or that the Washington meeting signals a willingness on the part of the US to go outside the UN framework for addressing climate change.

Another potential stumbling block is the continuing disagreement between industrialized and developing countries over who should make the most substantial commitments to cutting greenhouse-gas emissions. It was the exclusion of developing countries from the Kyoto Protocol that in part led Bush to reject the agreement.

Major developing powers like China, India, and Brazil are still wary of any accord that would place the same burden on them as on developed economies, which they say have much higher per capita emission rates.

But these developing countries are also beginning to signal a seriousness about global warming and to address pollution and sustainable-development issues on their own, leading some experts to find hope that the divide can be narrowed. “Among a number of developing countries, we’re seeing a growing realization that they have to take a new approach for their own well-being. And the leading example of that is China,” says Kinley of the UN.

“That is not to say they have changed their position that the industrialized world should take the lead,” he adds. But he says a door once shut tight has now been opened.

“What we hear more now is talk of incentives, of the right investment and technology flows into the developing countries, and that is bringing the two sides closer together,” he says. “That’s crucial, because it’s clearly only through international cooperation that this challenge can be addressed.”

Howard LaFranchi

LAFRANCHI, HOWARD. “UN REVS UP OVER GLOBAL WARMING.” CHRISTIAN SCIENCE MONITOR (SEPTEMBER 24, 2007).

See Also Climate Change; Ecosystem Diversity; Endangered Species; Extinction and Extirpation; Genetic Diversity; Global Warming; Human Impacts

BIBLIOGRAPHY

Books

Parry, M. L., et al, eds. Climate Change 2007: Impacts, Adaptation and Vulnerability: Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Periodicals

Araúo, Miguel B., and Carsten Rahbek. “How Does Climate Change Affect Biodiversity?” Science 313 (2006): 1396–1397.

Higgins, Paul A. T. “Biodiversity Loss Under Existing Land Use and Climate Change: An Illustration Using Northern South America.” Global Ecology and Biogeography 16 (2007): 197–204.

Jenkins, Martin. “Prospects for Biodiversity.” Science 302 (2003): 1175–1177.

Livingstone, Daniel A. “Global Climate Change Strikes a Tropical Lake.” Science 301 (2003): 468-469.

Pounds, J. Alan, et al. “Widespread Amphibian Extinctions from Epidemic Disease Driven by Global Warming.” Nature 439 (2006): 161-167.

Sala, Enric, and Nancy Knowlton. “Global Marine Biodiversity Trends.” Annual Review of Energy and the Environment 231 (2006): 93-122.

Sala, Osvaldo E., et al. “Global Biodiversity Scenarios for the Year 2100.” Science 287 (2000): 1770–1774.

Thomas, Chris D. “Extinction Risk from Climate Change.” Nature 427 (2004): 145-148.

Willis, K. J., and H. J. B. Birks. “What Is Natural? The Need for a Long-Term Perspective in Biodiversity Conservation.” Science 314 (2006): 1261–1265.

Zimmer, Carl. “Predicting Oblivions: Are Existing Models Up to the Task?” Science 317 (2007): 892-893.

Web Sites

Intergovernmental Panel on Climate Change (United Nations). “Climate Change and Biodiversity.” April 2002. http://www.ipcc.ch/pdf/technical-papers/climate-changes-biodversity-en.pdf (accessed June 25,2008).

Larry Gilman

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Biodiversity

Biodiversity

Biodiversity is the total richness of biological variation. The scope of biodiversity is usually considered to range from the genetic variation of individual organisms within and among populations of a species , to different species occurring together in ecological communities. Some definitions of biodiversity also include the spatial patterns and temporal dynamics of populations and communities on the landscape. The geographical scales at which biodiversity can be considered range from local to regional, state or provincial, national, continental, and ultimately to global.

Biodiversity at all scales is severely threatened by human activities; this is one of the most important aspects of the global environmental crisis. Humans have already caused permanent losses of biodiversity through the extinction of many species and extensive losses of distinctive, natural ecosystems. Ecologists predict that unless there are substantial changes in the ways that humans affect ecosystems, there will be much larger losses of biodiversity in the near future.


Species richness of the biosphere

About 1.7 million of Earth's species have been identified and designated with a scientific name. About 6% of the identified species live in boreal or polar latitudes, 59% in the temperate zones, and the remaining 35% in the tropics. However, the knowledge of Earth's species is highly incomplete, especially for tropical countries. According to some estimates, there could be as many as 30-50 million species on Earth , 90% of them occurring in tropical ecosystems. Tropical ecosystems are much richer in species than are those at higher latitudes.

Most of the described species on Earth are invertebrates , particularly insects , and most of the insects are beetles (order Coleoptera). A famous scientist, J.B.S. Haldane, was once asked by a theologian to briefly explain what his knowledge of biology told of God's purpose. Haldane reputedly said that God has "an inordinate fondness of beetles," reflecting the fact these insects are so much richer in species than any other group of creatures on Earth. Some biologists believe that beetles account for most of the undescribed tropical insects.

The suggestion of enormous numbers of undescribed insects in tropical forests initially emerged from the research of Terry Erwin. This entomologist performed experiments in which tropical-forest canopies in Amazonia were treated with an insecticide, and the subsequent "rain" of dead arthropods was collected using ground-level sampling devices. This innovative sampling procedure indicated that: (1) a large fraction of the insect species of tropical forests is unknown to science; (2) most insect species are confined to a single type of tropical forest, or even to a particular tree species, which may itself have only a local distribution; and (3) most species of tropical-forest insects have little ability to disperse very far. Erwin's studies of tropical rainforest found that beetles accounted for most of the insect species and that most of the beetles are narrowly endemic , that is, they have a local distribution and are found nowhere else. For example, the tree Luehea seemanii has more than 1,100 species of beetle in its canopy, of which 15% are specific to that plant . The emerging conclusion from this and other descriptive research is that there is an enormous abundance of undescribed species of insects and other invertebrates living in tropical forests.

Compared with invertebrates, the numbers of species (that is, the species richness) of other groups of tropical-forest organisms are better known. Although it is extremely difficult to do so, the numbers of species of vascular plants have been described for a few tropical forests. For example: a plot of only 0.0004 sq mi (0.1 ha) in a moist forest in Ecuador had 365 species of vascular plants; there were 98 species of large trees in 0.006 sq mi (1.5 ha) of forest in Sarawak, Malaysia; there were 90 tree species in 0.0032 sq mi (0.8 ha) of forest in Papua New Guinea; 742 woody species occurred in 0.012 sq mi (3 ha) of forest in Sarawak, with 50% of the species recorded as single individuals; and more than 300 species of woody plants were discovered on a 2-sq mi (50-ha) area of forest in Panama. These tropical forests are much richer than temperate forests, stands of which typically support fewer than 12-15 species of trees. The Great Smokey Mountains of the eastern United States have some of the richest temperate forests in the world, and they typically contain 30-35 species, far fewer than tropical rainforests.

It is extraordinarily difficult to determine the numbers of birds in tropical forest because the dense foliage and darkness of the understory make it inconvenient to see small animals, even if they are brightly colored. As a result, few studies have been made of the birds of tropical rainforest. However, one study in Peru discovered 245 resident and 74 transient species in 0.4 sq mi (97 ha) of Amazonian forest. Another study of rainforest in French Guiana recorded 239 species of birds, and another found 151 species in a forest in Sumatra. In comparison, stands of temperate forest in North America typically support only 15-30 species of birds.

Almost no systematic surveys have been made of all of the species of tropical ecosystems. In one case, a 42 sq mi (108 sq km) reserve of dry forest in Costa Rica was estimated to support about 700 plant species, 400 vertebrate species, and 13,000 species of insects, including 3,140 species of moths and butterflies .


Why is biodiversity important?

Biodiversity is valuable for the following classes of reasons:

  1. Intrinsic Value. Biodiversity has its own intrinsic value, regardless of its worth in terms of human needs. Because of its intrinsic merit, there are ethical considerations to any degradation of biodiversity. For example, do humans have the "right" to diminish or exterminate elements of biodiversity, all of which are unique and irretrievable? Is the human existence itself diminished by losses of biodiversity? Ethical issues cannot be resolved through science, but enlightened people would mourn any loss of species, or of natural ecosystems.
  2. Utilitarian Value. Humans have an absolute requirement for the products of other species. Because of this need, wild and domesticated species and their communities are exploited in many ways to provide food, materials, energy , and other goods and services. This fact can be illustrated in many ways. In the United States, for example, about one-quarter of prescription drugs have active ingredients obtained from higher plants, and these uses contribute about $14 billion per year to the U.S. economy, and $40 billion per year worldwide. Potentially, harvests of biodiversity can be conducted in ways that foster their renewal. Unfortunately, potentially renewable biodiversity resources are often harvested too intensively or inadequate attention is paid to regeneration, so the resource is degraded or becomes extinct.
  3. Provision of Ecological Services. Biodiversity provides many ecological services that are directly or indirectly important to human welfare. Examples of these services include biological productivity, nutrient cycling, cleaning water and air of pollutants, control of erosion , provision of atmospheric oxygen , removal of carbon dioxide , and other functions related to the integrity of ecosystems. According to the biologist Peter Raven: "Biodiversity keeps the planet habitable and ecosystems functional."

There are many cases of the discovery, through research on previously unexploited plants and animals, of bio-products useful to humans as food, medicine, or for other purposes. Consider the case of the rosy periwinkle (Catharantus roseus), a small plant native to the tropical island of Madagascar. During an extensive screening of wild plants for anti-cancer chemicals, an extract of rosy periwinkle was observed to inhibit the growth of cancerous cells. The active biochemicals are several alkaloids in foliage of the plant, which probably serve to deter herbivores. These natural substances are now used to prepare the drugs vincristine and vinblastine, which can be successfully used to treat childhood leukemia and a lymphatic cancer known as Hodgkin's disease . In this case, a species of wild plant known only to a few botanists has proven to be of great benefit to humans by treating previously incurable diseases, in the process sustaining a large pharmaceutical economy. There is a tremendous undiscovered wealth of other biological products useful to humans in unexplored biodiversity.


Biodiversity and extinction

Extinction refers to the loss of some species or other taxonomic unit (e.g., subspecies, genus, family, etc.; each is known as a taxon), occurring over all of its range on Earth. (Extirpation refers to a more local disappearance, with the taxon still surviving elsewhere.) The extinction of any species is an irrevocable loss of part of the biological richness of Earth, the only place in the universe known to support living creatures. Extinction can be a natural occurrence caused by an unpredictable catastrophe, chronic environmental stress, or ecological interactions such as competition , disease , or predation. However, there have been dramatic increases in extinction rates since humans have become Earth's dominant large animal and the cause of global environmental change.

Extinction has always occurred naturally. Almost all species that have ever lived on Earth have become extinct. Perhaps they could not cope with changes occurring in their environment, such as climate changes, the intensity of predation, or disease. Alternatively, many extinctions may have occurred simultaneously as a result of unpredictable catastrophes. From the geological record it is known that species, families, and even phyla have appeared and disappeared over time . For example, numerous phyla of invertebrates proliferated during an evolutionary radiation occurring at the beginning of the Cambrian era about 570 million years ago, but most of these animals are now extinct. The 15-20 extinct phyla from that period are known from the Burgess Shale of British Columbia, and they represent unique experiments in invertebrate form and function. Similarly, entire divisions of plants have appeared, radiated, and disappeared, such as the seed ferns Pteridospermales, the cycad-like Cycadeoidea, and woody plants known as Cordaites. Of the 12 orders within the class Reptilia, only three survive today: crocodilians, turtles , and snakes/lizards. Clearly, the fossil record displays a great deal of evidence of natural extinctions.

Overall, the geological record suggests that there have been long periods of time characterized by uniform rates of extinction, but punctuated by about nine catastrophic episodes of mass extinction . The most intense extinction event occurred at the end of the Permian period some 245 million years ago, when 54% of marine families, 84% of genera, and 96% of species are estimated to have become extinct.

Another famous, apparently synchronous, extinction of vertebrate animals occurred about 65 million years ago at the end of the Cretaceous period. The most renowned extinctions were of the last of the reptilian dinosaurs and pterosaurs, but many plants and invertebrates also became extinct at that time. In total, perhaps 76% of species and 47% of genera became extinct in the end-of-Cretaceous crisis. One hypothesis to explain the cause of this mass extinction involves a meteorite impacting the Earth, causing huge quantities of fine dust to be spewed into the atmosphere, and resulting in a climatic deterioration that most large animals could not tolerate. However, some scientists believe that the extinctions of the last dinosaurs were more gradual.

However, humans have been responsible for almost all of Earth's recent extinctions. These extinctions are occurring so quickly that they represent a modern mass extinction of similar intensity to those documented in the geological record. Examples of recent extinctions caused by humans include such well-known cases as the dodo, passenger pigeon, and great auk. Many other high-profile species have been taken to the brink of extinction, including the plains bison , whooping crane, ivory-billed woodpecker, right whale, and other marine mammals . These losses have been caused by insatiable overhunting and intense disturbance or conversion of natural habitats.

Beyond these well-known and tragic cases involving large animals, Earth's biodiversity is experiencing an even larger loss. This ruin is mostly being caused by extensive conversions of tropical ecosystems, particularly rainforest, into agricultural habitats that sustain few of the original species. As was described previously, tropical ecosystems sustain extremely large numbers of species, most of which have restricted distributions. The conversion of tropical forest into other habitats inevitably causes the loss of most of the locally endemic biota. This is a great tragedy, and the lost species will never occur again.

The most important human influences causing the extinction or endangerment of species are: (1) excessive exploitation, (2) effects of introduced predators, competitors, and diseases, and (3) habitat disturbance and conversion. These stressors can result in small and fragmented populations that experience the deleterious effects of inbreeding and population instability and then decline further, ultimately to extirpation or extinction.

The increased rate of extinction and endangerment of biodiversity during the past several centuries is best documented for vertebrates because, as noted previously, most invertebrate species, particularly insects, have not yet been described by scientists. During the last four centuries there have been more than 700 known extinctions globally, including about 100 species of mammals and 160 species of birds, all because of human influences.

A much larger number of species is facing imminent extinction; they are endangered. For example, more than 1,000 species of birds are considered to be threatened with extinction. Of this total, 46% live only on oceanic islands, a situation in which species are especially vulnerable to extinction caused by stresses associated with human activity. Birds of tropical forests account for 43% of the threatened bird species, wetland species for 21%, grassland and savanna species 19%, and other habitats 17%. Only 1.5% of the threatened species are North American, 4.2% are European or Russian, 33% Central and South American, 18% African, 30% Asian, and 14% from Australia and the Pacific.


Protection of endangered biodiversity

Biodiversity can be protected in ecological reserves. These are protected areas established for the conservation of natural values, usually the known habitat of endangered species , threatened ecosystems, or representative examples of widespread communities. In the early 1990s there were about 7,000 protected areas globally, with an area of 2.5 million sq mi (651 million ha.) Of this total, about 2,400 sites comprising 1.5 million sq mi (379 million ha) were fully protected and could be considered to be true ecological reserves.

Ideally, the design of a national system of ecological reserves would provide for the longer-term protection of all native species and their natural communities, including terrestrial, freshwater , and marine ecosystems. So far, however, no country has implemented a comprehensive system of ecological reserves to fully protect its natural biodiversity. Moreover, in many cases the existing reserves are relatively small and threatened by eenvironmental change and other stressors, such as illegal poaching of animals and plants and sometimes excessive tourism.

The World Conservation Union, World Resources Institute, and United Nations Environment Program are three important agencies whose mandates center on the conservation of the world's biodiversity. These agencies have developed the Global Biodiversity Strategy, an international program to help protect biodiversity. The broad objectives are to: (1) preserve biodiversity; (2) maintain Earth's ecological processes and life-support systems; and (3) ensure that biodiversity resources are used in a sustainable manner. As such, the Global Biodiversity Strategy is a mechanism by which countries and peoples can initiate meaningful actions to protect biodiversity for the benefit of present and future generations of people, and also for its intrinsic value. Because it only began in the late 1970s, it is too early to evaluate the success of this program. However, the existence of this comprehensive international effort is encouraging, as is the participation of most of Earth's countries, representing all stages of socioeconomic development.

Another important international effort is the Convention on Biological Diversity, negotiated under the auspices of the United Nations Environment Program and signed by many countries at a major conference at Rio De Janeiro in 1992. This international treaty requires signatory nations to take measures to systematically catalogue their indigenous biodiversity, and to take action to ensure that it is conserved.

Numerous other agencies are working to preserve biodiversity. In the United States, the World Wildlife Fund and Nature Conservancy are important organizations at the national level. There are numerous other national and local groups. The lead federal agency is the U.S. Fish and Wildlife Service, and all states have similar agencies.

Important progress is being made, and the progressive worldwide development of activities intended to identify, conserve, and preserve biodiversity will hopefully come to be regarded as an ecological "success story."

See also Biological community; Ecosystem.


Resources

books

Becher, A. Biodiversity: A Reference Handbook. Abo-Clio Pub, 1998.

Dobson, A.P. Conservation and Biodiversity. W.H. Freeman and Co., 1998.

Freedman, B. Environmental Ecology. 2nd edition. San Diego: Academic Press, 1994.

Gaston, K.J., and J.I. Spicer. Biodiversity: An Introduction. Blackwell Science Inc., 1998.

Hamblin, W.K., and E.H. Christiansen. Earth's Dynamic Systems. 9th ed. Upper Saddle River: Prentice Hall, 2001. Levin, Simon A., ed. Encyclopedia of Biodiversity. San Diego, CA: Academic Press, 2000.

Myers, Judith, and Dawn Bazely. Ecology and Control of Introduced Plants. Cambridge: Cambridge University Press, 2003.

Nebel, Bernard J., and Richard T. Wright. Environmental Science: Toward a Sustainable Future. 8th ed. Englewood Cliffs, NJ: Prentice Hall, 2002.

Schneiderman, Jill S. The Earth Around Us: Maintaining aLivable Planet. New York: W.H. Freeman & Co., 2000.

Wilson, E.O. The Diversity of Life. Cambridge: Harvard University Press, 1992.

Wilson, E.O., ed. BioDiversity. Washington, DC: National Academy Press, 1988.

periodicals

Caballero A., and M.A. Toro. "Interrelations Between Effective Population Size and Other Pedigree Tools for the Management of Conserved Populations." Genet Res 75(no. 3) (June 2000): 331–43.


Bill Freedman

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Binomial

—The scientific name of organisms consists of two words, and is therefore a binomial. Humans, for example, are named Homo sapiens, which designates our genus as Homo, and our species within that genus as sapiens. Binomials are always latinized words, and are written in italics, or underlined.

Endangerment

—Refers to a situation in which a species is vulnerable to extinction or extirpation.

Endemic

—Refers to species with a relatively local distribution, sometimes occurring as small populations confined to a single place, such as an oceanic island. Endemic species are more vulnerable to extinction than are more widespread species.

Extinction

—The condition in which all members of a group of organisms have ceased to exist. Extirpation means that a species no longer occurs in a place or country, although it survives elsewhere.

Species diversity

—An indicator of biodiversity at the community level, which accommodates both the number of species present (i.e., richness) and their relative abundance. Ecologists consider species diversity to be a good indicator of biodiversity within communities, because it accommodates differences amongst species in rarity and commonness.

Species richness

—The number of species occurring in a community, a landscape, or some other defined area.

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Biodiversity

BIODIVERSITY

Life on earth began as bacterial cells at least 4,000 million years ago, and it has—with notable, but rare, catastrophic declines in diversity subsequently—expanded, evolved, and complexified across time. In the early-twenty-first century the earth teems with countless species arranged in many diverse patterns and relationships spread across varied landscapes. As human populations have expanded since the industrial revolution, with technologies becoming more powerful and increasingly capable of pervasive impacts, biodiversity is again in decline, this time as a result of human activities, especially the fragmentation of forests and other wild habitats. How to reverse the dangerous trend toward biological simplification has become one of the most urgent global environmental questions.


What Is Biodiversity?

Biodiversity, a contraction of biological and diversity, was introduced as a convenient abbreviation during preparations for a national symposium on the subject in the United States, which was sponsored by the Smithsonian Institution and the National Academy of Sciences (NAS) in 1986. This term, though technically difficult to define, has come to refer to the rich and textured web of life on earth. The term, and the concepts and ideas associated with it, gained world political prominence at the World Conference on Environment and Development in Rio de Janeiro in 1992, where the United Nations Convention on Biodiversity, a document that was subsequently ratified by a majority of nations, was passed. This convention called for the sustainable use and protection of the earth's biological resources, and the term biodiversity has become the rallying point for conservationists and others concerned about the rapid simplification of natural systems in the face of human development.

There are two approaches to defining biodiversity (Wood 1997, 2000). Perhaps the most popular approach is to define it as an inventory of diverse biological items. One such inventory, which has been described as the standard definition of biodiversity, defines it as the sum total of species, genetic variation within species, and diversity of habitats and ecosystems in which species are found (Takacs 1996). Difference definitions, in contrast, define biodiversity as the total of differences among biological entities and processes (Takacs 1996; Wood 1997, 2000). These two approaches differ in that inventory definitions, which simply count elements of different types (species, genes, habitats), tend to count elements of the same type equally in their contribution to total diversity, whereas difference definitions highlight degrees of differentiation. Accordingly, under a difference definition, a species that is the lone member of its genus would be considered to contribute more diversity than a species that shares its genus with others (Solow et al. 1993, Weitzman 1998).

As noted, there are serious technical problems in defining biodiversity. It clearly would be desirable to have a definition that represents biodiversity as a measurable quantity—so that, for example, one could say that a given system is measurably more diverse than another, or that a given system is losing or gaining diversity at a specifiable rate. Unfortunately both inventory and difference definitions fail to provide a measurable index of biodiversity. Decisive arguments show that biodiversity cannot be represented as a list of countable and additive elements. This conclusion follows from the unavoidable fact that living nature can be organized into multiple, but incommensurable, hierarchies. For example, there is a phylogenetic hierarchy of species and genera, among others, as well as a spatial hierarchy of cells, organs, organisms, and ecosystems. Both hierarchies add significantly to the total diversity of life, but the elements of these hierarchies cannot be added together to create a meaningful sum. Similar arguments apply to difference definitions: Biological entities vary across many parameters and aspects, and these cannot be added together to represent a meaningful index of biological diversity (Wood 2000, Sarkar 2005).

This difficulty implies that biodiversity is too complex and multifaceted to be represented by a single measure or to be made a countable quantity, and has led to a search for proxy measures for biodiversity (Sarkar 2005). One popular proxy is simply to use species counts as conventional markers to represent total diversity, which has gained wide acceptance in practice because it is clear and allows relatively unambiguous measures. The consensus view of scientists, however, is that simplified measures such as this cannot capture the full richness and diversity of life. In the United States this simplification was nevertheless embodied in the Endangered Species Act of 1973 (ESA), which has become, despite its narrow focus on endangered species, one of the most important pieces of environmental legislation ever passed by a national legislature. The act concentrates heavily on avoidance of species extinction through a process that lists species as threatened or endangered, limiting damage to the listed species, subspecies, and special populations. Protection of habitat is mainly treated by the act as instrumental to the protection and recovery of endangered and threatened species.

Accordingly it has been suggested that the U.S. strategy—which can be referred to as a rare species paradigm—may be less effective than an alternative strategy developed by Australian practitioners, who develop algorithms that rank possible reserve designs according to their effectiveness, per area set aside, in saving biodiversity (defined in terms of a chosen proxy). The Australian approach, referred to as the declining species paradigm (Caughley 1994), has increasingly been applied in international settings. This approach is to develop and refine an algorithm that ranks various protection strategies according to their efficiency in using space to protect proxy variables chosen to represent managerial goals. This pragmatic approach—which emphasizes shared actions rather than abstract measures—can provide a rough operationalization of biodiversity: Biodiversity is what is saved by the actions of professionals who design reserves that are effective in responding to identifiable forces of simplification that are addressed in a real place (Sarkar 2005).

Speaking more generally, biodiversity can be thought of as the result of a magnificent and eternal process of change, as life has explored countless strategies for survival in countless climates and habitats. These explorations have led to an inexorable increase in diversity across time, because each increment in diversity opens up new possibilities and adaptations for other species, and to the hypothesis that diversity itself causes increases in diversity. This theory also has a negative side: Losses in diversity can increase the likelihood that further losses will occur as species are stressed by loss of mutualist species and populations (Whittaker 1970, Norton 1987). Thus whereas biodiversity has, in the big picture, increased over time, there have also been cataclysmic periods of species loss, and paleontologists speculate that there have been as many as six extinction events in which half or more species disappeared. At least some of these events are associated with meteor strikes on earth and, possibly, as a result of dust from enormous volcanic eruptions. Increasing rates of extinction and endangerment have led some scientists to speculate that the Earth is entering another such event, for the first time as a result of human activities. Whether the human species can survive such an event is not known, but the exponential effects of human activities are impacting the world at a scale previously produced only by global cataclysms.

Fear that the simplification of nature may cause an irreversible spiral of losses inspires scientists and conservationists to advocate strong measures to reverse simplification processes before it is too late. As noted, there exists a broad, practical consensus among experts about what actions are necessary to reverse, or at least slow, such processes such as establishing protected riparian corridors along rivers and developing core reserve areas while managing buffer zones around them. Whether the means, and the will, exists to rein in development that encroaches on wild habitats and drives species toward extinction remains uncertain. Conservationists agree that it is important to save as much biodiversity as possible, though there are seldom adequate resources to do even a fraction of the things that are widely recommended by experts for the protection of sensitive areas and diversity hotspots. Thus whereas success in protecting biodiversity is not assured, broad agreement in strategies to maximize biodiversity does inspire confidence that practitioners know what they are talking about—that the concepts used are clear enough to allow communication and cooperative action—even if no abstract definition of biodiversity can be considered to correspond precisely to any measurable quantity in nature (Norton 2005).


What Is the Value of Biodiversity?

Despite considerable agreement in conservation strategies and protective practices, there remain several crosscutting disagreements regarding why biodiversity protection is important (Norton 1987, 1986). These are: (1) the nature of the value biodiversity has; (2) the units of diversity that should be valued; and (3) the appropriate measures of the value of biodiversity. These disagreements are important because they affect the prioritization given biodiversity protection in competition with other socially valued objectives, and also among various possible conservation objectives.

Disagreements regarding the nature of the value of biodiversity reflect differing theories of value. Monistic theories of value account for all value in nature according to a single measure. Utilitarians, economically oriented and otherwise, advocate decisions based on impacts on human well-being or satisfaction. Other monists have extended ethical concepts, usually applied only to humans, to other species and even to ecosystems, treating elements of nature as ends-in-themselves, as possessing moral considerability, and as having goods-of-their-own that compete with human welfare. The prominence of these two opposed, monistic theories, has resulted in a polarized discussion, often pitting economists against environmental ethicists, and no consensus regarding how to place measurable value on biological diversity has emerged.

The value of biodiversity is better captured by a pluralistic evaluative method, which treats the many social values derived from biodiversity as reinforcing each other. Actions that protect biodiversity protect complex natural systems, reduce soil erosion, promote aesthetic enjoyment and scientific interest, hold open options for economic uses, and support the values of the many individuals who value nature noninstrumentally.

Pluralism, though unpopular within academic disciplines, seems more consistent with the many ways that humans express their dependence upon, and love for, nature. Under a pluralist approach, multiple competing values must be balanced and prioritized against each other, but opportunities also arise to protect multiple social values simultaneously, opening up the possibility of win-win management policies through the protection of natural habitats as homes for biodiversity and many other values. The pluralist approach encourages a more political understanding of the value of biodiversity. Some authors conceptualize the problem of biodiversity protection as one of accepting responsibility for conveying a trust, or a gift from previous to subsequent generations as an obligatory legacy (Weiss 1989, Brown 1994). In a variant on the trust idea, other theorists argue that future generations have rights to a full complement of species and ecosystems, and that these rights should be protected by constitutional constraints that require governments to protect biodiversity (Schlickeisen 1994, Wood 2000). These trust doctrines and the constitutional amendment recommendation, built on a moral concern for the future, complement the idea of sustainable use and development of resources. The goal of protecting the evolved web of life, what scientists call biodiversity—whether for its possible uses in fulfilling human needs, the diverse aesthetic experiences it affords humans, or its noninstrumental value to the fulfillment of human needs—will be one of the great challenges of the future.




BRYAN G. NORTON

SEE ALSO Biophilia; Deforestation and Desertification; Ecology; Environmental Ethics; Rain Forest; United Nations Environmental Program.



BIBLIOGRAPHY

Brown, Peter G. (1994). Restoring the Public Trust: A Fresh Vision for Progressive Government in America. Boston: Beacon Press.

Caughley, Graeme. (1994). "Directions in Conservation Biology." Journal of Animal Ecology 63: 215–244. Outlines the differences between rare species and declining species paradigms.

Norton, Bryan G. (1987). Why Preserve Natural Variety? Princeton, NJ: Princeton University Press. A monograph surveying the science, values, and policies associated with biodiversity.

Norton, Bryan G. (2005). "What Are We Trying to Save? And Why? Toward a Policy-Relevant Definition of Biodiversity." In The Endangered Species Act at 30, ed. J. Michael Scott, Dale Goble, and F. Davis. Washington, DC: Island Press.

Norton, Bryan G., ed. (1986). The Preservation of Species: The Value of Biological Diversity. Princeton, NJ: Princeton University Press. An anthology providing a multidisciplinary review of nature protection.

Sarkar, Sahotra. (2005). Biodiversity and Environmental Philosophy: An Introduction. Cambridge, UK: Cambridge University Press. A highly recommended survey of issues and methods, written from the viewpoint of a philosopher of biology.

Schlickeisen, Rodger. (1994). "Protecting Biodiversity for Future Generations: An Argument for a Constitutional Amendment." Tulane Environmental Law Journal 8: 181–221.

Solow, Andrew; Stephen Polasky; and James Broadus. (1993). "On the Measurement of Biological Diversity." Journal of Environmental Economics and Management 24: 60–68.

Takacs, David. (1996). The Idea of Biodiversity: Philosophies of Paradise. Baltimore: Johns Hopkins University Press. A very useful examination of biologists' ideas on biodiversity.

Weiss, Edith Brown. (1989). In Fairness to Future Generations: International Law, Common Patrimony, and Intergenerational Equity. Tokyo: United Nations University; Dobbs Ferry, NY: Transnational Publishers. An analysis based in the theory of international law, of obligations to the future.

Weitzman, Martin L. (1998). "The Noahs's Ark Problem." Econometrica 66(6): 1279–1298.

Whittaker, Robert H. (1970). Communities and Ecosystems. New York: Macmillan. Whittaker introduced many of the concepts used to discuss biodiversity.

Wood, Paul M. (1997). "Biodiversity As the Source of Biological Resources: A New Look at Biodiversity Values." Environmental Values 6: 251–268. A focused argument for a difference definition, including also a discussion of the value of biodiversity as a source of biological resources.

Wood, Paul M. (2000). Biodiversity and Democracy: Rethinking Society and Nature. Vancouver, British Columbia: UBC Press. An examination of the moral and political obligations associated with protecting biodiversity.

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Biodiversity

Biodiversity


Biodiversity, or biological diversity, is a broad term that includes all forms of life and the ecological systems in which they live. Biodiversity also refers to the degree of variety found in life and ecosystems (an area in which living things interact with each other and the environment). It suggests a level of healthy or balanced diversity of habitat, as well as animal and plant life. Biodiversity has also been described as the total richness of biological variety in a given place and can serve as a measure of the number of different types of organisms that live there. The opposite of biodiversity is the extinction of a species.

EDWARD WILSON COINS THE TERM BIODIVERSITY

As first put forth by the American biologist, Edward O. Wilson (1929–), biodiversity has become a standard against which scientists can measure the negative impact or damage that modern human societies have inflicted upon Earth and its creatures. The growing threat to biodiversity posed by human activities makes it one of the most important aspects of the present global environmental crisis that some scientists say we are experiencing. Humans have already caused permanent losses of biodiversity through extinction of certain species. Often this is caused indirectly by destroying a particularly distinctive natural environment in which these species lived. Some ecologists predict that unless there are major changes in the ways that humans affect ecosystems, there will be much larger losses of biodiversity in the near future. In the past, humans have hunted some creatures like the dodo bird into extinction, and sometimes simply crowded others out of their natural habitats. It is known that some 200 species of plants native to the United States already have become extinct, and that as much as 20 percent of all bird species around the world have gone extinct. Wilson estimates that at least 27,000 species of plants and animals are becoming extinct every year by cutting down the rain forests in Brazil's Amazon region. Since extinction is the permanent death of a species, the world will lose an enormous amount of biodiversity as the years pass.

EDWARD OSBORNE WILSON

Founder of the modern field of sociobiology (the study of what biologically determines social behavior) and the only person to receive both this nation's highest scientific and literary awards, American entomologist Edward O. Wilson (1929– )is one of the great naturalists in American history. His work has influenced the field of animal taxonomy (the science of classifying living things), and the discovery of pheromones (chemicals that are released by an animal and which affect another animal). He also has become a powerful voice condemning the steady loss of biodiversity (a broad term that includes all forms of life and the ecological systems in which they live).

Edward O. Wilson was born in Birmingham, Alabama, and is a descendant of farmers and shipowners. Always drawn to the outdoors, he decided at the age of seven to become a naturalist explorer. His plans changed, however, when he suffered an injury to his right eye while fishing, which made him change his plans. By the age of ten, after reading a National Geographicarticle titled, "Stalking Ants, Savage and Civilized," Wilson decided to become an entomologist. (Entomology is a branch of zoology that deals with insects.) After studying biology at the University of Alabama, he received his bachelor's degree in 1949. By the age of twenty-six, he had earned a Ph.D. in biology from Harvard University, where he continues to work. His early work led taxonomists (classifiers of organisms) to revise their procedures, and by the late 1950s, Wilson had begun to study how social insects, like ants, communicate. His work with the venom glands of fire ants led to his discovery that animal chemicals called pheromones are used to communicate complex instructions. He later wrote that pheromones were "not just a guidepost, but the entire message." In the 1960s, he offered the theory of species equilibrium, which demonstrates that the number of species on a small island would always remain constant.

In the 1970s, Wilson's work on the biological basis of social behavior caused a major controversy. In his 1975 book, Sociobiology: The New Synthesis, Wilson suggested that the way people act or behave in certain situations can sometimes be accounted for by their genetic makeup. This daring idea caused a great stir among many colleagues who argued that similar ideas had led to notions that people were "biologically determined" to act a certain way and were therefore not responsible. Wilson's critics also said that such an idea could lead to some of the policies followed by Nazi Germany during World War II (1939–45) when it claimed that certain races were genetically "inferior" to others. In 1978, Wilson defended his theory with his book On Human Naturein which he more fully explained his views. In this book and others, Wilson made a good case for not ignoring the role of biology in trying to understand human behavior.

In the 1990s, Wilson also became closely identified with the notion of biodiversity. Technically, this word means the variety of life or the biological diversity of species in an area. However, biodiversity also has come to mean the richness and balance of an ecological system. It does not necessarily mean huge numbers of life forms, but rather suggests equal numbers of individuals of different species. Biodiversity not only has commercial value to people but, argues Wilson, its continued loss is a signal of the worsening health of the environment. Wilson is very concerned with trying to minimize what he sees as mass extinctions that are happening in the modern world. As huge areas of rain forest are destroyed each year, species are going extinct in record numbers as they lose the habitat that support them. As people continue to drive plant and animal species to extinction, they also are killing the spirit and the beauty of the natural world. Today, Wilson is doing his best to prevent this from happening.

To biologists, biodiversity is not just a blanket term for the natural biological wealth found on Earth or a description of a healthy and richly varied ecosystem, but it is something that is good biologically. In other words, biodiversity is something to value, to maintain, and to try to protect. Both the term "biodiversity" and the concept were born in 1986 during the National Forum on Biodiversity, held in Washington, D.C. and sponsored by the National Academy of Sciences and the Smithsonian Institution. Most attribute both the word and the concept to Wilson. In his extensive writings, Wilson argues that the notion of biodiversity has a value of its own whether or not it is related to humans in any way. This argument brings up the ethical question of whether mankind has the "right" to do whatever it wants with Earth and its creatures—even to the point of destroying them. On a more practical level, Wilson says that preserving biodiversity has very specific benefits to humans, as illustrated by the fact that in the United States, one-fourth of our prescription drugs have active ingredients obtained from plants. Wilson gives two dramatic examples. The first is the rosy periwinkle plant that became the source of two of the most effective anticancer agents ever discovered. The other is cyclosporin, an obscure fungus that lives only in Norway. This fungus became a powerful immunosuppressant drug and is entirely responsible for our ability to do organ transplants. More generally, a biologically diverse planet is simply more liveable and functional since nature, if properly balanced, keeps water and air cleaner, recycles nutrients, removes waste, and even controls erosion.

Biodiversity is a very broad term. Overall, there are three general kinds of biodiversity: ecosystem or habitat diversity, species diversity, and genetic diversity. The diversity of an ecosystem refers to the variety of actual ecosystems or places where organisms live in a certain region. Thus a region with forests, streams, ponds, grasslands, and farmland is more biologically diverse than one that has only open agricultural fields. It goes without saying that when an ecosystem or habitat disappears, a great number of species disappear as well. Species diversity refers to the ability of many different types of organisms to exist at a certain time. Finally, genetic diversity refers to the level of variability that is found among individual members of a single species. Variability, or variation, refers to the natural differences between living things, and it is a very important phenomenon since it allows a species to adapt to environmental changes over time through evolution.

The threat to our planet's biodiversity is different from most other ecological problems in that it is irreversible. Once a certain species has gone extinct it has disappeared forever and its entire heritage that took millions of years to evolve is lost. Since scientists admit that the vast majority of species have not yet even been identified, humans may be destroying species about which nothing in known, and therefore never will. Finally, by trying to solve some of the problems associated with threats to biodiversity, people gain new knowledge about managing the Earth and using its natural products for the benefit of all.

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