Biodiversity

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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 ofpesticides 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