Biodiversity is the total richness of biological variation. A result of genetic diversity. The scope of biodiversity ranges from the genetic variation of individual organisms within and among populations of a species to different species existing together in ecological communities. Definitions of biodiversity may also include spatial patterns and time related (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.
About 1.7 million of Earth's species have been identified. 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, our knowledge of the full complement of species on Earth is far less than complete, especially for species inhabiting tropical countries. According to some estimates, there are as many as 30 to 50 million species, 90% of which are found in tropical ecosystems.
Most of the described species on Earth are invertebrates, particularly insects, and most of the insects are beetles. Some biologists believe that beetles account for most of the undescribed tropical insects. Tropical insect species are difficult to identify because most are confined to a single type of tropical forest, or even to a particular tree species, which may itself have only a local distribution. Additionally, the species may have limited dispersal ability.
Compared to invertebrates, the numbers of species of other groups of tropical-forest organisms are more well-known. The numbers of species of vascular plants have been described for a few tropical forests. For example, a plot of only 0.2 acres (0.1 ha) in a moist forest in Ecuador had 365 species of vascular plants. Tropical forests are much richer than temperate forests, stands of which typically support fewer than 12-15 species of trees.
Almost no systematic surveys have been made of all of the species of tropical ecosystems. Such surveys increasing add to our awareness of biodiversity and genetic diversity. For example, in one study, 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.
Biodiversity is valuable for several reasons. First, biodiversity has its own intrinsic value, regardless of its worth in terms of human needs. As such, ethical arguments exist regarding the loss of biodiversity. Scholars and the lay public alike debate the issues surround whether humans have the right to diminish or exterminate elements of biodiversity, all of which are unique and irretrievable. There are profound philosophical and practical question as to what extent the quality of human existence is diminished by these losses.
In addition to its intrinsic value, biodiversity offers a great deal of utilitarian value. Humans have a requirement for the products of other species and exploit wild and domesticated species and their communities to provide food, materials, energy, and services. In the United States, for example, about one-quarter of prescription drugs have active ingredients obtained from higher plants, and these uses contribute approximately $40 billion per year to the worldwide economy.
Biodiversity also provides extensive ecological services that are directly or indirectly important to human welfare. These include biological productivity, nutrient cycling, the cleansing of water and air pollutants, erosion control, provision of atmospheric oxygen, removal of carbon dioxide, and other functions related to the integrity of ecosystems.
The complete loss of a species or other taxonomic unit (e.g., subspecies, genus, family), thereby reducing biodiversity, is called extinction. The extinction of any species is an irrevocable loss of part of the biological richness. Extinction can be caused by an unpredictable catastrophe, chronic environmental stress, or ecological interactions such as competition, disease, or predation. Extinction represents a loss of the genes unique to that species to the total gene pool (synganmeon).
The geological record suggests that there have been long periods of time characterized by uniform rates of extinction. However, approximately nine catastrophic episodes of mass extinction punctuate the geological records. A severe 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 extinction of vertebrate animals occurred at the end of the Cretaceous period. The most renowned species lost were the last of the reptilian dinosaurs and pterosaurs, but many plants and invertebrates also became extinct at that time.
Since humans have become Earth's dominant large animal and the cause of global environmental change, there have been dramatic increases in extinction rates. Examples of species lost due to human activity include the dodo, passenger pigeon, and great auk. Still greater changes are currently caused by extensive conversions of tropical ecosystems, particularly rainforest, into agricultural habitats that sustain few of the original species. The most important human influences causing the extinction or endangerment of species are: (1) excessive use of natural resources, (2) effects of introduced (non-native) predators, competitors, and diseases, and (3) habitat disturbance and conversion.
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. 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. Numerous other agencies are working to preserve biodiversity. In the United States, the World Wildlife Fund and Nature Conservancy are important national organizations.
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