المساعد الشخصي الرقمي

مشاهدة النسخة كاملة : Biodiversity



Mohamed Omar
04-11-2009, 05:19 PM
Biodiversity is the variation of life forms within a given ecosystem, biome, or for the entire Earth
Biodiversity is often used as a measure of the health of biological systems. The biodiversity found on Earth today consists of many millions of distinct biological
species, which is the product of nearly 3.5 billion years of evolution


http://img692.imageshack.us/img692/7489/450pxbluelinckiastarfis.th.jpg (http://img692.imageshack.us/i/450pxbluelinckiastarfis.jpg/)
Some of the biodiversity of a coral reef


http://img25.imageshack.us/img25/5171/rivergambianiokolokoban.th.gif (http://img25.imageshack.us/i/rivergambianiokolokoban.gif/)


Rainforests are an example of biodiversity on the planet, and typically possess a great deal of species biodiversity. This is the Gambia River in Senegal's


Biologists most often define "biological diversity" or "biodiversity" as the "totality of genes, species, and ecosystems of a region". An advantage of this definition is that it seems to describe most circumstances and present a unified view of the traditional three levels at which biological variety has been identified to


Genetic Diversity
Species Diversity
Ecosystem Diversity


Genetic diversity is a level of biodiversity that refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary


Importance of genetic diversity
In survival and adaptation
Genetic diversity plays a very important role in survival and adaptability of a species because when a species’s environment changes, slight gene variations are necessary to produce changes in the organisms' anatomy
that enables it to adapt and survive


Agricultural relevance
When humans initially started farming, they used selective breeding to
pass on desirable traits of the crops while omitting the undesirable ones. Selective breeding leads to monocultures: entire farms of nearly
genetically identical plants. Little to no genetic diversity makes crops
extremely susceptible to widespread disease. Bacteria morph and
change constantly. When a disease causing bacterium changes to attack
a specific genetic variation, it can easily wipe out vast quantities of the
species. If the genetic variation that the bacterium is best at attacking
happens to be that which humans have selectively bred to use for
harvest, the entire crop will be wiped out


A very similar occurrence is the cause of the infamous Potato Famine in Ireland. Since new potato plants do not come as a result of reproduction but rather from pieces of the parent plant, no genetic diversity is developed, and the entire crop is essentially a clone of one potato, it is especially susceptible to an epidemic. In the 1840s, much of Ireland’s population depended on potatoes for food. They planted namely the “lumper” variety of potato, which was susceptible to a rot-causing plasmodiophorid called Phytophthora infestans. This plasmodiophorid destroyed the vast majority of the potato crop, and left tens of thousands of people to starve to death


Species diversity


Species diversity is an index that incorporates the number of species
in an area and also their relative abundance. It is generally a much
more useful value than species richness


Ecosystem diversity


Ecosystem diversity refers to the diversity of a place at the level of ecosystems. It is contrasted with biodiversity, which refers to variation in
species rather than ecosystems


Agriculture


The economic value of the reservoir of genetic traits present in wild
varieties and traditionally grown landraces is extremely important in
improving crop performance.Important crops, such as the potato and
coffee, are often derived from only a few genetic strains. Improvements
in crop plants over the last 250 years have been largely due to
harnessing the genetic diversity present in wild and domestic crop plants
Interbreeding crops strains with different beneficial traits has resulted in
more than doubling crop production in the last 50 years as a result of the
Green Revolution Crop diversity is also necessary to help the system
recover when the dominant crop type is attacked by a disease



Number one
The Irish potato blight of 1846, which was a major factor in the deaths
of a million people and migration of another million, was the result of
planting only two potato varieties, both of which were vulnerable
Number 2
When rice grassy stunt virus struck rice fields from Indonesia to India in the 1970s. 6273 varieties were tested for resistance. One was found to be resistant, an Indian variety, known to science only since 1966. This variety formed a hybrid with other varieties and is now widely grown
Number 3
Coffee rust attacked coffee plantations in Sri Lanka, Brazil, and Central America in 1970. A resistant variety was found in Ethiopia. Although the
diseases are themselves a form of biodiversity


Thanks