Biodiversity is the totality of genes, species and ecosystems in a region. The current richness of life on Earth is the product of hundreds of millions of years of evolutionary history. Over time, there were human cultures that have adapted to the local environment, discovering, using and altering local biotic resources. Many areas that now seem “natural” bears the mark of millennia of human habitation, crop cultivation and harvesting of resources. Biodiversity was shaped also by the domestication and hybridization of local varieties of crops and livestock.
Biodiversity can be divided into three hierarchical categories – genes, species and ecosystems – that describe different aspects of living systems and that scientists measure in different ways, namely:
For genetic diversity means the variation of genes within species. This includes populations of certain species (like the thousands of traditional rice varieties in India) or genetic variation of a population (which is very high among Indian rhinos, for example, and very low among cheetahs) . Until recently, measures of genetic diversity is mainly applied to domesticated species and populations kept in zoos or botanical gardens, but the techniques are increasingly applied to wild species.
For species diversity means the variety of species in a region. Such diversity can be measured in many ways, and scientists have not agreed on what the best method. The number of species in a region – their “wealth” in kind – is a measure often used, but a more accurate measure, the “taxonomic diversity takes into account the close relationship between species and others. For example, an island where there are two species of birds and a species of lizard has greater taxonomic diversity than an island where there are three species of birds but no lizards. Therefore, even if there are more species of ground beetles than all other species combined, they do not influence the species diversity because they are very closely related. Similarly, much larger number of species living on land that they live in the sea, but terrestrial species are more closely linked to oceanic species, so the diversity is higher in marine ecosystems that suggesting a strict count of the species.
The diversity of ecosystems is more difficult to measure than species or genetic diversity because the “boundaries” of communities – associations of species – and ecosystems are not well defined. However, in so far as to use a consistent set of criteria to define communities and ecosystems, can be measured in number and distribution. So far, these methods have been implemented primarily at national and subnational levels, but have developed some coarse global rankings.
Besides the diversity of ecosystems can be important many other expressions of biodiversity. These include the relative abundance of species, age structure of populations, community structure in a region, the variation in composition and community structure over time and to ecological processes such as predation , parasitism and mutualism. More generally, to achieve specific goals or policy management is often important to consider not only the diversity of composition – genes, species and ecosystems – but also the diversity of structure and function of ecosystems.
How many species are there?. Estimates
It is surprising that scientists know best how many stars are there in the galaxy than how many species there are on Earth. Estimates of the diversity of the world’s species to between two million and 100 million species, with the most accurate estimate of around 10 million, of whom only 1.4 million have been named. The problems posed by the limits of current knowledge on species diversity are complicated by the lack of a database or a centralized list of the world’s species.
New species are being discovered, including new birds and mammals. On average, each year we discover about three new species of birds, and as recently as 1990 years found a new species of monkeys. Other groups of vertebrates are still far from being fully described: it is estimated that 40% of freshwater fish from South America have not yet been classified.
Scientists were surprised in 1980 by the discovery of a huge diversity of insects in tropical forests. In a study of only 19 trees of Panama, around 80% of the 1,200 beetle species discovered were unknown to science. At least between 6 million and 9 million species of arthropods – and possibly more than 30 million – live, as now believed, in the tropics and only a small fraction has been described.
As scientists begin to investigate other poorly known ecosystems, such as soil and the depths of the sea, they become common findings “striking” of species. The surprise is unwarranted. Only one square meter of temperate forests can accommodate 200 000 mites and tens of thousands of other invertebrates. A similar extension of tropical pastures can accommodate 32 million nematodes, and one gram of that soil can hold 90 million bacteria and other microbes. Still completely unknown how many species contain these communities.
Marine systems also reveal an unexpected diversity. Scientists believe that the floor of the deep sea may contain not less than one million described species. Less than two decades, new found entire communities of organisms, communities of hydrothermal coelenterates. More than 20 new families or subfamilies, 50 new genera and 100 new species of these communities have been identified.