The extinction of several species or loss of biodiversity is a major environmental problem. Species are disappearing rapidly and there is growing consensus within the international community that a system should be put in place to slow or halt the process of extinction.
All the species are the integral part of ecosystem and extinction of some species diminishes the well-being of the remaining species, including human beings.
The concern about biological diversity is the shrinking genetic pool. It is estimated that tropical forests contain at least 50 per cent and perhaps 90 per cent of the world’s species. According to an estimate, 20 to 75 species are becoming extinct each day because of deforestation in the tropics.
Species do not persist indefinitely. Indeed, it was the realization that fossils are the remains or traces of organisms no longer to be found alive that led to the development of our present understanding of evolutionary processes.
Estimating the number of species existing at present as a proportion of all the species that have ever lived is difficult, but the plants and animals alive today probably constitute around 2-4 per cent of all the species that have lived in the last 600 million years.
Extinctions have not been spread evenly. There is a general background rate at which species go extinct, but there have also been at least five mass extinctions in which 65-85 per cent (and at the end of the Permian period, around 225 million years ago, 95 per cent or more) of all species disappeared.
Background extinctions have little or no effect on biodiversity, because their rate is matched or exceeded by that of speciation, in which one species divides into two and thus increases the number of species. Nor do mass extinctions produce more than a temporary reduction in the number of species, because historically they have been followed by the rapid adaptive radiation of surviving species into the vacated niches.
The extinction of the dinosaurs, for example, was followed by rapid speciation among mammals. Today, the number of land-dwelling species alive is about twice the average of the last 450 million years.
Throughout the geological history of the earth, species of plants and animals had been subjected to various evolutionary processes. Some species became extinct during the different geological periods.
The last major extinction of some species occurred at the close of the Cretaceous period, some 65 million years ago, when birds and mammals were particularly affected. The total disappearance of all dinosaurs occurred during that great extinction. It is generally agreed that they were triggered by natural environment phenomena during geological evolution of the earth. In recent history, biological resources have been lost at an accelerated rate, mainly due to anthropogenic causes.
Tropical deforestation between 1990 and 2020 may eliminate between 5 and 15 per cent of the world’s species. The World Conservation Monitoring Centre has recognised that some 22,000 species of plant and animals are actually threatened by extinction.
Amongst the causes identified for the loss of biological diversity are:
(i) habitat loss, fragmentation and modification: as forests are cleared, wetland drained, valleys flooded and roads built, so habitats are transformed and effectively lost for certain species; (ii) overexploitation of resources; for example, commercial harvesting has been a threat to many marine species, and also extinction of some large terrestrial animals, like the African elephant; (iii) pesticides and pollution have affected several species of birds and other organisms; and (iv) the impact of introduced exotic species as the threaten natural flora and fauna by predation, competition or altering natural habitat.
The introduction of new high yielding wheat and rice varieties, since the mid-1960s, has caused a loss of gene pool in many centres of crop diversity like Turkey, Iraq, Iran, Afghanistan, Pakistan and India.
The intense pressures on biological diversity are a direct reflection of the increasing human population. These pressures are expected to increase until population stabilises, as projected by the United Nations, by during the 2050-2070 period at about 10 billion. Such stabilisation would be achieved only if present efforts to curtail growth of human population are pursued vigorously.