Timetable For Catastrophe
‘‘Extinctions: No Comebacks’’
M A Haque
The average rate of natural extinction has been quite
low except under the special circumstances, i.e. during the mass extinctions. The approximate estimated rate has been one mammal species in each time period of 400 years. In case of the birds, the rate has been faster in comparative terms. Generally, one species of bird became extinct during each time period of 200 years. Nature had adjusted to that kind of extinction. The issue became complicated because during past few centuries, the rate of extinction has become very fast. More important is the fact that this kind of extinction is not because of any natural process. As a consequence, the nature has not adjusted to the high rates of extinctions. We know that this kind of fast extinction has occurred on account of human factor. Human race is exceptionally intelligent. It can learn to do things much faster than any other organism around. Human race can create new ideas and tools, with the help of these ideas and tools, it can modify the environment to a great extent in short time. Also, the human race can make drastic adjustments in its own behaviour and force many other organisms to change.
The changes made by the human race in Earth's environment favour selected species and not the total biodiversity. As a result, large number of organisms are in the position of disadvantage. It becomes obvious from the fact that during the last about three centuries, 58 species of mammals and 115 species of birds have become extinct indicating that the rate of extinction has increased to about 50 times to 106 when compared with the rate of natural or background extinction. The present extinction rate is not only fast, but it is becoming more and more faster with the passage of time. Therefore, the future scenario is even grimmer. It is estimated that in future, one to ten percent of the organisms present on Earth may be forced to extinction in only one decade. Reason is that we are modifying the Earth's environment significantly and thereby pushing large varieties of organisms towards extinction. For example, we are modifying and destroying the natural ecosystems without being concerned about its dire consequences. In the process, amphibians, primates and tropical birds are more adversely affected. According to some scientists, more than 120 amphibian species have become extinct since 1980, and another 32 percent are currently considered at the risk of extinction. It is interesting to know that the 300 million-year-old history of the amphibians on Earth is older than that of the earliest known dinosaurs. Scientists are concerned by the recent sudden decline in the numbers of different amphibian species. The decline in the population of the amphibians is being viewed by the scientists as an indicator of drastic degradation of the environment as a whole. It is so as the amphibians indicate reflections of changes in both the land and aquatic environment because amphibians are the only class of organisms which can live in both types of environments, i.e. in the aquatic environment as well as terrestrial environment.
Much more important is the prediction made by the scientists that in future this trend will not reverse. As the process of generation of new species through evolution is always very slow while the rate of extinction has become too fast. The kinds of changes that took place in millions of years are now happening in less than a few centuries, only because of human interventions. That is reflecting in the decrease in the populations of various organisms. For example, populations of about 75% of the bird species are declining. Therefore, these species are under threat. In case of primates, about 65% of the species are under threat. In case of plants, the threat is quite high for about three percent of species. The percentage looks insignificant. But if we consider in absolute terms, it means that about 8500 species of plants are either threatened or endangered. Nature cannot take care of such fast extinctions. It cannot produce new species too fast to compensate for the losses.
As an example, we can consider the Indian rice varieties. Till about four decades ago, India had around 30,000 rice varieties under cultivation at different places. Similarly, there has been a rich history of different types of other grains, pulses, oil seeds, vegetables being cultivated in the country. During last few decades, Indian farmers have been restricting the varieties and species in favour of only those few which according to their understanding give high yields or are easy to manage. As a result, a large number of varieties and species have disappeared or are on the verge of disappearing. Once these are lost, they cannot be brought back. We know that we can push a variety or species towards extinction, but we cannot recreate the same. Similar is the case with the domesticated animals and fowl varieties. We are restricting the varieties for more yield and better management and due to this, we may lose the age-old varieties. Along with them, we will lose the adaptabilities, resistance to diseases, fighting and self-defense capabilities present in those varieties. Certainly, that will be a big loss to our wealth of biodiversity.
[Excerpted from Dr M A Haque's book Extinctions : No Comebacks.
Courtesy : NBT Newsletter, January 2017]
Vol. 49, No.35, Mar 5 - 11, 2017