When human species started evolving about 2 million years ago, man’ interaction with nature was more direct and intimate since he was a hunter-gatherer and thus a predator like any other large animal predator. Agricultural and socio-cultural evolution through ages has changed the human species completely – no longer do we need to chase a wild buffalo with bow and arrows or dig out tuberous roots from soil with crude stone tools to satisfy our daily food requirements!
Yet, the impact of man on the biosphere had never been so massive and alarming as it is now. True, man does not interact directly with many plants and animals, except the domesticated varieties, but nevertheless he exerts profound influence on the living beings around him. His multifarious activities undertaken for his own benefit invariably alter the environment in ways that harm some species and at times benefit some undesirable species. Deforestation due to growing population pressure leads to habitat alteration – from forests to pastures to croplands, which causes the decline or total loss of forest-dwelling species. Often the changes in an ecosystem caused by human activity are gradual and not dramatic enough to be recognized readily.
With the advent of Indira Gandhi Canal in northwestern Rajasthan, the land use patterns are already changing .the traditional goat and sheep husbandry is being replaced by husbandry of cows and buffaloes.
Similarly, desert biologists are noticing that the truly desert rodent species are being replaced by species belonging to areas with more vegetation. In modern times, destruction and alteration of natural habitats are the greatest causes for the alarming rate of the disappearance of many species. Biologists believe that as a consequence of deforestation in the tropics, thousand (if not lakhs) of insect species are becoming extinct even before they are discovered, named and described.
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The importance of a predator being ‘prudent’. A prudent predator whose survival and growth are dependent on a particular prey species should not over exploit it to extinction but should ensure its continued well-being for his own benefit. Is man a prudent predator? The irrecoverable loss of commercial fishery of important fish species in the North Sea and a few other similar examples from elsewhere, cast doubts on a positive answer we might be tempted to give to this question.
The existence in nature of mechanism by which predators keep prey populations under control should have received due attention when we attempted pest control by chemical means. No doubt, some degree of chemical control of pests and competitors is necessary when the objective is to improve net food production and creation of a disease free environment. But in many instances the chemical control measure backfired because of the evolution of insecticide – resistant strains and due to the elimination of non-target organisms some of which were natural predators of pests. Having realized that it is impossible to win the war against insect pests, the present thinking is not in terms of pest control but pest ‘management’, an approach in which biological control methods play a vital role. Since many of the pesticides in use are not specific, they harm countless non-target species, seriously affecting the normal functioning of ecosystems.
Lastly, the ecological imbalance caused by human activities is not exclusively through the loss of certain species, but at times through introduction of exotic species into a community of indigenous flora and fauna. Some of these introductions were intentional, others accidental. These exotic species include the controversial Eucalyptus, the ubiquitous water hyacinth and the mosquito fish. Nearly all standing water bodies in India are being covered by the water hyacinth, which is now an uncontrollable weed. Another noxious weed spreading alarmingly in dry tracts all over the country is the Congress weed, Parthenium that is believed to heave ‘sneaked’ into our country as seed along with the wheat imported from USA under PL480.