Animals and their natural habitat exist in a relatively stable, if fluctuating, equilibrium and it is unlikely that primitive hunting much influenced this. But modern man, using the advanced technology of an industrial society, has had neither the time nor the desire to adapt to the ecosystem as anything but a destructive force. Much use has been made of fire, water and land development in ways which have often devastated local habitats and food cycles. The problems of conservation are complex, partly because of inadequate knowledge of the ecosystemic relationships, partly because of conflicts between groups with different interests.
Growing pressures from increasing human populations and the consequent greater need for agricultural land tend to reduce the areas of land available for wildlife. Once land is taken over for agricultural and pastoral practices, its wildlife will be largely exterminated and its natural vegetation disturbed, if not completely destroyed.
Since the area of land which can be set aside for nature reserves is limited, ecological influences on animal populations and their distribution are distorted. Natural fluctuations in animal numbers cannot be absorbed in a limited habitat. The danger of destruction of the habitat by population explosions within the reserves (often a result of the imbalance produced by restraining man from his traditional hunting activities) cannot be prevented by the overspill or dispersion of the surplus population into the neighbouring areas, which would occur in a completely natural state. The human need for farm activities, which are pressing ever more closely upon the borders of reserved areas, takes priority over the needs for unlimited space of uncontrolled game herds, and domestic herds need to be kept within tolerable limits.
In the USA up to 1889, the government made use of a policy of intentional extermination of the bison and buffalo herds as a device to starve out unpacified Indian tribes. As a result of that policy a population of some 60 million animals was reduced to less than 100 wild animals.