The intensity of reproduction of many species of wild animals is depending on fertility inherent in them which is limited to adverse living conditions in the nature. Human activity can promote increase in number of animals or, on the contrary, to serve as the reason of their disappearance.
1. The number of wild animals, mainly, depends on a condition of the environment occupied by them which can become the reason of decrease in fertility, increases in death of animals. There is no finished theoretical justification of the mechanism of regulation of number of wild animals yet, but scientists consider that to a lesser extent it depends on fertility of individuals. Despite periodic rises and recessions of birth rate and mortality of animals in the wild nature, in long-term consideration the number remains sufficiently balanced.
2. Temporary conditions of a natural situation influence change of fertility of animals which was formed in evolutionary process of adaptation of different types to environmental conditions. Reproduction of individuals decreases when population density of a concrete look increases (in this connection the quantity of a forage decreases and death of young growth increases), living conditions worsen. Natural disasters (droughts, floods, etc.), excessive destruction sharply reduce the number of animals, but it can be restored pretty fast at a favorable situation. Bears, deer, elks, roes, Pinnipedia are characterized by low fertility, and wolves, squirrels, foxes – high.
3. In the wild nature the life expectancy of animals is twice less than maximum. Large types usually are considered as long-livers. Many factors among which the most important reasons of reduction of quantity should be considered existence of fodder resources (abundance of high-calorie food and water, availability of food), climatic factors (for example, low temperature condition), death from predators and epidemic, movement to territories, adverse for existence of individuals, have serious impact on the number of animals.
4. In fauna there are rare species of animals, it is possible to carry to them elephants, rhinoceroses, leopards, tigers, lions. But there are also such, for example, wolves who are very numerous, despite the undertaken measures against them.
5. The number of wild animals very much depends on activity of people. For example, it is possible to increase quantity of the main fur-bearing animals, having forbidden or having limited hunting. Artificial resettlement and protection of endangered species promotes growth of number of animals too.
6. For the purpose of identification of dynamics of number and the list of wild animals the scientists carry out biological monitorings which also give the chance to consider quantity of trade animals. The similar form of account helps to accept the corresponding situations of a measure quickly.