What role do abiotic and biotic factors play in changing population density?

Various abiotic and biotic factors can be the reasons for sharp fluctuations in the number of populations of some organisms. Sometimes these fluctuations are in good agreement with changes in climatic conditions. However, in some cases, the influence of external factors cannot explain the changes in the size of a population. The causes of fluctuations in the number of populations may lie in themselves; then they talk about the internal factors of population dynamics.
There are cases when, under conditions of overpopulation, a number of mammals undergo sharp changes in their physiological state. Such changes primarily affect the organs of the neuroendocrine system, affecting the behavior of animals, changing their resistance to diseases and various types of stress.
Sometimes this leads to increased mortality of individuals and a decrease in population density. White hare, for example, during peak periods often suddenly die from the so-called “shock disease”.
Such mechanisms can undoubtedly be attributed to internal regulators of numbers. They work automatically as soon as the density exceeds a certain threshold value.
In general, all factors that influence the population size (it does not matter, limiting or favoring the reproduction of the population) are divided into two large groups:
– independent of population density;
– depending on population density.
The second group of factors is often called regulatory or density control.
One should not think that the presence of regulatory mechanisms should always stabilize the numbers. In some cases, their action can lead to cyclical fluctuations in numbers even under constant living conditions.