Population dynamics is one of the most significant biological and ecological phenomena. We can say that the life of a population is manifested in its dynamics. Populations could not exist in the changing conditions of the external environment without changing with them.
The ability to change allows populations to constantly adapt to changing living conditions.
Population dynamics are the processes of changes in its main biological indicators over time.
The main importance in the study of population dynamics is given to changes in numbers, biomass, and population structure.
Let us consider the mechanisms of changes in the population size.
In any natural population, the number of emerging individuals always exceeds the number of their parents (this is easy to verify by remembering how many seeds one plant gives or how many cubs are produced, for example, a cat, a she-wolf, a frog or a fish).
Thanks to fertility, the population tends to grow indefinitely.
However, not all individuals of new broods can survive to adulthood and leave offspring. Some of them die off.
Mortality limits population growth.
Both fertility and mortality are constantly changing depending on many factors.
When the birth rate exceeds the death rate, the population size increases, and vice versa: the number decreases when the death rate becomes higher than the birth rate.
Constant changes in the living conditions of organisms lead to the intensification of one or the other process. As a result, population numbers fluctuate.