Fertility and mortality are the most important factors in the fluctuation of the population. They are directly related to the biotic potential of the species. This phenomenon is intensively studied by ecologists. What is the biotic potential of a species? This is the maximum number of descendants that one individual per unit of time can provide.
What determines the biotic potential of a species?
The population of many rare animals is under strict control. For a long time, biologists and ecologists wondered what the biotic potential of the species depends on. Not so long ago, scientists were able to find the answer to this question.
The biotic potential of a species depends on the life span of the individual and the age at which it reached its generative state. This indicator varies in different groups of organisms and species. The number of offspring that appeared in a given year is also variable, but their survival is even more significant for the population, depending on the mortality rate at each age.
Life span
If the aging of organisms is the main cause of mortality, then in this case there is a slight drop in numbers at an early age. An example of such populations are species of annual plants and some mouse-like rodents.
In natural conditions, a rather rare case is a species with high mortality at an early age, relative stability in the generative period and an increase in mortality by the end of the life cycle.
Finally, the third type is characterized by uniform mortality throughout the life cycle. In this case, a significant role, for example, in plants, is played by intrapopulation competitive relations. This type is typical for stands of spruce and pine forests of the same age.
Moving from one population to another
What determines the biotic potential of a species in addition to life expectancy? In addition to the ratio of fertility and mortality, the movement of individuals from one population to another has a great influence on the number of populations. In plants, the introduction of new individuals is most noticeable when primordia (seeds, spores) from other habitats enter the population territory.
With a sufficiently high number of local populations, they, as a rule, do not change the situation, since they die in a competitive environment. In other cases, they can increase the size of their population. Migrations of animals occur either with an increase in the number, or with its decrease, which in any case changes the number. Often migrations are associated with the settlement of young animals. In general, the movement of the body is one of the mechanisms that regulate the number and method of interpopulation relations.
Competition
Maintaining numbers is possible by increasing immigration. With high fertility, equality is achieved through the emigration of an excess of individuals. In other cases, the population loses stability. Its fluctuations are not random, since there are a number of mechanisms that regulate it within certain limits, close to normal.
Let us dwell on some of these mechanisms. Competition is what the biotic potential of a species depends on. This phenomenon is characteristic not only for animals, but also for plants. Thus, intrapopulation competition leads to the death of an excessive number of individuals. The result is self-healing in plants. With a strong thickening of seedlings, physiologically weaker ones die.
In perennial plants, for example, in trees, this process continues for many years. This can be observed in thickened artificial plantations of pine or oak. A compromise situation often arises in the meadows, when the number of shoots and the total mass of the population decrease. In this case, stabilization is not due to the number of individuals, but due to their biomass.