Birth and death rates are the most important factors in population fluctuations. 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 offspring that one individual can provide per unit of time.
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 have wondered what determines the biotic potential of a species. Not so long ago, scientists managed to find the answer to this question.
The biotic potential of a species depends on the lifespan of an individual and the age at which it reaches the 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, which depends on the level of mortality at each age, is even more significant for the population.
If the aging of organisms is the main causemortality, then in this case there is a slight drop in the number at an early age. An example of such populations are species of annual plants and some mouse-like rodents.
Under natural conditions, a rather rare case - a species with high mortality at an early age, relative stability in the generative period and an increase in mortality towards 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.
Movement from one population to another
What determines the biotic potential of a species besides lifespan? In addition to the ratio of births and deaths, the number of populations is greatly influenced by the movement of individuals from one population to another. In plants, the introduction of new individuals is most noticeable when rudiments (seeds, spores) from other habitats enter the territory of the population.
With a sufficiently high local population, they usually do not change the situation, because they die in conditions of competition. In other cases, they can increase the size of their population. Animal migrations 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 resettlement of young animals. In general, the movement of an organism is one of the mechanisms that regulate the number andmethod of interpopulation relations.
Maintenance is possible by increasing immigration. With a high birth rate, equality is achieved through the emigration of an excess of individuals. In other cases, the population size loses stability. Its fluctuations are not random, since there are a number of mechanisms that regulate it within certain limits, close to the norm.
Let's dwell on some of these mechanisms. Competition is what determines the biotic potential of a species. This phenomenon is typical not only for animals, but also for plants. Thus, intrapopulation competition leads to the death of an excess number of individuals. As a result, self-thinning occurs in plants. With a strong thickening of seedlings, physiologically weaker ones die.
In perennials, like 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 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.