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Population dynamics


Populations have their own measurable characteristics.

Each member of a population can be born, grow, and die, but only one population as a whole has specific birth and growth rates, and a pattern of dispersion in time and space.

The size of a population can be assessed by its density.

Population density may change. Keeping the distribution area fixed, the population may increase due to births and immigration. The decrease in density may occur as a consequence of deaths or of emigrations.

Growth curves

THE S curve is the standard population growth expected for most populations in the wild. It is characterized by an early phase of slow growth, in which organisms adjust to their livelihoods. Then there is rapid exponential growth that culminates in a stabilization phase in which the population no longer grows. Small oscillations around a maximum numerical value happen, and the population then remains in a state of equilibrium.

Look at the chart below to get a better understanding:

Phase THE: slow growth, phase of adaptation of the population to the environment, also called lag phase.
Phase B: accelerated or exponential growth, also called the log phase.
Phase Ç: The population is subject to the limits imposed by the environment, the environmental resistance is greater on the population.
Phase D: stabilization of population size, where population size oscillations occur around an average.
Phase AND: is the theoretical curve of population growth without the interference of environmental resistance factors.

THE J curve It is typical of algae populations, for example, in which there is an explosive, geometric growth due to the increase in nutrient availability of the medium. This explosive growth is followed by a sharp drop in the number of individuals, because, due to the depletion of the environment resources, the mortality rate is high and may even lead to the extinction of the local population.

Factors that regulate population growth

The geometric phase of growth tends to be unlimited due to the biotic potential of the species, that is, the ability of individuals to reproduce and generate offspring in unlimited quantity.
There are however, natural barriers to this endless growth.

The availability of space and food, the climate and the existence of predatism and parasitism and competition are factors of environmental resistance (or the environment that regulate population growth).

The population size ends up reaching a maximum numerical value allowed by the environment, the so-called limiting capacity, also called load capacity.

THE curve (a) represents the biotic potential of the species; The curve (b) represents standard population growth; (ç) is the limiting capacity of the medium. The area between (a) and (b) represents environmental resistance.