Controlling Population Size: Phases

Communities and populations are made up of many organisms. Organisms have evolved to gather in large numbers, groups, as they gain more protection from predators. This protection allows organisms to rear young and feed successfully. But there are certain factors that need to be taken that can limit the growth of the populations and create balances in birth and death rate. When an organism competes against another organism for food, it is known as a pest. Pests need to be controlled so that other organisms are not affected by diseases or starvation caused by the pests. The pests can be controlled biologically with biological agents or chemically using chemicals.

Nutrients are needed in all living organisms. This includes carbon and nitrogen since these elements are needed to make proteins and nucleic acids. These elements are limited on the planet Earth. Microorganisms allow the decaying of organic matter to ‘recycle’ carbon, via carbon cycle, and nitrogen, via nitrogen cycle.

Factors that control population growth

Birth rate and death rate determines, at any particular time, the growth of a population of a species.

Phases of bacterium populations

- Lag Phase: This can last for a couple of minutes and up to a few days. This is where the bacteria adapts to its surroundings and prepares to grow. Then there is a period of slow growth due to being only a few organisms at the start, but when they start to reproduce, the number starts to increase significantly.

- Exponential Phase: As the numbers are increasing, more individual organisms are able to reproduce providing that there are no limitations. The rate that bacteria multiply cannot be controlled indefinitely.

- Stationary Phase: At this stage, the organisms are an equal amount of births and deaths so the population is steady. This is where the population has entered its maximum. This is known as the carrying capacity.

- Death Phase: At this phase, the death rate is larger than the birth rate. This might be due to the available nutrients being used up, disease and many other population factors.

Factors that regulate increase in populations

The factors that slow down population growth rate and the reasons that might cause populations to crash can be distinguished. Some factors are density dependant meaning that the effect of the factor increases as a population decreases. This factor can include accumulation of toxic wastes, disease, parasitism or even lack of nutrients and food. Other factors can be density independent. This factor doesn’t depend on the population density. All the species within the population are affected regardless of the population size. This factor can result from freezing or floods.


QR Code
QR Code biology_controlling_population_phases (generated for current page)