Population fluctuations, biotic potential, and carrying capacity is another set of attributes of the human population.

Population Fluctuation:

In all populations, numbers rise and fall over time. Once the population has reached equilibrium in a certain region, its number tends to vary above or below the equilibrium. This variation from the equilibrium is called population fluctuation. Fluctuations can be erratic, or deviations from a growth pattern. Sometimes the number of individuals can increase rapidly, causing a population outbreak. Four general types of population fluctuations in nature are stable, irruptive, cyclic, and irregular.

Stable Fluctuations:

A stable population fluctuates slightly above and below carrying capacity and is characteristic of many species living under fairly constant environmental conditions.

Irruptive Fluctuations:

Some species have a fairly stable population size that may occasionally irrupt to a high peak and then crash to below carrying capacity. This is characteristic of short-lived, rapidly reproducing species.

Periodic Fluctuations:

Periodic fluctuations occur over a regular time period, generally a multiple-year cycle. The fluctuations may be seasonal, annual or cyclic.

• Seasonal fluctuations are due to changes in the population size controlled by life history, adaptations and seasonal changes in the environment
• Annual fluctuations are due to changes in population density caused by annual differences in the environmental factors.
• Cyclic fluctuation shows up and down in population size but not seasonal or annual. It is due to predator-prey cycles.

Irregular Fluctuations:

Irregular behavior is poorly understood. Some scientists attribute irregular behavior to chaos in the system, others disagree. There is no apparent recurring pattern. It has poorly understood interactions

Biotic Potential:

The biotic potential is the potential for life, or how fast a species reproduces when not limited by its environment. The biotic potential is the potential ability or the inherent power of a population to increase in number when the age distribution in the population is stable and all the environmental conditions are optimum. It is also called reproductive potential.

Each species will have a different biotic potential due to variations in

• the species’ reproductive span (how long an individual is capable of reproducing)
• the frequency of reproduction (how often an individual can reproduce)
• “litter size” (how many offspring are born each time)
• survival rate (how many offspring survive to reproductive age)

Populations cannot grow exponentially indefinitely because there is always limit put by nature to the population growth. Exponential growth results in exploding populations, which ultimately reaches a size limit imposed by the shortage of one or more factors such as water, space, and nutrients or by adverse conditions such as disease, drought and temperature extremes, etc. The factors which act jointly to limit a population’s growth are termed environmental resistance. The interrelation between the biotic potential and environmental resistance keeps a population in balance.

Carrying Capacity:

If there are 10 Burgers and 10 people sit down at a lunch table, and if it is decided to distribute the food equally, each one will get 1 burger. If the number of people increases, everybody will get less than one. If the number increases too much, everybody will get part of the burger which is not sufficient for his/her survival. This is what happens in nature. If organisms that cannot get food will die or find a new place to live.

The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment. It is represented by letter ‘K’. The carrying capacity of any area is not static. It may be lowered by resource destruction and degradation during an overshoot period or extended through technological and social changes

For populations which grow exponentially, growth starts out slowly, enters a rapid growth phase and then levels off when the carrying capacity for that species has been reached. The size of the population then fluctuates slightly above or below the carrying capacity.

Reproductive lag time is defined as the time required for the birth rate to decline and the death rate to increase in response to resource limits.  Reproductive lag time may cause the population to overshoot the carrying capacity temporarily. In such case, the population suffers a crash to a lower level near the carrying capacity unless a large number of individuals can emigrate to an area with more favorable conditions. 

In nature, when the population size is small, there is sufficient food and other resources for each individual. Under such conditions of safe environment, organisms can easily reproduce, so the birth rate is high. As the population increases, the food supply, or the supply of necessary resource, may decrease. In absence of such supply, some individuals will die. Thus, the population cannot reproduce at the same rate, so the birth rates drop. When the population decreases to a certain level where every individual can get enough food and other resources, and the birth and death rates become stable, we can say that the population has leveled off at its carrying capacity.

Factors Affecting Carrying Capacity:

The major factors affect the carrying capacity of the environment are as follows

Life Supporting Capacity:

It is the ability to allow the withdrawal of resources like food, water, raw materials, etc. without causing lasting damage to the environment.

• Productive System: Such a system includes croplands, orchards, etc. which provide food and fibres. Food availability in any habitat is important for the survival of a species.
• Protective System: It includes the climate, forests, oceans and other river bodies, etc. These are important for maintaining different cycles like the water cycle, carbon dioxide cycle, nitrogen cycle, etc. This system is important for the moderation of extreme temperatures.

Assimilative Capacity:

It is capacity of the environment to absorb without ill effects. By this environment absorbs and assimilates the waste produced by human activities.

The carrying capacity of the human population has increased due to effective and clever manipulation of the environment and technological developments.

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