What is population growth?

An increase in the number of organisms in any habitat or niche is known as population growth. World population or the population of a specific geographical location can be considered. With time, major differences in the growth rate are possible due to better adaptation, improvements in medical technology, and agricultural productivity.

Population growth rate

Population growth rate depicts the changes in a population over a given time. The time-dependent changes every year are compared to determine the changes in percentage growth. Different levels of growth are observed over a given time depending on environmental factors, resources, natality, and mortality rate.

Depending on the availability of resources essential for the survival of the organisms, there are major types of growth. It depends on the geographical niche as the resources will vary in different regions. Thus, the growth rate will change with it.

Carrying capacity

The number of species in a population which can exist in their habitat without any competition is known as carrying capacity. The carrying capacity of the population depends on the resources present in the habitat. It depicts the average population size of a particular species that can exist freely in that given habit as there are enough resources for those individuals. Beyond this level competition starts among the individuals for the resources to survive.

Types of growth

Two different types of growth patterns are observed for separate niches. Some places have an abundance of resources. In such a habitat, reproduction and eventual growth in the number of organisms are high. Other places have limited resources, which leads to an inevitable decline in growth rate over the years. The two types of growth patterns are exponential growth and logistic growth respectively.

Exponential growth

Specific niches with unlimited resources show exponential growth with time. Exponential growth is a constantly increasing population with no probability of decline. Unlimited resources make it easier for a higher number of individuals to survive. In such a population, reproduction is more as the environment can sustain the new offspring as well as the previous population.

A J-shaped curve signifies the presence or occurrence of exponential growth concerning time. This character is because of the constantly increasing number of organisms in the population.

Sigmoidal growth

Sigmoidal growth or logistic growth is observed in the population which resides in a habitat with limited resources. A higher level of individuals will ultimately lead to more competition or demand for the resources and the growth rate keeps declining. Global population or a specific country's population follows sigmoidal growth. This is because the resources are limited and people tend to adapt according to limitations. After a few years, such a population reaches a stationary phase where very little or no growth takes place.

Sigmoidal growth is indicated by an S-shaped curve. Steady growth is observed for a certain period and after that population size becomes stable. The plateau phase on the sigmoidal curve depicts this condition.

Factors responsible for influencing the population growth

Four major factors are primarily associated or linked with population density. It directly influences the number of individuals increasing in a specific niche or even any of the nations.

• Natality (A)
• Mortality (Z)
• Emigration (E)
• Immigration (I)

Population growth can be indicated using the population density at two specific time intervals. If the population at time t is N(t) and at a time t+1 is N(t+1), then the formula for population growth is expressed as:

N(t+1) = N(t) + [(A-Z) + (I-E)]

This equation suggests that natality or birth rate and immigration increase the population of a country. But the mortality rate and emigration are responsible for reducing the population size. Changes in these factors lead to changes in the population growth rate. This indicates the population dynamics at the given point in time.

Elements detrimental to population growth

 Several environmental and biological factors are responsible for growth in the number of individuals of a given species. Biological factors like the fertility rate in any species lead to an increase in population size. Population estimates from different nations have different data suggestions for their growth rate. 

Therefore, specific biological factors like the fertility rate and death rate change with time. The population density keeps changing with it. This changes in every country and thus the population growth differs in those countries. Other factors like wider adaptability play an essential role in the survival of individuals in the population. 

Environmental factors like natural calamity or global pandemics like coronavirus disease 2019 (COVID-19) affect the population density. The loss of biodiversity and ecosystem loss are other major factors that negatively affect population growth. Overpopulation that leads to the exploitation of resources is the most common factor responsible for this. 

Possible types of age pyramid of a population

Age pyramids predict the future changes of any specific population. It is a pyramid of numbers that differentiate the population into different age groups. These age groups form different levels of the population pyramid show the population density for that particular age range. The younger generation forms the base of the pyramid while the older generation forms the top of the pyramid. 

Expanding pyramid

If the younger population is higher than the middle and older generations, then the population is said to be expanding. This is because the new generation will replace the middle generation over time increasing the population density at that age range. Species that are going through a rapid population growth experience this type of age pyramid.

Stable pyramid

If the newest generation has the population density same as that of the middle-age population, then the pyramid is said to be stable. It means a similarity will remain in the number of individuals of the middle age range and the younger population. This keeps the population stable when the new generation is going to move to the reproductive ages.

Declining pyramid

If the number of individuals of the young age range is lower than that of the reproductive individuals, then it is considered a declining population. This is because the new generation has a lower number of individuals. Hence, there will be a chance of population density getting reduced with every new generation. 

Major issues associated with population growth

Overpopulation is a major issue that the world population is facing right now. Countries like China have about 1.5 billion in population, which creates a huge demand for resources. Such a huge human population leads to overexploitation of resources. The scarcity of food keeps increasing due to this sudden population explosion. Due to lack of shelter, deforestation is going on creating an imbalance in the ecosystem. Drastic effects like this will decrease ecosystem balance to the brink of collapse unless proper measures are taken. 

Resources are limited for the global population and it is already reaching the carrying capacity. Heavy demand for food and shelter among individuals is imminent in the future. The natural increase upsurge in the population with the prevalent rate of growth undoubtedly is going to be a serious concern or problem for upcoming or future generations. Many countries facing such a population boom have population control laws. This is specific for the well-being of the individuals in the country and long-term benefits for the people living there. 

Recent trends of urbanization are helping the countries control the population. Census conducted by the United Nations all around the world suggested that most people have a proper understanding of birth control in the urban population. Better consciousness and understanding the ground reality of declining resources help people realize future concerns. This trend of an almost exponentially growing population is starting to slow down. 

Context and Applications

This topic is relevant for people pursuing their Bachelor's degree and also Master's degree. Students from the following fields are going to find this topic relevant:

• Ecology
• Population genetics
• Evolutionary Biology
• Population Statistics

Common Mistakes

Most students judge the idea of population growth considering the human population only. But similar conditions are observed for other species as well. It is somewhat imperative  to understand that the advancement in the different dimensions of science leads to a low mortality rate. This is responsible for one beneficial factor which causes the negative effects of population explosion. Thinking that population growth is never-ending is a wrong approach. The steady decline of resources will ultimately lead to a declining population in the forthcoming period. 

Practice Problems

1. What type of age pyramid is observed in the present world population?
   1. Increasing
   2. Stable
   3. Declining
   4. None of the above

Correct Answer: a. Increasing

Explanation- In the current world scenario, the percentage of the population is growing in the younger age group. It confirms the age pyramid to be increasing in nature.

2. What can you say about the carrying capacity of a population?

1. 1. It is always infinite.
   2. It is always finite.
   3. It is always unstable.
   4. It is always very flexible.

Correct Answer: b. It is always finite.

Explanation- Carrying capacity depends on the amount of food, space, water, and other necessities available for a species in a particular region. It is finite because it enables the maximum population to grow based on these conditions. When these factors are utilized by most of them, the growth rate decreases. 

3. Why is exponential growth not possible on earth?

1. 1. Resources are limited
   2. Adaptability will cease to exist
   3. Ecosystem imbalance
   4. All of the above

Correct Answer: a. Resources are limited.

Explanation- Exponential growth enables a population to grow faster when it gets larger. In the real world, it is not possible because an organism needs resources to survive. Resources are limited in the environment.

4. What is the major problem related to overpopulation to population dynamics?

1. 1. Pandemics similar to the one from coronavirus
   2. Competitive behavior in a specific country leading to economic unrest
   3. Shortage or scarcity of food and water 
   4. None of the above

Correct Answer: c. Shortage or scarcity of food and water.

Explanation- Population dynamics explain the reason for changing of the population in size and structure over time. Food and water are limited natural resources. Shortage of these factors can change the population over time. Pandemics, competition, and a few other factors can change a population for a certain time or in a particular region. These are not constant reasons.

5. What happens to the population density in a declining population?

1. 1. It decreases.
   2. It increases.
   3. It stays the same.
   4. It cannot be defined.

Correct Answer: a. It decreases.

Explanation- Population density depends on the number of individuals per unit geographic location. It decreases with the decrease in the number of individuals in a population.