What Is Population Growth Definition Types and Factors
Population growth is one of the main concerns of this world because the human population isn't a static factor. Rather, it's growing at a really alarming rate. In spite of the increasing world population, the resources of the world remain constant. Thus, the power to take care of sustainable development is becoming a serious challenge to mankind today.
Human increase is the increase in the number of people in a particular area. There has been a decrease in the death rate over the past 200 years due to the changes in public health and sanitation. The advent of antibiotics and vaccines has led to a decrease in the chances of infections in humans. Urbanization and advancements in agriculture have also led to a rise in population.
Factors that Influence Population Fluctuation
The fluctuations within the population during a given area are influenced by four major factors, which include the following:
Natality – it's the number of births during a given period of your time during a population
Mortality – It is defined as the number of deaths that takes place in a population at a given period of time.
Immigration – it's defined to be the number of people who come from another population and increase the population in consideration during a period of time.
Emigration – it's defined as the number of people from a population who leave the habitat and attend a special habitat at a given period of time.
Thus, it's clearly visible that the two factors Natality (N) and Immigration (I) increase a population, thus increasing population whereas, Mortality (M) and Emigration (E) decrease the population. The population density (Pt) at a given point of time is often given as:
Pt =P0 + (N + I) – (M + E)
Where P0 is the initial population density.
We Have Two Growth Models Which Describe the Essential Growth Trend During a Population. These Are
Exponential Growth
In a perfect condition where there's a vast supply of food and resources, the increase will follow an exponential order. Consider a population of size N and birth rate represented as b, death rate as d, Rate of change of N are often given by the equation.
dN/dt = (b-d) x N
If, (b–d) = r,
dN/dt = rN
Where r = intrinsic rate of natural increase
This equation is often represented with a graph that features a J shaped curve. According to calculus
Nt=N0ert
Where, Nt = Population density at time t
N0= Population density at time zero
r = intrinsic rate of natural increase
e = base of natural logarithms
Logistic Growth
This model defines the concept of ‘survival of the fittest’. Thus, it considers the very fact that resources in nature are exhaustible.
The limit of resources beyond which it cannot support any number of organisms can be defined as the carrying capacity. The carrying capacity can be represented as K.
The availability of limited resources cannot show exponential growth. As a result to which the graph will have a lag phase, followed by an exponential phase, then a declining phase and ultimately an asymptote. This is referred to as Verhulst-Pearl Logistic Growth and is represented using the equation:
dN/dt = rN((K-N) /K)
Population Pyramids
There are three types of population pyramids:
Expansive Pyramid
It is triangular in shape wherein each age bracket displays a bar shorter than the one preceding it, symbolising that more people die as we progress through the pyramid. A large base shows a high birth rate. The top of the graph shows a lesser life expectancy of a particular region.
Constrictive Pyramid
With a small reduction within the younger group, it's the opposite of the expansive pyramid. This shows that due to good living conditions, life expectancy is on the higher side indicating a high number of older citizens. Despite this, a decrease in population is seen thanks to fewer birth rates compared to the death rate.
Stable Pyramid
It is rectangular in shape indicating an equal distribution of individuals across all age groups. A slight tapering at the highest denotes more death occurring among the older people, which is natural. A stable birth rate indicates the utilization of contraception measures.
FAQs on Population Growth Overview and Basic Concepts
1. What is population growth in biology?
Population growth in biology is the increase in the number of individuals of a species in a given area over a specific period of time. It occurs when the number of births and immigration exceeds the number of deaths and emigration.
- It is measured as change in population size over time.
- It can be positive (increasing), negative (decreasing), or zero (stable).
- It is a key concept in population ecology and environmental biology.
2. What are the main factors that affect population growth?
The main factors that affect population growth are birth rate, death rate, immigration, and emigration. These factors determine whether a population increases or decreases in size.
- Birth rate (natality) – number of new individuals born.
- Death rate (mortality) – number of individuals that die.
- Immigration – individuals entering a population.
- Emigration – individuals leaving a population.
3. What is the difference between exponential and logistic population growth?
The difference between exponential and logistic population growth is that exponential growth occurs without resource limits, while logistic growth occurs when resources are limited.
- Exponential growth: Population increases rapidly in a J-shaped curve under ideal conditions with unlimited resources.
- Logistic growth: Population growth slows as it approaches the carrying capacity, forming an S-shaped (sigmoid) curve.
4. What is carrying capacity in population growth?
Carrying capacity is the maximum number of individuals an environment can support sustainably. It depends on the availability of food, water, shelter, and other resources.
- Represented by the symbol K in logistic growth models.
- When population size reaches carrying capacity, growth rate slows down.
- If the population exceeds carrying capacity, resources become scarce and the population may decline.
5. How is population growth rate calculated?
Population growth rate is calculated by subtracting deaths from births and adding immigration, then subtracting emigration. The basic formula is:
- Growth rate = (Births + Immigration) − (Deaths + Emigration)
6. Why is population growth important in ecology?
Population growth is important in ecology because it determines species survival, resource use, and ecosystem balance. Changes in population size affect:
- Food chains and trophic interactions.
- Competition for limited resources.
- Predator–prey relationships.
- Biodiversity and ecosystem stability.
7. What are density-dependent and density-independent factors?
Density-dependent factors are factors that affect population growth more strongly as population density increases, while density-independent factors affect populations regardless of their density.
- Density-dependent factors: competition, disease, predation, parasitism.
- Density-independent factors: natural disasters, floods, droughts, extreme temperatures.
8. What is meant by population doubling time?
Population doubling time is the time required for a population to double in size. It depends on the growth rate of the population.
- Short doubling time indicates rapid growth.
- It is commonly used in studies of human population growth and microorganisms.
- Higher growth rates result in shorter doubling times.
9. Can you give an example of exponential population growth?
An example of exponential population growth is bacteria multiplying in a nutrient-rich culture under ideal laboratory conditions. In such conditions:
- Resources are abundant.
- There is little competition.
- The population doubles at regular intervals.
10. What are the types of population growth patterns?
The two main types of population growth patterns are exponential growth and logistic growth.
- Exponential growth – rapid increase under unlimited resources (J-shaped curve).
- Logistic growth – growth slows as population reaches carrying capacity (K) (S-shaped curve).
