Key Factors Affecting Population Growth
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 Introduction to Population Growth
1. What is population growth and why is its study important?
Population growth refers to the increase in the number of individuals of a particular species residing in a specific geographical area over a period of time. It is a fundamental concept in ecology because it helps us understand how populations interact with their environment, manage resources, and predict future demographic trends. The study of population growth is crucial for resource management, urban planning, and conservation efforts.
2. What are the four primary factors that cause a population's size to change?
The size of a population is primarily influenced by four main factors:
- Natality: The birth rate, or the number of individuals born into the population over a specific period.
- Mortality: The death rate, or the number of individuals that die within the population over a specific period.
- Immigration: The influx of individuals into a population from another area.
- Emigration: The movement of individuals out of a population to another location.
3. What is the difference between exponential and logistic population growth models?
Exponential and logistic models describe two different patterns of population growth. Exponential growth (J-shaped curve) occurs when a population has unlimited resources and experiences a rapid, unchecked increase in size. In contrast, logistic growth (S-shaped or sigmoid curve) is more realistic, showing that a population's growth slows down and eventually stabilises as it approaches the environment's carrying capacity due to limited resources. You can learn more about these growth patterns in this detailed explanation of Population Growth.
4. What does 'carrying capacity' (K) signify in the context of population ecology?
Carrying capacity, represented by the variable 'K', is a critical concept in population ecology. It defines the maximum population size of a species that an environment can sustainably support over the long term without degrading the habitat. Once a population reaches its carrying capacity, its growth rate typically levels off to zero as factors like resource scarcity, competition, and predation increase. For more details, you can explore the concept of Carrying Capacity.
5. How does the intrinsic rate of natural increase ('r') help in understanding population dynamics?
The intrinsic rate of natural increase ('r') is a measure of a population's potential for growth under ideal conditions with unlimited resources. It is calculated as the difference between the per capita birth rate and the per capita death rate (r = b - d). A positive 'r' value indicates a growing population, a negative value indicates a declining one, and an 'r' of zero signifies a stable population. It is a key parameter in the exponential growth equation and helps ecologists assess a species' reproductive potential.
6. Why do most natural populations exhibit logistic growth instead of sustained exponential growth?
While populations may show short bursts of exponential growth, it is rarely sustained in nature because resources are always finite. As a population grows, it encounters environmental resistance, which includes limiting factors such as:
- Increased competition for food, water, and space.
- Higher rates of predation.
- Faster spread of diseases and parasites.
These density-dependent factors slow down the growth rate, causing the population to follow a logistic (S-shaped) curve and stabilise around the carrying capacity (K).
7. What are population pyramids and what do they reveal about a nation's growth?
A population pyramid is a graphical illustration that shows the distribution of various age groups in a population, typically forming the shape of a pyramid. These pyramids reveal a country's demographic trends:
- Expansive Pyramid: A broad base indicates a high birth rate and a young, rapidly growing population.
- Constrictive Pyramid: A narrow base suggests a lower birth rate and a shrinking population.
- Stationary Pyramid: A rectangular shape indicates a stable population with low birth and death rates.
Vedantu offers a complete guide on the Population Pyramid and its types.
8. How can population growth be represented mathematically?
Population growth is often represented by a simple equation: Nt+1 = Nt + [(B + I) - (D + E)]. In this formula:
- Nt+1 is the population size at time t+1.
- Nt is the initial population size at time t.
- B is the number of births (natality).
- I is the number of immigrants.
- D is the number of deaths (mortality).
- E is the number of emigrants.
This equation shows that population density changes based on additions (births and immigration) and removals (deaths and emigration).
