Population Growth: Definition, Meaning Characteristics, Classification, Types, Examples
Population growth is the increase in the number of individuals in a population over time. It is influenced by births, deaths, immigration, and emigration, and can follow exponential or logistic models. Understanding population dynamics is crucial for ecology, resource management, and NEET Biology.
This Story also Contains
- What is Population Growth?
- Types of Population Growth
- Factors Affecting Population Growth
- Population Growth Models
- Human Population Growth
- Consequences of Rapid Population Growth
- Additional Factors in Population Fluctuation
- Ecology NEET MCQs (With Answers & Explanations)
- The Recommended Video On Population Growth:
What is Population Growth?
Population growth refers to a change in population size over a given period. It is usually measured by births, natality, deaths, mortality, immigration, and emigration. It is expressed as a percentage or rate of change to the original population size.
Importance of Understanding Population Dynamics
The importance of studying population dynamics is manifold. This study in ecology affects several areas within ecosystems, such as the interaction with other species or competition for the same food.
Resource Management: Understanding the growth rates helps in the management of the available natural resources of food, water, and energy in a sustainable manner.
Public Health: Population dynamics can affect health care demand, the spread of diseases, and the deliberate set-up of health care infrastructural setup.
Social and Economic Planning: These demographic trends bear on employment, education, housing, and other social services.
Environmental Sustainability: Growth affects environmental degradation, and the loss of biodiversity, and mitigates climate change.
Types of Population Growth
The increase in population can be divided into several types, all having different patterns and characteristics. This paper considers two main models: exponential growth and logistic growth.
Exponential Growth
Exponential growth describes the increase of population where the growth rate remains constant per unit of time, which leads to a continually increasing rate of growth. In such an increase, it is assumed that the conditions are perfect, resources are limitless, and there are no factors that stop the population from growing.
The growth rate is proportional to the size of the population.
There are no considerations for environmental resistance factors or limiting factors.
Common in introduced species or under controlled conditions.
Logistic Growth
The population increases exponentially at first, then slows down and levels off at its carrying capacity due to the limiting factors in the environment. The carrying capacity is the highest number of a population an environment can support indefinitely.
Carrying capacity is the highest number of organisms of a given species that an ecosystem can continuously support. It's usually determined by factors like the availability of food, space, and environmental conditions.
The growth rate slows down as the population approaches carrying capacity.
It emulates real-world scenarios where there is a limit to the resources.
It is important to understand sustainable population management and conservation efforts.
Factors Affecting Population Growth
Some of the important forces behind population growth include birth rate, death rate, immigration, and emigration.
Natality (Birth Rate)
Natality refers to the number of births in a population in one year, generally expressed as births per 1,000 persons per year. Factors that affect birth rate:
Fertility Rate: Number of children born per child-bearing-age woman.
Age Structure: Proportion of the population in childbearing age groups.
Socioeconomic Factors: Availability of health care, education, and economic opportunities.
Mortality (Death Rate)
Mortality is the number of deaths in a population over some time, usually given as deaths per 1,000 persons per year. Factors that influence the death rate:
Access to Health Care: Availability and quality of medical care.
Nutrition and Sanitation: Good nutrition and clean water keep mortality rates low.
Diseases and Epidemics: The rate of mortality is affected by outbreaks of certain diseases.
Environmental Conditions: Climate, pollution, natural disasters.
Immigration
Immigration refers to the process of movement of persons or populations to a new habitat or country from their original habitat or country. Effects on population growth:
Immigration caused a direct increase in the total population size of the receiving area/country.
They bring genetic diversity that has the potential to enrich the gene pool of the population in which they settle.
Genetic diversity is good for the long-term viability, adaptability, and resilience of a population faced with changes and challenges in their environment.
Immigration can bring about immense economic and cultural impacts locally:
Some of the immigrants help to join the workforce, filling the labour gaps mostly in sectors that have a deficit of labour.
Others open new businesses, hence creating jobs, and thereby increasing economic growth through consumption and taxing.
Immigrants introduce cultural diversity: new ways of living, traditions, languages, etc. into the host population.
Cultural diversity is a remover of society but also can be the cause of social crises if integration policy is not arranged accordingly.
Amongst these, the integration process will include social and political processes to integrate immigrants into the population.
Successful integration requires effort in education, learning of the language, job creation opportunities, and social cohesion measures that may enable mutual understanding and respect.
Emigration
Emigration is the process by which individuals or populations move out from their current habitat or country into another area or country. Effects on the growth of population:
Emigration reduces the population size of the source area or country.
Emigration can result in skilled labour being lost from the source population, particularly in the case when highly skilled persons emigrate.
Such emigration brings about loss to the sectors related to economic activity that rely on specialised skills and knowledge; this may have a bearing on economic growth and development.
Out-migration of people, particularly skilled labour, can affect economic stability in the sending region.
This might cause labour shortages, and lower productivity in specific industries and hence may affect the local employment and wage rates.
Emigration changes the demographic structure in both sending and receiving regions:
The out-migration of people, particularly young adults or the working-age population, may alter population age structure and dependency ratios.
Commonly Asked Questions
Intraspecific competition occurs between individuals of the same species competing for limited resources. As population density increases, this competition intensifies, leading to reduced survival, reproduction, or growth rates. This self-regulating mechanism helps prevent populations from exceeding their environment's carrying capacity.
Life history traits, such as age at first reproduction, number of offspring, and lifespan, significantly impact population growth. Species with early maturation, large litter sizes, and short lifespans tend to have higher growth rates. Understanding these traits helps predict how populations might respond to environmental changes or management strategies.
Environmental stochasticity refers to random fluctuations in environmental conditions that affect population growth. These unpredictable changes can cause variations in birth rates, death rates, or carrying capacity. Understanding stochasticity is crucial for developing realistic population models and assessing extinction risks, especially for small populations.
Genetic diversity within a population provides the raw material for adaptation to changing environments. Populations with higher genetic diversity are more likely to contain individuals with traits that may be advantageous under new conditions. This can affect long-term population growth and survival, especially in the face of environmental changes or new selective pressures.
Source-sink dynamics describe a situation where some habitats (sources) produce an excess of individuals that migrate to less favorable habitats (sinks). In sink habitats, death rates exceed birth rates, and the population would decline without immigration. This concept is important for understanding metapopulation dynamics and habitat connectivity.
Population Growth Models
Population growth models provide frameworks to understand how populations change over time. Here, we explore two primary models: exponential growth and logistic growth.
Exponential Growth Model (Applications, Examples)
Exponential growth in a population occurs when the population has a constant rate of change per unit of time, and this would therefore be accelerating. It assumes perfect conditions in which resources are unlimited and nothing hinders population growth.
In many natural and human phenomena, the increase is exponential. For example:
Growth of bacteria in a very hospitable laboratory setting.
Invasive species populations in ecosystems without their predators.
Human population growth during the ages of industrialisation and medicine.
Logistic Growth Model (Applications, Examples)
Logistic growth most accurately defines a way that populations increase exponentially at first, due to environmental factors, then slow down and stabilise around a carrying capacity, K.
Logistic growth applies to humans in many ways:
Urban population growth is restricted by housing availability and other urban infrastructure.
Agricultural populations are limited by arable land and water resources.
Wildlife populations are in areas under conservation where habitat space is limited and food is finite.
Commonly Asked Questions
Exponential growth occurs when a population increases at a constant rate, resulting in a J-shaped curve. Logistic growth, on the other hand, starts exponentially but slows down as the population approaches carrying capacity, forming an S-shaped curve. Logistic growth is more realistic in natural populations due to environmental limitations.
The intrinsic growth rate (r) represents the maximum growth rate a population can achieve under ideal conditions, without resource limitations. It's a theoretical concept that helps ecologists understand a species' potential for growth and compare growth rates between different species or populations.
A population projection matrix is a mathematical tool used to predict future population size and structure based on current demographic data. It incorporates age-specific survival and fertility rates to model how a population will change over time. This tool is valuable for conservation planning and resource management.
The r/K selection theory describes two contrasting reproductive strategies. r-selected species produce many offspring with little parental care, favoring rapid population growth in unstable environments. K-selected species have fewer offspring but invest more in parental care, adapting to stable environments near carrying capacity. This theory helps explain different growth patterns observed in nature.
The Allee effect is a phenomenon where population growth rate decreases at low population densities. This can occur due to difficulties in finding mates, reduced defense against predators, or inefficient resource utilization. The Allee effect can make small populations vulnerable to extinction, highlighting the importance of population size in conservation efforts.
Human Population Growth
The human population growth has varied across time. In ancient times, it was slow but after the Industrial Revolution, better resources led to rapid growth.
Historical Trends (Agriculture, Industrial Revolution)
Human population growth has varied drastically across history. For most of human history, population growth was very slow due to high mortality and limited resources. The discovery of agriculture about 10,000 years ago provided a more stable food supply that gradually increased population growth. It was the Industrial Revolution in the 18th century that envisioned, with advances in medicine, sanitation, and technology, a much further increase in growth.
Present-Day Differences (Developed vs Developing Countries)
The global population is still rising today, although at varying rates across different regions. High growth rates characterise developing countries, most of which are in Africa and parts of Asia. This is occasioned by a higher total fertility rate and better healthcare in those regions. Most of the developed countries have low or even negative growth rates characterised by ageing populations and a lower birth rate. This has led greatly to divergent growth of global resources and the environment.
While highly increasing populations in certain parts of the globe can be accompanied by overexploitation of resources, environmental degradation, and rising carbon emissions, the counterpart is economic stagnation and a lack of able-bodied workforce in those countries with falling populations. The proper management of these trends is indispensable for sustainable development and world stability.
Commonly Asked Questions
Demographic transition is a model describing the shift from high birth and death rates to low birth and death rates as a country develops. It typically involves four stages, with population growth rate peaking in stage 2 and stabilizing in stage 4. This concept is crucial for understanding global human population trends and their socioeconomic implications.
Population momentum refers to the tendency for a population to continue growing even after reaching replacement-level fertility, due to its age structure. This concept is particularly important in human demographics, explaining why populations can continue to grow despite declining birth rates. It highlights the long-term effects of past growth on future population trends.
Life tables are tools that summarize age-specific survival and fertility rates within a population. They provide crucial information for calculating key demographic parameters like life expectancy and net reproductive rate. Life tables help ecologists understand population structure, predict future growth, and compare life history strategies between species or populations.
Compensatory mortality occurs when death rates at one life stage are offset by increased survival at another stage. This mechanism can help regulate population size by preventing excessive growth. Understanding compensatory mortality is important for wildlife management, as it affects how populations respond to harvesting or other human interventions.
Population synchrony refers to the tendency of geographically separated populations to fluctuate in unison. This can be caused by factors like dispersal, shared environmental conditions, or predator-prey interactions. Understanding synchrony is important for predicting large-scale population trends and managing interconnected populations across landscapes.
Consequences of Rapid Population Growth
Rapid growth in population causes exploitation of natural resources. It causes problems like unemployment, poverty, and inadequate facilities. It also increases environmental issues like global warming and puts pressure on infrastructure, and food security.
Resource Scarcity and Overuse
The effect of rapid population growth may therefore be that the pressure on basic resources such as food, water, and energy will rise. Such increased demand may result in the shortage of these natural resources or over-extract them, thereby putting additional pressure on already prevalent food insecurity, water scarcity, and energy crises.
Environmental Degradation
Combined with population growth, the degradation of the environment becomes more marked. Deforestation accelerates to accommodate further agriculture as well as the expansion of the cities. Pollution from industries increases, household pollution goes up, and so does the loss of habitat that puts biodiversity under threat, leading to an upset in ecological balance.
Pressure on Social Infrastructure
Faster population growth is bound to exert greater pressure on the social infrastructure, such that cities are congested and healthcare and educational institutions become overstretched. Inadequate public services reduced quality of life, and problems in resource and opportunity distribution will be the emanations from this strain.
Additional Factors in Population Fluctuation
The population density at a given time ( t ) can be calculated using the formula:
Pt = P0 + (N+I) − (M+E)
Where:
Pt is the population density at time ( t )
P0 is the initial population density.
N is the number of births (natality).
I is the number of immigrants.
M is the number of deaths (mortality).
E is the number of emigrants.
This is a formula that involves the dynamism of population change over time and, therefore, can consider all major factors contributing to increases and decreases in population. It can be applied in any sphere that requires population fortunes to be predicted or managed in areas such as ecology, demography, and urban planning.
Ecology NEET MCQs (With Answers & Explanations)
Important topics from the chapter for NEET preparation:
Population Interactions e.g., mutualism, predation, competition, parasitism, and commensalism.
Population Attributes such as population size, density, age distribution, birth rate, and mortality rate
Population Growth Models
Practice Questions for NEET
Q1. There are certain variables that limit the population's natural growth rate. As a result of these
Population growth control
Environmental resistance
Natural resistance of healthy population
None of the above
Correct answer: 2) Environmental resistance
Explanation:
Environmental resistance is a factor that works to prevent population increase from reaching its maximum potential.
Population control may entail culling, transfer, or alteration of reproductive potential. Environmental variables like as food supply and predation may limit population expansion.
Natural resistance to infection, which does not rely on medicines, is a potent defence system shared by all humans and has historically been crucial in ensuring the survival of our species for many millennia.
Hence, the correct answer is option 2) Environmental resistance.
Q2. Which of the following factors influences population density in normal circumstances?
Pyramid
Immigration
Deaths
Emigration
Correct answer: 3) Deaths
Explanation:
Under normal circumstances, the death rate—or the number of deaths in a given location at a given time—influences the population density (mortality). It is the total number of fatalities in a population at a particular time.
Births and deaths impact population density under normal circumstances, with the other two components only being present in certain circumstances. The population pyramid shows how the population is divided into different age groups and genders at any given period. Populations grow as a result of births and immigration. Individuals are lost due to death and emigration. These elements work together to influence how quickly a population expands.
Hence, the correct answer is option 3) Deaths.
Q3. Which letter represents the birth rate (Natality)?
B
E
I
K
Correct answer: 1) B
Explanation:
According to the theory of population ecology, natality is the ratio of births to the total population size for a particular population. Another name for natality is the birth rate. Because it increases the number of people in a population, it has a favorable impact on population density. The letter 'B' represents natality (birth rate). It is the number of people born in a population at a certain point in time. It is defined for humans as the number of persons born per 1000 of the population every year.
Hence the correct answer is option 1) B.
Also Read:
The Recommended Video On Population Growth:
Frequently Asked Questions (FAQs)
Population genetics studies how genetic variation within populations changes over time. It's crucial for understanding evolutionary processes that affect long-term population growth, such as adaptation to changing environments or the effects of inbreeding in small populations. This field provides insights into the genetic health and future viability of populations.
Trophic cascades occur when changes in the abundance of one trophic level affect population sizes at other levels. For example, removing top predators can lead to increases in herbivore populations and subsequent decreases in plant populations. Understanding trophic cascades is essential for predicting how changes in one species can ripple through an ecosystem, affecting multiple populations.
The rescue effect occurs when immigration from high-quality habitats (sources) prevents local extinction in low-quality habitats (sinks). This process can maintain populations in unfavorable areas and increase overall metapopulation stability. Understanding the rescue effect is important for managing fragmented landscapes and designing effective conservation strategies.
Niche construction theory proposes that organisms can modify their environment, creating new selective pressures that influence their own and other species' evolution. This process can affect population growth by altering resource availability or environmental conditions. Understanding niche construction helps explain how species can shape their own evolutionary trajectories and those of other species in their community.
Ecological stoichiometry examines how the balance of chemical elements affects ecological processes. Mismatches between the elemental composition of consumers and their resources can limit population growth and influence nutrient cycling in ecosystems. Understanding stoichiometric constraints helps explain patterns of population growth and ecosystem functioning.
Eco-evolutionary dynamics describe the interplay between ecological and evolutionary processes occurring on similar timescales. Rapid evolution can influence population dynamics, while changes in population size can drive evolution. Understanding these dynamics is crucial for predicting how populations will respond to environmental changes and management interventions over both short and long time scales.
Phenotypic plasticity is the ability of an organism to change its phenotype in response to environmental conditions. It allows populations to adapt quickly to new or changing environments without genetic changes. This flexibility can influence population growth and persistence, especially in variable or rapidly changing environments.
Population connectivity refers to the movement of individuals or genes between populations. It's crucial for maintaining genetic diversity, facilitating recolonization of empty habitats, and enhancing population resilience. Understanding and preserving connectivity is essential for effective conservation, especially in fragmented landscapes or for species with limited dispersal abilities.
Predator-prey relationships can lead to coupled oscillations in population sizes. As prey populations increase, predator populations follow, leading to increased predation and subsequent decline in prey numbers. This, in turn, causes predator populations to decrease. These dynamics can result in cyclical patterns of growth and decline in both populations.
Parasites and diseases can significantly impact population growth by increasing mortality rates or reducing reproductive success. Their effects are often density-dependent, becoming more pronounced as population density increases. This can lead to cyclical patterns in population size or help regulate populations near carrying capacity.