FACTORS AFFECT POPULATION SIZE AND GROWTH

 FACTORS AFFECT POPULATION SIZE AND GROWTH

Population Size

The number of individuals in the population

 

Population Growth

How the size of the population is changing over time

 

Population Growth

What does population growth mean?

You can probably guess that it means the number of individuals in a population is increasing. The population growth rate tells you how quickly a population is increasing or decreasing.

Population growth is the increase in the number of individuals in a population.

Global human population growth amounts to around 83 million annually, or 1.1% per year. The global population has grown from 1 billion in 1800 to 7.9 billion in 2020. The UN projected population to keep growing, and estimates have put the total population at 8.6 billion by mid-2030, 9.8 billion by mid-2050 and 11.2 billion by 2100.However, some academics outside the UN have increasingly developed human population models that account for additional downward pressures on population growth; in such a scenario population would peak before 2100.

World human population has been growing since the end of the Black Death, around the year 1350. A mix of technological advancement that improved agricultural productivity and sanitation and medical advancement that reduced mortality have caused an exponential population growth. In some geographies, this has slowed through the process called the demographic transition, where many nations with high standards of living have seen a significant slowing of population growth. This is in direct contrast with less developed contexts, where population growth is still happening.

Population growth alongside overconsumption is a key driver of environmental concerns, such as biodiversity loss and climate change, due to resource-intensive human development that exceed planetary boundaries. International policy focused on mitigating the impact of human population growth is concentrated in the Sustainable Development Goals which seek to improve the standard of living globally while reducing the impact of society on the environment.

Population size is defined as the number of individuals present in a subjectively designated geographic range. Despite the simplicity in its concept, locating all individuals during a census (a full count of every individual) is nearly impossible, so ecologists usually estimate population size by counting individuals within a small sample area and extrapolating that sample to the larger population

 

Carrying Capacity

"The theoretical maximum number of individuals that an environment can support for an indefinite time period is it carrying capacity." (Horfnagels. pg. 792)

 

Per Capita Rates

Per capita rates are calculated as the number of events (births, deaths, or growth) divided by the number of individuals in the population over a specific time period.

 

Population growth can be described with two models, based on the size of the population and necessary resources. These two types of growth are known as exponential growth and logistic growth

Exponential Growth

If a population is given unlimited amounts of resources, such as food and water, land if needed, moisture, oxygen, and other environmental factors, it will grow exponentially. Exponential growth occurs as a population grows larger, dramatically increasing the growth rate. This is shown as a "J-shaped" curve. You can see that the population grows slowly at first, but as time passes, growth occurs more and more rapidly.

Logistic Growth

Usually, populations first grow exponentially while resources are abundant. But as populations increase and resources become less available, rates of growth slow down and slowly level off, reaching the carrying capacity. The carrying capacity is the upper limit to the population size that the environment can support. This type of growth is shown as an "S-shaped" curve below and is called logistic growth.

 

Factors that Affect Population Size

            Population size in an area is influenced by four main factors: birth rate, death rate, immigration and emigration (Migration)

 

•           Birth rate (Natality) - The crude birth rate in a period is the total number of live births per 1,000 population divided by the length of the period in years. The number of live births is normally taken from a universal registration system for births; population counts from a census, and estimation through specialized demographic techniques. This refers to the number of newborns in a region at a given time.

•           Death rate (Mortality) - Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of deaths per 1,000 individuals per year; thus, a mortality rate of 9.5 (out of 1,000) in a population of 1,000 would mean 9.5 deaths per year in that entire population, or 0.95% out of the total. It is distinct from "morbidity", which is either the prevalence or incidence of a disease, and also from the incidence rate (the number of newly appearing cases of the disease per unit of time). This refers to the number of deaths in a region at a given time.

 

First, we will consider the effects of birth and death rates. You can predict the growth rate by using this simple equation: growth rate = birth rate – death rate.

If the birth rate is larger than the death rate, then the population grows. If the death rate is larger than the birth rate, the population size will decrease. If the birth and death rates are equal, then the population size will not change.

 

Effects of Birth and Death Rates

Depending on whether birth rate/ death rate is more, the following trends are observed in a population:

•                     Steady population - The term stable population refers to a population with an unchanging (but possibly nonzero) rate of growth and an unchanging age composition (i.e., the population pyramid does not change in shape) as a result of age-specific birth rates and age-specific death rates that have remained constant for a sufficiently long time.

A stable population may or may not have zero population growth. We can have stable populations that are growing, and we can also have stable populations that are declining. This is when the birth rate is equal to the death rate. There is neither increase/decrease in the population.

•                     Declining population - A population decline (sometimes underpopulation or depopulation) in humans is a reduction in a human population size caused by short term events such as pandemics, wars, famines or other catastrophes, or by long-term demographic trends, as in sub-replacement fertility rate, or persistent emigration. This is when death rate is more than the birth rate.

•                     Growing population - This is when birth rate is more than the death rate.

Migration

Migration is the movement of individual organisms into, or out of, a population. Migration is a way to move from one place to another in order to live and work. Movement of people from their home to another city, state or country for a job, shelter or some other reasons is called migration.

Nowadays, many people decide to migrate to have a better life. Employment opportunities are the most common reason due to which people migrate. Except this, lack of opportunities, better education, construction of dams, globalization, natural disaster (flood and drought) and sometimes crop failure forced villagers to migrate to cities.

 

Migration affects population growth rate. There are two types of migration:

Immigration - is the movement of individuals into a population from other areas. To immigrate is to settle in a country where you were not born. This increases the population size and growth rate.

Emigration - is the movement of individuals out of a population. Emigrate is not an alternative spelling of immigrate. Emigrate means to leave a place, such as a country of origin, to settle in another location. This decreases the population size and growth rate.

 

The earlier growth rate equation can be modified to account for migration: growth rate = (birth rate + immigration rate) – (death rate + emigration rate).

 

FACTORS AFFECT POPULATION GROWTH

Population growth is determined by fertility rates (the number of children per adult) – fatality rates. Birth rates and mortality rates are, in turn, determined by a combination of factors. Often economic growth and economic development have led to a decline in population growth, but there are no hard and fast rules and other factors, such as availability of family planning, social expectations and government intervention can play an important role.

Factors influencing population growth

Economic development.

Countries who are in the early stages of economic development tend to have higher rates of population growth. In agriculturally based societies, children are seen as potential income earners. From an early age, they can help with household tasks and collecting the harvest.

Education.

In developed countries, education is usually compulsory until the age of 16. As education becomes compulsory, children are no longer economic assets – but economic costs. In the US, it is estimated a child can cost approx $230,000 by the time they leave college. Therefore, the cost of bringing up children provides an incentive to reduce family size.

 

Quality of children.

Gary Becker produced a paper in 1973 with H. Gregg Lewis which stated that parents choose the number of children based on a marginal cost and marginal benefit analysis. In developed countries with high rates of return from education, parents have an incentive to have a lower number of children and spend more on their education to give their children not just standard education but a relatively better education than others.

 

Welfare Payments/State Pensions.

A generous state pension scheme means couples don’t need to have children to provide an effective retirement support when they are old. Family sizes in developing countries are higher because children are viewed as ‘insurance’ to look after them in old age. In modern societies, this is not necessary and birth rates fall as a result.

Social and Cultural Factors

India and China (before one family policy) had strong social attachments to having large families. In the developed world, smaller families are the norm.

Availability of Family Planning

Increased availability of contraception can enable women to limit family size closer to the desired level. In the developing world, the availability of contraception is more limited, and this can lead to unplanned pregnancies and more rapid population growth. 

Female Labor Market Participation

In developing economies, female education and social mobility are often lower. In societies where women gain a better education, there is a greater desire to put work over starting a family. 

Death Rates – Level of Medical Provision.

Often death rates are reduced before a slowdown in birth rates, causing a boom in the population size at a certain point in a country’s economic development. In the nineteenth and early twentieth century, there was a rapid improvement in medical treatments which helped to deal with many fatal diseases. 

Immigration Levels

Some countries biggest drivers of population growth come from net migration. In the UK from 2000 to 2013, around 50% of net population growth came from net international migration. Countries like Japan with very strict immigration laws have seen a stagnation in the population.

Historical Factors/War.

In the post-war period, western countries saw a ‘boom’ in population, as couples reunited at the end of the Second World War began having families. The ‘baby-boomer’ period indicates population growth can be influenced by historical events and a combination of factors which caused a delay in having children until the war ended.

Related

• GDP and development
• Harrod-Domar Growth model
• Does GDP measure economic development?
• Causes of economic growth