Population is the total number of inhabitants that live in a specific area, such as the country or the entire world. The population structure or the number of inhabitants counted in a population is being constantly changed by increases from births and immigrations, and losses from deaths and emigrations. The size of human populations, such is the case with any biological population, is limited by environmental factors such as the available food supply, sickness and disease.
Furthermore, human populations are especially affected by social customs regarding reproduction and innovations in technology. The latter is specifically observable in the fields of medicine and public health practices, both of which have contributed greatly to the decrease in mortality and the extension of the average life-span.
Population and its various elements such as size, composition, and rate of change all play significant roles in human society. These effects of these factors are palpable in economy, culture, language, family structure, education, health, and even crime patterns. Nearly all areas of human society are affected by the trends and developments in population.
Population demographics allow us to effectively understand a population’s size, status, and behaviour. Populations are examined according to how the individuals of the population interact with each other, and how the population interacts with its environment. In order to study populations, population ecologists have developed demographic parameters. These are statistical measures used to describe a given population.
Demography, the study of the characteristics of populations, gives us a mathematical description of how the different characteristics of a population changes over time. Any statistical factor that has an effect on population growth or decline is included in demographics. However, certain parameters are specifically essential to demographics. These are population size, population density, fertility, mortality, sex ratio, and age structure.
Population size is the number of individuals within a population. It is the most fundamental demographic parameter. Alternatively, population size is also defined to be the number of individuals that can be found in a subjectively designated geographic range.
Counting all the individuals living in an area through a census may seem like a simple task, but in reality tracking all the members of a population is close to impossible. Instead, ecologists estimate the size of a population by counting the number of individuals within a small sample area and extrapolating an estimate to be applied to the larger population. Despite the challenges associated with taking account of all members of a population, population size remains to be a very important element of a population, as it has significant implications on the dynamics of the whole population.
Population density is the size of a population in relation to the area it occupies. The description of the size of a population is completed by its population density. The density of a population is often expressed as the number of individuals per unit of area. Similar to all other characteristics of a population, population density is dynamic. Over time, this number changes as individuals are either added or subtracted from a population. Factors such as birth and immigration can lead to an increase in a population’s density. On the other hand, death and emigration have the potential to decrease it.
Fecundity is a person’s biological potential for reproduction. On the other hand, fertility is the level of reproduction that is actually achieved by an individual. In general, human fertility is limited by factors such as culture, custom, circumstance, and personal choice. This makes fertility significantly lower than fecundity.
Various intervening factors contribute to the difference between fecundity and fertility. These include: (1) women don’t usually reproduce as soon as they hit puberty, (2) not all women who can reproduce actually do so, (3) not all widows remarry, (4) many elements of social behaviour put a restriction on fertility, and (5) human couples often choose to not reproduce through abstinence, contraception, abortion, or sterilisation.
Mortality, simply put, is the death of human individuals. In a population, mortality represents loss. The science of demography recognises that although mortality in a population is made up of unpredictable events, there is still a statistical regularity when observed across a large group. A statistical tool known as the life table or mortality table shows how the longevity of members of a population is spread out throughout a period of years.
The life table can be used to effectively compare overall human mortality levels by measuring the life expectancy at birth. This is the number of years a newborn baby is expected to live based on the current mortality rates of people of all ages. In populations before the modern age, life expectancy was as short as 25-30 years of age. This was largely due to the poor conditions of sanitation and health care during those times. It is estimated that during those times, death tolls were highest during infancy and childhood. In the premodern age, 20 percent of newborns are thought to have died within their first year of life, and 30 percent of children were said to have died before they turned five.
At present, life expectancies have extended way beyond those observed before modern time. In the 1980s, life expectancy in developing countries rose to 55-60 years. Meanwhile, developed countries in western Europe and North America reached as high as 75 years. Additionally, less than 1 percent of newborn children died within their first 12 months after being born.
The life expectancy of females typically surpasses that of males, although it is not fully understood why this is so. As overall life expectancies have grown throughout the centuries, so did the female advantage. In industrial market economies such as western Europe, North America, Japan, Australia, and New Zealand, this advantage was measured to be seven years in the late 20th century. In the nonmarket economies of eastern Europe, it was a bit higher at eight years.
Second to age, sex is also an important characteristic of the composition of a population. Typically, there are slightly more males born than females, with a ratio of 105 or 106 males to every 100 females. On the contrary, due to biological differences, males are more prone to mortality at practically any age after birth. However, for some countries the reverse is true. In India for example, females have higher mortality during childhood and the ages of childbearing. This is due to the unequal provision of resources within the family during childhood and poor maternal health care in adulthood.
Taking these generalities into consideration, with more males being born but females experiencing lower mortality rates, the number of males and females eventually become equal at some point. However in later ages, females dominate the number of males in terms of number.
Age distribution is possibly the most essential characteristic of a population. Demographers, people who study populations, often represent both the age and sex distributions of a population using population pyramids. These are graphs or bar charts where the number or percentage of individuals in an age group are each represented by the length of a horizontal bar. Each bar is then partitioned according to the numbers of males and females. Most populations have a greater number of young persons at the base of the chart and taper off when approaching the older ages. The graph, as the name suggests, then follows a pyramid shape. Alternatively, older populations have a more uniform age distribution and do not follow a triangular outline.
The fertility rate is the factor most in charge of changing the age distribution of a population. In effect, it is also responsible for changing the shape of the population pyramid. Mortality rates, whether rising or declining, have a general effect on all age groups. Therefore it does little to change the proportions of the age distribution. However a rise or decline in fertility immediately affects a single age group, changing the number of people who are newly born. The influence of a rise or decline in fertility rates is then focused towards the bottom of an age distribution, and can inadvertently change the whole profile of the age distribution.
Developing countries typically have youthful age structures alluding to populations high in fertility. Meanwhile, the low fertility populations of developed and industrialised countries account for their older age structures.
A population pyramid is a graphic visualisation of age and sex as variables of a population. A population pyramid is a graph that is split down the middle, with the male members of the population on one side and the females on the other side. In addition to this, it depicts the age distribution of a population, starting from the youngest at the bottom to the oldest at the top of the pyramid.
Despite what the name suggests, population pyramids are not actually always pyramid-shaped. However, in the case of a growing population, the number of babies being born are greater than the number of people dying, hence the population pyramid appears to follow the shape of a triangle.
Population pyramids graph the size of the population along the horizontal axis, while age is depicted on the vertical axis. This organises the given population data in rows of bars stacked atop one another, with each bar representing a specific age range. Usually, each bar is composed of five year age groups. The youngest age group can be found at the bottom of the population pyramid, while the oldest age group is found at the top.
When used for the comparison of two or more populations, population pyramids must be drawn to the same scale and depict the same age categories.
Interpreting Population Pyramids
Population pyramids may be used to draw comparisons between the male and female populations in a certain area. They may also be used to determine the number of dependents–children and elderly people–and the general structure of the population at a specific moment.
The shape of a population pyramid is influenced by three main trends found in a population. The first trend is characterised by the coincidence of high fertility and high mortality rates among more youthful members of the population. This is known as an expansive population, and creates a population pyramid shaped like a sharp triangle. Populations that follow this shape have many young people and do not experience much numerical increase.
The second is when a population’s mortality rate is decreasing, while its fertility rate stays constant. This trend, known as a constrictive population, is represented by population pyramids that are wider at the middle. This is due to the higher middle-aged and elderly population and fewer youth in the population.
The third trend is known as a stationary population. Populations that fall under this type have the combination of low mortality and low fertility rates. Stationary populations appear to be shaped like squares or pillars rather than triangles or pyramids. Population pyramids that belong to the third type belong to stable populations that are resistant to any abrupt changes to either fertility or mortality rates.
The use of population pyramids prove to be especially useful in the prediction of the future of a region and the study of both current and historical trends in population. Population pyramids can also be used to visualize how future populations will be affected by sudden changes. Some events that lead to such sudden changes include deaths resulting from armed conflict, high mortality of women during childbirth, and the migration of young workers out of less prosperous regions. Population pyramids may also be utilized to aid both the public and private sectors in distributing services in a region based on the needs of a population.
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