Human Population

Population: Population is defined as the total number of individual of a species present in a particular area at a given time.

Demography: The study of population is known as demography. It mainly deal with the change in population, composition & distribution of population.

Population Census: It is the total process of collecting, compiling, publishing demographic, economic & social data pertaining to specific time to all person in a country. People census is conducted every 10 years.

Demographic cycle: The demographic cycle as population cycle or Demographic transition model (DTM) refers to the evolution overtime of the population with respect to country, region or other geographical area. Four stage of population changes have been identified in the demographic cycle by American demographer Warren Thompson in 1929.

1. The first high stationary phase marked by high birth & high death rates & relatively low population.
2. The second phase with uneven population density due to increased urbanization & industrialization i.e early expanding.
3. The third phase where the birth & death rates are much lower resulting in a relatively steady population growth & death rate (late expanding).
4. The fourth phase of population cycle is characterized be an actual decline in the population of a country due to an excess death over births (low stationary).

So, these are the factors which are responsible for the change in population. Thus population begins to decline birth rate is lower than death rate.

Characteristics features of the Population

Population density: The population density denotes the individual per unit area or volume at a given time & space.
D = N / S
(N = no. of total individual)
S = space occupied by them
D = Density

Natality: The rate of births per unit time. It is denoted as the number of birth per 1,000 individuals in the population year.

Mortality: The rate of death per unit time. It depends upon environmental quality, disease etc. It is the number of death per one thousand per year.

Vital Index = It is the percentage of natality over mortality.
V = N / M × 100
N = natality, M = mortality

Immigration: The arrival of individual into a population for permanent settlement. It leads to increase the density of population.

Emigration: is the act of leaving a resident country or place of residence with the intent to settle elsewhere (to permanently leave the country). It leads to decrease in population.

Sex ratio: Sex ratio is the ratio between male & females in a given population.

Crude Population density: It is a measure of the average number of people per unit area (usually per sq. km).

Population explosion: The rapid & unplanned growth in number of population is named as population explosion.

Age ratio: The ratio amongst the pre-reproductive (below 18 yrs), reproductive (19 yrs) & post reproductive (60 yrs onwards) age group in a particular population group in a given time.

Maximum Carrying Capacity: The capacity of an area or particular habitat that can support the maximum number of species through out the reasons. It is indicated by the letter 'K'.

Biotic Potential (Reproductive Potential): It is the physiological capacity of the organism to produce offspring. It is influenced by environmental factors such as availability of food, premature death due to infections diseases.

Population Growth:

The growth rate of any population of a paticular or place can be estimated on the basis of the count of decrease, increase or remaining constant no at a given time.

PGR = [B - D + (I - E)] / P × k

Where,
PGR = Poplⁿ growth rate
B = No. of Birth
D = No. of Death
I = No. of immigrants
E = No. of emigrants
P = mid-year total Poplⁿ

Population Growth Curve:

When the number of organism in a population is plotted against the time, it produce the population growth curve. The growth curve are of two types.

• i) 'J' - shaped curve (exponential growth curve)
• ii) 'S' - shaped curve (logistic growth / sigmoid curve)

i) Exponential growth curve

In the curve, the population increases, slowly & gradually as the animals are few in number (lag phase) but the resources are unlimited so after getting adjusted with the nature the population increases rapidly in geometrical rate. The growth curve takes the shape of the letter 'J'. So the maximal growth rate for a given population is called biotic potential. Ex. Growth of human population. Bacteria growth in a culture.

ii) Logistic Growth ('S' - shaped curve)

This is common type of curve seen in most of species if the species are introduced into a new habitat or new environment. In the begining they grow & reproduce rapidly but ultimately population slows do gradully.

As the resources availability becomes limiting at certain point of time so on population can continue to grow exponentially. In nature in a given habitat there are enough resources to support a particular maximum number of individual - beyond which no further increase in population size is possible. This limit is called carrying capacity.

The population growth in a logistic fashion assumes a sigmoid curve when N is plotted in relation to time such a growth is also called Verhulst - Pearl logistic growth.

dN / dt = rN [(K - N) / K]

N = Population density with time
r = intrinsic rate of natural

The logistic growth model is more realistic because no population can sustain exponential growth indefinitely as there will competition for basic needs.

This curve is divided into 3 types.

• (i) Early or lag phase: It is slowly growing phase. There is no growth or little growth in population.
• (ii) Middle or log or exponential phase: In the beginning the growth is slow but soon It becomes fast & reproduce & grows rapidly so the growth line rises straight in upward direction.
• (iii) Stationary phase: This is the last phase in which the growth remains constant i.e there is no further increase due to equalization of birth rate & death rate. Ex yeast cell.

Malthus theory of human population growth

Thomas Robert Malthus a british economic proposed a theory of human population growth which is popularly called as 'Malthus theory'. This theory is based on following facts:-

1. Unchecked population grows geometricaly whereas the means of supporting life like food grows arithmeticaly.
2. The rapid growth of population creates imbalance with the environment.
3. The imbalances at higher degree causes malnutrition hunger spread of disease, war which ultimately reduce.