Introduction.                                                                                                                                                           

History of man is only about 50,000 years old. In the course of human history there have been three major explosions, each corresponding to a major changes in the environment. The first population explosion occurring about 20,000 years ago. It was brought about by the use of tools that allowed improvement in hunting and food gathering methods. The second revolution occurred about 6,000 years ago, and was brought by improvements in farming. The third revolution was brought about 300 years ago and was caused by improvement in food production, industry and medicine. If the present birth rate is maintained, it is stated that only one square feet of the earth surface will be available per one person within the next 700 years.

Definition : The term population refers to the total number of individuals of the same species occupying a particular geographic area at a given time. This definition of population was given by Clark in 1954.

Demography : The scientific study of human population is called demography. It deals with

1. Change in population i.e. growth or decline in population.
2. Composition of population i.e. age groups, sex ratio etc.
3. Distribution of population in space.

Census : Census is an official count of the people of a country, state, or district, with statistics as to age, sex, employment, education, etc. In India census started in 1891, and, since then, it has been conducted uninterruptelly every ten years. Census is conducted as per the provision made under the census Act, 1948, as amended.

 Population Dynamics.                                                                                                                                         

1. Population density : Population density is the number of individuals present per unit area or volume at a given time. For instance, number of animal per square kilometer, number of trees per area in a forest, or number of plank tonic organism per cubic meter of water. If the total number of individuals is represents by letter N and the number of units of space by Letter S, the population density D can be obtained as D=N/S. Space is indicated in two dimensions (m²) for land organisms, and in three dimensions (m³) for aquatic organisms and for the organisms suspended in space.
2. Birth rate or Natality : The birth rate of a population refers to the average number of young ones produced by birth, hatching or germination per unit time (usually per year). In the case of humans, it is commonly expressed as the number of births per 1000 individuals in the population per year.

The maximum birth rate of a species can achieve under ideal environmental conditions is called potential natality. However, the actual birth rate under the existing conditions is much less. It is termed realised natality. Crude birth rate is the number of births per 1000 persons in the middle of a given year i.e. on July. Natality increases the population size (total number of individuals of a population) and population density.

3. Death rate or mortality : The death rate of a population is the average number of individuals that die per unit time (usually per year). In humans it is commonly expressed as the number of death per 1000 persons in a population per year. Lowest death rate for a given species in most favourable conditions is called potential mortality, while the actual death rate being observed in existing conditions is called realized mortality. Crude death rate is the number of deaths per 1000 persons in the middle of a given year i.e. on July. Mortality decreases the population size and population density both.

 

 

 

Difference between Natality rate and Mortality rate

Character

Natality rate

Mortality rate

(1) Definition

Number of births population per year.

per

1,000

individuals

of a

Number of deaths population per year.

per

1,000

individuals

of

a

(2) Population

density

Increases population size and population density.

Decreases population size and population density.

 

4. Vital index : The percentage ratio of natality over mortality is known as vital index i.e. natality / mortality

×100. It determines the growth of a population.

5. Immigration : It is permanent entry of additional person into the existing population of a country or region from out side. Example; Many Nepalese and Chinese come to settle in India.
6. Emigration : It is the permanent departure of some persons from the existing population of a region to a different state or a foreign country. Example; Many Indians go to Western countries to settle there.

Immigration and emigration bring about redistribution of population, and are common in animals. These occur for various reasons, such as search for food, escape from competition due to overcrowding, need of shelter etc.

7. Sex ratio : The number of females in a population per 1000 males is called sex ratio.

Sex ratio = No. of females

1000(males)

8. Age structure : The age structure of a population is the percentage of individual of different ages such as young, adult and old. Age-sex structure of a population can be shown by a pyramid-like diagram by plotting the percentage of population of each sex in each age-group. Figure shows the age-sex structural pyramids for India over the 20-year period from 1971 to 1991. These pyramids show that Indian population may still take many years to be

stabilized.

Age 70+

Females 60-69

 

50-59

 

40-49

 

30-39

 

20-29

 

10-19

 

0-9

 

15   12     9      6      3     0      3       6      9     12   15                      15   12     9      6      3     0      3       6      9     12 15

(A)

Percent of population

(B)

Fig : Comparative age-sex pyramids for India : (A) Year 1971 (B) Year 1991

9. Age distribution : The relative abundance of the organisms of various age groups in the population is called age distribution of population. With regard to age distribution, there are three kinds of population.

1. Rapidly growing or Expanding population : It has high birth rate and low death rate, so there are more number of young individuals in the population.
2. Stationary or stable population : It has equal birth and death rates, so population shows zero population growth.

 

 

 

3. Declining population : It has higher death rate than birth rate, so the population of young members is lower than that of old members e.g. Japan (Ageing population) .

Human population has three age groups : Pre reproductive, Reproductive, and post reproductive.

 

Postreproductive

 

 

Reproductive

 

Prereproductive

 

Expanding population

 

Stable population

 

Declining population

Factors affecting the age composition

1. Number of infants below one year of age and the older people as these have higher mortality rate than individuals of other age groups.
2. Proportion of reproductive active males and females in a population.
3. Number of females in active reproductive age (i.e. between 15 to 44 years)

10.  

Change in Population Size and Growth Rate : Whether a population grows, declines or maintains it size depends upon the balance between the above factors:

 

The above expression in words may be represented in a simple way by a mathematical model. suppose N = population size and t = time. The Greek letter delta, D , indicates change. We can now represent change in

population as D N, and time interval as Dt . The verbal equation can be written as DN/Dt=(B+I) – (D+E) in which

B is absolute number of births in the population during the time interval, and D =the absolute number of deaths during that interval; I means immigrant and E, emigrants. I and E , being insignificant, may be ignored. Then the equation simplifies to DN/Dt =B-D.

Migration is a two-way movement of a population for adjusting to seasonal changes. It occurs in some fishes (Anguilla, an eel), birds (Siberian crane), and mammals (fur seal). Migration is not considered a determinant of population size.

Annual average growth rate is the percentage of increase in population size per year. It can be calculated with the help of following equation :

æ P2 - P1 ö

 

 

Annual growth rate (%) = ç

P

÷ ´ 100

• N

è   1           ø

Where P₁= Population size of previous census. P₂= Population size of present census.

N= Number of years between the two census.

 Growth of Human Population.                                                                                                                          

Population growth refers to the increase in its size. It is determined by the number of individuals added to the population and the number of individuals lost from the population. Addition occurs by births and immigration. Loss results from deaths and emigration. If more individuals are added than are lost i.e., the vital index is more than 100, the population will increase or show positive growth. If more individuals are lost than are added i.e., the vital index is less than 100, the population will decrease or show negative growth. If addition and loss are balanced, i.e., the vital index is 100, the population will become stationary or show zero growth.

 

 

 

1. Malthus Theory of Human Population Growth : Thomas Malthus, a British political economist, put forward a theory of human population growth in 1778. Malthus in his "Essay on the principle of population" pointed out that population tends to increase in geometric progression while food supply increase only in arithmetic progression. Faster growth of population than of its requirements causes an imbalance between the two. When this imbalance reaches a certain limit, environmental factors like famine, epidemic of a disease, earth quake, flood, war etc reduce the population to a size, the available resources can support. The factors that control the population size were called positive checks by Malthus.
2. Natural Control of Population Growth : Growth of a population is controlled by an interaction between three factors : biotic potential, environmental resistance and carrying capacity of environment.

1. Biotic or reproductive potential : Biotic potential is the natural capacity of a population to increase at its maximum rate under ideal environmental conditions and stable age and sex ratios. The biotic potential for all animals is very high. If unchecked, the numbers of any species will quickly over run the world. Biotic potential in the human female is estimated to be about 12 per female during its reproductive period between the puberty and the menopause period.
2. Environmental Resistance : In nature full biotic potential of an organism or population is never realized, since conditions are rarely ideal. Various harmful environmental (abiotic) factors like non-availability of food and shelter, natural calamities like drought, cloud bursts, floods, fires, temperature fluctuations, accidents, etc. and certain biotic factors like pathogens, parasites, predators etc. check the biotic potential from being realized. The sum of all these inhibitory factors is called environmental resistance. Thus, actual increase is the balance between biotic potential and environmental resistance. Thus environmental resistance does not allow population growth so soar towards infinity.
3. Carrying capacity : It is defined as “Feeding capacity of an environment of an ecosystem for a population of a species under provided set of conditions”. It is also defined as the “Level beyond which no major increase can occur”. This limit is a constant and represented by K. When a population reaches the carrying capacity of its environment, the population has zero growth rate. So the population generally stabilizes around the carrying capacity. The carrying capacity of the earth for human population is considered to be about 8 to15 billions. Carrying capacity of the environment for a population depends upon three major components :
   1. Productive systems which produce food and fibre e.g. croplands, orchards, etc.
   2. Protective systems which buffer air and water cycles

and keep moderate environmental temperatures e.g. ocean etc.

3. Assimilative systems which utilize the wastes produced by human activities e.g. waterways, wetlands, etc.

Productive system and protective systems collectively form the life-supporting capacity, while assimilative systems collectively form the waste assimilative capacity.

4. Population fluctuations and population cycles : The populations are not stable and do change due to a number of extrinsic as well as intrinsic factors. These variation in the population size are of two types :

Biotic potential           curve (J-shaped)

 

 

 

 

 

 

 

 

 

 

 

 

Time

Environmental

resistance        Carrying capacity

 

Stabilized population level

 

 

    Population growth curve (S-shaped)

1. Population fluctuations or irruptive variations : In these changes, population density tends to fluctuate irregularly above and below some steady-state level. These are

Fig : The theoretical relationships between biotic potential, environmental resistance and carrying capacity

 

 

 

 

 

 

 

 

 

characterized by sudden increase in population in short time which is followed by equally quick decrease in population size. These are caused by random seasonal or annual changes in availability of resources (food or energy) or extrinsic factor (e.g. temperature, rainfall etc.) e.g. more birds during early summer due to their hatching period, more insects during summer months and more weeds in rainy season.

2. Population cycles : These are regular changes in the population size. In these, population size is nearly constant over long period of time. These are caused by seasonal changes in environment e.g. population cycles (of 3 to 4 years) of lemmings of Tundras (Elton, 1942) Lemmings (Lemmus lemmus) (small mouse-

 

 

Irruptive fluctuations Cyclic fluctuations

 

 

 

 

 

 

 

 

 

 

Time

 

 

 

 

 

Carrying capacity

like rodents found in arctic regions of Canada and Norway) increase in their number for a period of about 3 years when it reaches a peak

Fig : Cyclic and irruptive fluctuations in

populations

beyond the carrying capacity of that area. They eat up all the available food. In the winter months, the lemmings migrate in large numbers in the sea and swim till they are drowned due to exhaustion. The surviving lemmings multiply and repeat the process.

3. Patterns of Population Growth : Growth of a population can be expressed by a mathematical expression, called growth curve in which logarithm of total number of individuals in a population is plotted against the time factor. Growth curves represent interaction between biotic potential and the environmental resistance.

Two basic types of growth curves :

1. Sigmoid or S-shaped growth curve : It is shown by yeast cells and most of organisms. It is formed of five phases :
   1. Lag phase. In which the individuals adapt themselves to the new environment, so there is no or very little increase in population.
   2. Positive Acceleration phase. It is the period of slow increase in population in the beginning.
   3. Logarithmic or Exponential phase : It is the period of rapid rise in population due to availability of food and requirements of life in plenty and there being no competition.
   4. Negative Acceleration phase : In which again there is slow rise in population as the environmental resistance increases.
   5. Stationary (Plateau) phase : Finally, growth rate becomes stable because mortality and natality rates become equal to each other. So there is zero growth rate. A stable population is said to be in equilibrium, or at saturation level. This limit in population is a constant K and is imposed by the carrying capacity of the environment. S-shaped curve is also called logistic curve. Sigmoid growth curve was described by Verhulst, (1839)
2. J-shaped Growth curve : It is shown by small population of Reindeer experimentally reared in a natural environment with plenty of food but no predators. It has only two phases:
   1. Lag phase : It is period of adaptation of animals to new environment so is characterized by slow or no growth in population.
   2. Logarithmic or Exponential phase : It is characterized by rapid growth in population which continues till enough food is available. But with the increase in reindeer population, there is corresponding decrease in the availability of food and space, which finally become exhausted, which leads to mass starvation and mortality. This sudden increase in mortality is called population crash. Lemming of Tundra, some insect, algal blooms and annual plants also show J-shaped curves. The population growth curve is S- shaped in most of the organisms, Human population also shows S-shaped curve.

 

 

 

 

Reproductive Health

 

 

 

 

 

Lag

Positive

 

Exponential

Negative

 

Stationary

 

Lag

 

Exponential

 

 

 

700

 

600

 

500

 

400

 

200

 

100

acceleration

phase   phase

 

phase

acceleration phase

phase

 

K

 

 

2000

 

 

1500

 

 

1000

 

 

500

phase

phase

 

 

2      4      6      8     10   12   14   16

1             2             3             4

Time in decades

Time in hours

Fig : The S-shaped growth curve of yeast cells

Fig : The J-shaped growth curve of reindeer

Difference between S-shaped and J-shaped Growth curves.

 

S.No.	S-shaped Growth Curve		J-shaped Growth Curve
(1)	It is formed of 5 phases : lag phase, positive acceleration phase, exponential phase, negative acceleration phase and stationary phase.	(1)	It is formed of 2 phases : lag phase and exponential phase.
(2)	Finally the population shows zero growth rate as birth rate equals death rate.	(2)	Finally, the population shows a population crash due to rapid increase in mortality rate.
(3)	Examples. Yeast cells in a culture medium.	(3)	Examples. Reindeers, algae blooms, lemmings of Tundras

3. Human Population Growth Curve : The modern man (Homo sapiens sapiens) appeared about 25,000 years ago. For a very long time, the human population remained in the lag phase, having little or very slow growth. By the year 1 A.D., there were about 0.25 billion people in the world, and by 1600 about 0.5 billion. Thus, it took 1600 years for the population to become double. The exponential phase of growth of the human population started about 1750. Since then, the time taken by the population to become double has considerably shortened. It doubled in 200 years (1600-1800 A.D.), becoming 1 billion; then doubled in 130 years (1800-1930 A.D.), growing to 2 billion; then doubled in only 45 years

(1930-1975 A.D.), reaching about 4 billion.

At present, the world human population grows at a rate of 2 percent a year, and it has now reached 6 billion. If the present growth rate persists, there would be 8 billion people on earth by the year 2017.

World population gain is 2 persons every second; 200,000 people every day; 8 million every month; and 70 million every year. The high rate of growth is often referred to as “population explosion” The word “explosion” may be defined as a rapid and expansive change of state.

7

6

 

5

 

4

 

3

 

2

 

1

 

0

500,000 10,000            8,000              6,000              4,000           2,000                  0

Years before present                                BC     AD

 

 

 

 

 

 

 

 

The future of human population is difficult to predict. It may stabilize and have S-shaped growth curve or decline rapidly and have J-shaped growth curve. The population will stabilize if the birth and death rates are balanced in the near future. It will rapidly decline if it overgrows the carrying capacity of the environment.

 

2.5

 

 

2.0

 

 

1.5

 

 

1.0

 

 

0.5

 

 

0

1950     1960      1970       1980       1990       2000      2010       2020     2030       2040     2050

Year

Fig : Projected world population growth rate between 1950 and 2050 (based on United States census bureau, international data)

A demographic cycle is formed of 5 stages

 

(a) First stage (High stationary)	High birth rate and high death rate. Population stationary.	India till 1920.
(b) Second stage (Early expanding)	Declining death rate but high birth rate.	Many countries in S. Asia and Africa.
(c) Third stage (Late expanding)	Declining birth and death rates but still birth rate higher than death rate.	India, China and Singapore.
(d) Fourth stage (Low stationary)	Low birth rate and low death rate. Population stationary.	Austria (with zero growth rate during 1980- 85) Denmark, Sweden, Belgium etc.
(e) Fifth stage (Declining)	Birth rate lower than death rate.	Germany and Hungary.

a      Total population b        Death rate

c       Birth rate

 

Stages    1                      2                      3                 4

 

Time

Fig : Different stages of the demographic transition

1. High birth rate but fluctuating death rate
2. Declining death rate and continuing high birth rate
3. Declining birth and death rate
4. Low death rate but fluctuating birth rate

 

 

 Population Trends in the world and India.                                                                                                     

(i)Population Trends in the World

The distribution of human population is not uniform throughout the world. Only about one third of the total land area is inhabited. Of the inhabited areas, some are thickly populated, others sparsely. This depends upon the availability of the requirements of life. About 56% of the total world population resides in Asia alone. Bangladesh is the most thickly populated country, and Australia, the most thinly populated.

Annual Birth, Death and Growth Rates for Human Population in 1973

 

S. No	Region	Population (Millions)	Average Annual Birth Rate per 1,000 Individuals	Average Annual Death Rate per 1,000 Individuals	Annual Growth Rate Percent
(1)	World	3860	33	13	2.0
(2)	Developed Countries	1120	17	9	0.8
(3)	Developing Countries	2740	39	14	2.5

Birth and Death rates in selected countries in 1979

 

S.No.	Country	Birth Rate	Death Rate
(1)	Sweden	11.6	11.0
(2)	England	13.0	12.1
(3)	Japan	14.6	6.0
(4)	Canada	15.5	8.3
(5)	USA	15.8	8.7
(6)	China	18.0	6.0
(7)	India	35.0	13.6
(8)	Bangladesh	45.7	14.2
(9)	Pakistan	45.7	14.2

 

(ii)Population Trends in India

1. Population : India with a population of 1027 million as 2001 census stands second in the world. The world leader in the matter of population is China with a population of 1160 million. India has only 2.42% of the world's land area but supports over 15.5% of the world's population. Thus, one in every 6 persons in the world is an Indian. India's population has been steadily rising since 1921. However, from the year 1921, often called the "big divide", its population started to swell up sharply. India's population has increased 3 times since independence (1947) when its population was 340 million. About 1800 individuals are born every hour, 17 million every year. India's population crossed one billion (100 crores) mark on May 11, 2000.
2. Sex Ratio : Sex ratio is defined as the number of females per thousand males in a country or state. Sex composition is affected by three factors : (i) differentials in male-female ratio at birth, (ii) differentials in mortality conditions of males and females, and (iii) sex-selective migration. India is one of the few countries where the males

 

 

are more than the females. There has been a steady decrease in the female population since 1901 except during the period 1971-81 when there was some increase. There are at present 531,277,078 males and 495,738,169 females in our country. The sex ration is 933 females per 1,000 males. In Kerala, there are 1058 females per 1000 males, highest sex ratio among the states, In Daman & Diu, there are only 709 females per 1000 males. In Haryana, there are 861 females per 1000 males, lowest sex ratio among the states.

3. Literacy Rate : The literacy rate was 65.28% according to the 2001 census. It was 76.40 % for males and 54.16% for females. The literacy rate has been steadily increasing since 1951. Among the Union Territories, Lakshadweep has the highest literacy rate of 87.52%. Literacy rate is highest in Kerala (90.92%) and lowest in Bihar (47.53%). Any person who can read and write with understanding in any language is recorded as literate in census. All children below 7 years are shown as illiterate in the census.

(d)Factors Favouring Population Growth

1. Decrease in death rate.
2. Increase in average life span.
3. Better medical facilities.
4. Control of insect vector's of fatal diseases and epidemics.
5. Better sanitation.
6. Proper care of new-born children and their mothers.
7. Better nutrition and life amenities.
8. Protection against wild life and adverse whether through living in houses.

Details of India's Population of 1981, 1991 and 2001

 

Data		1981 Census	1991 Census	2001 Census	Rise/ Fall
Population :	Total