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Wednesday, March 16, 2011

Theory of Demographic Transition, & Population Interaction

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The term ‘Demographic’ relates to the scientific study of populations and the term ‘Transition’ means- ‘the process and periods of changing from one state or condition to the other state or condition’. Thus, the Demographic Transition means- ‘The scientific study of the process or period of changes in a population from one state or condition to another state or condition..

An eminent demographer Frank Notestien outlined a theory which emerged out of his observations pertaining to the effect of economic and social development on the growth of population. His theory of demographic transition has provided the conceptual basis for demographic researches.

According to the theory of demographic transition, all the human societies may pass through any one of the three phases at a particular point of time. These phases are – First phase or  Lag Phase, Second phase or  rapid growth phase, Third phase or Stabilization phase and the Fourth phase. The change over in population dynamics from one phase to the other is called as demographic transition.

According to this theory, high birth rates and high death rates to low birth-rates and low death rates are important parts of the economic development of a country from pre-industrial to an industrialized economy. This theory is usually described through demographic transition model (DTM) which describes population changes overtime.

The Demographic Transition Model involves four stages that are summarised below-
(i)                 Birth rates and death rates are high in pre-industrial societies. Their population fluctuates rapidly according to natural events like drought, diseases etc. Thus relatively constant young population is produced.
(ii)               The death rates drop rapidly in developing countries due to improvements in food supply, sanitation and healthcare facilities. It increases life spawn and reduces diseases. Countries in this stage experience heavy increase in population.
             (iii)     Birth rates fall due to contraception. This supports increase in wages, urbanisation,            reduction in subsistence agriculture, an increase in the status and education of women and other social changes.
(iii)             Both low birth rate and low death rates are observed in stage four. Low birth rates results in shrinking of population which is a threat to many industries that rely on population growth. Death rates may remain consistently low or increase slightly due to increases in lifestyles.

Now that the birth rates have started declining, it appears that India has entered into the third stage of demographic transition since 1971.

Vital statistics of mortality and life expectancy for different age groups of people  in the population can be represented through specific tables. These tables are called as Life Tables. These are tables designed to evaluate how characteristics of population influence the overall growth rate of a population.

Life tables are used for many different purposes like -
(i)                 Computation of average longevity of a population,
(ii)               Representation of age-composition
(iii)              Indication of critical stages in the life cycle at which mortality is high,
(iv)             Showing differences between species etc.

Life Tables were originally developed by Insurance Companies to provide a means of determining how long any person of a particular age could be expected to live. Life Tables are also used by ecologists for plant, animal and microbial populations and for making projections about life expectancies. On the basis of life tables demographers and Ecologists plot Survivorship Curves. These curves represent number of individuals in a population that can be expected to survive to any specific age.

POPULATION INTERACTION
Groups of populations interact in various ways within an ecosystem. Some population show specific behavioural interactions like Territoriality, and Dominance Hierarchy.

A rule of survival of the fittest exists in the forest. Strong animals enjoy special shares in obtaining resources whereas weaker animals come on the second place. Thus a hierarchy according to dominance exist in the animal world which is called as dominance hierarchy. This phenomenon is best noticed in social mammals like baboons, wolves and birds. We frequently come across the peculiar form of animal behaviour in which one animal attempts through appeasement displays to avoid the attack by a dominant member of its own species. This is called as submissive behaviour of the animal.

Many animals show territorial behaviours in which they take a particular area fixed by them. They do not allow even animals of the same species to move in or to occupy a place in that area. This is called as territoriality. This behaviour is frequently observed among birds, dogs, fishes etc. thus territoriality can be defined as – The pattern of animal behaviour marked by the establishment, demarcation, and defence of an area that can support the growth and activity of an animal or group of animals.

Key Words : theory, demographic transition, dominance hierarchy, submissive behaviour, Frank Notestien

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