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Organisms and Populations

Organisms and Environment


  • It is a group of similar individuals living in a geographical area, sharing similar resources, and capable of interbreeding.
  • Population has certain attributes, which individual organisms do not possess:

    • Birth rate per capita births

    • Death rate per capita deaths

    • Sex ratio − Ratio of number of males to females in a population

  • Demography: It refers to the statistical study of human population considering the following factors:
    • Distribution of population
    • Size and Density of population
    • Birth rate
    • Death rate 
    • ​Growth rate of population (​Growth rate = Birth rate - Death rate)

Age distribution

  • A population can be composed of individuals of different age groups.

  • Age distribution plot for a given population is given by the age pyramid.

  • The structure of the age pyramid determines the growth status of the population, whether it is growing, stable, or declining.

Population size, more technically, is referred to as population density (N), which indicates the number of individuals inhabiting a particular niche.

If the population is huge, then relative density is measured instead of absolute density whose measurement is time-consuming.

  • The size of a population is an ever-changing aspect since it depends upon availability of food, predation, weather conditions, etc.

  • This gives us an idea whether …

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