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Organisms and Population

Organisms and Environment

  • 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 a certain population is growing or declining.

  • Some of the reasons for the increase or decrease in population:

    • Natality (B) − Number of births during a given period in the given population

    • Mortality (D) − Number of deaths during a given period in the given population

    • Immigration (I) − Number of individuals of the same species who have come into the habitat from elsewhere during a given period

    • Emigration (E) − Number of individuals of the same species who have left the habitat and gone elsewhere during a given period

  • If N is the population at time t, then its density at t + 1 is

Nt + 1 = Nt + [(B + I) − (D + E)]

Growth Models

  • Exponential Growth − When the resources are unlimited, population tends to grow in an exponential pattern.

    • If the population size is N and the birth and death rates (not per capita) are b and d respectively, then increase or decrease in N at t (time period) is given by,

dN …

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