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CBSE class 12th biology notes Population and Population Growth

CBSE class 12th biology notes Population and Population Growth

There are four variables/ causes that govern the population growth/population size:
  1. Birth rate(Natality): It is defined as a number of births per 1000 individuals in one year.
  2. Death rate (Mortality): It is defined as a number of death per 1000 individuals per year.
  3. Immigration: Entry of individuals in a given population.
  4. Emigration: Exit of individuals from a given population.
A population gains individuals by birth and immigration and loses them by deaths and emigration.
Thus, population change = (Births + Immigration) – (Deaths + Emigration)
Effect of Age Distribution on Population growth
In many organisms, the generations overlap. It is shown, from a theoretical point of view, that competition between the different ages classes in such organisms will have important population dynamics consequences. Strong competition between age classes can be either a stabilizing or destabilizing force depending on the stage of the life cycle—juvenile survival or adult survival/reproduction—at which density dependence occurs. When juvenile survival is density dependent, competition has a stabilizing effect. On the other hand, when reproduction is density dependent, strong competition tends to be destabilizing, i.e. it will cause population density to fluctuate. It is also shown that delayed effects on reproduction, caused by strong competition as the adults grow up, tend to be destabilizing. These findings have interesting implications for the population dynamic behavior in organisms with different types of life cycles, and these theoretical findings might be relevant to the interpretation of patterns of population dynamic behavior.
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