CBSE class 12th biology notes Population and Population Growth There are four variables/ causes that govern the population growth/population size: Birth rate(Natality): It is defined as a number of births per 1000 individuals in one year. Death rate (Mortality): It is defined as a number of death per 1000 individuals per year. Immigration: Entry of individuals in a given population. 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
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