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Organisms and Populations — BIOLOGY STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceBIOLOGYOrganisms and Populations4 Marks
Question
The size of a population for any species is not a static parameter. Explain.###Explain population growth###Explain in brief - population growth.
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Answer

→ The size of a population for any species is not a static parameter. It keeps changing with time, depending on various factors including food availability, predation pressure and adverse weather.
→ In fact, it is these changes in population density that give us some idea of what is happening to the population whether it is flourishing or declining.
→ Whatever might be the ultimate reasons, the density of a population in a given habitat during a given period, fluctuates due to changes in four basic processes, two of which (natality and immigration) contribute to an increase in population density and two (mortality and emigration) to a decrease.
(I) Natality : refers to the number of births during a given period in the population that are added to the initial density.
(ii) Mortality : is the number of deaths in the population during a given period.
(iii) Immigration : is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.
(iv) Emigration : is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.
→ So, if N is the population density at time t, then its density at time t + 1 is
Nt + 1 = Nt + [(B + I) - (D + E)]
→ Population density will increase if the number of births plus the number of immigrants (B + 1) is more than the number of deaths plus the number of emigrants (D+E).
→ Under normal conditions, births and deaths are the most important factors influencing population density, the other two factors assuming importance only under special conditions.
→ For instance, if a new habitat is just being colonized, immigration may contribute more significantly to population growth than birth rates.
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