Which two factors are considered most important under normal...

So, if N is the population density at time t, then its density at time t +1 is N_(t+1) = N_(t) + [(B + I) – (D + E)] You can see from the above equation (Fig. 11.2) that population density will increase if the number of births plus the number of immigrants (B + I) 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.