Choose the equation that represents the calculation of population density at time t+1, given the following representations:

If natality is represented by –B

If mortality is represented by –D

If immigration is represented by –I

If emigration is represented by –E

If population density is represented by –N

   N _{t + 1} = N _t + [(B + I) – (D + E)]

The correct answer is Option (2) - N _{t + 1} = N _{t +} [(B + I) – (D + E)]

This equation represents the calculation of population density at time t+1. It takes into account the changes in population due to natality (B), mortality (D), immigration (I), and emigration (E).

In the equation, N _t represents the population density at time t. The terms within the brackets [(B + I) – (D + E)] represent the net change in population due to births, deaths, immigration, and emigration. Adding this net change to the population density at time t (N _t) gives us the population density at time t+1 (N _{t + 1}).

By using this equation, we can assess how the population density changes over time based on the rates of natality, mortality, immigration, and emigration.

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 colonised, immigration may contribute more significantly to population growth than birth rates.