Practice question

BIDE is an accounting framework named for the four processes that directly change the number of individuals within a defined population: births, immigration, deaths, and emigration. Its balance equation is ΔN = B + I − D − E. Dispersion describes how individuals are spatially arranged—clumped, random, or uniform—rather than a direct demographic entry or exit. Dispersion can influence encounter rates, competition, reproduction, and movement, and thereby affect BIDE rates indirectly, but it is not itself one of the four accounting terms. Immigration and emigration must be distinguished from general dispersal: dispersal is the movement process, whereas immigration and emigration specify crossing into or out of the chosen population boundary. This boundary dependence is important in metapopulations, where an emigrant from one patch becomes an immigrant to another. The BIDE identity is exact as bookkeeping when all events are counted, although estimating each component can be difficult. It separates changes caused by local birth–death balance from those caused by spatial exchange.