Practice question

Net reproductive rate R0 is the expected number of daughters produced by a female over her lifetime, adjusted for survival to each reproductive age. If R0 exceeds 1, each generation more than replaces itself, so abundance increases from generation to generation under stable conditions. R0 = 1 denotes exact replacement, and R0 below 1 indicates generational decline. This discrete-generation criterion parallels λ > 1 for finite growth and r > 0 for continuous growth, although the quantities are not numerically interchangeable without information about generation time and age structure. A negative r and an R0 below 1 both signal decline, while λ = 1 signals stability. The R0 criterion assumes that age-specific survival and fecundity schedules remain constant and that density dependence or migration does not overturn the projection. It is especially useful in life-table analysis because it combines reproduction and survivorship across the entire life cycle. The threshold of unity follows directly from replacement: one daughter per female maintains the female lineage, whereas more than one produces multiplicative generational gain.