Practice question

In the standard continuous population-growth notation, b denotes the per-capita birth rate: the expected number of births contributed per individual per unit time. Multiplying b by population size gives the total birth input B = bN under a homogeneous model. Similarly, d is the per-capita death rate and D = dN. Their difference gives the instantaneous per-capita growth rate r = b − d, leading to dN/dt = (b − d)N for a closed population. A raw birth number is an absolute count and is usually written B, so distinguishing uppercase totals from lowercase per-capita rates prevents dimensional errors. Body mass and biomass are unrelated ecological quantities despite sharing the initial letter. Per-capita rates allow comparison among populations of different sizes: 100 births in a population of 1,000 is a higher birth rate than 100 births in a population of 10,000. The notation is conventional rather than universal, so any analysis should define symbols and time units explicitly, especially when age-specific birth schedules replace a single average b.