Net reproduction rate
= Net reproduction rate
{title2=$R_0=\int_0^\infty b(a)S(a)\,da$}
The mean lifetime number of offspring is the birth rate integrated against the probability of surviving to each age. For a continuous age model it is $\int_0^\infty b(a)\exp[-\int_0^a\mu(s)ds]da$. The <Euler-Lotka equation> compares this with one to locate positive population growth.