Where lx is the female survival rate at t age (at birth, assuming that lx of x=0 is 1.0). Mx is the average litter size of X-year-old females (only females are counted). If R0= 1, the number of individuals between generations will not increase or decrease, and R0 >;; 1 Increase the number of individuals. When R0< is 1, the number of individuals decreases. On the contrary, the sum of mx is the average female post-algebra of a woman without considering death, which is called the crude reproduction rate. Inherent natural reproduction rate refers to the highest instantaneous reproduction rate per unit time when the population is not limited by space or food and the age composition of the population is relatively stable. R can be obtained by the following formula:
R represents the inherent proliferation ability of a species under given environmental conditions, so it is appropriate to compare the species from the average value measured in unit time. In population genetics, it can be used to measure the fitness of a population (Darwinian fitness). λ=ex, called the finite natural growth rate, represents the multiple of the increase in the number of individuals per unit time. In addition, when λt=2, the time required to double the number of individuals is called doubling time (time doubling).