The model assume that the population sizes for each stage depend only on the female population and that the probability of survival of an individual female from one year to next year depends only on the stage of the life cycle and not on the actual age of individual. For example, let us consider a four-stage model for analysing the population dynamics of the loggerhead sea turtle.
At each stage, we estimate the probability of survival over a one-year period. We also estimate the ability to reproduce in terms of the expected number of eggs laid in a given year. The results are summarized in Table 1. The approximate ages for each stage are listed in parentheses next to the stage description.
If di represents the duration of the ith stage and si is the annual survivorship rate for that stage, then it caan be shown that the proportion remaining in stage i the following year will be:
I can't understand the equation at all, and I have casted two hours on it, so may I get your help? Thanks in advance!