Period
A vector of length 2 specifying the minimum and maximum values
for the period of the recruitment cycles. e.g., if Period = c(10,10), then
recruitment cycle occurs every 10 years exactly.
Amplitude
A vector of length 2 specifying the minimum and maximum
values for the amplitude of the recruitment cycles. e.g., if Amplitude =
c(0,0.5), the average recruitment will increase (or decrease) by a factor
between 0 and 0.5 each cycle.