Fox Births
The number of foxes born, Fborn, depends on the number of foxes, Fstart, and the amount of food available per fox, x.
Fborn = Fstart/2 * 5 * fFB(x)
where Fstart/2 is the number of fox mating pairs alive at the beginning of the month; "5" is the maximum litter size; and fFB(x) is the fox-birth efficiency, which depends on the number of rabbits available per fox, x.
Assumptions
Foxes scavenge only - they do not hunt.
There are equal numbers of female and male foxes.
There are an equal number of female and male foxes born each year.
Fox births are spread out over an entire year.
Foxes that eat more are more likely to produce larger litters. Foxes that eat more than 40 rabbits per month have maximum sized litters. On the other hand, the foxes that eat less than 20 rabbits per month do not reproduce.
The fox-birth efficiency is shown in the graph below. The maximum efficiency is 1/12th so that if the foxes eat well over the entire year (12 months), the accumulated efficiency is 1, which means the foxes will have the maximum number of cubs each year. Remember that the model predicts one month at a time.
