Appendix II

Summary

Simulation model of the white rhino population

The model was formulated in PASCAL for implementation on an Apple II microcomputer. The basis of the model is a population made up of 46 year groups, which were grouped into functional age classes differing in their mortality, natality and dispersal rates. The age classes were as follows: old – 36–45 y; adult – 11–35 y; subadult – 6–10 y; immature – 3–5 y; juvenile – 1–2 y; infant – 0 y.

The sex ratio was considered to be 50:50 throughout all age classes. Demographic parameters operated on the year groups in the following order: first emigration, then mortality, then natality. Thus the number of animals entering age group 0 was calculated by multiplying the number of females surviving within the age classes, OLD, ADULT and SUBADULT by the age-class specific natality rates, by a factor of 0.5 to adjust for the sex ratio, and finally by the infant survival rate.

Simple model of expanding and stable populations

In the initial use of the model in Chapters 11 and 13, fixed values were assigned to demographic parameters as in Table II.1 (all rates expressed per annum):

The class of subadults is assumed to operate as a mix of males, still exhibiting immature mortality rates, and females exhibiting adult mortality rates. Subadult females have a varying natality rate depending on the age at first parturition; a natality of 0.07 means that females first give birth in year class 10.