Age Structure, Sex Ratio and Population Density in the Harvesting of Natural Animal Populations

Interest in game ranching of natural animal populations as a food source has been extensive for some considerable time. This has led to a variety of studies on the population dynamics of possible candidate species for cropping. Talbot et al. (1965) list over 400 references and the Journal of Wildlife Management and the East African Wildlife Journal contain many studies of this type. In comparison, possible cropping strategies for game have received little attention. Two main research approaches have been adopted. The first involves the basic demographic equations developed by Lotka (1907) Sharpe and Lotka (1911) and extended by Caughley (1967). Using these equations, the 'Rate of increase' is calculated and then used to estimate the sustainable yield from the population (Caughley Clark 1971, 1972). Both approaches may lack appeal to the wildlife manager since the assumptions concerning the animal's population are invariably false. In addition, it is difficult to apply management prescriptions obtained from such approaches as they omit important criteria. The manager needs to know what age groups to crop, what sex ratio to aim for, what density of population is possible, and what compromises he can make between trophy shooting of males and cropping for meat. Of more importance still, the manager needs to know what information he should seek in trying to find answers to these questions. This paper considers a general class of mathematical models that are applicable to most species likely to be found in a game cropping situation. It shows how these models can be adapted to investigate harvesting strategies of various kinds and then considers what are the important parameters to be measured.