MODELING THE RELATIVE EFFICACY OF CULLING AND STERILIZATION FOR CONTROLLING POPULATIONS

Simple logistic models are used to investigate and compare the effects of continuous control by culling or sterilisation on population densi ty. The models consider populations regulated by density-dependent mor tality or density-dependent recruitment, with monogamous or polygamous mating systems, and with one or both sexes sterilised. For the first time, an analytical solution is presented for the effect of sterilisat ion on density-dependent population growth. The models suggest that th e mating system has a considerable effect on the relative efficacy of sterilisation, and that previous models for sterilisation may have ove restimated the impact of sterilisation by assuming idealised monogamou s mating. In general, and except for populations with monogamous matin g or 'harem' systems and both sexes sterilised, culling gives a more r apid reduction in density than does sterilisation. However, the long-t erm degree of suppression obtained with the same levels of control app lied is likely to be similar. Populations with density-dependent morta lity will be reduced by sterilisation more quickly than those regulate d by density-dependent recruitment, and the effect on the steady-state density of a given proportion that is sterile is greater in the first case than in the second. However, the effect of a given continuous st erilisation rate (e.g. baiting effort) on density is the same in both cases. We compare our model results with those of others and question previous conclusions about the circumstances under which sterilisation is most effective.