Comparing strategies for controlling an African pest rodent: An empirically based theoretical study

Abstract

1. Small rodents in general and the multimammate rat Mastomys natalensis in particular cause major economic losses in Africa through damage to crops. Attempts to develop dynamic population models for this and other pest rodents are ongoing. 2. Demographic estimates from a capture-mark-recapture (CMR) study in Tanzania were used to parameterize a population model for this species. This model incorporated three functional age categories (juveniles, subadults and adults) of both sexes and used density-dependent and density-independent factors, the latter represented by rainfall. 3. The model was used to analyse the effect of rodent control on the population dynamics and resulting number of rats. Control measures affecting survival as well as reproduction were considered. 4. The model showed that control measures reducing survival will only have long-term effects on population size if they are also applied when rodent densities are low. Control measures applied only when rodent densities are high will not have persistent effects, even at high mortality rates. 5. The model demonstrated that control measures reducing reproduction are likely to prevent Mastomys outbreaks, but will keep densities low over a long period only when the contraceptive effect is strong (> 75% reduction). 6. Provided that CMR data are available, we recommend developing Leslie-type population models for rodent pests on the basis of CMR-estimated demographic schedules. Such models have great potential in rodent management and allow the evaluation of different strategies. 7. Besides improving the ecological basis of the population modelling, economic considerations need to be incorporated into decisions about rodent control. We suggest that appropriate population models will provide important input into such decision making.