Do farming practices influence population dynamics of rodents? A case study of the multimammate field rats, Mastomys natalensis, in Tanzania

A capture-mark-recapture study was conducted in crop fields in Morogoro, Tanzania, to investigate how the population dynamics of multimammate field rats, Mastomys natalensis, was influenced by the commonly practised land preparation methods and cropping systems. Two land preparation methods (tractor ploughing and slash and burn) and two cropping systems (mono-cropping with maize and inter-cropping with maize and beans) were investigated in a Complete Randomized Design experiment with 2 · 2 factors, and two 0.5 ha replicates per treatment. Mastomys natalensis comprised 97.8% of the abundance of the three rodent species captured in the study area. The slash and burned fields had higher rodent population densities than tractor ploughed fields (P < 0.05). Recruitment rates were higher in the slash and burn fields than in the tractor ploughed fields, suggesting that the former were more favourable habitats for M. natalensis. Land preparation methods appeared to influence the population dynamics of M. natalensis through recruitment of new individuals in the population and most probably survival. Apart from the temporal changes in population density, which were reflected in both tractor ploughed and slash and burn fields, cropping systems (monoand inter-crop) had little effect on the population dynamics of M. natalensis [F(1,8) 1⁄4 6.50; P > 0.05]. The study shows that land preparation methods should be considered a component of rodent pest management in ecologically based or integrated management practices. In maize fields in Tanzania, the crop is most susceptible to damage by M. natalensis in the first 2 weeks after planting, and therefore, lower densities of rodents will result into lower crop damage in tractor ploughed fields.