Spatio-temporal patterns in the distribution of the multi-mammate mouse, Mastomys natalensis , in rice crop and fallow land habitats in Tanzania

An understanding of the dispersion patterns of a pest is an important pre-requisite for developing an effective management programme for the pest. In this study, rodents were trapped in two rice fields and two fal- low fields for three consecutive nights each month from June 2010 to May 2012. Mastomys natalensis was the most abundant rodent pest species in the study area, account- ing for > 95% of the trapped rodent community. Rattus rattus , Dasymys incomtus , Acomys spinosissimus and Grammomys dolichurus comprised relatively small pro- portions of the trapped population. Morisita ' s index of dispersion was used to measure the relative dispersal pat- tern (aggregate, random, uniform) of individuals across each trapping grid as a means of comparing rodent dis- tribution in rice and fallow fields over time. This analysis revealed that the rodents in rice fields generally exhibited an aggregated spatio-temporal distribution. However, the rodents in fallow fields were generally less aggregated, approaching a random distribution in some habitats and seasons. Heat maps of trapping grids visually con- firmed these dispersal patterns, indicating the clumped or random nature of captured rodents. ANOVA showed that the parameters of habitat (rice, fallow), crop stage (transplanting, vegetative, booting, maturity) and crop- ping season (wet, dry) all significantly impacted the num- ber of rodents captured, with the vegetative, dry season, fallow habitat having the highest number of rodents; and the transplanting, wet season, rice habitat with the least number of rodents. Therefore, such spatio-temporal pat- terns can serve as a tool for developing stratified biodi- versity sampling plans for small mammals and decision making for rodent pest management strategies.