Survival and maturation rates of the African rodent, Mastomys natalensis: density-dependence and rainfall

Survival and maturation rates of female Mastomys natalensis were analysed based on a ten-year monthlycapture-recapture data set. We investigated whether direct and delayed density dependent and independent (rainfall)variables accounted for the considerable variation in demographic traits. It was estimated that seasonal and annualcovariates accounted for respectively 29 and 26% of the total variation in maturation rates and respectively 17 and11% of the variation in survival rates. Explaining the between-year differences in maturation rates with annual pastrainfall or density did not improve the model fit. On the other hand we showed that maturation rates were correlatednegatively with density the previous month and positively to cumulative rainfall over the past three months.Survival estimates of both adults and subadults varied seasonally, with higher estimates during the increase phase(dry season). The subadults were characterised by a very high survival rate (> 0.95) during this phase. In thedecrease phase only minor differences were found between survival rates of subadults and adults. We found that39% of the between-year variation in survival can be explained by accumulated rainfall over the past year.

Soil type limits population abundance of rodents in crop fields:case study of the multimammate rat Mastomys natalensis Smith,1834 in Tanzania

Studies of populations of the multimammate rat Mastomys natalensis in Morogoro, Tanzania, show that soil textureappears to influence the population abundance and distribution of these rats in agricultural fields. The lowest rodentpopulation abundance was found on sandy clay soils (F(2, 5) = 8.42;P = 0.025). The population abundances of M.natalensis on sandy clay loam and sandy loam soils did not differ significantly (P ≤ 0.05), possibly because thesesoils have a very similar texture. The results of this study suggest that M. natalensis prefers loam-textured soilswith a high percentage of sand, which are probably better than clay soils for burrowing and nesting, particularly inthe rainy season. The lower preference for clay soils is probably related to the poor aeration in these soils and thewaterlogging that occurs during the wet season.

Relationship between sampling intensity and precision for estimating damage to maize caused by rodents

In this study we aimed to determine the relationship between sampling intensity and precision for estimating rodentdamage. We used the systematic row sampling technique to provide data to achieve precision and accuracy inestimations of rodent damage in maize fields at the planting and seedling stages. The actual rodent damage to maizein 15 fields, each 0.5 ha in size, in Morogoro, Tanzania, was established at the seedling stage. These data were usedto simulate the sampling intensities that would provide precision and accuracy. The variations between estimateswere plotted against the sampling intervals. The results of this study show that the relationship between averagestandardized variances and sampling intervals is linear. The heterogeneous distribution of damage in some plotscaused variations in the accuracy of the estimates between plots, but a sampling interval of five rows consistentlyproduced estimates with a variance of less than 10%. We provide a standard curve that will allow a decision to bemade on the sampling intensity as a function of required precision using the systematic row sampling technique inmaize fields.