Reproduction and population dynamics of Mastomys natalensis Smith, 1834 in an agricultural landscape in the Western Usambara Mountains, Tanzania

Abstract

The multimammate rat, Mastomys natalensis Smith 1834, is a dominant species in agro-ecosystems in Sub-Saharan Africa, but adapts quickly to changes in non-agricultural landscape, particularly woodlands and forests. In this study we report on reproduction and population dynamics of M. natalensis in deforested high elevation localities in the Usambara Mountains, north-east Tanzania. We conducted Capture-Mark-Recapture studies in [2002][2003][2004], and established that reproduction of M. natalensis takes place in the extended wet season between February and June, and the population density peaks in June-August. Reproduction cease in July to January and population density drops from July onwards. Reproduction and population density fluctuations are linked to the duration and amount of rainfall. In years when rainfall was below average and the wet season was short, the population density was significantly lower (below 10 animals/ha and 60 animals/ha in 2003 and 2004 respectively, compared to >100 animals/ha in 2002 when rainfall was above the seasonal average) (F df 2, 13 = 9.092, p<0.01 for in between years variations and F df 12, 15 = 5.389, p<0.01 for effect of cumulative annual rainfall on population density). These densities were much lower than in the lowland savannah habitats in central and southwest Tanzania. A comparison between the farmland/fallow mosaic fields and agro-forestry areas showed higher population densities in the former, which have similarities to the preferred habitats in the lowland savannahs. The increasing abundance of M. natalensis in the Usambara could have some consequences: M. natalensis is major pest and is involved in the plague cycle in the western Usambara Mountains. Mastomys natalensis is also a strong competitor and the impact on endemic rodent species, e.g. Lophuromys flavopunctatus and Praomys delectorum is unknown.

Vegetation habitats and small mammals in a plague endemic area in Western Usambara Mountains, Tanzania

“…It is worth noting that M. natalensis was captured at high altitude (~2,000m) and this is in agreement with a report by Makundi et al (2007) and Mulungu et al (2008) who found that some small mammals including M. natalensis gained pest status by forest disturbance and cultivation while others preferred complex and heterogeneous habitats in different landscapes. It was observed that many small mammal individuals were captured in the plateau landscape compared with other landscapes.…”

“…Therefore, disturbance of natural forest may lead to different responses on the flora (Brooks et al, 2002;Foley et al, 2010) and on the small mammal diversity (Mulungu et al, 2008). The conversion of land cover is thought to induce stress conditions in animals (Krebs, 1989), and pest re-emergence (Makundi et al, 2007). In the current study, variations in vegetation cover of dominant vegetation species were observed.…”

“…This is consistent with other findings such as the study by Corominas (2004) in the forest habitat of the Natural Park and Reserve of Barcelona. However, this could have been due to habitat variability as observed by Mulungu et al (2008) who reported more trap success within natural forest in the middle altitude of Mount Kilimanjaro compared to moorland in the high elevation and agricultural land in the lower altitude, which could be attributed to food availability and stability of the forest (Dueser & Shugart, 1978;Clausnitzer & Kityo, 2001;Makundi et al, 2007). On the other hand Mena & Vazquez-Domınguez (2005), observed that the presence of small mammals was linearly correlated with altitude.…”

“…It was observed that shrubs are dominant both in the plateau and escarpment. These upland shrubs seem to have developed after natural forests were cleared for cultivation (Makundi et al, 2007;Annaert, 2010) and later regenerated to secondary vegetation. To date, only 30% of the natural forest on the Usambara plateau remains (Burgess et al, 2007).…”

Integration of ecology and biology for the management of rodents: International perspectives 2

“…The results suggest that rainfall affects both maturation rates (cumulative rainfall in previous three months) and survival (cumulative rainfall in previous year) and that maturation rates in addition are dependent on the population density of the previous month. The population dynamics of the same species was investigated in upland regions of Tanzania where Mastomys natalensis expands its range due to the conversion of forest habitat to crop fields (Makundi et al 2007). There, above average rainfall seemed to support population growth in Mastomys natalensis but overall population density was much lower than in lowland habitats.…”