Abstract:
Conversion of native habitats into agricultural monocultures is a major cause of biodiversity
loss favouring a small number of generalist species. Rodents can cause significant
declines in crop yield, hence understanding the factors affecting their population dynamics
is of importance to the agricultural sector. Sugarcane plantations in African savannas
harbour a low diversity of small mammals, with a single genus (Mastomys spp.) often
dominating the community. Our study investigated the factors that shape the composition
of the small mammal community and the life-history traits of the dominant species in a
savanna-sugarcane landscape mosaic. We surveyed small mammals at eight sites, six in
sugarcane and two in neighbouring savannas at five-week intervals over the course of a
year. Sugarcane and native savanna sites were categorised into vegetation height classes.
We captured a total of 845 individual small mammals belonging to eight species across all
sites. Species diversity was higher in the savanna than in sugarcane fields. Although the
composition of the community overlapped in the two habitats, it was most similar between
tall sugarcane and savanna, than between sites that had recently planted (emerging
or short) sugarcane and either tall sugarcane or savanna. Furthermore, population densities
of the dominant species (Mastomys natalensis) were significantly higher in sugarcane
than in native savanna. Additionally, the interactions between habitat and season influenced
survival and body condition of M. natalensis; apparent survival decreased in savanna
and body condition improved in sugarcane during the wet season. Furthermore, the survival
of M. natalensis was also significantly reduced in sugarcane fields that had been burnt
prior to harvesting. However, there was no significant difference in the extent of breeding
between the two habitats. This study provides novel insight into the mechanisms that
allow for the persistence of high densities of rodent pest species.
