Influence of sugarcane plantations on the population dynamics and community structure of small mammals in a savanna-agricultural landscape

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.