Tempo and mode in biological invasions: exotic rodents in the small mammal community of Bamako (Mali)

Abstract Small mammals are regular inhabitants of urban centres worldwide. The house mouse Mus musculus and rats of the genus Rattus , major invasive alien species, are increasingly present, particularly in West Africa where house mice and black rats ( Rattus rattus ) are frequently met in commensal small mammal communities. We studied the case of Bamako the capital of Mali, through intensive city-wide trapping, and found a strong dominance of invasive alien species over native ones, with house mouse representing more than half and the brown rat ( Rattus norvegicus ) nearly one quarter of the captures. Shrews ( Crocidura olivieri ) and multimammate rats ( Mastomys natalensis ) represented the main native species still found in the city. The spatial and ecological determinants of these species’ distribution were analysed, showing segregation between species at different spatial scales. At the housing unit scale, M. musculus and M. natalensis appeared associated with inner parts of buildings, while R. norvegicus and C. olivieri occured at the interface between the indoor and outdoor environments. At the city scale, invasive species were more abundant in older quarters than in more recent peripheral ones. This was particularly true for the house mouse which probably colonized Bamako during the 21 st century, while the brown and the black rats had done so a century before. This process of invasion of a native community of small mammals by cosmopolitan invasive species is discussed in a regional context, as are the potential consequences it may have in terms of public health and social well-being.