Distribution of rat species (Rattus spp.) on the atolls of the Marshall Islands: past and present dispersal

Résumé

The study of dispersal processes of small mammals, and especially of rodents, has a wide range of applications and until recent years there were few publications discussing the colonisation of 'oceanic' islands by small mammals (cf. Crowell, 1986; Diamond, 1987; Hanski, 1986;Heany, 1986; Lomolino, 1986). This essay will be concerned with the distribution of rat species in the Marshall Islands and its implications on the interpretation of the settlement and human use of the atolls. It will be argued that in all instances the introduction of rats was caused by people and that accidental transport, such as rafting on drift wood and the like, is as unlikely as introduction by means of ship wrecks. Human transport as well as the rats' own inability to cross great distances of water makes them bad zoogeographical markers, as already pointed out by Braestrup (1956), but it is precisely this trait that is of concern here. This paper will argue that the Polynesian rat (Rattus exulans) was an intentional introduction to the area and that its distribution throughout the Marshall Islands was a deliberate strategy.