Redrawing Wallace’s Line based on the fauna of Christmas Island, eastern Indian Ocean

Abstract

Based on a comprehensive literature survey, we determined the sources of the terrestrial vertebrate species on Christmas Island, asking where they originated relative to Wallace’s Line (the southern end of the divide lies 1100 km to the east, where the Lombok Strait adjoins the eastern Indian Ocean). The two bats, Pipistrellus murrayi and Pteropus natalis, are from the west. Concerning the endemic and ‘resident’ bird species, one is from the west (Collocalia natalis), four are from the east (Accipiter fasciatus, Egretta novaehollandiae, Falco cenchroides and Ninox natalis) and the other 15 are ambiguous or indeterminate. Most of the land-locked species are also from the east: rodents Rattus macleari and Rattus nativitatis, and squamates Cryptoblepharus egeriae, Emoia nativitatis and Lepidodactylus listeria. Additionally, two have westerly origins (Crocidura trichura and Cyrtodactylus sadleiri), one is ambiguous (Emoia atrocostata) and another is unknown (Ramphotyphlops exocoeti). West-directed surface currents that flow across the eastern Indian Ocean towards Christmas Island would have facilitated most of the land-animal colonizations. We therefore suggest that Wallace’s Line be redrawn such that the landmass is placed on the Australasian side of this fundamental biogeographical boundary.