Recent immigrants from islands dominate two keystone forest herbivore assemblages in Australia

Successful upstream colonisation from islands to continents has now been documented in many taxa, however as yet there are no examples of upstream dispersal playing a dominant role in the assembly of regional biotas. Here we use supermatrix phylogenies for two groups of highly mobile volant keystone herbivores - nocturnal megabats and diurnal pigeons - to show that Australian rainforest communities in both groups are entirely derived from at least 17 independent colonisations from the islands of Melanesia and Wallacea. These colonisations are concentrated within the last 5 million years and there is also no evidence of in situ diversification post colonisation of Australia. This inference contrasts against perceptions of Australian rainforests being dominated by ancient Gondwanan relicts. Furthermore, given the importance of megabats and pigeons for pollination and fruit dispersal in forest environments, these data indicate that recent upstream colonisation from the islands of Melanesia through the late Tertiary likely had a major impact on the floral composition and ecological functioning of Australian lowland forests.