Population structure in Mixornis tit-babblers across Sunda Shelf matches interfluvia of paleo-rivers.

Rivers constitute an important biogeographic divide in vast areas of tropical rainforest, such as the Amazon and Congo Basins. Southeast Asia's rainforests are currently fragmented across islands divided by sea, which has long obscured their extensive history of terrestrial connectivity as part of a vast (but now submerged) subcontinent - Sundaland - during most of the Quaternary. The role of paleo-rivers in determining population structure in Sundaic rainforests at a time when these forests were connected remains little understood. We examined the coloration of museum skins and used the genomic DNA of museum samples and freshly-collected blood tissue of a pair of Sundaic songbird species, the pin-striped and bold-striped tit-babblers (Mixornis gularis and M. bornensis, respectively), to assess the genetic affinity of populations on small Sundaic islands that have largely been ignored by modern research. Our genomic and morphological results place the populations from the Anambas and Natuna Islands firmly within M. gularis from the Malay Peninsula in western Sundaland, even though some of these islands are geographically much closer to Borneo, where M. bornensis resides. Our results reveal genetic structure consistent with the course of Sundaic paleo-rivers and the location of the interfluvia they formed, and add to a small but growing body of evidence that rivers would have been of equal biogeographic importance in Sundaland's former connected forest landscape as they are in Amazonia and the Congo Basin today.

A global analysis of avian island diversity-area relationships in the Anthropocene.

Research on island species-area relationships (ISAR) has expanded to incorporate functional (IFDAR) and phylogenetic (IPDAR) diversity. However, relative to the ISAR, we know little about IFDARs and IPDARs, and lack synthetic global analyses of variation in form of these three categories of island diversity-area relationship (IDAR). Here, we undertake the first comparative evaluation of IDARs at the global scale using 51 avian archipelagic data sets representing true and habitat islands. Using null models, we explore how richness-corrected functional and phylogenetic diversity scale with island area. We also provide the largest global assessment of the impacts of species introductions and extinctions on the IDAR. Results show that increasing richness with area is the primary driver of the (non-richness corrected) IPDAR and IFDAR for many data sets. However, for several archipelagos, richness-corrected functional and phylogenetic diversity changes linearly with island area, suggesting that the dominant community assembly processes shift along the island area gradient. We also find that archipelagos with the steepest ISARs exhibit the biggest differences in slope between IDARs, indicating increased functional and phylogenetic redundancy on larger islands in these archipelagos. In several cases introduced species seem to have 're-calibrated' the IDARs such that they resemble the historic period prior to recent extinctions.