Upstream Colonization and Faunal Dominance

• Main Authors: Mayr, Ernst, Diamond, Jared
• Format: Book Part
• Language: unknown
• Published: Oxford University PressNew York, NY 2001
• Subjects: Bering Strait
• Online Access: http://dx.doi.org/10.1093/oso/9780195141702.003.0014; https://academic.oup.com/book/chapter-pdf/52324743/isbn-9780195141702-book-part-14.pdf

Abstract As we have seen in chapter 13, the main direction of avian colonization of Northern Melanesia has been from west to east: from Asia through New Guinea to the Bismarcks, and from the Bismarcks to the Solomons. Similarly, for tropical Southwest Pacific archipelagoes east of the Solomons, the main direction of colonization has been from west to east: from the Solomons to the New Hebrides to Fiji to Samoa (Diamond & Marshall 1976). This pattern is to be expected because land masses decrease in area and species richness from west to east, from giant, species-rich Asia to New Guinea to the Bismarcks to the Solomons to the New Hebrides. However, as discussed by Diamond and Marshall (1976), the asymmetry of fauna! exchanges between neighboring tropical Southwest Pacific archipelagoes is quantitatively greater than expected from the ratio of their areas or species numbers. This phenomenon appears to be essentially the same as the phenomenon of faunal dominance often discussed in the biogeographic literature—for instance, in connection with Asian/Australian faunal exchanges in Wallacea, Old World/New World exchanges across the Bering Strait, and North American/South American exchanges across the Isthmus of Panama. In addition, those eastern colonists that do succeed in spreading “upstream” from east to west in the Pacific fit a distinctive pattern of ecological distributions in the colonized archipelagoes to the west. The eastern invaders are concentrated in species-poor western communities, while western invaders establish themselves in species-rich as well as in species-poor eastern communities. We now discuss these asymmetrical faunal exchanges between the New Hebrides and Northern Melanesia, between the Solomons and Bismarcks, and between Northern Melanesia and New Guinea. We then suggest a probable reason for these asymmetries.