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A comment on Cowie, R.H. & Holland, B.S. (2006) Dispersal is fundamental to biogeography and the evolution of biodiversity on oceanic islands. Journal of Biogeography, 33, 193–198.

In a guest editorial Cowie & Holland (2006) treat as entirely unproblematic a dispersal model of the Hawaiian Islands (their Fig. 1). They neglect to mention the alternative vicariance model: the long history of a single ‘Big Island’ (the Hawaiian Ridge) that through volcanism grows toward the south-east and that disintegrates toward the north-west through erosion, subsidence and submarine slumping and landsliding. Their figure implies dispersal from older to younger islands in accordance with the ‘progression rule’ (of Hennig; Platnick, 1981). This imaginary dispersal is an unnecessary ‘explanation’ if biota, by colonizing younger lava flows and coalescing volcanoes, maintain themselves on the growing part of the ridge.

The vicariance model is enhanced by the discovery during the 1960s to late 1980s of ‘rapid and dramatic subsidence’ (Moore, 1987, p. 99) and ‘giant Hawaiian [undersea] landslides’ (Moore & Normark, 1994), rendering bathymetry around the modern islands a dubious basis for inferring past geological isolation of islands, even of seamounts, in this archipelago, contrary to traditional (dispersalist) interpretation (e.g. Zimmerman, 1948, Figs 6, 21; Carson & Clague, 1995, Fig. 2.2).

Cowie and Holland allow that ‘vicariance has played a role’ with reference to the Maui Nui island complex, held to be emergent during periods of low sea level during the late Pleistocene, but they consider the islands earlier to have been ‘sequentially produced’ in isolation of each other – the dispersal model of their figure. Evidently the model is that of Wilson (1963, Fig. 5; often reproduced as in Clague & Dalrymple, 1987, Fig. 1.16): each volcano-island emerges from the sea in isolation from older islands, in Wilson's words ‘like a series of bubbles’ arising ‘from a point beneath the island of Hawaii’ (Wilson, 1963, p. 868).

In 1970 ‘Maui Nui’ was proposed for a complex of islands: Molokai, Lanai, Kahoolawae and Maui (Macdonald & Abbott, 1970, p. 319). As now understood their early geological history includes also Oahu: ‘Penguin Bank Volcano [Molokai] was connected to the island of O'ahu via a land bridge; …newer volcanoes in the Maui Nui complex coalesced with older ones, ultimately forming a single landmass larger than the current island of Hawai'i; …this [pre-to-mid Pleistocene, 2.2–0.8 Ma] landmass gradually divided into separate islands’ (Price & Elliott-Fisk, 2004, p. 28) – the vicariance model so far as the story of Oahu-Maui Nui goes.

The Oahu-Molokai subaerial contact seems unproblematic, reinforced in a second area: ‘In addition, …there was a broad plain connecting Oahu and [the] West Molokai [Volcano]’ (Price & Elliott-Fisk, 2004, p. 37). Similar Maui-Hawaii contact is possible but its discovery is complicated by co-varying histories of subsidence and tilt of the volcanoes. Between Maui and Hawaii are contiguous shore features (terraces, breaks-in-slope) at great depth (2000 m) due to tilt toward Hawaii of the Maui landform (Moore, 1987, Figs 2.8 and 2.9 ; Price & Elliott-Fisk, 2004, Fig. 4). A recent model of the subsidence-tilt shows little or no separation of the two islands: ‘When the oldest volcanoes of the Hawai'i Island completed their shield development around 0.5–0.6 Ma, the shoreline associated with the M terrace [of Hawaii] would have been less than 15 km from Maui Nui's shoreline…considerably less than the current distance between Maui and Hawai'i (nearly 50 km)’ (Price & Elliott-Fisk, 2004, p. 42).

In sum, further generalization of the vicariance model – future discovery permitting – would involve the islands of Hawaii, and perhaps Kauai and many others.

References

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  2. References
  • Carson, H.L. & Clague, D.A. (1995) Geology and biogeography of the Hawaiian Islands. Hawaiian biogeography: evolution on a hot spot archipelago (ed. by W.L.Wagner and V.A.Funk), pp. 1429. Smithsonian Institution Press, Washington, DC.
  • Clague, D.A. & Dalrymple, G.B. (1987) The Hawaiian-Emperor volcanic chain. Part I. Geologic evolution. Volcanism in Hawaii (ed. by R.W.Decker, T.L.Wright and P.H.Stauffer), US Geological Survey Professional Paper 1350, pp. 554. United States Government Printing Office, Washington, DC.
  • Cowie, R.H. & Holland, B.S. (2006) Dispersal is fundamental to biogeography and the evolution of biodiversity on oceanic islands. Journal of Biogeography, 33, 193198.
  • Macdonald, G.A. & Abbott, A.T. (1970) Volcanoes in the sea: the geology of Hawaii. University of Hawaii Press, Honolulu.
  • Moore, J.G. (1987) Subsidence of the Hawaiian Ridge. Volcanism in Hawaii (ed. by R.W.Decker, T.L.Wright and P.H.Stauffer), U.S. Geological Survey Professional Paper 1350, pp. 85100. United States Government Printing Office, Washington, DC.
  • Moore, J.G. & Normark, W.R. (1994) Giant Hawaiian landslides. Annual Review of Earth and Planetary Sciences, 22, 119144.
  • Platnick, N. (1981) The progression rule or progress beyond rules in biogeography. Vicariance biogeography: a critique. Symposium of the Systematics Discussion Group of the American Museum of Natural History, May 2–4, 1979 (ed. by G.Nelson and D.E.Rosen), pp. 144150. Columbia University Press, New York.
  • Price, J.P. & Elliott-Fisk, D. (2004) Topographic history of the Maui Nui complex, Hawai'i and its implications for biogeography. Pacific Science, 58, 2745.
  • Wilson, J.T. (1963) A possible origin of the Hawaiian Islands. Canadian Journal of Physics, 41, 863870.
  • Zimmerman, E.C. (1948) Insects of Hawaii, Volume I Introduction. University of Hawaii Press, Honolulu (reissued 2001).

Editor: Robert Whittaker