FLOATING ISLANDS: A GLOBAL BIBLIOGRAPHY [WITH AN EDITION AND TRANSLATION OF G.C. MUNZ'S EXERCITATIO ACADEMICA DE INSULIS NATANTIBUS (1711)].

Chet Van Duzer (2004)

Cantor Press, Los Altos Hills, California

ISBN: 0-9755424-0-0 (hardback) $44.95

Buy this book

Envisaging hippopotami lined up under starter's orders on an east African coast, Prue Napier relished the suggestion that hippos reached Madagascar during a Pleistocene low sea level event. This dispersal theory is plausible only if hippos had been impatiently determined to cross. Otherwise, as competent swimmers, any washed out to sea are more likely to have turned back, drowned or been killed by sharks. There being no evidence for a land bridge during the 100 million year isolation of Madagascar, hippos probably reached it accidentally on floating islands. Such islands earlier probably also transported the ancestral lemurs. If this seems far-fetched then Chet Van Duzer's informative and astonishingly comprehensive, Floating Islands: A global bibliography is essential reading.

The concept of rafting as a means of dispersal conjures images of animals clinging precariously to floating logs while facing exposure, dehydration and starvation, not to mention the possible lack of suitable habitat and a mating partner if the log happens to make landfall. Although logs may disperse epiphytes, seeds, invertebrates, reptiles and perhaps rats, they are probably insignificant in dispersal compared to floating islands. Not appreciating their potential scale, frequency and durability, biologists have tended to overlook this alternative. One floating island supported 60 cattle on the San Joaquin River, California, in 1862. Wild pigs, alligators, caimans, snakes, lizards and monkeys were seen on floating islands of the Iberá system and the Paraná River in Argentina. Many such creatures invaded Buenos Aires from a 50-acre floating island which arrived in the 1880's. In 1924, Captain Jonas Pendelbury encountered a 7-acre floating island in the Palawan Passage between Borneo and the Malay Peninsula. Higher than the radio masts of his steamship, its palm trees harboured chattering monkeys and singing birds. Through binoculars, Pendelbury saw large masses of flowering vegetation and abundant cobras. In 1902, about 50 km from San Salvador in the Bahamas, Captain Warnecke steamed close to a floating island whose numerous stately trees proved to be full-grown coconut palms laden with fruit of the largest size. He and the first mate landed on the island and captured two of a small troop of monkeys who shied them with coconuts. If the account is reliable, these were probably guenons from St. Kitts, in which case they had drifted over 1400 km.

Not only Madagascar was probably colonized by sea. Their sweepstake distribution in the Malay Archipelago belies the assumption that animals could disperse overland when sea level recessions exposed the Sunda Shelf during the Pleistocene glaciations. These recessions, creating a subcontinent, merely intensified the desiccative effects of the cool glacial climate. Most, if not all, of the intermittently exposed land was probably grassland-encompassed desert (Brandon-Jones 1996, 1998). Remnants of this grassland and its former occupant, the striped rabbit still survive in Sumatra. The closest relative of this endemic species was recently discovered 1500 km away in Laos and Vietnam. Their geographic disjunction demonstrates that even the grassland suffered when the desert was at its most arid. Externally almost indistinguishable, their genetic divergence improbably indicates an 8 million year separation (Surridge et al. 1999). Like the claim that Bornean and Sumatran orang-utans have been split for 4.5 million years (Xu & Arnason 1996), this suggests our molecular clocks are at least tenfold too slow. Orangs have probably not existed on Borneo that long.

The expansion and contraction of dry zones in Sundaland, Thailand, Burma and northern India were far more influential than sea barriers in controlling faunal distributions in the Oriental Region. The Sundaland desert extirpated some fauna and prevented tigers and wild pigs from reaching Borneo (Brandon-Jones 2001). It would have stymied primates. They remained stranded in small pockets until the climate moderated, rain forest regenerated and floating islands carried them down rivers and across straits. Islands like Sulawesi were difficult to colonize, not because the Makassar Strait was impassable, but because of fluctuating climate and the unattainability of an appropriate embarkation point. Macaques and tarsiers are better adapted than most primates for colonizing relatively dry environments. Other species may have reached Sulawesi, but either perished on arrival or later through loss of habitat. Sea barriers were crucial only for islands such as the Mentawai archipelago, off Sumatra, where constant marine isolation protected the islands from excessive desiccation. As all these islands were colonized by floating island, it is rash to contend that Homo erectus must have constructed water craft in order to reach Flores 840 000 years ago (Smith 2001). Modern humans may have originally reached Australia 40-60 000 years ago on floating islands.

My interest in floating islands is primarily as a means of marine dispersal. Van Duzer's bibliography covers all aspects of their biology, mainly concerning those of freshwater lakes and rivers, including artificial floating islands used for agriculture or habitation. Being a bibliography, if you wish for more than a brief résumé, you will have to consult the article itself. Web addresses are given for works available online. A translation interleaved with the Latin text of Munz's (1711) dissertation on floating islands occupies the first 33 pages of the book. With accompanying annotations occupying a further 33 pages, this provides a good introduction to the subject, documenting such phenomena back to ancient times. The book ends with 24 fascinating colour and monochrome photographs and plates. There is unfortunately no general index, but the bibliography is followed by a thematic index and a geographical index. The latter regrettably excludes marine floating islands, so is of limited use to the biogeographer. Once you have become accustomed to the book it will provide hours of happy hunting among the excess of 1800 citations.

DOUG BRANDON-JONES

Richmond, Surrey

Brandon-Jones D (1996) The Asian Colobinae (Mammalia: Cercopithecidae) as indicators of Quaternary climatic change. Biological Journal of the Linnean Society 59:327-350.

Brandon-Jones D (1998) Pre-glacial Bornean primate impoverishment and Wallace’s line. In Hall R & Holloway JD, eds. Biogeography and geological evolution of SE Asia. Leiden: Backhuys, pp. 393-403.

Brandon-Jones D (2001) Borneo as a biogeographic barrier to Asian-Australasian migration. In Metcalfe I, Smith JMB, Morwood M & Davidson I, eds. Faunal and Floral Migrations and Evolution in SE Asia-Australasia. Lisse: Balkema, pp. 365-372.

Smith JMB (2001) Did early hominids cross sea gaps on natural rafts? In Metcalfe I, Smith JMB, Morwood M & Davidson I, eds. Faunal and Floral Migrations and Evolution in SE Asia-Australasia. Lisse: Balkema, pp. 409-416.

Surridge AK, Timmins RJ, Hewitt GM & Bell DJ (1999) Striped rabbits in Southeast Asia. Nature 400:726.

Xu X & Arnason U (1996) The mitochondrial DNA molecule of Sumatran orangutan and a molecular proposal for two (Bornean and Sumatran) species of orangutan. Journal of Molecular Evolution 43:431-437.