Towards a glacial-sensitive model of island biogeography

Although the role that Pleistocene glacial cycles have played in shaping the present biota of oceanic islands world-wide has long been recognized, their geographical, biogeographical and ecological implications have not yet been fully incorporated within existing biogeographical models. Here we summarize the different types of impacts that glacial cycles may have had on oceanic islands, including cyclic changes in climate, shifts in marine currents and wind regimes and, especially, cycles of sea level change. The latter have affected geographical parameters such as island area, isolation and elevation. They have also influenced the configurations of archipelagos via island fusion and fission, and cycles of seamount emergence and submergence. We hypothesize that these sea level cycles have had significant impacts on the biogeographical processes shaping oceanic island biotas, influencing the rates and patterns of immigration and extinction and hence species richness. Here we provide a first step toward the development of a glacial-sensitive model of island biogeography, representing the tentative temporal evolution of those biogeographical parameters during the last glacial cycle. From this reasoning we attempt to derive predictions regarding the imprint of sea level cycles on genetic, demographic or biogeographical patterns within remote island biotas

Vegetation History of Laysan Island, Northwestern Hawaiian Islands.

v. ill. 23 cm.QuarterlyPaleoenvironmental investigations were undertaken on Laysan Island in the remote Northwestern Hawaiian Islands to investigate its flora before historical observations. Substantial impacts occurred to the island as a result of late nineteenth- and early twentieth-century guano mining, commercial feather collecting, and denudation of vegetation by feral rabbits. An account of Laysan’s historically known vegetation is presented, followed by discussion of results from the investigation of a 16.41-m sediment core from Laysan’s central hypersaline lake. The 7,000-year pollen and seed record, besides indicating the former importance of Pritchardia palms on Laysan, showed the former presence of seven previously unknown taxa, only four of which could be identified. Diatom analysis indicated fresh to brackish lake water during the early Holocene, a finding supported by the mollusk assemblage. Diatom diversity gradually decreased over time until there is a near monoculture, with types indicating a gradual increase of salinity. Hypersaline conditions were first recognizable near the top of the sequence with the appearance of Artemia zooplankton. Generally wetter conditions seem to have characterized the island before about 5,150 yr B.P., with drier conditions thereafter. The pollen record also suggests two possibly very brief periods of much drier conditions, conceivably related to El Nin˜o– Southern Oscillation episodes

Prehistoric maritime migration in the Pacific Islands: an hypothesis of ENSO forcing

Long-distance human migration across the Pacific Ocean occurred during the late Holocene and originated almost entirely in the west. As prevailing tradewinds blow from the east, the mechanisms of prehistoric seafaring have been debated since the sixteenth century. Inadequacies in propositions of accidental or opportunistic drifting on occasional westerlies were exposed by early computer simulation. Experimental voyaging in large, fast, weatherly (windward-sailing) double-canoes, together with computer simulation incorporating canoe performance data and modern, averaged, wind conditions, has supported the traditional notion of intentional passage-making in a widely accepted hypothesis of upwind migration by strategic voyaging. The critical assumption that maritime technology and sailing conditions were effectively the same prehistorically as in the historical and modern records is, however, open to question. We propose here that maritime technology during the late-Holocene migrations did not permit windward sailing, and show that the episodic pattern of initial island colonization, which is disclosed in recent archaeological data, matches periods of reversal in wind direction toward westerlies, as inferred from the millennial-scale history of ENSO (El Niño-Southern Oscillation)