. Bonner zoologische Beiträge : Herausgeber: Zoologisches Forschungsinstitut und Museum Alexander Koenig, Bonn. Biology; Zoology. Subspecies Species Ocyceros Anthraooceros Buceros Genus. Fig. 3: Cladograms of the genera Anorrhinus, Penelopides and Aceros, showing the species (underlined), subspecies and subgenera recognized in this study. (Read manilloe instead of manillae). boundaries and geographically isolated populations. The common features suggest the primary ecological determinants of hornbill ranges and indicate how and where populations might have become isolated in the past. It is po
. Bonner zoologische Beiträge : Herausgeber: Zoologisches Forschungsinstitut und Museum Alexander Koenig, Bonn. Biology; Zoology. Subspecies Species Ocyceros Anthraooceros Buceros Genus. Fig. 3: Cladograms of the genera Anorrhinus, Penelopides and Aceros, showing the species (underlined), subspecies and subgenera recognized in this study. (Read manilloe instead of manillae). boundaries and geographically isolated populations. The common features suggest the primary ecological determinants of hornbill ranges and indicate how and where populations might have become isolated in the past. It is possible to allocate each species and subspecies to a zoogeographical area (Fig. 4, Table 2). By comparing the ranges of taxa with their position on the cladograms (Figs. 2 and 3), it is possible to suggest the interfaces between zoogeographical divisions at which taxa became isolated from one another. This does not imply necessarily the exact geographical position at which this isolation oc- curred. Hornbills have broad ecological requirements, being widespread in forests in the Oriental-Australasian regions with only one species inhabiting savanna. Only major climatic events are likely, therefore, to have fragmented their habitats and so produce the isolated populations in which divergence could proceed. A succession of warm and cold episodes have been documented for the past 20 Myr (Brain 1981, 1983) and could produce such fragmentation. Sea levels appear to have ranged between about —70 and +6 m of present levels since the Cainozoic (Aharon et al. 1980, Brain 1983, Haile 1971, Miller & Fairbanks 1985). These variations in sea level can be compared to present submarine topography, with the caution that the Oriental area has ex- perienced complex subduction, rifting, faulting and island arc collision during the Tertiary (Hamilton 1979, Lee & McCabe 1986). It is assumed here that cool, dry periods would be associated with a fall in sea level, interconnection of land m
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