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Case Studies

Case Studies

(p.259) Seven Case Studies
Land Bridges
Alan Graham
University of Chicago Press

In the case studies of taxa presented here, where times and directions of migrations and reintroductions have been suggested, 27 or ca. 60% appear to have used land bridges, based on the fossil record or on their limited means of long-distance dispersal. That means ca. 40% migrated by other means over, around, or through barriers by birds, ocean currents, or wind, or were residues of ancient land collision and fragmentation. In all cases climatic conditions and trends were an important if not overriding factor in determining movements and successful establishment in the arrival area. That places land bridges in a better perspective for understanding past and present radiation, diversification, and patterns of distribution among organisms. Certain taxa have a reasonably good fossil record and a sound taxonomy/phylogeny and can be used for establishing parameters in models proposed for those less well known. Pinus, Ilex, Nipa, Lythraceae, Rhizophoraceae, and many deciduous trees (Nothofagus) are examples.

Keywords:   alternative routes, ferns, gymnosperms, angiosperms, fossils, dispersal vectors

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