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(p.1) Introduction
Land Bridges
Alan Graham
University of Chicago Press

The Introduction outlines the beginnings of the New World land bridges—Bering, North Atlantic, Antillean, Central American, and Magellan. The assumptions are that patterns of distribution are residues of history; land bridges were important in determining those patterns; and that knowledge of the geology, environments, and fossil record of the connections is essential for proper understanding the origin of biological affinities and disjunctions. The factors past and present are numerous, interactive, and dynamic including landscape evolution, edaphic features, climates, and the role of pollinators, pathogens, and dispersal vectors. This necessitates a multidisciplinary approach each with its own set of strengths and limitations (fragmentary nature of the fossil record; variable accuracy of molecular approaches for calibrating phylogenies and determining radiation and diversification histories of taxa in the absence of a fossil record; accuracy of models in predicting conditions and vegetation types often necessitated for regions of damaged, threatened, or inadequately-collected biotas), and recognizing the impact of recent human-environmental interactions that modify by introductions and extinctions the modern vegetation analogs used to reconstruct the paleocommunities. This further requires interpretations be made within the broadest context of independent information.

Keywords:   beginnings, assumptions, vegetation, factors, approaches, multidisciplinary, context, humans

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