Molecular Panbiogeography of the Tropics

Preface

vii The theme of this book is the distribution of plants and animals and how it developed. The subject is approached using the methods of panbiogeography , a synthesis of plant geography, animal geography, and geology (Craw et al., 1999). The methodology is based on the idea that distribution is not due to chance dispersal; instead, range expansion (dispersal) and allopatric differentiation are both mediated by geological and climatic change. The biogeographic patterns discussed below mainly concern spatial variation in DNA, and so the subject can be termed “molecular panbiogeography.” The book focuses on molecular variation in plants and animals as this shows such clear geographic structure. Molecular analysis has revealed an intricate, orderly, geographic pattern in most groups examined, even in those that are apparently well dispersed, such as birds and marine taxa. This molecular/ geographic structure has often been described as “surprising,” as, for example, by Worth et al. (2010), reporting on bird-dispersed trees in Winteraceae, and it is certainly impressive. The discovery of this structure has been one of the most exciting developments in molecular biology , and it has intriguing, far-reaching implications for evolutionary studies in general. This book analyzes and integrates inherited information at the largest scale—the geographic distributions—and at the smallest scale—the molecular variation. Molecular research has had a revolutionary impact on all aspects of biology and has led to revised ideas on the evolution and classification Preface Heads_6480007_FM.indd vii Heads_6480007_FM.indd vii 10/20/11 2:39 PM 10/20/11 2:39 PM viii | Preface of many groups. Yet molecular variation is just morphology on a small scale, and there is no real conflict between the traditional morphological data and the new molecular data. Traditional taxonomic groups that were well supported in morphological studies are often corroborated in molecular work, and many of the radical realignments suggested by molecular studies are in groups and areas that morphologists have acknowledged as difficult. With respect to biogeography, most patterns shown in molecular clades were already documented in earlier systematic studies of some group or other. In order to assess the reliability and importance of a proposed phylogeny , it is necessary to know many details of the particular study.These include the sample size, the part or parts of the genome sequenced, the methods of establishing sequences, the methods of analyzing them in order to produce a phylogeny, and the statistical support of the groups. These are not provided here because the book is not about these parameters . In the same way, accounts of biogeography using morphological taxonomy do not cite the morphological characters that were used to construct the taxonomies. The distributional and phylogenetic data cited herein are introduced as “facts” for discussion, that, hopefully, the reader will accept. This may not always be the case, but most of the studies referred to are exemplary accounts and most of the clades mentioned have good statistical support. The first two chapters in this book deal with general aspects of interpreting evolution in space and time. The next eight chapters comprise a biogeographic “transect” around the tropics, from America to Africa, Asia, the Pacific, and back to America. The book does not give a systematic , area-by-area treatment, and only selected localities are covered in any detail. Australasia is covered in a separate volume. The main aim in this book is to provide worked examples and to illustrate principles using a new method of analysis. The groups that are discussed were chosen because their distributions are reasonably well known and they have been the subject of recent, detailed molecular study. Heads_6480007_FM.indd viii Heads_6480007_FM.indd viii 10/20/11 2:39 PM 10/20/11 2:39 PM ...