Introduction: on the causes and consequences of rare—common differences

The purpose of this volume is to begin the complicated process of separating pattern from process. In a sense, it is an exercise that could be performed with any interesting pattern of species and their associated characteristics. We choose to focus our attention here on one particularly intriguing case: the differences between rare and common species. The choice is not completely arbitrary. The causes and consequences of species abundance have been a central concern of ecologists since the discipline began; indeed, some define ecology as the study of the distribution and abundance of species. The rise of conservation biology as a sub-discipline in recent years has served to focus additional attention on rarity and its implications, and has added to the importance of understanding the nature of rare—common differences.