Extinction is one of the most fundamental processes in ecology-it shapes evolution, community structure, and patterns of biodiversity. Yet studies of extinction are scarce, and studies involving hard data rather than theoretical models are almost totally lacking. We will take advantage of an extraordinary database concerning Sonoran Desert fishes to investigate relationships between extirpation and patterns of rarity and life-history traits. Key to our project is the development of new methods for quantifying patterns of rarity that are independent of the spatial scale of analyses. Investigations of rarity are important because most species are in some way rare. The details of how species differ in the "way in which they are rare" (e.g., in numbers, in spatial distribution) may be key to understanding a diversity of issues in ecology, including the assembly of communities and how species persist in the face of disturbances. Our unique database includes over 25,000 locality records spanning 160 years of field research for all 50 known taxa of Sonoran Desert fishes. These fishes collectively constitute a gravely endangered biota for which data on the linkages among rarity, extinction-proneness, and life-history traits are of critical conservation importance. The methods we apply are modifications of Kunin's (1998) notion of "scale-area curves," which provide a means of quantifying rarity patterns across spatial scales. Specifically, we will examine how the patterns of rarity these fish exhibit relate to their extinction dynamics (e.g., frequency and spatial pattern of extirpation events) and current levels of endangerment. We will also determine the extent to which patterns of rarity and extinction can be predicted by life-history attributes. Biodiversity databases are an untapped storehouse of information on distributions of species. They allow us to ask questions at different scales and with greater taxonomic breadth than any experiment or focused field study can. They also allow us to ask altogether different questions-such as questions about extinction. The research proposed here will explore linkages between rarity, extinction risk, and life-history traits, along the way defining limits on how existing databases can be used and clarifying how to improve development of new databases.
