Introduction to special issue on biodiversity 1

The study of biodiversity is fundamental to our understanding of life on Earth and to confronting some of the problems caused by our own species. Further, we increasingly count on biodiversity for a wide variety of ecosystem functions and services amid a gauntlet of anthropogenic changes, including exploding human population levels; global climate change; the spread of invasive species, pests, and pathogens; and overharvesting ( Millennium Ecosystem Assessment, 2005 ). In fact, biodiversity is diminishing at a rate even faster than the last mass extinction at the end of the Cretaceous Period, 65 million years ago, with possibly two-thirds of existing terrestrial species likely to become extinct by the end of this century — the vast majority of them unknown to science at the time they disappear ( Millennium Ecosystem Assessment, 2005 ). The term biodiversity, coined after the National Academy of Sciences/Smithsonian Institution symposium in 1986 ( Wilson, 1988 ), evokes a great number of perspectives among the general populace and academic sectors. To most laypeople and in colloquial terms, biodiversity implies some indication of the numbers and types of species, genes, and/or species functions. Tropical areas are generally taken to be more biodiverse than temperate and arctic regions; national parks and other protected areas strive to preserve areas of high or unique biodiversity; zoos and botanical gardens make the concept of biodiversity accessible to and appreciated by millions of visitors on a daily basis. The academic study of biodiversity can be roughly divided into four categories, each of which is essential to our understanding, and ultimately, the preservation, of this essential feature of life. (1) Taxonomy and systematics. The categorization and description of species, how they are related to one another, and how they are distributed across the globe are essential components of biodiversity studies. Fewer scientists are being trained in this area, however, and funding and other opportunities are somewhat limited. Fortunately, museums and botanical gardens continue to provide leadership in this venue, although training opportunities for students are somewhat limited. Other programs, including the National Science Foundation ’ s Tree of Life program, provide incentives and opportunities to move this area forward. (2) Evolutionary biology and biogeography. Charles Darwin and Alfred Russel Wallace, among other early evolutionary biologists, showed how the powerful study of biogeographic patterns of species biodiversity, as well as patterns of species traits and distributions, within and among taxonomic groups can shed light onto important evolutionary processes. This area of study remains a mainstay of evolutionary studies, including macroevolutionary and phylogeographic approaches, and has been greatly enhanced in the recent past by the advent of powerful molecular and statistical approaches (e.g., Wiens and Donoghue, 2004 ).