Introduction to special issue on biodiversity.

Cover Illustration: 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 amidst a gauntlet of anthropogenic changes. In fact, biodiversity is disappearing 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. This Biodiversity Special Issue looks at taxonomy and systematics, evolutionary biology and biogeography, ecology, and conservation/ restoration, and the images on the cover represent these areas of focus. Image credits: Palm tree with lianas from Barro Colorado Island (courtesy of Brian McGill); basidiomata of Pycnoporus sp., a wood-decaying polypore (courtesy of Meredith Blackwell); angiosperm family supertree used in analyses of diversification (courtesy of Steven Vamosi); pollinating fly visiting Helianthella quinquenervis (Maroon Bells-Snowmass Wilderness, Colorado) (courtesy of Laura A. Burkle); diverse alpine wildflower meadow near Twin Lakes, Cumberland Basin, Colorado (courtesy of Laura A. Burkle); male bee (Andrena sp.) emerged before spring flowers (Carlinville, Illinois); (courtesy of Laura A. Burkle); aquatic habitats rich with microalgae that regulate numerous ecological functions (courtesy of Danuta Bennett); aerial view of Barro Colorado Island, Panama (image by Jason Drake, Warnell School of Forest Resources, University of Georgia, using QuickBird data courtesy DigitalGlobe); howler monkey from Barro Colorado Island (courtesy of Brian McGill); bilaterally symmetrical flower of snapdragon (Antirrhinum majus L., Plantaginaceae) (courtesy of Jill C. Preston).