From microbial to plant ecosystems, this book examines how changes in UV radiation, caused by anthropogenic ozone depletion, as well as changes in radiation levels throughout the evolution of life on Earth, can alter species composition and interspecies competitiveness. It focuses on the evolutionary aspects of the effects of UV as well as the various synergistic interactions of UV radiation with other environmental factors. Because our knowledge of UV effects on whole ecosystems is still at a relatively early stage, an important part of each chapter is an overview of future research directions and indications of where new date and knowledge is needed.