Biodiversity may be a buzzword, but as a concept it sits at the heart of ecological research. Some ecological communities, such as pristine coral reef systems, are astonishingly rich in the number and types of species that they support, whereas others are relatively species poor. Natural communities also differ greatly in the proportion of species performing different ecological functions. What determines such differences and how these differences are related to ecosystem functioning are questions that have occupied the minds of ecologists for decades.

But these questions are so much more pressing now. We live at a time of rapid environmental change, resulting largely from our own activities, and a concomitant, accelerating rate of habitat loss and species extinctions. Like children playing with fire, we do not fully understand, and therefore cannot predict, the ultimate consequences of tampering with global biodiversity. This collection of reviews — the second in our new section called ‘Nature Insight’ — focuses on the science of biodiversity.

David Tilman has been a driving force in furthering our understanding of the relationship between biodiversity and ecosystem function, and on page 208 he provides an overview of biodiversity research. Biodiversity means more than counting species. On page 212, Andy Purvis and Andy Hector examine the multifaceted concept of biodiversity, showing how different biodiversity measures can illuminate ecological and evolutionary processes. Biological diversity is not evenly distributed over the Earth’s surface, and Kevin Gaston summarizes global patterns in biodiversity on page 220. If high biodiversity favours ecological stability, accelerating species loss could destabilize or even lead to the collapse of whole ecosystems. Understanding the relationship between diversity and stability is a central goal of ecological research, and Kevin McCann explores the theoretical and empirical evidence on page 228. A gloomy picture is painted on page 234 of the global environmental problems ensuing from biodiversity loss and ecosystem degradation, but Stuart Chapin and colleagues also provide a blueprint for international action needed to avert the main effects of global change. Finally, Chris Margules and Bob Pressey argue on page 243 for a more systematic approach to reserve location and design, incorporating ecological principles, to protect biodiversity at the regional scale.

We are pleased to acknowledge the financial support of the Center for Applied Biodiversity Science (CABS), a division of Conservation International, in producing this Insight. The content is in accord with the philosophy that biodiversity conservation is a human-centred pursuit that must be underpinned by solid science. Of course, Nature carries sole responsibility for all editorial content and rigorous peer-review.

This Insight is deliberately broad in scope, covering underlying concepts, pure and applied research, and biodiversity loss from the human perspective. We hope that scientists, policy-makers and general readers alike will find the reviews both informative and thought provoking. Given that environmental change and biodiversity loss is a global concern, and understanding that not everyone will have easy access to the print version, this Insight is freely available to all readers, regardless of subscriber status, on our website at http://www.nature.com/nature.

Rory Howlett Deputy Biological Sciences Editor Ritu Dhand Insight Editor

Publisher and liaison for corporate support Liz Allen (e.allen@nature.com )