An understanding of ecology is vital if we are going to manage the Earth's biosphere in a sustainable way. This book examines established ecological ideas and also includes ideas from emerging areas of ecology such as molecular and landscape ecology. The emphasis throughout the text is on applying ecological ideas to current environmental concerns, such as conserving biodiversity, managing habitats and controlling pests. The book is part of a series designed to make a particular subject easily accessible. Each book contains short accounts of 101 key ideas arranged in alphabetical order. Each account gives an informative summary of the term.