Introduction

The word 'ecology' comes from the Greek oikos, meaning 'house', and logos, meaning 'study' -- so ecology is, quite literally, the study of the environmental 'house': every organism living in it, and every process that keeps that house able to support life. This study is organised across several nested levels -- organism, population, community, and ecosystem, among others. The term 'population', which originally just meant a group of people, has been broadened in ecology to cover any group of individuals belonging to one kind of organism. All the populations sharing a given area together make up a 'biotic community', and when that community is considered together with its non-living, abiotic surroundings, the two function as a single ecological system, or ecosystem. At an even larger scale, a 'biome' describes a whole regional or sub-continental system defined by its dominant vegetation type, and the largest, most self-sufficient biological system of all -- the entire planet's living organisms interacting with the physical Earth to shape their own distribution, abundance, and evolution -- is called the ecosphere.