Introduction

Before turning to formal definitions, the chapter frames ecology as the branch of biology concerned with how organisms relate to the environment they live in. This relationship can be examined at several different scales — a single organism, a population, a community, a biome, or the entire biosphere — and each level, paired with its own surrounding environment, reveals something different about how life is organised. Simply watching the world around us raises natural questions: why do plants and animals differ from place to place? What explains the differences in biological diversity seen across regions? How do soil, climate, and other physical conditions shape the plants and animals found somewhere — and how, in turn, do those organisms shape their physical surroundings right back? Ecology exists to answer exactly these kinds of questions, and it does so as a fundamentally practical, evidence-driven science: ecologists design experiments and make sustained field observations, then use what they learn to predict how organisms will respond to a given set of environmental circumstances.