Symposium introduction: The importance of scale in ecology

Conceptual issues about scale, both spatial and temporal, have had considerable influence on the way in which ecologists view populations, communities and ecosystems. Scale includes two aspects: the extent over which a community or ecosystem is studied, and the resolution or 'grain' at which measurements or experiments are conducted. We illustrate the influence of extent and grain on perceptions of ecological patterns and processes, derived from fundamental measurements, field experiments and theory and modelling. These concepts provide background for a series of subsequent papers that were presented at a symposium on spatial and temporal scaling in freshwater systems. These papers conclude that multi-scale measurements and experiments plus novel medhodologies for analysing large-scale surveys and manipulations should be priorities for future research in freshwater systems.