Function and functioning in ecology: what does it mean?

Many investigations in current ecological research focus on ecological functions, the functions of biodiversity, or the functioning of ecological systems. However, within ecology function is used in several different meanings. The most important ones are those of function as denoting either processes, roles, services or the functioning of whole systems. Some of these meanings pose considerable problems in terms of their ability to apply them in empirical research. These problems together with the ambiguity of the term function constitute considerable impediments for generalizations of research results. In order to improve this situation, the current paper describes the different meanings of function and discusses the requirements necessary to unambiguously apply the concept(s) in practice. This is illustrated by the example of current discussions on the functions of biodiversity.