Role of fish in ecosystem functioning

The functional relationships between the species in an ecosystem are still poorly understood, but represent one of the main concerns of modern ecology. The role of biological diversity in the functioning of ecological systems is of particular interest. Are all the species found in an ecosystem truly needed to ensure its proper functioning? Do some species have redundant functions, and are there species with more important roles than others (keystone species)? Scientists also wonder about the role of biological diversity in the stability of ecosystems and their capacity to resist or adapt to disturbances, and study the relationships between specific richness and biological productivity.The answers to these questions are important for the management of aquatic environments and the preservation of biodiversity. But their complexity makes it difficult to propose satisfactory hypotheses. It is nevertheless possible to analyse available data and attempt to find partial answers to the questions raised (Lévêque, 1995b and 1997)