Biodiversity and ecology : some theoretical and practical ideas. Biodiversity is a concept which has received recently a great deal of publicity but is more complex than sometimes thought. Present at every level of biological organisation, biodiversity can be defined as the quantity and the quality of information contained in any biosystem, from genetic material through to lanscapes. Examples are examined using the pine genus (Pinus) in Europe and regional bird communities : these demonstrate the need to complete the quantitative concept of richness by qualitative notions of rarity and local occurence. Two cases taken within natural pares of the Rhône-Alpes region (France) also underline the need to situate biodiversity in an overall and ...