Ecosystems: development, functions and consequences of disturbances, with special reference to the oral cavity

Some general rules for the development and maintenance of microbial ecosystems are outlined. Studies on germ-free animals have given valuable baselines concerning structures and functions in the host per se. The oral cavity represents several consortia of micro-organisms, governed by factors deriving from the host, the diet and/or the micro-organisms. Alterations in these factors, as well as intake of antibiotics, etc., may give disturbances, which can be analyzed according to general guidelines.