ABSTRACT
The common denominator of all islands is isolation. Islands are, in general terms, areas of land isolated from others of similar character and relatively inaccessible by reason of the extent and character of the surrounding area. The biological significance of islands is related to their contribution to an understanding of the processes of organic dispersal and evolution and to species variability. Islands vary widely in location, size, physical environment, biotic characteristics and degree of isolation. Human settlement has been later, particularly on the oceanic islands, than on the mainland. The existing indigenous island species are those with an originally high dispersal capability by wind, by floating, by flying or, in the case of animals, by swimming. Evidence for the importance of competition in the organisation of vertebrate communities is the niche shift characteristic of many island species. The interaction between oceanic island ecosystems and the surrounding marine ecosystem is of considerable importance because of the high shoreline to area ratio.
