IMPACT OF GULL COLONIES ON THE FLORA OF THE RIOU ARCHIPELAGO (MEDITERRANEAN ISLANDS OF SOUTH-EAST FRANCE)

The effects of an increasingly large yellow-legged gull Larus cachinna ns colony on the flora of a Mediterranean limestone archipelago (south -east France) were studied through the analysis of floristical changes which have occurred in the past 36 years. Island plant lists can be d istinguished first according to the island area, but all the islands s how a common pattern of historical changes in flora. This floristical change appears to be correlated with the gull density and the percenta ge of ruderal plant species. Disturbance by gulls favours the massive establishment of non-native plant species which has led to the extinct ion of some endangered taxa through this plant species 'enrichment'. S mall islets appear to be more affected than large islands. Some prelim inary conservation measures are presented. (C) 1998 Elsevier Science L td. All rights reserved.