Évolution de la structure des peuplements de Laro-limicoles nicheurs

Résumé En

The aim of this paper is to provide information on the composition of the breeding population of waders and gulls in the Camargue (Southern France). It also gives details on the changes in status of these species between 1937 and 1970. The profound changes the Camargue has undergone (embankments of the lagoons, invasion of ricefields, various other agricul¬ tural developments, increase in the number of rubbish dumps just outside the area) have had a great effect on these populations : 1) three new species have become established as breeding birds. 2) most species have shown no noticeable changes in status, except the Black-headed Gull and the Yellow-legged Herring Gull which have increased strikingly ; these two species have been able to take advantage of the possibilities provided by changes in the ecosystem. 3) the diversity (measured with the Shannon & Weaver diversity index) has first increased then decreased when the numbers of Yellow-legged Herring Gulls and Black-headed Gulls reached a given high level. 4) on the contrary, the dominance (measured with the Mc Naughton & W oi.f dominance index has first decreased and then increased. This indicates that the Camargue ecosystem has become «harsh». The predominance of the Black-headed Gull and the Yellow-legged Herring Gull is due essentially to the widening of their ecological niches, but they have not displaced any other species.