Organisation et distribution des communautés de Coléoptères dons les interfaces steppe-friches post-culturales en Crau

Abstract

The culture of cereals and rock melon, between 1965 and 1985, were very destructive for dry grasslands or "coussou" in Crau (southern France). Over a twenty-year period, three previously cultivated plots developed original old field floristic structures differing according to the agricultural practice and time since abandonment. The self restoration capacity of the "coussou" on these old field areas is slow : only a few metres of coussou extension over a twenty year period. In order to understand the response of Coleoptera communities to these floristic changes, several trapping campaigns were undertaken between April and November 2001. Buried, non-attractive traps with glycol were placed on three borders between the oldfields and the coussou resulting in the collection of 2305 Coleoptera, from 126 species. These results were subjected to various statistical techniques (Spearman rank test, similarity and diversity indexes, COA, CCA. . .). Results showed that the overall insect richness is likely to be indirectly dependent of floristic richness. Agricultural practices and time since abandon seemed to drive insect species composition and structure. Species composition was also dependent of distance from the border, while community structure was not. However, plant richness and density, like boulder cover, appeared to be the main driving factors of the insect community structure.