IMPACT OF EARTHWORMS ON THE DIVERSITY OF MICROARTHROPODS IN A VERTISOL (MARTINIQUE)

In a study of a 15-year-old pasture in Martinique (French West Indies) , abundance and organization of microarthropod communities were correl ated with the spatial distribution of the earthworm Polypheretima elon gata (Megascolecidae). In patches of high earthworm density (133 indiv iduals m(-2)), microarthropod density was significantly higher (80 000 individuals m(-2)) than in patches with few earthworms (31 worms m(-2 ) and 49 000 microarthropods m(-2)). The diversity of microarthropod c ommunities followed a similar pattern, the Shannon index for Collembol a communities being, respectively, 3.12 and 1.82 in and outside earthw orm patches. These results suggest that mesofauna abundance and divers ity might be at least partly determined by the activity of larger inve rtebrates, as a result of the dramatic effects that the latter group e xerts upon soil structure, pore distribution and food resources.