Community structure of ground-ants:: the role of single trees in a Mediterranean pastureland

A study was carried out to determine the effect of single tree (Quercus ilex subsp, ballota) shaded microhabitats on the community structure of ground-nesting ants in a semi-natural Mediterranean ecosystem (dehesa). A total of 1156 ant nests belonging to 20 species were detected in the study area, with a mean density of 10-11 nests per 100 m(2). Ground ant nests were denser under tree cover than on exposed grassland. Species richness and diversity also tended to increase in areas under tree canopies. These effects were found to be proportional to the area of tree cover up to a certain limit, beyond which the trend became negative. Species composition differed between open ground and tree-shaded microhabitats. Shade-tolerant species such as Plagiolepis pygmaea were more common near trees, whereas the seed harvester ant Messor barbarus was more common in open areas. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.